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Research on fabric characteristics and borehole instability mechanisms of fractured igneous rocks

Research on fabric characteristics and borehole instability mechanisms of fractured igneous rocks borehole instability occur frequently during drilling igneous formations, which is a serious impediment to oil and gas exploration and production. The lack of systematic understanding of the inherent instability mechanisms is an important problem. A series of experiments were conducted on several igneous rock samples taken from the sloughing formations in the Tuha area in an attempt to reveal the inherent mechanisms of wellbore instability when drilling in fractured igneous rocks. Research methods involved VOXUU\FKHPLVWU\DQDO\VLVRIPLFURJHRORJLFDOIHDWXUHV 0LFUR&7LPDJLQJ6(0 DQGURFNPHFKDQLFV testing. The experimental results indicated that clay minerals were widely distributed in the intergranular space of the diagenetic minerals, crystal defects, and microcracks. Drilling fluid filtrate would invade the rock along the microcracks. The invasion amount gradually increased over time, which constantly LQWHQVL¿HGWKHK\GUDWLRQDQGVZHOOLQJRIFOD\PLQHUDOVOHDGLQJWRFKDQJHVLQWKHPLFURVFRSLFVWUXFWXUH of igneous rocks. Primary and secondary microcracks can propagate and merge into single cracks and thus reducing rock cohesion and the binding force along cleavage planes. Based on this result the authors propose that a key towards solving wellbore instability in igneous formations is that specific micro-geological characteristics of the igneous rocks should be taken into consideration in the design of antisloughing drilling muds. Igneous rocks, microcracks, clay minerals, hydration, instability Key words: to suffer from borehole instability consist mainly of smectite, 1 Introduction whose physical and chemical properties present strong Borehole instability caused by clay mineral hydration GLVSHUVLELOLW\RUH[SDQVLELOLW\ %KX\DQDQG3DVVH\ during drilling is a major problem in the oil industry. This 6WMHUQHWDO7KRPVRQ5RKUPDQ :KHQ SKHQRPHQRQXVXDOO\RFFXUVLQWKHFOD\ULFKPXGVKDOH FRQWDFWHGZLWKLQFRPSDWLEOHGULOOLQJÀXLG¿OWUDWHWKHVHFOD\ however, with expansion of exploration, it is also found in minerals would be hydrated (in the forms of dispersion or WKHGULOOLQJRILJQHRXVIRUPDWLRQV 0LWVXKDWDHWDO H[SDQVLRQ WKXVOHDGLQJWRZHOOERUH,QLQVWDELOLW\WKH-LGRQJ Sahabudin and Darren, 2000). In recent years, borehole 2LO¿HOGWKHEDVDOWDQGIWXIIRUPDWLRQVLQWKH*XDQWDR*URXS collapse, hole enlargement, lost circulation, pipe sticking where borehole instability occurs contain a large number and other complex problems often emerge in most of oil of clay minerals, up to 36%-78%, with a relative content of and gas basins when drilling into igneous rocks (basalt, smectite of 90%-97%. The high content and wide distribution tuff-based), resulting in the expansion of the drilling cycle of opaline silica which also expands easily may also be one and increase in drilling cost. To reduce wellbore instability of the reasons for borehole instability (Yuan et al, 2007). problems in igneous rock formations, several researchers Tuff is easily to disperse, with a core recovery rate of less KDYHLQYHVWLJDWHGWKHIDFWRUVLQÀXHQFLQJERUHKROHLQVWDELOLW\ than 10%, while basalt and altered basalt have relatively low Researchers focusing on metasomatic alteration petrology dispersibility, but