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Research on a novel composite gel system for CO2 breakthrough

Research on a novel composite gel system for CO2 breakthrough Pet.Sci.(2010)7:245-250 245 245 DOI 10.1007/s12182-010-0028-6 Research on a novel composite gel system for CO breakthrough 1 2 Hou Yongli and Yue Xiang’an Production Optimization, China Oilfi eld Services Limited, Tianjin 300450, China Enhanced Oil Recovery Research Center, China University of Petroleum, Beijing 102249, China © China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2010 Abstract: A composite gel was prepared for plugging CO channeling, which is a serious problem for enhanced oil recovery with CO . A composite gel which is one of the materials for successful control of CO channeling during CO injection process was studied in this paper. SEM and nano particle size 2 2 analysis were used to describe this material’s microstructure. Its effect on CO channeling control was evaluated with core fl ow experiments. Both the rheological test and core plugging experiments indicated that both acrylamide monomer concentration and reaction pressure had positive influences on gel properties. The gel system with an acrylamide monomer concentration of 2% and 5% sodium silicate was proved to have excellent strength, elastic and plugging effi ciency, which confi rmed huge development potential and wide application of the composite gel system. The high-pressure acid environment arising from the CO injection not only reacts with solid silicate to form silicic acid gel, but also facilitates effi cient polymerization. Key words: Enhanced oil recovery, CO , channeling, composite gel, acrylamide monomer channeling through the fractures or high permeability 1 Introduction layers in oil reservoirs. These divert fluid flow to lower In field application, the viscosity of CO is lower by 2 permeability layers and improve the oil recovery (Asghari more than an order of magnitude than that of either crude and Taabbodi, 2004). However, the strength and stability oil or the brine occupying the remainder of the pore space of conventional gel systems still needed to be improved, of the reservoir rock. Additionally, large-scale reservoir especially in the complicated environment of CO injection heterogeneities, such as fractures, channels, or high- (Orr et al, 1982). Consequently, several composite gel permeability streaks always exist in reservoirs. So gravity systems were developed. Organic gel systems would present segregation and viscous fingering usually causes early better mechanical performance (Maiti et al, 2002), swelling breakthrough of injected CO and thus reduces oil recovery 2 properties, and thermal stability (Yoon et al, 2002) after the (Gozalpour, 2005). addition of inorganic materials. Messersmith et al (1997) Many methods have been proposed for mobility control obtained a composite gel which gelled in a suspension of during CO flooding: the water-alternating-gas (WAG) 2 montmorillonite after the addition of n-isopropyl acrylamide process (Kulkarni and Rao, 2005; Nezhad et al, 2006), and methylenebisacrylamide. Haraguchi and Li (2006) the use of foam to reduce gas mobility (Xie et al, 1990; prepared hydrogels with improved mechanical properties Gauglitz et al, 2002; Grigg et al, 2002), direct thickening of starting from AAm-based monomers together with Laponite the CO (Enick et al, 2000; Xu and Enick, 2001), chemical 2 (a synthetic clay product) as a physical cross-linker, gel (Martin and Kovarik, 1987; Seright, 2007), carbonate replacing the traditional chemical cross-linkers. Song et precipitation (Aminian et al, 1989; Zhu and Raible, 1994), al (2006) added SiO nano-particles in a solution of N-N- gel foam (Yang et al, 2003), etc. However, these methods methylenebisacrylamide and acrylamide, then ultrasonically have their own limitations in the field application, such as treated the solution and added an initiator and then a catalyst, technical feasibility, application efficiency, environmental forming a composite gel in a nitrogen atmosphere. Jiang et requirements, safety, etc (Moritis, 1995). So it is particularly al (2008) proposed a novel bio-degradable composite gel necessary in petroleum industry to develop an environmental- in aqueous solution using CaCl as crosslinking agent and friendly, highly-effective CO plugging system. 2 konjac glucomannan (a natural food additive) and sodium Chemical gels are introduced to reduce or block alginate as main materials. Wang et al (2005) formed a high- strength composite gel by adding inorganic rigid fillers and crosslinking agent successively into a polymer solution with *Corresponding author. email: yxa@cup.edu.cn the fi xed pH value. Received October 16, 2008 246 Pet.Sci.