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Synergistic inhibition of polyethylene glycol and potassium chloride in water-based drilling fluids

Synergistic inhibition of polyethylene glycol and potassium chloride in water-based drilling fluids Mud shale hydration and swelling are major challenges in the development of water-based drilling fluids (WBDFs). In this work, the inhibition performance and inhibition mechanism of polyethylene glycol (PEG) and potassium chloride (KCl) were investigated by hot rolling recovery tests, linear swell tests, Fourier transform infrared spectroscopy, X-ray diffraction, atomic absorption spectrophotometry and X-ray photoelectron spectroscopy. The experimental results show that the com- bination of PEG and KCl achieved higher recovery and lower linear swelling rate than those obtained by individual PEG or KCl. Compared to the d-spacing of Na-montmorillonite (Na-Mt) with PEG or KCl, the d-spacing of Na-Mt with PEG+KCl was lower, which indicates that KCl and PEG have synergistic inhibition effect. This synergistic effect can replace sodium ions and water molecules from the interlayer space of Na-Mt and decrease the d-spacing of Na-Mt. Based on the above experimental results and analysis, a method for optimizing PEG and KCl concentrations was proposed and further verified by rheological and hot rolling recovery tests of WBDFs. Hence, the results of this work can provide valuable theoretical guidance for developing other synergistic inhibitors. Keywords Clay hydration · Inhibitor · Synergistic inhibition · Polyethylene glycol · Water-based drilling fluids 1 Introduction 2020). When water-sensitive shale comes into contact with water-based drilling fluids (WBDFs), hydration and swelling Shale oil and gas resources have been attracting a consider- of clay minerals occur, which can generate wellbore insta- able amount of attention in recent years (Qian et al. 2020; bility (Cook et al. 1993; Mody and Hale 1993; van Oort Li et al. 2020). Severe wellbore instability frequently occurs 2003; Guo et al. 2006; Al-Bazali 2011). This results in sev- during drilling of water-sensitive shale formations, which eral downhole complications, including wellbore collapse, account for 75% of the drilling formations (Bol et al. 1994; wellbore shrinkage, pipe sticking and bit balling, which can Dzialowski et al. 1993; Steiger and Leung 1992; Li et al. increase both drilling times and costs (Khodja et al. 2010; Liu et al. 2006; Wang et al. 2009; Cai et al. 2008; Baohua et al. 2013; Li et al. 2015). In many cases, oil-based/syn- Edited by Yan-Hua Sun thetic-based drilling fluids are used to ensure swelling inhi- bition in water-sensitive formations (Li et al. 2016a, 2019). * Gang Xie Despite their benefits, such as well inhibition ability, tem- 201899010129@swpu.edu.cn perature resistance and lubricity, the oil-based drilling fluids * Ping-Ya Luo lead to environmental pollution and high costs, limiting their luopy@swpu.edu.cn application in the field. Therefore, WBDFs are the focus of State Key Laboratory of Oil & Gas Reservoir Geology much research, and the most important task in the research and Exploitation, Southwest Petroleum University, of WBDFs is to develop an excellent swelling inhibitor. Chengdu 610500, Sichuan, China In the field of WBDFs, amine inhibitors have emerged as College of Chemistry and Chemical Engineering, Southwest a research focus, but there are some environmental problems Petroleum University, Chengdu 610500, Sichuan, China associated with this class of chemicals. However, polyols, as College of Chemistry and Chemical Engineering, Xi’an inhibitors for WBDFs, satisfy international environmental Shiyou University, Xi’an 710056, Shanxi, China Vol.:(0123456789) 1 3 828 Petroleum Science (2021) 18:827–838 standards in terms of toxicity and biodegradability (Twynam 71.30% SiO , 13.22% Al O , 4.79% Na O, 7.10% MgO and 2 2 3 2 et  al. 1994). In addition, polyols have the advantages of 3.59% Fe O , which was determined with the X-ray diffrac- 2 3 water solubility, lubricity, thermal stability and compat- tion method. The cation exchange capacity (CEC) of Na-Mt ibility with conventional treatment in the WBDFs (Bland was 113 meq/100 g. Drill cuttings were purchased from the et al. 1996; Bland 1992). In 1940, Cannon (1940) success- Center for Well Completion and Logging Laboratory and fully tackled the shale swelling problem during drilling of had 58.7% clay and 41.3% non-clay. Polyacrylamide (PAM) a water-sensitive formation with 30% ethylene glycol and (anionic; mean molecular weight of 3 × 10 ), carboxymethyl propylene glycol in the WBDFs. A large number of field cellulose (CMC), polyethylene glycol (PEG, mean molecu- applications and laboratory studies have shown that polyols lar weight of 500), Na CO and KCl were purchased from 2 3 have an excellent inhibition performance in the presence of Chengdu Micxy Chemical Co., Ltd. Bentonite was pur- KCl (Bland 1992). Low-salinity glycol WBDFs have been chased from Xinjiang Zhongfei Xiazi Street Bentonite Co., developed for shale drilling in environmentally sensitive Ltd. locations (Brady et al. 1998). KCl-PHPA-polyols were used to maintain borehole stability and reduce torque in the Sob- 2.2 Sample preparation hasan oilfield of India (Raza Khan et al. 2006). Moreover, polyol and potassium carbonate were applied as inhibitors The sample pretreatment process is as follows. Na-Mt was to the Kanina oilfields of Albania (Isinak et al. 2005). In the dried at 150 °C for 24 h. Then, 1 g of dry Na-Mt was added deep exploratory wells of the Assam oilfield, polyol-KCl to 25 mL of distilled water. After 3 h of stirring at 30 °C, the drilling fluids effectively inhibited clay swelling, improved Na-Mt dispersion was added to 25 mL of inhibitor solution wettability of drill pipe and reduced torque. The combina- of different concentrations. Then, the dispersion was stirred tion of polyethylene glycol (PEG) and KCl exhibits better at 30 °C for 24 h and centrifuged at 5000 rpm for 25 min. inhibition performance than that provided by individual PEG The centrifugal sediment was added to 25 mL of distilled or KCl. The mechanism of synergistic inhibition is related water and stirred with a glass rod. After that, the samples to a complexation between PEG and K , which can weaken were centrifuged and washed three times by water. the hydration of K (Sartori et al. 1990; Tasaki et al. 1999). In order to facilitate the description and comparison of the Boulet (2004) demonstrated that PEG+KCl can decrease the experimental results, two types of samples are defined: wet layer spacing of Mt crystalline to 1.40 nm, and PEG adopts Na-Mt/inhibitor samples and dry Na-Mt/inhibitor samples. a single-layer structure. However, the mechanism of syner- The pre-treated samples are wet Na-Mt/inhibitor samples. gistic inhibition caused by PEG+KCl is still not well under- Dry Na-Mt/inhibitor samples were obtained through drying stood and needs to be theoretically explored. Moreover, no the wet sample at 150 °C for 24 h and complete grinding. studies have yet proposed a general principle to optimize the concentrations of these two inhibitors for WBDFs. 2.3 Methods In this study, the synergistic inhibition effect of PEG and KCl was investigated through linear swell tests and hot roll- 2.3.1 Inhibition performance evaluation ing recovery tests. After that, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), elemental Hot rolling recovery tests are performed as follows. A total analysis (EA), atomic absorption spectrophotometry (AAS), of 50 ± 0.01 g drill cuttings were passed through a 10-mesh X-ray photoelectron spectroscopy (XPS) and scanning elec- sieve and dried at 105 ± 3 °C for 4 h. The drill cuttings were tron microscopy (SEM) were used to demonstrate and reveal added to high-temperature aging tanks with 350 mL of 1% the complex mechanism of this synergistic inhibition. Based inhibitor solution. The tanks were aged in a roller oven at on the proposed mechanism, a principle of optimizing con- 120 °C for 16 h. After hot rolling, the drill cuttings were centrations of PEG and KCl in WBDF was put forward. passed through a 40-mesh sieves and dried at 105 ± 3 °C for Both the inhibition mechanism and optimization principle 4 h. Cuttings were cooled to room temperature and weighed were verified against the results of drilling fluid tests in the (m). The first hot rolling recovery (R ) was the ratio of resid- laboratory. ual drill cuttings after first aging. The cuttings from the first recovery were aged a second and a third time. The first, second and third hot rolling recovery of the drill cuttings 2 Experimental (R , R , R ) were calculated using Eq. (1): 1 2 3 2.1 Materials R = × 100% (1) The chemical composition of Na-montmorillonite (Na-Mt) (obtained from the Nanocor Company) was as follows: 1 3 Petroleum Science (2021) 18:827–838 829 where m is the recovery mass of cuttings (i = 1, 2, 3); R is scanning electron microscope (SEM). SEM was per- i i the cutting recovery, %. formed with a Quanta 650F instrument. Linear swell tests were performed as follows. A total of 10 ± 0.01 g of drill cuttings were passed through a 100- 2.3.3 Inhibition performance evaluation of WBDF mesh sieve and dried at 105 ± 3 °C for 4 h. After that, the drill cuttings were added to test tubes and compressed at To evaluate the inhibition performance of WBDF with inhib- 4 MPa for 5 min. The pressure was then relieved, and the itors, the following steps are required. (1) The preparation original height of the cutting column (H) was measured of the WBDF with inhibitors. The formulation of the basic with a Vernier caliper. WBDF is listed in Table 1. The bentonite and N a CO were 2 3 Then, the cutting column was installed in the linear added to 200 mL of freshwater and pre-hydrated at room dilatometer. Certain concentrations of inhibitor solution temperature for 24 h. Then, the other agents (as shown in were added to the linear dilatometer until the solution is Table 1) were slowly added to the system and stirred thor- above the top of the cutting column. With the change of oughly in a high-speed mixer at a rate of 11,000 rpm (Li time, the changes in the height of the cutting column were et al. 2016c). At last, certain concentrations of inhibitors recorded. At last, the linear swell ratio was calculated were added to the basic WBDF. (2) The evaluation of inhibi- using Eq. (2): tion performance of WBDF with inhibitors. For the WBDF with inhibitors, their rheological parameters including apparent viscosity (AV), plastic viscosity (PV), yield point W = × 100% (2) (YP), yield point and plastic viscosity ratio (YP/PV), and gel strength, API filtrate volume after hot rolling (120 °C, where W is the percentage of linear swell ratio; H is the 16 h) were measured in light of the standard test recom- original height of the cutting column in mm; and H is the mended by API RP 13B-2 (2005). According to the method height of the cutting column at time t, mm. in Sect. 2.3.1, the hot rolling recovery of the drill cuttings in the WBDF with inhibitors was obtained. 2.3.2 Structure characterization and morphology observation 3 Results and discussion Fourier transform infrared spectroscopy (FTIR) was 3.1 Inhibition performance of KCl and PEG used to investigate the organic adsorption on clay. FTIR was performed using a Nicolet 6700 FTIR spectrometer 3.1.1 Hot rolling recovery tests (Thermo Scientific Corporation, USA). The layer spacing of Mt (d ) crystal plane is usually Hot rolling recovery tests were used to evaluate the swelling defined as d-spacing (Chaudhary et al. 2013; Lee et al. ability of the shale. An improved inhibitive capacity can be 2005). X-ray diffraction (XRD) can be used to study the indicated by higher cuttings recovery (Khodja et al. 2010). d-spacing of Na-Mt. The XRD patterns of the samples In application, 3%–10% KCl and 5%–7% PEG (by weight) were obtained with an X’Pert Pro MPD diffractometer (a are commonly used (Hale and Blytas 1993; Reid et al. 2003; Cu Kα radiation source) at 2θ angles scanned from 3° to Smith and Balson 2004). After hot rolling at 120 °C for 16 h, 40°. The d-spacing of the samples were analyzed through the cutting recovery of the different systems was measured Bragg’s equation (Xie et al. 2017). (Fig. 1). The hot rolling recovery of cuttings in the KCl solu- Ion adsorption can be investigated through elemen- tion was lower than that in the PEG+KCl solution, as shown tal analysis, atomic absorption spectroscopy (AAS) and in Fig. 1a. With increasing the KCl concentration from 0 to X-ray photoelectron spectroscopy (XPS). In this study, the carbon content was measured using a Var10EL-III ele- mental analyzer (Germany). Dry Na-Mt samples, which Table 1 Formulation of basic WBDF were prepared in Sect.  2.2, were used to evaluate the content of potassium and sodium ions on a SHIMADZU Composition Dosage, wt% Function AA-6300C atomic absorption spectrophotometer. XPS Fresh water 93.3 Dispersion medium analysis of the compacted samples was assessed with an Bentonite 4.0 Increase viscosity ESCALAB 250X-ray photoelectron spectrometer. and shear force The morphology of wet Na-Mt samples, which were Na CO 0.2 Increase viscosity 2 3 prepared in Sect. 2.2, was observed with environmental PAM 0.5 Increase viscosity CMC 1.0 Reduce filtration loss 1 3 830 Petroleum Science (2021) 18:827–838 (a) (b) 42 45 34 36 KCl PEG 3% PEG + KCl 7% KCl + PEG 0369 12 15 18 0369 12 15 18 KCl concentration, % PEG concentration, % Fig. 1 Hot rolling recovery of cuttings in solutions containing different inhibitors performance. From the data, both PEG and KCl have inhibi- Deionized water 3% KCl tive capacity, which are lower than the inhibitive capacity 7% PEG 3% KCl + 7% PEG of PEG+KCl. The order of linear swell rates was deionized 40 water > KCl > PEG > PEG+KCl. Compared with the linear swell rate of deionized water, the linear swell rates of KCl, PEG and PEG+KCl were reduced by 69%, 51% and 26%, respectively, after 72 h. According to the results of hot rolling recovery test and linear swell test, it can be concluded that PEG+KCl showed an improved inhibition performance than that of PEG or KCl. PEG+KCl has synergistic inhibition effect. 3.2 Analysis of the inhibitive mechanism Time, h 3.2.1 Fourier transform infrared spectroscopy Fig. 2 Linear swell rate of the different inhibitive systems In order to reveal the adsorption relationship between PEG and Na-Mt, FTIR spectrums of Na-Mt with different inhibi- 19%, the hot rolling recovery of cuttings in the KCl solution tors were measured with Nicolet 6700 FTIR spectrometer, whose results are shown in Fig.  3. The absorption bands increased from 27% to 35% and increased from 27% to 41% −1 in the PEG+KCl solution. As shown in Fig. 1b, the hot roll- at 1000 and 1631 cm were observed in three FTIR spec- trums, corresponding to the Si–O stretching vibration of ing recovery of cuttings in the PEG solution was also lower than that in the PEG+KCl solution. With increasing the PEG tetrahedral sheets and Si‒OH bending vibration (Biasci et al. 1995). For Na-Mt/3% KCl + 7% PEG and Na-Mt/7% concentrations from 0 to 18%, the hot rolling recovery of −1 cuttings in the PEG solution increased from 28% to 40% PEG, bands at 3450, 1481 and 1220 cm corresponded to H‒O stretching vibrations, C‒H bending vibrations and and increased from 28% to 45% in the PEG+KCl solution. This shows that the order of inhibition capacity of the three ‒O‒ stretching vibrations, respectively (Theng 1974). −1 −1 Bands at 2915 cm and 2875 cm were attributed to the systems is PEG+KCl > PEG > KCl. C‒H stretching vibration. Therefore, PEG adsorbed onto the Na-Mt with or without KCl. It is proved that the adsorption 3.1.2 Linear swell tests of PEG is related to synergistic effect of PEG+KCl. Linear swell tests are widely used to evaluate shale expan- sibility (van Oort et  al. 2016). The linear swell rates of the three different inhibition systems are shown in Fig.  2. Lower linear swell rate indicates an improved inhibition 1 3 Swelling rate, % Cuttings recovery, % Cuttings recovery, % Petroleum Science (2021) 18:827–838 831 d-spacing, nm 1.330 25 II 1.348 1.366 1.384 1.402 1.420 1.438 1.456 1.474 2927 & 2877 IV III 3% KCl+7% PEG 2468 10 7% PEG 3% KCl KCl concentration, % 3500 3000 2500 2000 1500 1000 500 -1 Fig. 5 Changes in d-spacing of wet Na-Mt according to KCl and PEG Wavenumber, cm concentrations Fig. 3 FTIR spectrums of Na-Mt in the presence of different inhibi- tors follows: PEG+KCl > KCl > PEG. Moreover, the results of XRD also show the synergistic effect on the reduction in d-spacing. 2.0 When the mixed solution (PEG+KCl) was used, changes 1.8 in d-spacing in the presence of each KCl and PEG con- 1.6 centration are shown in Fig. 5. Two obviously changes are 1.4 observed. In terms of PEG dosage, Fig. 5 can be divided into 1.2 two regions by red dash line (1.40 nm of d-spacing as the dividing line). In terms of KCl dosage, Fig. 5 can be divided 1.0 into two regions by blue dash line (7% of KCl dosage as the 0.8 dividing line). And the two dash lines divide Fig. 5 into four 0.6 regions (I, II III, IV). 