still expand easily with an expansion ratio pointed out that the neutral or basic igneous rocks, especially XSWR =KDQJHWDO pyroclastic rocks under hydrothermal conditions (contact In addition, the particular petrological structure of igneous ZLWKWKHIRUPDWLRQÀXLGXQGHUKLJKWHPSHUDWXUHFRQGLWLRQV rocks is also a potential factor of borehole instability (Sato would be vulnerable to argillization. Plagioclase is often HWDO.DZDPRWRDQG6DWR-HUUDPHWDO altered to kaolinite and smectite minerals. Numerous studies .DUDNXODQG8OXVD\DQJ:HWDO HDN:SODQHV show that clay minerals in igneous rock formations tending and non-homogeneous structure greatly weakens the strength RIIRUPDWLRQURFN0RUHRYHUWKHPLFURVWUXFWXUHVRILJQHRXV rocks also have an impact on the deformation mode (Crosta *Corresponding author. email: liuxiangjunswpi@163.com HWDO+RVVDLQDQG6HVKDJLUL/XW]HWDO Received August 31, 2012 Pet.Sci.(2013)10:212-218 213 so that the traditional Hoek-Brown instability criterion is QRORQJHUDSSOLFDEOH 0DVRXPLDQG'RXJODV 7KH hardness of amygdaloid differs substantially from that of the basalt matrix drilled in amygdaloidal basalt in the Tahe 30 Oilfield (the amygdaloid are composed of calcite, opaline silica, and chlorite). The released stress, surge pressure, drilling tool collision, and other mechanical factors during drilling make it easy to produce stress concentration at the amygdale, which results in sloughing of surrounding rock and lost circulation in basalt with abundant pores (Li et al, 2011). S-1-2 S-22 S- 3 S-30 S-48 S-5 S- 8 S-23 52 51 5 &DYLQDWRHWDO%DXHUHWDO IRFXVHGPRUH Sample number on investigating the factors affecting the geo-mechanical Fig. 1 Whole-rock mineral analysis of clay content in tuff specimens properties of rocks and the relationship with acoustic parameters, but they did not pay attention to understanding the mechanisms of borehole instability in igneous formations. The understanding obtained from the studies on drilling IOXLGVXVHGLQLJQHRXVIRUPDWLRQVDQ 7HWDO$EXUWR DQG&O\GH&KHQHWDO ZDVWKDWWKHRULJLQDO collapse pressure of the igneous rock was high and wellbore stabilization was achieved by continuously adjusting the drilling fluid density. But so far, when wellbore instability occurs in newly drilled igneous rocks (such as Yubei), it is still necessary to take a lot of time and effort to come up 0 36 35 S-33 27 S-17 S-21 S-25 S-31 S-34 S-37 S-28 with countermeasures. The fundamental reason is the lack of Sample number a clear and systematic understanding of the mechanisms of wellbore instability in igneous rock formations. Fig. 2 Whole-rock mineral analysis of clay content in basalt specimens In view of the above problems, which are related to Table 1 lists the clay mineral composition of some test physical and mechanical properties of igneous rocks under samples. It can be seen from Table 1 that in all test samples, specific geological and engineering conditions, a series of WKHGRPLQDQWFOD\PLQHUDOLVVPHFWLWHLQWKHIRXUPDLQFOD\ experiments were conducted on several igneous rock samples minerals (kaolinite, chlorite, illite, and smectite), the relative taken from the sloughing formations in the Tuha area, to percentages of smectite is generally more than 50%, except attempt to reveal the inherent instability mechanisms of these samples S-32 and S-28, even exceeding 95%. The relative fractured igneous rocks. contents of smectite in samples S-32 and S-28 are 19% and 32%, respectively. 