(2010)7:245-250 A new kind of organic-inorganic composite gel is of reaction pressures and at different amounts of acrylamide proposed in this paper which is endowed with dual excellent monomer, as shown in Table 1. characteristics of polymer gels and inorganic gels, such Table 1 Preparation parameters of composite gel samples as resistance to high temperature and pressure, and high elasticity. The sodium silicate solution and organic polymer solution are blended, and then gelled at the high-pressure acid Sodium silicate Acrylamide Reaction pressure Sample environment formed by CO . Overcoming the collapsibility of concentration, wt% monomer, wt% MPa silicic acid gel and poor effi ciency in plugging macrospores 1# 5.0 2.0 6 of polymer gels, the new gel system has good potential for 2# 5.0 2.0 4 plugging gas channeling. 3# 5.0 1.5 6 2 Experimental 4# 5.0 1.5 4 2.1 Experimental materials Sodium silicate, provided by the Hebei Fine Chemistry 2.3.2 Determination of particle size Company, has a density of 1.36 g/cm , modulus of 2.8- Twenty milliliters of sample 1# were put into a flask 3.2, and mass concentration of 40%. Acrylamide monomer, with distilled water and ultrasonically treated for 2, 4, and potassium persulfate, and N-N-methylenebisacrylamide are 16 minutes, respectively. The supernatant liquid was placed all commercial analytical grade (Beijing Chemical Reagents in the particle size analyzer for determining the particle Company), which have the purities of 96%, 99.5%, and 99%, distribution. The experiment temperature was kept at 45 ºC. respectively. Artificial cores were constructed by packing 2.3.3 Rheological experiment inorganic adhesive material, clay mineral, and outcrop Yield pressure and creep recoverability of four gel sand from an outcrop at Qinhuangdao into steel moulds samples were measured with the HAAK RS600 rheometer. (80cm×80cm×20cm). The water used in all experiments 2.3.4 Environmental scanning electron microscopy is distilled water. CO and N , provided by Beijing Haipu 2 2 Microstructure and surface characteristics of sample 1# Company, both have the purity of 99.99%. were examined with the FEG-ESEM. 2.3.5 Plugging effect in porous media 2.2 Apparatus Cores were prepared and their diameters, lengths and A high-pressure reactor made by Jiangsu Haian Instrument weights were measured. After being evacuated and water- was used to control conditions for gellation. A set of core saturated, the wet weights, permeabilities to gas and water fl ow test equipment made also by Jiangsu Haian Instrument of the cores were tested. When the experimental apparatus was used to determine the permeability of sand packs and was prepared, 0.4 pore volume of composite gel solution evaluate plugging effi ciency of gel systems and foam stability and 0.6 pore volume of CO were injected into the cores in porous media. A HAAK RS600 rheometer made in German and the reaction pressure was adjusted to 4 or 6 MPa. Then was used to perform rheological property measurements. A permeabilities to gas and water were measured again after KQ3200 ultrasonic cleaning machine was used to cause the gelling for 12 hours. Fig. 1 shows the experimental equipment shedding of inorganic particles from the polymer network, in which the composite gel was formed. and the particle size was measured with a laser particle size analyzer (Malvern instruments, UK). The microstructure of surfaces of the composite gel was observed with a field emission gun environmental scanning electron microscope (FEG-ESEM) (made in the Netherlands). 2.3 Experimental procedures 10 2.3.1 Sample preparation A sodium silicate mother liquor of 12.5 grams was added 3 to 87.5 milliliters of distilled water. After stirring evenly, acrylamide monomer, initiator, and crosslinking agent were added to the solution which was stirred until the solution was clear. Twenty milliliters of mixed solution were charged into the reaction vessel, and the temperature-controlling system of the reactor was turned on. CO was then injected into the reaction vessel through a piston-cylinder container until the inward pressure reached the fixed point. The reaction ves- Fig. 1 Core fl ow experimental equipment sel was then sealed and stirred for about 20 minutes. After 1, 2, 3: Piston containers for blocking agent, gas, and back-up pressure; standing at 45 ºC for about 12 hours, the sample was taken 4: Constant-fl ow pump; 5-11: Valves; 12: Core holder; 13: Thermostat out. The above laboratory procedure was repeated at a series Pet.Sci.(2010)7:245-250 247 248 Pet.Sci.(2010)7:245-250 ensured that these particles could be easily attached to the 3.3.2 Creep-recovery properties of the composite system polymer fi ber skeleton and thus strengthened the gel system Materials will creep under certain external stress and will (Zhao, 2009). recover in an opposite direction when the stress is removed. With an increase in ultrasonic treatment time, the gel Besides this, the strain of materials in the recovery process particle size showed a nonlinear decrease (see Fig. 5). Silicic decreases with time. This phenomenon is referred to as creep- acid gel particles, regularly inlaid on the network formed by recovery behavior. The creep-recovery capacity of the gel, polymer gel, started shedding in the process of ultrasonic indicating the viscoelastic effect of polymer solution, refl ects treatment. With the treatment time prolonged, more and more its resistance to internal slip deformation. When a gel is particles were shed. studied in its linear viscoelastic region, its creep curve can be divided into a recoverable strain part and an unrecoverable strain part. Fig. 6 showed the creep-recovery curves as well as their comparisons for three different samples. As was seen in Fig. 6, the larger the concentration of acrylamide monomer and the higher the reaction pressure, the higher the creep compliance of the gel system. So it could be concluded that 1200 high pressure conditions were beneficial to polymerization of acrylamide monomer and that high concentration of acrylamide monomer could strengthen the affinity of molecular chains. 