0.4 0.2 (1) Analysis of differences between d -spacing and KCl concentration relations with low PEG and high PEG Without inhibitor3% PEG 7% KCl7% KCl + 3% PEG concentration PEG When the PEG concentration was below the red dash line, the d-spacing of Na-Mt rapidly decreased from Fig. 4 d-spacing of the wet Na-Mt with different inhibitors 1.47 to 1.33 nm with an increase in KCl concentration. When the PEG concentration was above the red dash line, the d-spacing of Na-Mt slowly decreased with an 3.2.2 X‑ray diffraction increase in KCl concentration. When the concentra- tion of KCl increased, an increase in the number of K To study the effect of inhibitors on the structure of Na-Mt, could strengthen the interaction between PEG and K , the d-spacing of Na-Mt with different inhibitors was tested which resulted in a decrease in d-spacing (Sun et al. by XRD, as shown in Fig. 4. The d-spacing of Na-Mt with 2005). The differences between the d -spacing and the 3% PEG was 1.81 nm. The d-spacing of Na-Mt with 7% KCl KCl concentration relations with low PEG and high was 1.53 nm. The d-spacing of Na-Mt with 3% PEG and 7% PEG concentration may be due to the filling conditions KCl was 1.40 nm. The three d-spacing values were lower of PEG in the interlayer spacing of Na-Mt. When the than the d-spacing related to hydrated Na-Mt (1.91 nm) (Xie PEG concentration was below the red dash line, the et al. 2017), which indicates that the three inhibition sys- PEG molecules did not fill up the whole interlayer spac- tems (KCl, PEG and PEG+KCl) can decrease d-spacing, ing of Na-Mt, as shown in Fig. 6a. There were some repel water molecules of interlayer and inhibit hydration of gaps in the spacing. Thus, the d-spacing could rapidly Na-Mt. Therefore, the order of inhibition performance is as decrease by compressing the gaps when the concentra- 1 3 d-spacing, nm PEG concentration, % 832 Petroleum Science (2021) 18:827–838 (a)(b) Water PEG Mt Fig. 6 Schematic of the PEG filling conditions. a PEG concentration below red dash line in Fig.  5; b PEG concentration above red dash line in Fig. 5 Table 2 The critical factors of d-spacing of Na-Mt with difference Table 3 Mutual behavior of different regions in Fig. 5 KCl and PEG concentrations Regions Mutual behaviors The region in Fig. 5 Critical factors I, II d-spacing slowly increases with an increase in KCl con- I Accumulation height of PEG centration II Accumulation height of PEG III, IV d-spacing rapidly increases with an increase in KCl concentration III Hydration radius of K I, III d-spacing initially decreases and then increases with an IV Accumulation height of PEG increase in PEG concentration II, IV d-spacing increases with an increase in PEG concentration tion of KCl increased. When the PEG concentration was above the red dash line, it can be considered that PEG filled up the whole interlayer spacing of Na-Mt, number of coordinated water molecules of coordination as shown in Fig. 6b. The d-spacing of Na-Mt slowly compound of PEG and KCl was significantly reduced decreased with KCl concentration, because there were at the KCl concentration above 7%. not compressible gaps in the spacing of interlayer of Na-Mt. In summary, based on the results and analysis of Fig. 5, (2) Analysis of differences between d -spacing and PEG the change of d-spacing with changes of KCl and PEG con- concentration relations with low KCl and high KCl centrations can be concluded into two tables (Tables 2 and concentration 3). Table 2 gives the critical factors of d-spacing of Na-Mt When the KCl concentration was below 7%, the with difference in KCl and PEG concentrations. Table  3 d-spacing of Na-Mt initially decreased and then gives the mutual behavior of different regions in Fig.  5. increased with an increase in PEG concentration. However, the d-spacing of Na-Mt showed an increased 3.3 KCl–PEG–Mt interaction mechanism trend with increasing PEG concentration at the KCl by chemical characterization and SEM concentration greater than 7%. The main difference characterization of above behavior is at PEG concentration below the red dash line of Fig.  5. The differences between the In the above part, we discussed the influence of two inhibi- d-spacing and the PEG concentration with low KCl and tors on Na-Mt structure at different concentrations by tak - high KCl concentrations may be due to their different ing d-spacing as the index. However, the d-spacing is the critical factors (accumulation height of PEG and hydra- result of multiple physical processes. In this section, these tion radius of K ). When the KCl concentration was processes are studied further. below 7%, the critical factor was the hydration radius of K . When the concentration of PEG increased, more 3.3.1 Elemental analysis water molecules bonded with K were replaced by PEG molecules, which resulted in decreases in the hydration In order to reveal the interaction between KCl and PEG, radius of K and d-spacing of Na-Mt. When the KCl the carbon content of Na-Mt/inhibitor complexes was tested concentration was above 7%, the d-spacing of Na-Mt by elemental analysis. Because Na-Mt only has low levels increased with increasing PEG concentration, because of organic carbon, the carbon content of Na-Mt/inhibitor more PEG molecules accumulated in the interlayer of complexes shows the adsorption quantity of PEG on Na-Mt. Na-Mt. More importantly, it can be concluded that the The carbon content analysis of the Na-Mt with 3% PEG 1 3 Petroleum Science (2021) 18:827–838 833 4.15 3.3.2 Atomic absorption spectroscopy 4.10 + + To study the adsorption quantity of K and Na , a series 4.05 of Na-Mt with different concentrations of KCl and PEG were analyzed with an atomic absorption spectrophotom- 4.00 eter. The adsorption capacity of Na-Mt with 3% PEG and 3.95 different concentrations of KCl are shown in Fig.  8a. With an increase in KCl concentration, the adsorption quantity 3.90 + + of Na rapidly decreased. The adsorption quantity of K 3.85 adsorbed onto the clay surface increased with an increase in KCl concentration. The adsorption quantity of K and 3.80 Na of Na-Mt with 7% KCl and different concentrations 3.75 of PEG are shown in Fig.  8b. With an increase in PEG 02468 10 12 concentration, the adsorption quantity of Na remained KCl concentration, % unchanged, because the amount of K is sufficient to dis- place all the exchangeable cations at the KCl concentra- Fig. 7 Carbon content of Na-Mt/inhibitor complexes with different tion of 7%. Additionally, the adsorption amount of K KCl concentrations and 3% PEG decreased as the PEG concentration increased from 0.5% to 5%, and the adsorption amount remained constant after and different KCl concentrations are shown in Fig.  7. With the PEG concentration was above 7%. These phenomena increasing KCl concentration from 0.1% to 4%, the adsorp- can be attributed to the different types of adsorption of K . tion quantity of PEG increased, implying that KCl promoted On the surface of Na-Mt, there are three types of adsorp- PEG adsorption at this concentration range. This promotion tion sites: oxygen atom of hexagonal site of silica, H and Al effect is attributed to the mutual attraction between KCl and T , which are defined in Fig.  9 (Ruankaew et al. 2020). Al PEG (Yanagida et al. 1977, 1978a, b). With increasing KCl The main adsorption force of K is the isomorphic substi- concentration from 4% to 11%, the adsorption quantity of tution in tetrahedral sheet and octahedral sheet (Li et al. PEG decreased, which indicates that KCl can inhibit the 2018). So, the adsorption strength of the oxygen atom of adsorption of PEG. This was likely due to the competitive hexagonal site of silica is lower than those of H and Al adsorption relationship between PEG and KCl on the surface T . Based on the experimental results of atomic absorp- Al of Na-Mt. It can be concluded that the promotion effect was tion spectroscopy, it can be considered that the adsorp- dominant when the KCl concentration was lower than 4%, tion sites of H and T are only occupied by K , whose Al Al while the competitive adsorption was dominant when the adsorption is not affected by PEG. The adsorption sites of KCl concentration was higher than 4%. the oxygen atom of hexagonal site of silica can be occu- pied by both K and PEG. And the adsorption amounts of K and PEG depend on their concentration ratio. Their (a) (b) + + K K + + Na Na 0 0 01234567 02468 10 12 14 16 KCl concentration, % PEG concentration, % Fig. 8 Variations in cation content according to inhibitor concentrations: a different KCl concentrations and 3% PEG; b different PEG concen- trations and 7% KCl 1 3 Carbon content, % Cation content, mmol/100 g Cation content, mmol/100 g 834 Petroleum Science (2021) 18:827–838 capacity reached its peak when the KCl concentration is 4%. Nevertheless, as considering the adsorption of K , the total adsorption reached its peak value when the KCl concentration is above 7%. Considering the cost, the KCl Al T concentration range of 6%–8% is the most suitable. When Si the total adsorption reached the peak, the synergistic effect was most likely to be exerted. Therefore, the estimated H H Al Si concentration range had a good effect. 