2 Microstructure and clay mineral analysis of igneous rocks Table 1 Clay mineral content and composition The mechanical properties of rocks are affected by Relative content, % Total clay mineral mineral composition, rock texture, clay content and clay type. Sample content, % Kaolinite Chlorite Illite Smectite Therefore, analysis of mineral component, rock texture, and clay type and content of igneous rocks may greatly contribute S-3 39 0.1 0.2 3.8 96 to understanding the borehole instability mechanisms. S-47 13 0.3 0.2 0.8 99 2.1 Whole-rock mineral analysis by X-ray diffraction S-9 15 0.0 0.1 0.3 99 (XRD) S-22 22 0.1 0.2 0.6 99 IUDFWLRQDQDO\VLVLVDIDVWUHOLDEOHDQGFRQYHQLHQW;UD\GLI S-26 26 21.2 14.2 0.0 65 method for determining clay mineral type and content. Several rock samples taken from the sloughing formations S-32 16 31.2 15.6 34.7 19 LQWKHVWXG\DUHDZHUHJURXQGWR¿QHSRZGHUDQGWKHQ;5' S-28 32 50.3 16.8 0.5 32 was applied to determine the total clay mineral content in S-23 23 0.3 0.2 0.8 99 the powder. Compared with the intercrystalline distance and intensity of diffracted ray for different types of clay 52 26 0.1 0.2 0.4 99 minerals, the types and relative contents of clay minerals 36 23 0.0 22.7 6.1 71 ZHUHLGHQWLILHG7KHUHVXOWVRI;5'DQDO\VLVVKRZHGWKDW both types of igneous rock samples had high clay contents (see 5 10 0.3 0.2 46.6 53 Figs. 1 and 2). The average clay content of the tuff samples 53 39 0.6 0.7 2.0 97 was 18% and that of the basalt samples was 23%. Clay content, % Clay content, % DOHW7]LDOODV6RWKFRWWDQG $VVHIDUHVHDUFKHUV6HYHUDO 214 Pet.Sci.(2013)10:212-218 6FDQQLQJHOHFWURQPLFURVFRS\ 6(0 LVDQH[WUHPHO\ useful technique commonly used to observe the microscopic structure of clay minerals and their occurrence modes. Fig. 3 shows the morphological characteristics of clay minerals in a EDVDOWVDPSOH,WFDQEHVHHQIURPWKH6(0LPDJH )LJ D that clay minerals in the basalt samples were well developed. 6PHFWLWHZDVLGHQWL¿HGLQWKHVFDQQLQJHOHFWURQPLFURJUDSKV DWDPDJQL¿FDWLRQRIXSWRWLPHV )LJ E Fig. 4 shows the morphological characteristics of clay PLQHUDOVLQDWXIIVDPSOH7KH6(0UHVXOWVVKRZHGWKDW a large number of clay minerals were observed in the intergranular space, crystal defects and the micro-cracks of the diagenetic minerals, in both types of specimen. The main mineral occurred as a small flaky texture, which was LGHQWL¿HGDVVPHFWLWH Fig. 40LFURVFRSLFPRUSKRORJ\RIFOD\PLQHUDOVLQPLFURSRUHVDQG microcrack present in a tuff sample (S-32) indicated that the underground igneous rocks exhibited a strong heterogeneity, and weak planes were well developed, most of which were filled with other minerals, showing banded mineral filling characteristics (Fig. 5(c), 5(d)). However, there were also developed a small number of XQ¿OOHGFUDFNV )LJ D Fig. 6 shows the microscopic structures of basalt and tuff samples obtained with the scanning electron microscope. A small number of pores were observed in both basalt and tuff samples. They were mainly intergranular micropores, which were connected by microcracks and cleavage planes widely distributed in the samples. The existence of abundant micropores, microcracks and cleavage planes greatly reduced the mechanical properties of igneous rocks, so the rock Fig. 3 0LFURVFRSLFPRUSKRORJ\RIFOD\PLQHUDOVLQDEDVDOWVDPSOH 6 mass may be easily damaged by external force along the PLFURFUDFNVDQGFOHDYDJHSODQHV¿QDOO\UHVXOWLQJLQZHOOERUH