0.10 0.09 1# 0.08 0.07 0.06 0 5 10 15 20 Vibration time, min 0.05 0.04 Fig. 5 The infl uence of vibration time on particle diameter 0.03 2# 0.02 3.3 Rheological properties of the composite gel 0.01 3# In the experiments, two methods were used to evaluate the 0 100 200 300 400 500 600 rheological properties of the gel system. One was creep and t, s recovery experiments which measured the creep compliance of the gel system. The other was the determination of the Fig. 6 The creep-recovery properties of three different gel systems dynamic yield stress which measured yield stress to assess the gel strength. 3.4 Core plugging experiments 3.3.1 Yield stress of the composite gel system The yield stress refers to the minimum critical external According to above experiments and oilfi eld conditions, force when materials begin to flow when the external force the composite gel systems with the acrylamide monomer is higher than internal structural force. If the external force concentration of 1.5% or 2%, reaction pressure of 4 or 6 MPa, is lower than the yield stress, materials usually show elastic were chosen as experimental parameters in the core plugging behavior like solid materials. Otherwise, materials exhibit experiments. The gel performance was evaluated mainly by deformation and elastic failure. plugging strength in porous media, which was denoted by For the composite gel, the flexible chains of polymer plugging rate S and residual resistance factor F . Table 2 RR gel showed extensional deformation at first under external and Table 3 showed the core parameters and experimental force, but silicic acid gel particles embedded in the results. The plugging rate and residual resistance factor were structure hindered the extensional deformation and resisted calculated as follows: pressure, which ensured the strength of the gel system. KK The introduction of sodium silicate greatly improved the (1) performance-price ratio of the gel, which made this system practical and economic for plugging CO channeling. When the experimental temperature was at 45 ºC and the vibration (2) RR frequency was 0.1 Hz, the range of yield stress for four different samples fl uctuated from 16,010 to 17,630 Pa, which where K is the permeability to water before plugging; K is 0 1 is much higher than that of a conventional gel system. the permeability to water after plugging. Particle diameter, nm -1 J, Pa Pet.Sci.(2010)7:245-250 249 Table 2 Physical properties of cores used As was indicated in Table 3, the composite gel had a favorable breakthrough pressure gradient which was not Length Diameter Cross-sectional Volume Pore volume Porosity Core 2 3 3 cm cm area, m cm cm % lower than 18.39 MPa/m. So it was fairly applicable in actual fi eld plugging if the length of the core was converted to the FH 1-1 8.826 2.556 5.13 45.26 10.83 23.92 actual well spacing. The constant-flow pump, used in the FH 1-5 8.736 2.53 5.02 43.90 9.92 22.59 experiments as a displacement power source, has a maximum pressure endurance of 20 MPa. In the experiments, the FH 1-6 8.662 2.534 5.04 43.66 10.49 24.03 displacement pressure sometimes got close to the maximum HF 1-7 8.608 2.532 5.03 43.32 13.26 30.62 pressure endurance, especially when back pressure was used. In that case, the final pressure shown in the form of italics HF 1-9 8.668 2.55 5.10 44.25 13.55 30.62 in Table 3, was chosen as equilibrium pressure to calculate HF 1-10 8.607 2.532 5.03 43.28 11.80 27.27 the permeabilities, plugging rate, and residual resistance Table 3 The results of core plugging experiments AM concentration Reaction pressure K K Breakthrough pressure gradient 0 1 Core SF RR wt% MPa mD mD MPa/m FH 1-1 2.0 4 53.97 2.41 0.96 22.38 29.53 FH 1-5 1.5 4 19.23 7.23 0.62 2.66 18.39 FH 1-6 1.5 4 18.95 1.32 0.93 14.37 44.56 FH 1-7 1.5 4 161.27 36.12 0.78 4.47 14.86 FH 1-9 2.0 6 50.38 0.02 0.99 2279.09 147.70 FH 1-10* 2.0 6 34.10 0.02 0.99 1461.73 141.95 FH 1-10 2.0 6 34.10 0.02 0.99 2162.55 210.02 Notes: denotes the introduction of back-up pressure in the experiments factor for the convenience of comparison. Fig. 7 showed the variation in the pressuredrop across the core before and after plugging by sample 1#. 