3.3.3 X‑ray photoelectron spectroscopy + + In order to demonstrate the substitution of N a by K and the synergistic effects of KCl and PEG, dry Na-Mt samples Fig. 9 A most top surface of Mt with the isomorphous replacement of with different inhibitors were tested by XPS, as shown in silica by aluminum. Atomic legends were colored highlight as silica Fig. 11. XPS can be used to investigate the surface com- (light blue), oxygen (red), hydrogen (white) and aluminum (orange). position of Na-Mt with different inhibitors (Jiang et al. Dotted triangles, T and T , represent the triangular site of silica Si Al and aluminum, respectively. Dotted hexagons, H and H , represent 2016). The XPS spectra of Na 1s of Na-Mt with differ - Si Al the hexagonal site next to the triangular site of silica and aluminum, ent inhibitors are shown in Fig. 11a. Blank spectrum was respectively tested with Na-Mt without inhibitors. Compared with the blank spectrum, the signal peak of Na-Mt with 3% KCl became weaker, which showed that KCl replaced Na in Na-Mt. In addition, the signal peak of Na-Mt with 3% KCl and 7% PEG was similar to that with 3% KCl. It sug- gests that PEG cannot influence the displacement of Na by KCl. In the XPS spectra of K 2p of Na-Mt with different inhibitors (Fig.  11b), the blank spectrum was obtained without inhibitor and showed no K 2p signal, which indicates that Na-Mt does not contain K . After addi- tion of 3% KCl, the signal peak became stronger. Then, after further addition of 7% PEG, the signal peak became weaker, which possibly resulted from competitive adsorp- tion between KCl and PEG on Na-Mt. This was confirmed C+K through the elemental analysis in Sect. 3.3.1. Moreover, 02468 10 12 the Na-Mt/KCl binding energy of K 2p increased from KCl concentration, % 295.8, 293.1 to 295.9, 293.2 eV after PEG addition, imply- ing that PEG undergoes binding with K . This was also Fig. 10 Elemental contents with different KCl concentrations demonstrated through the elemental analysis in Sect. 3.3.1. competitive adsorption capacity increased when the PEG 3.3.4 Scanning electron microscopy concentration increased from 0.5% to 5%, which resulted in an increase in the adsorption amount of PEG. When the SEM was used to observe the morphology of wet Na-Mt PEG concentration was above 7%, all the sites of H and with different inhibitor systems. The morphology of pure Al T were occupied by K , and all the sites of the oxygen Na-Mt was a layered structure, as shown in Fig. 12a. Fol- Al atom of hexagonal site of silica were occupied by PEG. lowing the addition of 3% PEG, the morphology of Na-Mt Therefore, the adsorption amount of K is not affected by with PEG was still layered structure in Fig. 12b, which was PEG concentration. similar to that of pure Na-Mt. After the addition of 7% By comprehensive analysis of the results of elemen- KCl, some of the Na-Mt particles showed spherical struc- tal analysis and atomic absorption spectrophotometry as tures, as illustrated in Fig. 12c. When 3% PEG and 7% KCl shown in Fig.  10, the initial assessment of the optimal were used together as a synergistic inhibitor, the majority KCl concentrations can be performed. The PEG adsorption of Na-Mt particles exhibited spherical structures, as shown in Fig.  12d. Inhibitors usually have strong adsorption 1 3 Element content, mmol/100 g Petroleum Science (2021) 18:827–838 835 (a) (b) 293.1 3% KCl 3% KCl Na 1s K 2p 3% KCl + 7% PEG 3% KCl + 7% PEG 7% PEG 1071.7 7% PEG 293.2 Blank Blank 1071.7 295.8 295.9 1071.7 1071.7 1066 1068 1070 1072 1074 1076 298 296 294 292 290 Binding energy, eV Binding energy, eV Fig. 11 XPS patterns of Na-Mt with the different inhibitors: a Na 1 s pattern; b K 2p pattern Fig. 12 SEM images of wet Na-Mt/inhibitors: a Na-Mt; b Na-Mt/PEG; c wet Na-Mt/KCl; d wet Na-Mt/PEG + KCl capacity, which allows them to replace water molecules by comparing the morphology of wet Na-Mt with different and decrease d-spacing of Na-Mt. The strong adsorption inhibitor systems, the order of inhibition performance was capacity causes Na-Mt to aggregate, which results in the deter mined to be PEG+KCl > KCl > PEG. spherical structure of Na-Mt (Xie et al. 2017). Therefore, 1 3 836 Petroleum Science (2021) 18:827–838 The optimal KCl and PEG concentrations should be near the 3.4 Optimization of PEG and KCl concentrations intersection of the above two boundaries. Then, several con- centrations were selected, as shown in Fig. 13. The optimal The optimization of PEG and KCl concentrations was as fol- lows: (1) XRD was used to identify the boundary of chang- KCl and PEG concentrations were chosen from the different concentrations by the shale hot rolling recovery test. ing trend in d-spacing with an increase in PEG concentra- tion. When concentration ranges of PEG and KCl were on For the Na-Mt sample studied in this work, the optimal concentrations of PEG and KCl were obtained as 7% KCl the boundary (the red dash line in Fig.  5), the interlayer spacing of Na-Mt was filled up by PEG. Hence, the optimal and 5% PEG. Then, the optimization of PEG and KCl con- centrations was verified by a series of tests on Na-Mt. A concentration of PEG was in this range. (2) XRD was also used to identify the boundary of changing trend in d-spacing set of water-based drilling fluids with different concentra- tions of KCl and PEG was designed. The corresponding with an increase in KCl concentration. At the KCl concentra- tion above the boundary, the number of coordinated water basic rheological properties and API filtrate volumes are given in Table 4. The rheological properties and filtrate molecules of the PEG–KCl coordination compound was sig- nificantly reduced. In consideration of cost, the optimal con- properties of the water-based drilling fluids are acceptable according to API RP 13B-2 (2005). centration of KCl should be near the boundary (the blue dash line in Fig. 5). (3) The intersection of the above two bounda- The shale hot rolling recovery results of water-based drilling fluids with different inhibitors are shown in ries represents the optimal KCl and PEG concentrations. Fig. 14. KCl and PEG improved the cutting recovery of the drilling fluids, indicating that both KCl and PEG can (a-1, b+1) (a, b+1) (a+1, b+1) improve inhibition properties of water-based drilling flu- ids. The synergistic inhibitive effects of KCl and PEG were obvious, which resulted in higher cutting recovery. Moreo- ver, the higher the concentration, the higher the cutting recovery. When 14% KCl and 5% PEG were used together as synergistic inhibitors (Fig. 14h), both the rheological properties and filtrate properties of the drilling fluid were (a-1, b)(a, b) (a+1, b) unacceptable for engineering practice. Thus, for the Na-Mt studied in this paper, 7% KCl and 5% PEG were deemed to be the optimal concentrations. 4 Conclusions (a-1, b-1) (a, b-1) (a+1, b-1) The synergistic inhibition performance of PEG and KCl a: PEG concentration, %; b: KCl concentration, % was evaluated through hot rolling recovery tests and lin- ear swell tests on shale cuttings. For the inhibition of Fig. 13 Schematic diagram of concentration optimization Na-Mt hydration, the synergistic effect of KCl and PEG Table 4 Rheological properties and API filtrate volumes of drilling fluids with different inhibitors after hot rolling (120 °C, 16 h) Sample No. Inhibitors AV, mPa s PV, mPa s YP, Pa YP/PV, Pa/ Gel strength Filtrate (mP s) (10 s/10 min), Pa volume, cm a Blank sample 27.0 24.0 6.0 0.25 4.0/4.5 11.4 b 7% KCl 19.0 14.0 8.0 0.57 3.5/4.0 12.6 c 5% PEG 27.0 23.0 7.0 0.30 3.0/4.0 8.4 d 7% KCl + 1% PEG 24.0 20.0 7.0 0.35 3.0/4.0 10.6 e 1% KCl + 5% PEG 26.5 22.0 7.5 0.34 3.0/3.5 7.8 f 3.5% KCl + 2.5% PEG 28.0 24.0 8.0 0.35 3.5/4.0 8.2 g 7% KCl + 5 wt% PEG 25.5 20.0 8.5 0.43 3.0/3.5 9.9 h 14% KCl + 10% PEG 16.0 11.0 9.0 0.73 2.5/3.0 14.3 1 3 Petroleum Science (2021) 18:827–838 837 100 Open Access This article is licensed under a Creative Commons Attri- bution 4.0 International License, which permits use, sharing, adapta- 87.80 88.15 85.50 tion, distribution and reproduction in any medium or format, as long 81.20 76.40 as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes 63.65 were made. The images or other third party material in this article are 61.05 included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not 42.70 permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativ ecommons .or g/licenses/b y/4.0/. References ab cd ef gh Inhibitive system Al-Bazali TM. The consequences of using concentrated salt solu- tions for mitigating wellbore instability in shales. J Pet Sci Eng. 2011;80(1):94–101. Fig. 14 Cutting recovery of different inhibitors: a blank sample; b 7% API. API RP 13B-2, recommended practice for field testing of oil- KCl; c 5% PEG; d 7% KCl + 1% PEG; e 1% KCl + 5% PEG; f 3.5% based drilling fluids. 4th edn. Washington, DC; 2005. 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Synergistic inhibition of polyethylene glycol and potassium chloride in water-based drilling fluids

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Springer Journals
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Copyright © The Author(s) 2021