instability. On the other hand, these micropores, microcracks 2.2 Weak structural plane and microscopic pore and cleavage planes also provided channels or passages structure description for the water phase of the drilling fluid penetrating into the The development of cracks, cleavage, and weak structural formation and interacting with clay minerals (especially the planes directly determine the rock mechanical properties. smectite), increasing the possibility of the invasion of drilling This also affects the permeability in vicinity of the wellbore. ÀXLG¿OWUDWHVGHHSLQWRWKHIRUPDWLRQ'XULQJGULOOLQJLQWKLV Analysis of drill core samples from the study area (Fig. 5) DUHDZKHQGULOOLQJÀXLG¿OWUDWHVSHQHWUDWHLQWRWKHIRUPDWLRQ Pet.Sci.(2013)10:212-218 215 Fig. 5 Weak planes in full-size drilling cores DORQJWKHPLFURFUDFNVRUFOHDYDJHSODQHVWKH¿OWUDWHVRIWHQ it split along the cleavage planes or microcracks, finally exacerbate the hydration, expansion and dispersion of clay resulting in wellbore instability. When the filtrate loss of minerals, thereby reducing the bonding strength of the rock the drilling fluid gets higher, it can easily lead to borehole and the binding force between cleavage planes, then causing sloughing and sticking. Fig. 6IVDPSOHV6(0LPDJHVRIEDVDOWDQGWXI 216 Pet.Sci.(2013)10:212-218 It can be seen from Fig. 7(b) that both the mass and 3 Mechanical properties of rock samples density of the core samples increased with soak time. This VRDNLQJLQWKHGULOOLQJÀXLGDIWHU indicated that the amount of drilling fluid filtrate invading the core samples gradually increased over time and the core To further investigate the instability mechanisms of the IHFWHGE\WKHGULOOLQJÀXLGZLWKLQVDPSOHZDVQRW\HWIXOODI fractured igneous rocks, the mechanical properties of rock h. samples were measured after soakng in the drilling fluid Previous research indicated that the acoustic velocity (Table 2). Triaxial compression tests were conducted to increased with an increase in fluid saturation (Pujol and analyze the dynamic characteristics of rock samples after 6PWKVRQDQJ:DQG'DL=KXHWDO ,Q VRDNLQJLQWKHGULOOLQJÀXLGIRUIHUHQWGLIRWLPHV7JXDUDQWHH WKHVHWHVWVWKHGULOOLQJÀXLG¿OWUDWHLQYDGHGWKHFRUHVDPSOH the comparability of the experimental results, from the as it was soaked, so the fluid saturation increased in the same lithologic type of core samples, we selected integrated sample and the effective pore space with gas decreased due samples with similar initial density and initial acoustic travel to swelling of clay minerals which are sensitive to water. This time as experimental core samples (Table 3). resulted in a reduction in acoustic travel time (i.e. increase Table 2'ULOOLQJÀXLGIRUPXODWLRQ in wave velocity) of the core samples (Fig. 7(a)). Thus even ZLWKRXWH[WHUQDOSUHVVXUHIHUHQFHGLIWKHGULOOLQJÀXLG¿OWUDWH Component Content, % Component Content, % may invade the core sample and react with clay minerals $0.3 0.3 NaCOOH 5 under capillary pressure when the core sample was soaked in HV-PAC 0.5 WD801 1 WKHGULOOLQJÀXLG7KLVLVDQLPSRUWDQWIDFWRUIRUWKHUHGXFWLRQ ;& 0.3 BST-II 0.5 of rock strength. Triaxial compression test results showed NaHPAN 1.5 &0&+9 0.5 that the compressive strength of igneous rock sample was VLJQL¿FDQWO\ORZHUDIWHUVRDNLQJWKDQLWVLQLWLDOYDOXHDQGWKH LYDF 3.0 SPNH 2 overall elasticity modulus also decreased (Fig. 8). Table 3 Basic parameters of core samples The experimental