4000 Experimental results indicated that both the concentration of acrylamide monomer and reaction pressure had important influence on plugging effects. The higher the acrylamide Water flooding before plugging monomer concentration and the higher the reaction pressure, Water flooding after plugging the better the plugging effect. When the concentration of acrylamide monomer in the gel system was kept at 1.5%, the plugging effect changed irregularly. So it was concluded that 0 5 10 15 20 25 30 35 40 the performance stability of the composite gel formed at this Water injected, PV concentration needed to be increased. When the concentration Fig. 7 The variation in the pressure drop across the core of acrylamide monomer was increased to 2%, the gel system showed excellent plugging strength and stability, the plugging In conclusion, the system had excellent plugging rate of all experiments was above 95%. Additionally, the performance and good potential for fi eld applications. plugging effect of the gel system was improved with the increase in reaction pressure, which was consistent with the 4 Conclusions rheological experiments. Therefore, the reaction pressure had a positive infl uence on gel performance. Taking all the above 1) The gel strength was greatly enhanced with nanoscale into account, the gel system had excellent toughness and inorganic particles effi ciently embedded in the fi ber network pressure-resistance, which was qualifi ed for plugging viscous of polymer gel. The composite gel system possessed strong fi ngering or channeling of CO . The back pressure was used elasticity and high deformation capacity when the acrylamide to simulate reservoir pressure conditions and avoid core monomer concentration was 2% and reaction pressure was 6 structure failure. It was found that the plugging rate could MPa. be increased to 99% or above when the back pressure was 2) The high-pressure acid environment generated by applied, which confi rmed the stability of the composite gel in CO not only accelerated the gel formation, but also made reservoir conditions. the network of the organic system swell, thus improving Pressure drop ∆P, kPa 250 250 Pet.Sci.(2010)7:245-250 Mar tin F D and Kovarik F S. Chemical gels for diverting CO : Baseline the viscoelasticity of the composite gel. The gel system had 2 experiments. Paper SPE 16728 presented at SPE Annual Technical excellent plugging effect which could reach 95% or above. Conference and Exhibition, 27-30 September 1987, Dallas, Texas 3) The composite gel system fl owed freely and could be Mes sersmith P B, Znidarsich F, Komarneni S, et al. Nanophase and injected into the formation easily. Additionally, it was a new nanocomposite materials II. Materials Research Society Symposium type of pollution-free gas plugging system, which has good Proceedings, Materials Research Society, Pittsburgh, PA, 1997: 457- potential for oilfi eld applications. Mor itis G. Impact of production and development RD&D ranked. Oil References and Gas Journal. 1995. 93(44): 37-39 Nez had S A T, Mojarad M R R, Paitakhti J S, et al. Experimental study Ami nian K, Ameri S, Cunningham L E, et al. CO mobility control on applicability of Water-Alternating-CO injection in the secondary by carbonate precipitation: A modeling study. Paper SPE 19321 and tertiary recovery. Paper SPE 103988 presented at the First presented at SPE Eastern Regional Meeting, 24-27 October 1989, International Oil Conference and Exhibition, 31 August-2 September Morgantown, West Virginia 2006, Cancun, Mexico Asg hari K and Taabbodi L. Laboratory investigation of indepth gel Orr F M, Heller J P, Taber J J, et al. Carbon dioxide flooding for placement for carbon dioxide fl ooding in carbonate porous media. enhanced oil recovery: Promise and problems. Journal of the Paper SPE 90633 presented at SPE Annual Technical Conference American Oil Chemists’ Society. 1982. 59(10): 810-817 and Exhibition, 26-29 September 2004, Houston, Texas Ser ight R S. Gels for conformance improvement in gas EOR. Flooding Eni ck R M, Beckman E J, Shi C M, et al. Direct thickeners for CO . Syringe Pump Application Note AN8. 2007 Paper SPE 59325 presented at SPE/DOE Improved Oil Recovery Son g R, Xie Q L, He L H, et al. Synthesis and characterization Symposium, 3-5 April 2000, Tulsa, Oklahoma polyacrylamide/silica composite hydrogel. Chinese Journal of Gau glitz P A, Friedmann F, Kam S I, et al. Foam generation in porous Spectroscopy Laboratory. 2006. 23(3): 609-612 (in Chinese) media. Paper SPE 75177 presented at SPE/DOE Improved Oil Wan g J J, Zhu J H, Xia S L, et al. Evaluation of the sealing ability of Recovery Symposium, 13-17 April 2002, Tulsa, Oklahoma; also a new multi-function composite gel. Natural Gas Industry. 2005. published at Chemical Engineering Science. 2002. 57(19): 4037- 25(9): 101-103 (in Chinese) Xie S X, Yan W H and Han P H. Mobility control by foam in CO Goz alpour F, Ren S R and Tohidi B. CO EOR and storage in oil fl ooding. Oilfi eld Chemistry. 1990. 7(3): 289-291 (in Chinese) reservoirs. Oil and Gas Science and Technology. 2005. 60(3): 537- Xu J H and Enick R M. Thickening carbon dioxide with the fluoroacrylate-styrene copolymer. Paper SPE 71497 presented at Gri gg R B, Tsau J S and Martin D F. Cost reduction and injectivity SPE Annual Technical Conference and Exhibition, 30 September-3 improvements for CO foams for mobility control. Paper SPE 75178 October 2001, New Orleans presented at SPE/DOE Improved Oil Recovery Symposium, 13-17 Yan g B, Tang R Z, Luan C Z, et al. The technology of preventing CO April 2002, Tulsa, Oklahoma breakthrough and gravity segregation abroad. Fault-block Oil & Gas Har aguchi K and Li H J. Mechanical properties and structure Field. 