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1672-5107
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1995-8226
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10.1007/s12182-020-00543-w
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Abstract

Mud shale hydration and swelling are major challenges in the development of water-based drilling fluids (WBDFs). In this work, the inhibition performance and inhibition mechanism of polyethylene glycol (PEG) and potassium chloride (KCl) were investigated by hot rolling recovery tests, linear swell tests, Fourier transform infrared spectroscopy, X-ray diffraction, atomic absorption spectrophotometry and X-ray photoelectron spectroscopy. The experimental results show that the com- bination of PEG and KCl achieved higher recovery and lower linear swelling rate than those obtained by individual PEG or KCl. Compared to the d-spacing of Na-montmorillonite (Na-Mt) with PEG or KCl, the d-spacing of Na-Mt with PEG+KCl was lower, which indicates that KCl and PEG have synergistic inhibition effect. This synergistic effect can replace sodium ions and water molecules from the interlayer space of Na-Mt and decrease the d-spacing of Na-Mt. Based on the above experimental results and analysis, a method for optimizing PEG and KCl concentrations was proposed and further verified by rheological and hot rolling recovery tests of WBDFs. Hence, the results of this work can provide valuable theoretical guidance for developing other synergistic inhibitors. Keywords Clay hydration · Inhibitor · Synergistic inhibition · Polyethylene glycol · Water-based drilling fluids 1 Introduction 2020). When water-sensitive shale comes into contact with water-based drilling fluids (WBDFs), hydration and swelling Shale oil and gas resources have been attracting a consider- of clay minerals occur, which can generate wellbore insta- able amount of attention in recent years (Qian et al. 2020; bility (Cook et al. 1993; Mody and Hale 1993; van Oort Li et al. 2020). Severe wellbore instability frequently occurs 2003; Guo et al. 2006; Al-Bazali 2011). This results in sev- during drilling of water-sensitive shale formations, which eral downhole complications, including wellbore collapse, account for 75% of the drilling formations (Bol et al. 1994; wellbore shrinkage, pipe sticking and bit balling, which can Dzialowski et al. 1993; Steiger and Leung 1992; Li et al. increase both drilling times and costs (Khodja et al. 2010; Liu et al. 2006; Wang et al. 2009; Cai et al. 2008; Baohua et al. 2013; Li et al. 2015). In many cases, oil-based/syn- Edited by Yan-Hua Sun thetic-based drilling fluids are used to ensure swelling inhi- bition in water-sensitive formations (Li et al. 2016a, 2019). * Gang Xie Despite their benefits, such as well inhibition ability, tem- 201899010129@swpu.edu.cn perature resistance and lubricity, the oil-based drilling fluids * Ping-Ya Luo lead to environmental pollution and high costs, limiting their luopy@swpu.edu.cn application in the field. Therefore, WBDFs are the focus of State Key Laboratory of Oil & Gas Reservoir Geology much research, and the most important task in the research and Exploitation, Southwest Petroleum University, of WBDFs is to develop an excellent swelling inhibitor. Chengdu 610500, Sichuan, China In the field of WBDFs, amine inhibitors have emerged as College of Chemistry and Chemical Engineering, Southwest a research focus, but there are some environmental problems Petroleum University, Chengdu 610500, Sichuan, China associated with this class of chemicals. However, polyols, as College of Chemistry and Chemical Engineering, Xi’an inhibitors for WBDFs, satisfy international environmental Shiyou University, Xi’an 710056, Shanxi, China Vol.:(0123456789) 1 3 828 Petroleum Science (2021) 18:827–838 standards in terms of toxicity and biodegradability (Twynam 71.30% SiO , 13.22% Al O , 4.79% Na O, 7.10% MgO and 2 2 3 2 et  al. 1994). In addition, polyols have the advantages of 3.59% Fe O , which was determined with the X-ray diffrac- 2 3 water solubility, lubricity, thermal stability and compat- tion method. The cation exchange capacity (CEC) of Na-Mt ibility with conventional treatment in the WBDFs (Bland was 113 meq/100 g. Drill cuttings were purchased from the et al. 1996; Bland 1992). In 1940, Cannon (1940) success- Center for Well Completion and Logging Laboratory and fully tackled the shale swelling problem during drilling of had 58.7% clay and 41.3% non-clay. Polyacrylamide (PAM) a water-sensitive formation with 30% ethylene glycol and (anionic; mean molecular weight of 3 × 10 ), carboxymethyl propylene glycol in the WBDFs. A large number of field cellulose (CMC), polyethylene glycol (PEG, mean molecu- applications and laboratory studies have shown that polyols lar weight of 500), Na CO and KCl were purchased from 2 3 have an excellent inhibition performance in the presence of Chengdu Micxy Chemical Co., Ltd. Bentonite was pur- KCl (Bland 1992). Low-salinity glycol WBDFs have been chased from Xinjiang Zhongfei Xiazi Street Bentonite Co., developed for shale drilling in environmentally sensitive Ltd. locations (Brady et al. 1998). KCl-PHPA-polyols were used to maintain borehole stability and reduce torque in the Sob- 2.2 Sample preparation hasan oilfield of India (Raza Khan et al. 2006). Moreover, polyol and potassium carbonate were applied as inhibitors The sample pretreatment process is as follows. Na-Mt was to the Kanina oilfields of Albania (Isinak et al. 2005). In the dried at 150 °C for 24 h. Then, 1 g of dry Na-Mt was added deep exploratory wells of the Assam oilfield, polyol-KCl to 25 mL of distilled water. After 3 h of stirring at 30 °C, the drilling fluids effectively inhibited clay swelling, improved Na-Mt dispersion was added to 25 mL of inhibitor solution wettability of drill pipe and reduced torque. The combina- of different concentrations. Then, the dispersion was stirred tion of polyethylene glycol (PEG) and KCl exhibits better at 30 °C for 24 h and centrifuged at 5000 rpm for 25 min. inhibition performance than that provided by individual PEG The centrifugal sediment was added to 25 mL of distilled or KCl. The mechanism of synergistic inhibition is related water and stirred with a glass rod. After that, the samples to a complexation between PEG and K , which can weaken were centrifuged and washed three times by water. the hydration of K (Sartori et al. 1990; Tasaki et al. 1999). In order to facilitate the description and comparison of the Boulet (2004) demonstrated that PEG+KCl can decrease the experimental results, two types of samples are defined: wet layer spacing of Mt crystalline to 1.40 nm, and PEG adopts Na-Mt/inhibitor samples and dry Na-Mt/inhibitor samples. a single-layer structure. However, the mechanism of syner- The pre-treated samples are wet Na-Mt/inhibitor samples. gistic inhibition caused by PEG+KCl is still not well under- Dry Na-Mt/inhibitor samples were obtained through drying stood and needs to be theoretically explored. Moreover, no the wet sample at 150 °C for 24 h and complete grinding. studies have yet proposed a general principle to optimize the concentrations of these two inhibitors for WBDFs. 2.3 Methods In this study, the synergistic inhibition effect of PEG and KCl was investigated through linear swell tests and hot roll- 2.3.1 Inhibition performance evaluation ing recovery tests. After that, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), elemental Hot rolling recovery tests are performed as follows. A total analysis (EA), atomic absorption spectrophotometry (AAS), of 50 ± 0.01 g drill cuttings were passed through a 10-mesh X-ray photoelectron spectroscopy (XPS) and scanning elec- sieve and dried at 105 ± 3 °C for 4 h. The drill cuttings were tron microscopy (SEM) were used to demonstrate and reveal added to high-temperature aging tanks with 350 mL of 1% the complex mechanism of this synergistic inhibition. Based inhibitor solution. The tanks were aged in a roller oven at on the proposed mechanism, a principle of optimizing con- 120 °C for 16 h. After hot rolling, the drill cuttings were centrations of PEG and KCl in WBDF was put forward. passed through a 40-mesh sieves and dried at 105 ± 3 °C for Both the inhibition mechanism and optimization principle 4 h. Cuttings were cooled to room temperature and weighed were verified against the results of drilling fluid tests in the (m). The first hot rolling recovery (R ) was the ratio of resid- laboratory. ual drill cuttings after first aging. The cuttings from the first recovery were aged a second and a third time. The first, second and third hot rolling recovery of the drill cuttings 2 Experimental (R , R , R ) were calculated using Eq. (1): 1 2 3 2.1 Materials R = × 100% (1) The chemical composition of Na-montmorillonite (Na-Mt) (obtained from the Nanocor Company) was as follows: 1 3 