results showed that drilling fluid LQYDVLRQVLJQL¿FDQWO\UHGXFHGWKHPHFKDQLFDOVWUHQJWKRIWKH Sample Density Acoustic time Porosity Permeability 3 -2 igneous rocks. However, the reduction of the rock mechanical number g/cm ȝVP % ×10 mD properties is only the representation in macro physics, which 2 2.52 225.4 3.6 1.5 cannot reveal the intrinsic yield failure of rocks. This cannot 10 2.57 232.3 2.9 5.1 describe the relationship between the internal structure of 11 2.58 233.1 3.8 6.2 the rock and its mechanical properties (Sulukcu and Ulusay, 12 2.58 252.0 4.7 6.8 2001). The question is: how does the interaction between the drilling fluid and the microcracks and the clay minerals 45 2.53 242.5 4.2 2.2 change the rock structure, affect the propagation of the 46 2.46 229.5 3.7 2.6 internal cracks, and then reduce the stability of the igneous 47 2.53 237.7 4.1 1.7 rock? In our laboratory, a micro-CT scanner was used to 53 2.54 238.5 3.9 1.6 image the igneous core samples before and after soaking in the drilling fluid to record visually the subtle evolution The core samples were soaked in the drilling fluid for of microcracks in core samples, thus revealing the intrinsic 24, 48, and 72 h, respectively, at atmospheric temperature failure mechanism. and pressure. During soaking, the acoustic travel time, and The microcracks were found to present an increasing mass, and densities of core samples measured at certain time trend with soak time (Fig. 9). With the continuous invasion intervals. Finally, triaxial compression tests were conducted RIWKHGULOOLQJÀXLG¿OWUDWHSURSDJDWLQJPLFURFUDFNVWHQGHG XQGHUWKHVLPXODWHGIRUPDWLRQFRQ¿QLQJSUHVVXUH to bifurcate in the core samples until full communication 2.49 66.30 66.15 2.48 66.00 Core mass 65.85 Core density 2.47 65.70 2.46 65.55 0.0 5.0 10.0 15.0 20.0 25.0 30.0 020 40 60 80 100 Soak time, h Soak time, h (a) (b) Fig. 7 Petrophysical properties of core sample S-12# after different times of soaking Acoustic travel time, s/m Core mass, g Core density, g/cm Pet.Sci.(2013)10:212-218 217 Fig. 8 IHFWRIGULOOLQJÀXLGLQYDVLRQRQPHFKDQLFDOSDUDPHWHUV(I occurred. The depth of crack propagation was related to the Fig. 10 shows the photos of specimens S-9 and S-7 degree of development of the initial cracks. Filtrate invasion ZKLFKZHUHVRDNHGLQWKHGULOOLQJÀXLGIRUK&UDFNVDQG and the corrosion and erosion of clay minerals in weak disintegration of rock were observed on the end portion of planes would decrease the friction strength of the surface of the specimen under atmospheric pressure. Combined with weak planes and lead to the microcracks being interconnected CT scan analysis, we drew the conclusion that continuous with the main crack, resulting in macroscopic damage. propagation and evolution of internal microcracks would This resulted in a decrease in rock strength at the borehole communicate themselves with the cracks on the core surface, wall with weak planes and then borehole sloughing during which reduced the binding force between layers, then caused drilling. For the basalt block with higher hardness, even more WKHHQGSRUWLRQWRIÀDNHWKHRIEORFN7KHUHIRUHEDVHGRQWKH complicated conditions such as sticking would occur. micro-geological characteristics analysis in this paper, we CT-scan images Fig. 9 summarized a failure mechanism of borehole instability in IUDFWXUHGLJQHRXVURFNVIRUPDWLRQV7KHGULOOLQJÀXLG¿OWUDWH can penetrate along the cracks and microcracks and react with some clay minerals (swelling and hydration), which causes a decrease in cohesion of mineral particles. Therefore, primary or secondary microcracks may continuously propagate and merge into single cracks until partial or total collapse occur in the core samples. 