2003. 3(2): 64-66 (in Chinese) of polymer-clay nanocomposite gels with high clay content. Yoo n P J, Fornes T D and Paul D R. Thermal expansion behavior of Macromolecules. 2006. (39): 1898-1905 nylon 6 nanocomposites. Polymer. 2002. (43): 6727-6741 Jia ng P, Chen L G, Yuan X Q, et al. Study of preparation and swelling Zha o R B. Infl uence of carbon dioxide on the polymerization behavior property of composite gel KGM/ALG. Journal of Anhui Agricultural of sodium silicate-acrylamide solution and products properties. Sciences. 2008. 36(31): 13504-13505 (in Chinese) Chemical Journal of Chinese Universities. 2009. 30(3): 596-600 (in Kul karni M M and Rao D N. Experimental investigation of miscible Chinese) and immiscible Water-Alternating-Gas (WAG) process performance. Zhu T and Raible C. Improved sweep effi ciency by alcohol-induced salt Journal of Petroleum Science and Engineering. 2005. 48: 1-20 precipitation. Paper SPE 27777 presented at SPE/DOE Improved Oil Mai ti P, Yamada K, Okamoto M, et al. New polylactide/layered silicate Recovery Symposium, 17-20 April 1994, Tulsa, Oklahoma nanocomposites: Role of organoclays. Chemistry of Materials. 2002. (Edited by Sun Yanhua) 14 (11): 4654-4661 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Petroleum Science Springer Journals

Research on a novel composite gel system for CO2 breakthrough

Hou, Yongli; Yue, Xiang’an
Petroleum Science , Volume 7 (2) – Jun 3, 2010
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Springer Journals
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Copyright © 2010 by China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg
Subject
Earth Sciences; Mineral Resources; Industrial Chemistry/Chemical Engineering; Industrial and Production Engineering; Energy Economics
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1672-5107
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1995-8226
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10.1007/s12182-010-0028-6
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Abstract

Pet.Sci.(2010)7:245-250 245 245 DOI 10.1007/s12182-010-0028-6 Research on a novel composite gel system for CO breakthrough 1 2 Hou Yongli and Yue Xiang’an Production Optimization, China Oilfi eld Services Limited, Tianjin 300450, China Enhanced Oil Recovery Research Center, China University of Petroleum, Beijing 102249, China © China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2010 Abstract: A composite gel was prepared for plugging CO channeling, which is a serious problem for enhanced oil recovery with CO . A composite gel which is one of the materials for successful control of CO channeling during CO injection process was studied in this paper. SEM and nano particle size 2 2 analysis were used to describe this material’s microstructure. Its effect on CO channeling control was evaluated with core fl ow experiments. Both the rheological test and core plugging experiments indicated that both acrylamide monomer concentration and reaction pressure had positive influences on gel properties. The gel system with an acrylamide monomer concentration of 2% and 5% sodium silicate was proved to have excellent strength, elastic and plugging effi ciency, which confi rmed huge development potential and wide application of the composite gel system. The high-pressure acid environment arising from the CO injection not only reacts with solid silicate to form silicic acid gel, but also facilitates effi cient polymerization. Key words: Enhanced oil recovery, CO , channeling, composite gel, acrylamide monomer channeling through the fractures or high permeability 1 Introduction layers in oil reservoirs. These divert fluid flow to lower In field application, the viscosity of CO is lower by 2 permeability layers and improve the oil recovery (Asghari more than an order of magnitude than that of either crude and Taabbodi, 2004). However, the strength and stability oil or the brine occupying the remainder of the pore space of conventional gel systems still needed to be improved, of the reservoir rock. Additionally, large-scale reservoir especially in the complicated environment of CO injection heterogeneities, such as fractures, channels, or high- (Orr et al, 1982). Consequently, several composite gel permeability streaks always exist in reservoirs. So gravity systems were developed. Organic gel systems would present segregation and viscous fingering usually causes early better mechanical performance (Maiti et al, 2002), swelling breakthrough of injected CO and thus reduces oil recovery 2 properties, and thermal stability (Yoon et al, 2002) after the (Gozalpour, 2005). addition of inorganic materials. Messersmith et al (1997) Many methods have been proposed for mobility control obtained a composite gel which gelled in a suspension of during CO flooding: the water-alternating-gas (WAG) 2 montmorillonite after the addition of n-isopropyl acrylamide process (Kulkarni and Rao, 2005; Nezhad et al, 2006), and