Petroleum Science (2021) 18:827–838 829 where m is the recovery mass of cuttings (i = 1, 2, 3); R is scanning electron microscope (SEM). SEM was per- i i the cutting recovery, %. formed with a Quanta 650F instrument. Linear swell tests were performed as follows. A total of 10 ± 0.01 g of drill cuttings were passed through a 100- 2.3.3 Inhibition performance evaluation of WBDF mesh sieve and dried at 105 ± 3 °C for 4 h. After that, the drill cuttings were added to test tubes and compressed at To evaluate the inhibition performance of WBDF with inhib- 4 MPa for 5 min. The pressure was then relieved, and the itors, the following steps are required. (1) The preparation original height of the cutting column (H) was measured of the WBDF with inhibitors. The formulation of the basic with a Vernier caliper. WBDF is listed in Table 1. The bentonite and N a CO were 2 3 Then, the cutting column was installed in the linear added to 200 mL of freshwater and pre-hydrated at room dilatometer. Certain concentrations of inhibitor solution temperature for 24 h. Then, the other agents (as shown in were added to the linear dilatometer until the solution is Table 1) were slowly added to the system and stirred thor- above the top of the cutting column. With the change of oughly in a high-speed mixer at a rate of 11,000 rpm (Li time, the changes in the height of the cutting column were et al. 2016c). At last, certain concentrations of inhibitors recorded. At last, the linear swell ratio was calculated were added to the basic WBDF. (2) The evaluation of inhibi- using Eq. (2): tion performance of WBDF with inhibitors. For the WBDF with inhibitors, their rheological parameters including apparent viscosity (AV), plastic viscosity (PV), yield point W = × 100% (2) (YP), yield point and plastic viscosity ratio (YP/PV), and gel strength, API filtrate volume after hot rolling (120 °C, where W is the percentage of linear swell ratio; H is the 16 h) were measured in light of the standard test recom- original height of the cutting column in mm; and H is the mended by API RP 13B-2 (2005). According to the method height of the cutting column at time t, mm. in Sect. 2.3.1, the hot rolling recovery of the drill cuttings in the WBDF with inhibitors was obtained. 2.3.2 Structure characterization and morphology observation 3 Results and discussion Fourier transform infrared spectroscopy (FTIR) was 3.1 Inhibition performance of KCl and PEG used to investigate the organic adsorption on clay. FTIR was performed using a Nicolet 6700 FTIR spectrometer 3.1.1 Hot rolling recovery tests (Thermo Scientific Corporation, USA). The layer spacing of Mt (d ) crystal plane is usually Hot rolling recovery tests were used to evaluate the swelling defined as d-spacing (Chaudhary et al. 2013; Lee et al. ability of the shale. An improved inhibitive capacity can be 2005). X-ray diffraction (XRD) can be used to study the indicated by higher cuttings recovery (Khodja et al. 2010). d-spacing of Na-Mt. The XRD patterns of the samples In application, 3%–10% KCl and 5%–7% PEG (by weight) were obtained with an X’Pert Pro MPD diffractometer (a are commonly used (Hale and Blytas 1993; Reid et al. 2003; Cu Kα radiation source) at 2θ angles scanned from 3° to Smith and Balson 2004). After hot rolling at 120 °C for 16 h, 40°. The d-spacing of the samples were analyzed through the cutting recovery of the different systems was measured Bragg’s equation (Xie et al. 2017). (Fig. 1). The hot rolling recovery of cuttings in the KCl solu- Ion adsorption can be investigated through elemen- tion was lower than that in the PEG+KCl solution, as shown tal analysis, atomic absorption spectroscopy (AAS) and in Fig. 1a. With increasing the KCl concentration from 0 to X-ray photoelectron spectroscopy (XPS). In this study, the carbon content was measured using a Var10EL-III ele- mental analyzer (Germany). Dry Na-Mt samples, which Table 1 Formulation of basic WBDF were prepared in Sect.  2.2, were used to evaluate the content of potassium and sodium ions on a SHIMADZU Composition Dosage, wt% Function AA-6300C atomic absorption spectrophotometer. XPS Fresh water 93.3 Dispersion medium analysis of the compacted samples was assessed with an Bentonite 4.0 Increase viscosity ESCALAB 250X-ray photoelectron spectrometer. and shear force The morphology of wet Na-Mt samples, which were Na CO 0.2 Increase viscosity 2 3 prepared in Sect. 2.2, was observed with environmental PAM 0.5 Increase viscosity CMC 1.0 Reduce filtration loss 1 3 830 Petroleum Science (2021) 18:827–838 (a) (b) 42 45 34 36 KCl PEG 3% PEG + KCl 7% KCl + PEG 0369 12 15 18 0369 12 15 18 KCl concentration, % PEG concentration, % Fig. 1 Hot rolling recovery of cuttings in solutions containing different inhibitors performance. From the data, both PEG and KCl have inhibi- Deionized water 3% KCl tive capacity, which are lower than the inhibitive capacity 7% PEG 3% KCl + 7% PEG of PEG+KCl. The order of linear swell rates was deionized 40 water > KCl > PEG > PEG+KCl. Compared with the linear swell rate of deionized water, the linear swell rates of KCl, PEG and PEG+KCl were reduced by 69%, 51% and 26%, respectively, after 72 h. According to the results of hot rolling recovery test and linear swell test, it can be concluded that PEG+KCl showed an improved inhibition performance than that of PEG or KCl. PEG+KCl has synergistic inhibition effect. 3.2 Analysis of the inhibitive mechanism Time, h 3.2.1 Fourier transform infrared spectroscopy Fig. 2 Linear swell rate of the different inhibitive systems In order to reveal the adsorption relationship between PEG and Na-Mt, FTIR spectrums of Na-Mt with different inhibi- 19%, the hot rolling recovery of cuttings in the KCl solution tors were measured with Nicolet 6700 FTIR spectrometer, whose results are shown in Fig.  3. The absorption bands increased from 27% to 35% and increased from 27% to 41% −1 in the PEG+KCl solution. As shown in Fig. 1b, the hot roll- at 1000 and 1631 cm were observed in three FTIR spec- trums, corresponding to the Si–O stretching vibration of ing recovery of cuttings in the PEG solution was also lower than that in the PEG+KCl solution. With increasing the PEG tetrahedral sheets and Si‒OH bending vibration (Biasci et al. 1995). For Na-Mt/3% KCl + 7% PEG and Na-Mt/7% concentrations from 0 to 18%, the hot rolling recovery of −1 cuttings in the PEG solution increased from 28% to 40% PEG, bands at 3450, 1481 and 1220 cm corresponded to H‒O stretching vibrations, C‒H bending vibrations and and increased from 28% to 45% in the PEG+KCl solution. This shows that the order of inhibition capacity of the three ‒O‒ stretching vibrations, respectively (Theng 1974). −1 −1 Bands at 2915 cm and 2875 cm were attributed to the systems is PEG+KCl > PEG > KCl. C‒H stretching vibration. Therefore, PEG adsorbed onto the Na-Mt with or without KCl. It is proved that the adsorption 3.1.2 Linear swell tests of PEG is related to synergistic effect of PEG+KCl. Linear swell tests are widely used to evaluate shale expan- sibility (van Oort et  al. 2016). The linear swell rates of the three different inhibition systems are shown in Fig.  2. Lower linear swell rate indicates an improved inhibition 1 3 Swelling rate, % Cuttings recovery, % Cuttings recovery, % Petroleum Science (2021) 18:827–838 831 d-spacing, nm 1.330 25 II 1.348 1.366 1.384 1.402 1.420 1.438 1.456 1.474 2927 & 2877 IV III 3% KCl+7% PEG 2468 10 7% PEG 3% KCl KCl concentration, % 3500 3000 2500 2000 1500 1000 500 -1 Fig. 5 Changes in d-spacing of wet Na-Mt according to KCl and PEG Wavenumber, cm concentrations Fig. 3 FTIR spectrums of Na-Mt in the presence of different inhibi- tors follows: PEG+KCl > KCl > PEG. Moreover, the results of XRD also show the synergistic effect on the reduction in d-spacing. 2.0 When the mixed solution (PEG+KCl) was used, changes 1.8 in d-spacing in the presence of each KCl and PEG con- 1.6 centration are shown in Fig. 5. Two obviously changes are 1.4 observed. In terms of PEG dosage, Fig. 5 can be divided into 1.2 two regions by red dash line (1.40 nm of d-spacing as the dividing line). In terms of KCl dosage, Fig. 5 can be divided 1.0 into two regions by blue dash line (7% of KCl dosage as the 0.8 dividing line). And the two dash lines divide Fig. 5 into four 0.6 regions (I, II III, IV). 