4 Conclusions ;5'DQG6(0DQDO\VHVLQGLFDWHWKDWFOD\PLQHUDOVDUH common in the intergranular space of the diagenetic minerals, crystal defects, and microcracks. The dominant clay mineral is smectite. 2) Triaxial compression test results show that the 218 Pet.Sci.(2013)10:212-218 Hong Kong, China compressive strength of an igneous rock sample is -6'X6/L0DR+7HWDO5HVHDUFKDQGDSSOLFDWLRQRIGULOOLQJÀXLG significantly lower after soaking in drilling fluid filtrate technology in igneous rock formation of deep exploration wells in than its initial value, and the overall elasticity modulus also Tuha. Petroleum Geology and Engineering. 2011. 25(Suppl.): 49-52 (in decreases. Chinese) 0LFUR&7LPDJLQJLQGLFDWHVWKDWSULPDU\DQG ]6-/XW&OLQH(-DQG0DUWLQ-:5RFNPHFKDQLFDOWHVWLQJIRUWKH secondary microcracks may propagate and merge into single desert peak enhanced geothermal system (EGS) project, Nevada. FUDFNVGXHWRLQYDVLRQRIWKHGULOOLQJÀXLG¿OWUDWHOHDGLQJWR $PHULFDQ5RFN0HFKDQLFV$VVRFLDWLRQ-XQH6DOW/DNH partial collapse of the rock. City, Utah 4) The inherent instability mechanism of fractured igneous 0DV RXPL+DQG'RXJODV.-([SHULPHQWDOVWXG\RIVL]HHIIHFWVRI rocks is revealed. The presence of weak planes, microcracks URFNRQ8&6DQGSRLQWORDGWHVWV$PHULFDQ5RFN0HFKDQLFV and cleavage planes in the igneous rock exacerbates the $VVRFLDWLRQ-XQH&KLFDJR,OOLQRLV VXKDWD0DWVXR<0LW.DQG0LQHJLVKL00DJQHWRWHOOXULFVXUYH\IRU hydration and swelling of clay minerals, and thereby changes exploration of a volcanic rock reservoir in the Yurihara oil and gas the mechanical properties of rock in the vicinity of the ¿HOG-DSDQ*HRSK\VLFDO3URVSHFWLQJ borehole. This eventually causes borehole instability. RO-DQG6PWKVRQ66HLVPLFZDYHDWWHQXDWLRQLQYROFDQLFURFNVIURP3XM VSP experiments. Geophysics. 1991. 56(9): 1441-1455 Acknowledgements UPDQ05RK3URVSHFWLYLW\RIYROFDQLFEDVLQVUDS7GHOLQHDWLRQDQG acreage de-risking. AAPG Bulletin. 2007. 91(6): 915-939 The authors are grateful for financial support from the Sah abudin S and Darren E. Reducing well costs by optimizing drilling National Natural Science Foundation of China (Grant No. including hard/abrasive igneous rock section offshore Vietnam. U1262209). 6HSWHPEHUHFKQRORJ\$VLD3DFL¿F'ULOOLQJ7,$'&63( 0DOD\VLD 63( .XDOD/XPSXU References R.6DW: ULJKW&$DQG,FKLNDZD03RVWIUDFDQDO\VHVLQGLFDWLQJ UWR0DQG$EX&O\GHU57KHHYROXWLRQRIURWDU\VWHHUDEOHSUDFW LFHVWR multiple fractures created in a volcanic formation. SPE India Oil and drill faster, safer and cheaper deepwater salt sections in the Gulf Gas Conference and Exhibition, 17-19 February 1998, New Delhi, RI0H[LFR63(,$'&'ULOOLQJ&RQIHUHQFHDQG([KLELWLRQ India (SPE 39513) 06 $PVWHUGDP1HWKHUODQGV 63(0DUFK Stj ern G, Agle A and Horsrud P. Local rock mechanical knowledge $VV HID6DQG6RWKFRWW-$FRXVWLFDQGSHWURSK\VLFDOSURSHUWLHVRI improves drilling performance in fractured formations at the Heidrun VHDÀRRUEHGURFNV63()RUPDWLRQ(YDOXDWLRQ   ¿HOG-RXUQDORI3HWUROHXP6FLHQFHDQG(QJLQHHULQJ (SPE 37164) 96 HU6%DX- )ULHGPDQ0DQG+DQGLQ-(IIHFWVRIZDWHUVDWXUDWLRQRQ Sul ukcu S and Ulusay R. Evaluation of the block punch index test with strength and ductility of three igneous rocks at effective