methylenebisacrylamide. Haraguchi and Li (2006) the use of foam to reduce gas mobility (Xie et al, 1990; prepared hydrogels with improved mechanical properties Gauglitz et al, 2002; Grigg et al, 2002), direct thickening of starting from AAm-based monomers together with Laponite the CO (Enick et al, 2000; Xu and Enick, 2001), chemical 2 (a synthetic clay product) as a physical cross-linker, gel (Martin and Kovarik, 1987; Seright, 2007), carbonate replacing the traditional chemical cross-linkers. Song et precipitation (Aminian et al, 1989; Zhu and Raible, 1994), al (2006) added SiO nano-particles in a solution of N-N- gel foam (Yang et al, 2003), etc. However, these methods methylenebisacrylamide and acrylamide, then ultrasonically have their own limitations in the field application, such as treated the solution and added an initiator and then a catalyst, technical feasibility, application efficiency, environmental forming a composite gel in a nitrogen atmosphere. Jiang et requirements, safety, etc (Moritis, 1995). So it is particularly al (2008) proposed a novel bio-degradable composite gel necessary in petroleum industry to develop an environmental- in aqueous solution using CaCl as crosslinking agent and friendly, highly-effective CO plugging system. 2 konjac glucomannan (a natural food additive) and sodium Chemical gels are introduced to reduce or block alginate as main materials. Wang et al (2005) formed a high- strength composite gel by adding inorganic rigid fillers and crosslinking agent successively into a polymer solution with *Corresponding author. email: yxa@cup.edu.cn the fi xed pH value. Received October 16, 2008 246 Pet.Sci.(2010)7:245-250 A new kind of organic-inorganic composite gel is of reaction pressures and at different amounts of acrylamide proposed in this paper which is endowed with dual excellent monomer, as shown in Table 1. characteristics of polymer gels and inorganic gels, such Table 1 Preparation parameters of composite gel samples as resistance to high temperature and pressure, and high elasticity. The sodium silicate solution and organic polymer solution are blended, and then gelled at the high-pressure acid Sodium silicate Acrylamide Reaction pressure Sample environment formed by CO . Overcoming the collapsibility of concentration, wt% monomer, wt% MPa silicic acid gel and poor effi ciency in plugging macrospores 1# 5.0 2.0 6 of polymer gels, the new gel system has good potential for 2# 5.0 2.0 4 plugging gas channeling. 3# 5.0 1.5 6 2 Experimental 4# 5.0 1.5 4 2.1 Experimental materials Sodium silicate, provided by the Hebei Fine Chemistry 2.3.2 Determination of particle size Company, has a density of 1.36 g/cm , modulus of 2.8- Twenty milliliters of sample 1# were put into a flask 3.2, and mass concentration of 40%. Acrylamide monomer, with distilled water and ultrasonically treated for 2, 4, and potassium persulfate, and N-N-methylenebisacrylamide are 16 minutes, respectively. The supernatant liquid was placed all commercial analytical grade (Beijing Chemical Reagents in the particle size analyzer for determining the particle Company), which have the purities of 96%, 99.5%, and 99%, distribution. The experiment temperature was kept at 45 ºC. respectively. Artificial cores were constructed by packing 2.3.3 Rheological experiment inorganic adhesive material, clay mineral, and outcrop Yield pressure and creep recoverability of four gel sand from an outcrop at Qinhuangdao into steel moulds samples were measured with the HAAK RS600 rheometer. (80cm×80cm×20cm). The water used in all experiments 2.3.4 Environmental scanning electron microscopy is distilled water. CO and N , provided by Beijing Haipu 2 2 Microstructure and surface characteristics of sample 1# Company, both have the purity of 99.99%. were examined with the FEG-ESEM. 2.3.5 Plugging effect in porous media 2.2 Apparatus Cores were prepared and their diameters, lengths and A high-pressure reactor made by Jiangsu Haian Instrument weights were measured. After being evacuated and water- was used to control conditions for gellation. A set of core saturated, the wet weights, permeabilities to gas and water fl ow test equipment made also by Jiangsu Haian Instrument of the cores were tested. When the experimental apparatus was used to determine the permeability of sand packs and was prepared, 0.4 pore volume of composite gel solution evaluate plugging effi ciency of gel systems and foam stability and 0.6 pore volume of CO were injected into the cores in porous media. A HAAK RS600 rheometer made in German and the reaction pressure was adjusted to 4 or 6 MPa. Then was used to perform rheological property measurements. A permeabilities to gas and water were measured again after KQ3200 ultrasonic cleaning machine was used to cause the gelling for 12 hours. Fig. 1 shows the experimental equipment shedding of inorganic particles from the polymer network, in which the composite gel was formed. and the particle size was measured with a laser particle size analyzer (Malvern instruments, UK). The microstructure of surfaces of the composite gel was observed with a field emission gun environmental scanning electron microscope (FEG-ESEM) (made in the Netherlands). 