0.4 0.2 (1) Analysis of differences between d -spacing and KCl concentration relations with low PEG and high PEG Without inhibitor3% PEG 7% KCl7% KCl + 3% PEG concentration PEG When the PEG concentration was below the red dash line, the d-spacing of Na-Mt rapidly decreased from Fig. 4 d-spacing of the wet Na-Mt with different inhibitors 1.47 to 1.33 nm with an increase in KCl concentration. When the PEG concentration was above the red dash line, the d-spacing of Na-Mt slowly decreased with an 3.2.2 X‑ray diffraction increase in KCl concentration. When the concentra- tion of KCl increased, an increase in the number of K To study the effect of inhibitors on the structure of Na-Mt, could strengthen the interaction between PEG and K , the d-spacing of Na-Mt with different inhibitors was tested which resulted in a decrease in d-spacing (Sun et al. by XRD, as shown in Fig. 4. The d-spacing of Na-Mt with 2005). The differences between the d -spacing and the 3% PEG was 1.81 nm. The d-spacing of Na-Mt with 7% KCl KCl concentration relations with low PEG and high was 1.53 nm. The d-spacing of Na-Mt with 3% PEG and 7% PEG concentration may be due to the filling conditions KCl was 1.40 nm. The three d-spacing values were lower of PEG in the interlayer spacing of Na-Mt. When the than the d-spacing related to hydrated Na-Mt (1.91 nm) (Xie PEG concentration was below the red dash line, the et al. 2017), which indicates that the three inhibition sys- PEG molecules did not fill up the whole interlayer spac- tems (KCl, PEG and PEG+KCl) can decrease d-spacing, ing of Na-Mt, as shown in Fig. 6a. There were some repel water molecules of interlayer and inhibit hydration of gaps in the spacing. Thus, the d-spacing could rapidly Na-Mt. Therefore, the order of inhibition performance is as decrease by compressing the gaps when the concentra- 1 3 d-spacing, nm PEG concentration, % 832 Petroleum Science (2021) 18:827–838 (a)(b) Water PEG Mt Fig. 6 Schematic of the PEG filling conditions. a PEG concentration below red dash line in Fig.  5; b PEG concentration above red dash line in Fig. 5 Table 2 The critical factors of d-spacing of Na-Mt with difference Table 3 Mutual behavior of different regions in Fig. 5 KCl and PEG concentrations Regions Mutual behaviors The region in Fig. 5 Critical factors I, II d-spacing slowly increases with an increase in KCl con- I Accumulation height of PEG centration II Accumulation height of PEG III, IV d-spacing rapidly increases with an increase in KCl concentration III Hydration radius of K I, III d-spacing initially decreases and then increases with an IV Accumulation height of PEG increase in PEG concentration II, IV d-spacing increases with an increase in PEG concentration tion of KCl increased. When the PEG concentration was above the red dash line, it can be considered that PEG filled up the whole interlayer spacing of Na-Mt, number of coordinated water molecules of coordination as shown in Fig. 6b. The d-spacing of Na-Mt slowly compound of PEG and KCl was significantly reduced decreased with KCl concentration, because there were at the KCl concentration above 7%. not compressible gaps in the spacing of interlayer of Na-Mt. In summary, based on the results and analysis of Fig. 5, (2) Analysis of differences between d -spacing and PEG the change of d-spacing with changes of KCl and PEG con- concentration relations with low KCl and high KCl centrations can be concluded into two tables (Tables 2 and concentration 3). Table 2 gives the critical factors of d-spacing of Na-Mt When the KCl concentration was below 7%, the with difference in KCl and PEG concentrations. Table  3 d-spacing of Na-Mt initially decreased and then gives the mutual behavior of different regions in Fig.  5. increased with an increase in PEG concentration. However, the d-spacing of Na-Mt showed an increased 3.3 KCl–PEG–Mt interaction mechanism trend with increasing PEG concentration at the KCl by chemical characterization and SEM concentration greater than 7%. The main difference characterization of above behavior is at PEG concentration below the red dash line of Fig.  5. The differences between the In the above part, we discussed the influence of two inhibi- d-spacing and the PEG concentration with low KCl and tors on Na-Mt structure at different concentrations by tak - high KCl concentrations may be due to their different ing d-spacing as the index. However, the d-spacing is the critical factors (accumulation height of PEG and hydra- result of multiple physical processes. In this section, these tion radius of K ). When the KCl concentration was processes are studied further. below 7%, the critical factor was the hydration radius of K . When the concentration of PEG increased, more 3.3.1 Elemental analysis water molecules bonded with K were replaced by PEG molecules, which resulted in decreases in the hydration In order to reveal the interaction between KCl and PEG, radius of K and d-spacing of Na-Mt. When the KCl the carbon content of Na-Mt/inhibitor complexes was tested concentration was above 7%, the d-spacing of Na-Mt by elemental analysis. Because Na-Mt only has low levels increased with increasing PEG concentration, because of organic carbon, the carbon content of Na-Mt/inhibitor more PEG molecules accumulated in the interlayer of complexes shows the adsorption quantity of PEG on Na-Mt. Na-Mt. More importantly, it can be concluded that the The carbon content analysis of the Na-Mt with 3% PEG 1 3 Petroleum Science (2021) 18:827–838 833 4.15 3.3.2 Atomic absorption spectroscopy 4.10 + + To study the adsorption quantity of K and Na , a series 4.05 of Na-Mt with different concentrations of KCl and PEG were analyzed with an atomic absorption spectrophotom- 4.00 eter. The adsorption capacity of Na-Mt with 3% PEG and 3.95 different concentrations of KCl are shown in Fig.  8a. With an increase in KCl concentration, the adsorption quantity 3.90 + + of Na rapidly decreased. The adsorption quantity of K 3.85 adsorbed onto the clay surface increased with an increase in KCl concentration. The adsorption quantity of K and 3.80 Na of Na-Mt with 7% KCl and different concentrations 3.75 of PEG are shown in Fig.  8b. With an increase in PEG 02468 10 12 concentration, the adsorption quantity of Na remained KCl concentration, % unchanged, because the amount of K is sufficient to dis- place all the exchangeable cations at the KCl concentra- Fig. 7 Carbon content of Na-Mt/inhibitor complexes with different tion of 7%. Additionally, the adsorption amount of K KCl concentrations and 3% PEG decreased as the PEG concentration increased from 0.5% to 5%, and the adsorption amount remained constant after and different KCl concentrations are shown in Fig.  7. With the PEG concentration was above 7%. These phenomena increasing KCl concentration from 0.1% to 4%, the adsorp- can be attributed to the different types of adsorption of K . tion quantity of PEG increased, implying that KCl promoted On the surface of Na-Mt, there are three types of adsorp- PEG adsorption at this concentration range. This promotion tion sites: oxygen atom of hexagonal site of silica, H and Al effect is attributed to the mutual attraction between KCl and T , which are defined in Fig.  9 (Ruankaew et al. 2020). Al PEG (Yanagida et al. 1977, 1978a, b). With increasing KCl The main adsorption force of K is the isomorphic substi- concentration from 4% to 11%, the adsorption quantity of tution in tetrahedral sheet and octahedral sheet (Li et al. PEG decreased, which indicates that KCl can inhibit the 2018). So, the adsorption strength of the oxygen atom of adsorption of PEG. This was likely due to the competitive hexagonal site of silica is lower than those of H and Al adsorption relationship between PEG and KCl on the surface T . Based on the experimental results of atomic absorp- Al of Na-Mt. It can be concluded that the promotion effect was tion spectroscopy, it can be considered that the adsorp- dominant when the KCl concentration was lower than 4%, tion sites of H and T are only occupied by K , whose Al Al while the competitive adsorption was dominant when the adsorption is not affected by PEG. The adsorption sites of KCl concentration was higher than 4%. the oxygen atom of hexagonal site of silica can be occu- pied by both K and PEG. And the adsorption amounts of K and PEG depend on their concentration ratio. Their (a) (b) + + K K + + Na Na 0 0 01234567 02468 10 12 14 16 KCl concentration, % PEG concentration, % Fig. 8 Variations in cation content according to inhibitor concentrations: a different KCl concentrations and 3% PEG; b different PEG concen- trations and 7% KCl 1 3 Carbon content, % Cation content, mmol/100 g Cation content, mmol/100 g 834 Petroleum Science (2021) 18:827–838 capacity reached its peak when the KCl concentration is 4%. Nevertheless, as considering the adsorption of K , the total adsorption reached its peak value when the KCl concentration is above 7%. Considering the cost, the KCl Al T concentration range of 6%–8% is the most suitable. When Si the total adsorption reached the peak, the synergistic effect was most likely to be exerted. Therefore, the estimated H H Al Si concentration range had a good effect. 