2.3 Experimental procedures 10 2.3.1 Sample preparation A sodium silicate mother liquor of 12.5 grams was added 3 to 87.5 milliliters of distilled water. After stirring evenly, acrylamide monomer, initiator, and crosslinking agent were added to the solution which was stirred until the solution was clear. Twenty milliliters of mixed solution were charged into the reaction vessel, and the temperature-controlling system of the reactor was turned on. CO was then injected into the reaction vessel through a piston-cylinder container until the inward pressure reached the fixed point. The reaction ves- Fig. 1 Core fl ow experimental equipment sel was then sealed and stirred for about 20 minutes. After 1, 2, 3: Piston containers for blocking agent, gas, and back-up pressure; standing at 45 ºC for about 12 hours, the sample was taken 4: Constant-fl ow pump; 5-11: Valves; 12: Core holder; 13: Thermostat out. The above laboratory procedure was repeated at a series Pet.Sci.(2010)7:245-250 247 248 Pet.Sci.(2010)7:245-250 ensured that these particles could be easily attached to the 3.3.2 Creep-recovery properties of the composite system polymer fi ber skeleton and thus strengthened the gel system Materials will creep under certain external stress and will (Zhao, 2009). recover in an opposite direction when the stress is removed. With an increase in ultrasonic treatment time, the gel Besides this, the strain of materials in the recovery process particle size showed a nonlinear decrease (see Fig. 5). Silicic decreases with time. This phenomenon is referred to as creep- acid gel particles, regularly inlaid on the network formed by recovery behavior. The creep-recovery capacity of the gel, polymer gel, started shedding in the process of ultrasonic indicating the viscoelastic effect of polymer solution, refl ects treatment. With the treatment time prolonged, more and more its resistance to internal slip deformation. When a gel is particles were shed. studied in its linear viscoelastic region, its creep curve can be divided into a recoverable strain part and an unrecoverable strain part. Fig. 6 showed the creep-recovery curves as well as their comparisons for three different samples. As was seen in Fig. 6, the larger the concentration of acrylamide monomer and the higher the reaction pressure, the higher the creep compliance of the gel system. So it could be concluded that 1200 high pressure conditions were beneficial to polymerization of acrylamide monomer and that high concentration of acrylamide monomer could strengthen the affinity of molecular chains. 0.10 0.09 1# 0.08 0.07 0.06 0 5 10 15 20 Vibration time, min 0.05 0.04 Fig. 5 The infl uence of vibration time on particle diameter 0.03 2# 0.02 3.3 Rheological properties of the composite gel 0.01 3# In the experiments, two methods were used to evaluate the 0 100 200 300 400 500 600 rheological properties of the gel system. One was creep and t, s recovery experiments which measured the creep compliance of the gel system. The other was the determination of the Fig. 6 The creep-recovery properties of three different gel systems dynamic yield stress which measured yield stress to assess the gel strength. 3.4 Core plugging experiments 3.3.1 Yield stress of the composite gel system The yield stress refers to the minimum critical external According to above experiments and oilfi eld conditions, force when materials begin to flow when the external force the composite gel systems with the acrylamide monomer is higher than internal structural force. If the external force concentration of 1.5% or 2%, reaction pressure of 4 or 6 MPa, is lower than the yield stress, materials usually show elastic were chosen as experimental parameters in the core plugging behavior like solid materials. Otherwise, materials exhibit experiments. The gel performance was evaluated mainly by deformation and elastic failure. plugging strength in porous media, which was denoted by For the composite gel, the flexible chains of polymer plugging rate S and residual resistance factor F . Table 2 RR gel showed extensional deformation at first under external and Table 3 showed the core parameters and experimental force, but silicic acid gel particles embedded in the results. The plugging rate and residual resistance factor were structure hindered the extensional deformation and resisted calculated as follows: pressure, which ensured the strength of the gel system. KK The introduction of sodium silicate greatly improved the (1) performance-price ratio of the gel, which made this system practical and economic for plugging CO channeling. When the experimental temperature was at 45 ºC and the vibration (2) RR frequency was 0.1 Hz, the range of yield stress for four different samples fl uctuated from 16,010 to 17,630 Pa, which where K is the permeability to water before plugging; K is 0 1 is much higher than that of a conventional gel system. the permeability to water after plugging. Particle diameter, nm -1 J, Pa Pet.Sci.