3.3.3 X‑ray photoelectron spectroscopy + + In order to demonstrate the substitution of N a by K and the synergistic effects of KCl and PEG, dry Na-Mt samples Fig. 9 A most top surface of Mt with the isomorphous replacement of with different inhibitors were tested by XPS, as shown in silica by aluminum. Atomic legends were colored highlight as silica Fig. 11. XPS can be used to investigate the surface com- (light blue), oxygen (red), hydrogen (white) and aluminum (orange). position of Na-Mt with different inhibitors (Jiang et al. Dotted triangles, T and T , represent the triangular site of silica Si Al and aluminum, respectively. Dotted hexagons, H and H , represent 2016). The XPS spectra of Na 1s of Na-Mt with differ - Si Al the hexagonal site next to the triangular site of silica and aluminum, ent inhibitors are shown in Fig. 11a. Blank spectrum was respectively tested with Na-Mt without inhibitors. Compared with the blank spectrum, the signal peak of Na-Mt with 3% KCl became weaker, which showed that KCl replaced Na in Na-Mt. In addition, the signal peak of Na-Mt with 3% KCl and 7% PEG was similar to that with 3% KCl. It sug- gests that PEG cannot influence the displacement of Na by KCl. In the XPS spectra of K 2p of Na-Mt with different inhibitors (Fig.  11b), the blank spectrum was obtained without inhibitor and showed no K 2p signal, which indicates that Na-Mt does not contain K . After addi- tion of 3% KCl, the signal peak became stronger. Then, after further addition of 7% PEG, the signal peak became weaker, which possibly resulted from competitive adsorp- tion between KCl and PEG on Na-Mt. This was confirmed C+K through the elemental analysis in Sect. 3.3.1. Moreover, 02468 10 12 the Na-Mt/KCl binding energy of K 2p increased from KCl concentration, % 295.8, 293.1 to 295.9, 293.2 eV after PEG addition, imply- ing that PEG undergoes binding with K . This was also Fig. 10 Elemental contents with different KCl concentrations demonstrated through the elemental analysis in Sect. 3.3.1. competitive adsorption capacity increased when the PEG 3.3.4 Scanning electron microscopy concentration increased from 0.5% to 5%, which resulted in an increase in the adsorption amount of PEG. When the SEM was used to observe the morphology of wet Na-Mt PEG concentration was above 7%, all the sites of H and with different inhibitor systems. The morphology of pure Al T were occupied by K , and all the sites of the oxygen Na-Mt was a layered structure, as shown in Fig. 12a. Fol- Al atom of hexagonal site of silica were occupied by PEG. lowing the addition of 3% PEG, the morphology of Na-Mt Therefore, the adsorption amount of K is not affected by with PEG was still layered structure in Fig. 12b, which was PEG concentration. similar to that of pure Na-Mt. After the addition of 7% By comprehensive analysis of the results of elemen- KCl, some of the Na-Mt particles showed spherical struc- tal analysis and atomic absorption spectrophotometry as tures, as illustrated in Fig. 12c. When 3% PEG and 7% KCl shown in Fig.  10, the initial assessment of the optimal were used together as a synergistic inhibitor, the majority KCl concentrations can be performed. The PEG adsorption of Na-Mt particles exhibited spherical structures, as shown in Fig.  12d. Inhibitors usually have strong adsorption 1 3 Element content, mmol/100 g Petroleum Science (2021) 18:827–838 835 (a) (b) 293.1 3% KCl 3% KCl Na 1s K 2p 3% KCl + 7% PEG 3% KCl + 7% PEG 7% PEG 1071.7 7% PEG 293.2 Blank Blank 1071.7 295.8 295.9 1071.7 1071.7 1066 1068 1070 1072 1074 1076 298 296 294 292 290 Binding energy, eV Binding energy, eV Fig. 11 XPS patterns of Na-Mt with the different inhibitors: a Na 1 s pattern; b K 2p pattern Fig. 12 SEM images of wet Na-Mt/inhibitors: a Na-Mt; b Na-Mt/PEG; c wet Na-Mt/KCl; d wet Na-Mt/PEG + KCl capacity, which allows them to replace water molecules by comparing the morphology of wet Na-Mt with different and decrease d-spacing of Na-Mt. The strong adsorption inhibitor systems, the order of inhibition performance was capacity causes Na-Mt to aggregate, which results in the deter mined to be PEG+KCl > KCl > PEG. spherical structure of Na-Mt (Xie et al. 2017). Therefore, 1 3 836 Petroleum Science (2021) 18:827–838 The optimal KCl and PEG concentrations should be near the 3.4 Optimization of PEG and KCl concentrations intersection of the above two boundaries. Then, several con- centrations were selected, as shown in Fig. 13. The optimal The optimization of PEG and KCl concentrations was as fol- lows: (1) XRD was used to identify the boundary of chang- KCl and PEG concentrations were chosen from the different concentrations by the shale hot rolling recovery test. ing trend in d-spacing with an increase in PEG concentra- tion. When concentration ranges of PEG and KCl were on For the Na-Mt sample studied in this work, the optimal concentrations of PEG and KCl were obtained as 7% KCl the boundary (the red dash line in Fig.  5), the interlayer spacing of Na-Mt was filled up by PEG. Hence, the optimal and 5% PEG. Then, the optimization of PEG and KCl con- centrations was verified by a series of tests on Na-Mt. A concentration of PEG was in this range. (2) XRD was also used to identify the boundary of changing trend in d-spacing set of water-based drilling fluids with different concentra- tions of KCl and PEG was designed. The corresponding with an increase in KCl concentration. At the KCl concentra- tion above the boundary, the number of coordinated water basic rheological properties and API filtrate volumes are given in Table 4. The rheological properties and filtrate molecules of the PEG–KCl coordination compound was sig- nificantly reduced. In consideration of cost, the optimal con- properties of the water-based drilling fluids are acceptable according to API RP 13B-2 (2005). centration of KCl should be near the boundary (the blue dash line in Fig. 5). (3) The intersection of the above two bounda- The shale hot rolling recovery results of water-based drilling fluids with different inhibitors are shown in ries represents the optimal KCl and PEG concentrations. Fig. 14. KCl and PEG improved the cutting recovery of the drilling fluids, indicating that both KCl and PEG can (a-1, b+1) (a, b+1) (a+1, b+1) improve inhibition properties of water-based drilling flu- ids. The synergistic inhibitive effects of KCl and PEG were obvious, which resulted in higher cutting recovery. Moreo- ver, the higher the concentration, the higher the cutting recovery. When 14% KCl and 5% PEG were used together as synergistic inhibitors (Fig. 14h), both the rheological properties and filtrate properties of the drilling fluid were (a-1, b)(a, b) (a+1, b) unacceptable for engineering practice. Thus, for the Na-Mt studied in this paper, 7% KCl and 5% PEG were deemed to be the optimal concentrations. 4 Conclusions (a-1, b-1) (a, b-1) (a+1, b-1) The synergistic inhibition performance of PEG and KCl a: PEG concentration, %; b: KCl concentration, % was evaluated through hot rolling recovery tests and lin- ear swell tests on shale cuttings. For the inhibition of Fig. 13 Schematic diagram of concentration optimization Na-Mt hydration, the synergistic effect of KCl and PEG Table 4 Rheological properties and API filtrate volumes of drilling fluids with different inhibitors after hot rolling (120 °C, 16 h) Sample No. Inhibitors AV, mPa s PV, mPa s YP, Pa YP/PV, Pa/ Gel strength Filtrate (mP s) (10 s/10 min), Pa volume, cm a Blank sample 27.0 24.0 6.0 0.25 4.0/4.5 11.4 b 7% KCl 19.0 14.0 8.0 0.57 3.5/4.0 12.6 c 5% PEG 27.0 23.0 7.0 0.30 3.0/4.0 8.4 d 7% KCl + 1% PEG 24.0 20.0 7.0 0.35 3.0/4.0 10.6 e 1% KCl + 5% PEG 26.5 22.0 7.5 0.34 3.0/3.5 7.8 f 3.5% KCl + 2.5% PEG 28.0 24.0 8.0 0.35 3.5/4.0 8.2 g 7% KCl + 5 wt% PEG 25.5 20.0 8.5 0.43 3.0/3.5 9.9 h 14% KCl + 10% PEG 16.0 11.0 9.0 0.73 2.5/3.0 14.3 1 3 Petroleum Science (2021) 18:827–838 837 100 Open Access This article is licensed under a Creative Commons Attri- bution 4.0 International License, which permits use, sharing, adapta- 87.80 88.15 85.50 tion, distribution and reproduction in any medium or format, as long 81.20 76.40 as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes 63.65 were made. The images or other third party material in this article are 61.05 included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not 42.70 permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativ ecommons .or g/licenses/b y/4.0/. References ab cd ef gh Inhibitive system Al-Bazali TM. The consequences of using concentrated salt solu- tions for mitigating wellbore instability in shales. J Pet Sci Eng. 2011;80(1):94–101. Fig. 14 Cutting recovery of different inhibitors: a blank sample; b 7% API. API RP 13B-2, recommended practice for field testing of oil- KCl; c 5% PEG; d 7% KCl + 1% PEG; e 1% KCl + 5% PEG; f 3.5% based drilling fluids. 4th edn. Washington, DC; 2005. 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Journal

Petroleum ScienceSpringer Journals

Published: Feb 15, 2021

Keywords: Clay hydration; Inhibitor; Synergistic inhibition; Polyethylene glycol; Water-based drilling fluids

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