(2010)7:245-250 249 Table 2 Physical properties of cores used As was indicated in Table 3, the composite gel had a favorable breakthrough pressure gradient which was not Length Diameter Cross-sectional Volume Pore volume Porosity Core 2 3 3 cm cm area, m cm cm % lower than 18.39 MPa/m. So it was fairly applicable in actual fi eld plugging if the length of the core was converted to the FH 1-1 8.826 2.556 5.13 45.26 10.83 23.92 actual well spacing. The constant-flow pump, used in the FH 1-5 8.736 2.53 5.02 43.90 9.92 22.59 experiments as a displacement power source, has a maximum pressure endurance of 20 MPa. In the experiments, the FH 1-6 8.662 2.534 5.04 43.66 10.49 24.03 displacement pressure sometimes got close to the maximum HF 1-7 8.608 2.532 5.03 43.32 13.26 30.62 pressure endurance, especially when back pressure was used. In that case, the final pressure shown in the form of italics HF 1-9 8.668 2.55 5.10 44.25 13.55 30.62 in Table 3, was chosen as equilibrium pressure to calculate HF 1-10 8.607 2.532 5.03 43.28 11.80 27.27 the permeabilities, plugging rate, and residual resistance Table 3 The results of core plugging experiments AM concentration Reaction pressure K K Breakthrough pressure gradient 0 1 Core SF RR wt% MPa mD mD MPa/m FH 1-1 2.0 4 53.97 2.41 0.96 22.38 29.53 FH 1-5 1.5 4 19.23 7.23 0.62 2.66 18.39 FH 1-6 1.5 4 18.95 1.32 0.93 14.37 44.56 FH 1-7 1.5 4 161.27 36.12 0.78 4.47 14.86 FH 1-9 2.0 6 50.38 0.02 0.99 2279.09 147.70 FH 1-10* 2.0 6 34.10 0.02 0.99 1461.73 141.95 FH 1-10 2.0 6 34.10 0.02 0.99 2162.55 210.02 Notes: denotes the introduction of back-up pressure in the experiments factor for the convenience of comparison. Fig. 7 showed the variation in the pressuredrop across the core before and after plugging by sample 1#. 4000 Experimental results indicated that both the concentration of acrylamide monomer and reaction pressure had important influence on plugging effects. The higher the acrylamide Water flooding before plugging monomer concentration and the higher the reaction pressure, Water flooding after plugging the better the plugging effect. When the concentration of acrylamide monomer in the gel system was kept at 1.5%, the plugging effect changed irregularly. So it was concluded that 0 5 10 15 20 25 30 35 40 the performance stability of the composite gel formed at this Water injected, PV concentration needed to be increased. When the concentration Fig. 7 The variation in the pressure drop across the core of acrylamide monomer was increased to 2%, the gel system showed excellent plugging strength and stability, the plugging In conclusion, the system had excellent plugging rate of all experiments was above 95%. Additionally, the performance and good potential for fi eld applications. plugging effect of the gel system was improved with the increase in reaction pressure, which was consistent with the 4 Conclusions rheological experiments. Therefore, the reaction pressure had a positive infl uence on gel performance. Taking all the above 1) The gel strength was greatly enhanced with nanoscale into account, the gel system had excellent toughness and inorganic particles effi ciently embedded in the fi ber network pressure-resistance, which was qualifi ed for plugging viscous of polymer gel. The composite gel system possessed strong fi ngering or channeling of CO . The back pressure was used elasticity and high deformation capacity when the acrylamide to simulate reservoir pressure conditions and avoid core monomer concentration was 2% and reaction pressure was 6 structure failure. It was found that the plugging rate could MPa. be increased to 99% or above when the back pressure was 2) The high-pressure acid environment generated by applied, which confi rmed the stability of the composite gel in CO not only accelerated the gel formation, but also made reservoir conditions. the network of the organic system swell, thus improving Pressure drop ∆P, kPa 250 250 Pet.Sci.(2010)7:245-250 Mar tin F D and Kovarik F S. Chemical gels for diverting CO : Baseline the viscoelasticity of the composite gel. The gel system had 2 experiments. Paper SPE 16728 presented at SPE Annual Technical excellent plugging effect which could reach 95% or above. Conference and Exhibition, 27-30 September 1987, Dallas, Texas 3) The composite gel system fl owed freely and could be Mes sersmith P B, Znidarsich F, Komarneni S, et al. Nanophase and injected into the formation easily. Additionally, it was a new nanocomposite materials II. Materials Research Society Symposium type of pollution-free gas plugging system, which has good Proceedings, Materials Research Society, Pittsburgh, PA, 1997: 457- potential for oilfi eld applications. Mor itis G. Impact of production and development RD&D ranked. Oil References and Gas Journal. 1995. 93(44): 37-39 Nez had S A T, Mojarad M R R, Paitakhti J S, et al. Experimental study Ami nian K, Ameri S, Cunningham L E, et al. CO mobility control on applicability of Water-Alternating-CO injection in the secondary by carbonate precipitation: A modeling study. Paper SPE 19321 and tertiary recovery. 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Petroleum Science – Springer Journals

Published: Jun 3, 2010

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