pressures particular reference to the size effect, failure mechanism and its WR03DDQGWHPSHUDWXUHVWRSDUWLDOPHOWLQJ$PHULFDQ5RFN HIIHFWLYHQHVVLQSUHGLFWLQJURFNVWUHQJWK,QWHUQDWLRQDO-RXUQDORI &DPEULGJH$VVRFLDWLRQ-XQH±-XO\0HFKDQLFV 5RFN0HFKDQLFV 0LQLQJ6FLHQFHV Bhu yan K and Passey Q R. Clay estimation from GR and neutron- &,QWHJUDWHG3DQ7URFNPHFKDQLFVDQGGULOOLQJÀXLGGHVLJQDSSURDFK density porosity logs. The 35th Annual Logging Symposium WRPDQDJHVKDOH63(,6505RFN0HFKDQLFVLQ3HWUROHXP Transactions. Society of Professional Well Log Analysts, 1994 URQGKHLP1RUZD\ 63( 7(QJLQHHULQJ-XO\ &DY LQDWR*3&UDYHUR0,DELFKLQR*HWDO*HRVWUXFWXUDODQG Tho mson K. Extrusive and intrusive magmatism in the North Rockall geomechanical characterization of rock exposures for an endangered Trough. Petroleum Geology. 2003. 2(10): 6-9 DOSLQHURDG$PHULFDQ5RFN0HFKDQLFV$VVRFLDWLRQ-XQH Tzi allas G P, Tsiambaos G and Saroglou H. Rock strength and 2005, Anchorage, AK GHIRUPDELOLW\PHDVXUHPHQWVZLWKLQGLUHFWPHWKRGV,650 Q;DQ&KH7&3DQG'H WRXUQD\&$VWXG\RQZHOOERUHVWDELOLW\LQ ,QWHUQDWLRQDO6\PSRVLXPRQ5RFN0HFKDQLFV0D\ IUDFWXUHGURFNPDVVHVZLWKLPSDFWRIPXGLQILOWUDWLRQ-RXUQDORI Hong Kong, China Petroleum Science and Engineering. 2003. 38(1): 145-155 J-*/LX+4DQG=KDR;6WXGLHVRQIUDFWXUHLGHQWL¿FDWLRQRIWKHDQ: Cro sta G, Agliardi F, Fusi N G, et al. Rock fabric controls on the failure volcanic-rock reservoir by well logging. International Oil and Gas mode of strongly deformed gneisses. International Society for Rock &RQIHUHQFHDQG([KLELWLRQ-XQH%HLMLQJ&KLQD 63( 0HFKDQLFV-XQH/DXVDQQH6ZLW]HUODQG 130965) Hos sain N K and Seshagiri R. Role of the texture characteristics on Wan g L and Dai H. Estimating anisotropic parameters from PS WKHVWUHQJWKSURSHUWLHVRIFU\VWDOOLQHURFNV,650,QWHUQDWLRQDO FRQYHUWHGZDYHGDWD-RXUQDORI6HLVPLF([SORUDWLRQ 6\PSRVLXPWK$VLDQ5RFN0HFKDQLFV6\PSRVLXP 1-3 November 2008, Tehran, Iran 5DQ4;X=6HWDO<6WUDWHJ\QRI6KLJKHI¿FLHQF\GHYHORSPHQWXD< UDP'$6LQJOH-HU57+REEV5HW:DO8QGHUVWDQGLQJWKHIVKRUHRI for volcanic gas reservoirs. Acta Petrolei Sinica. 2007. 28(1): 73-77 flood basalt sequence using onshore volcanic facies analogues: An (in Chinese) H[DPSOHIURPWKH)DURH6KHWODQGEDVLQ*HRORJLFDO0DJD]LQH QJ/=KD:/L-+X<+<HWDO&KDUDFWHULVWLFVDQGGLVWULEXWLRQ 146: 353-367 prediction of lithofacies of Carboniferous igneous rocks in Dixi Kaw amoto T and Sato K. Geological modelling of a heterogeneous $FWD3HWURORJLFD6LQLFD   LQDUHD(DVW-XQJJDU volcanic reservoir by the petrological method. SPE Asia Pacific Chinese) &RQIHUHQFHRQ,QWHJUDWHG0RGHOOLQJIRU$VVHW0DQDJHPHQW +/=KX/LX;-DQG/LX+([SHULPHQWDOUHVHDUFKRQIHFWVHIRIJDV RNRKDPD-DSDQ 63( <$SULO saturation on acoustic wave velocity of carbonate rock. Chinese Kar akul H and Ulusay R. Evaluation of strength anisotropy and -RXUQDORI5RFN0HFKDQLFVDQG(QJLQHHULQJ 6XSS empirical models for estimating strength of rock materials with 2784-2789 (in Chinese) LQFOLQHGZHDNQHVVSODQHVXVLQJEORFNSXQFKLQGH[WHVW,650 ,QWHUQDWLRQDO6\PSRVLXPRQ5RFN0HFKDQLFV0D\ (Edited by Sun Yanhua) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Petroleum Science Springer Journals

Research on fabric characteristics and borehole instability mechanisms of fractured igneous rocks

Liu, Xiangjun; Zhu, Honglin; Liang, Lixi
Petroleum Science , Volume 10 (2) – May 18, 2013
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Publisher
Springer Journals
Copyright
Copyright © 2013 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
ISSN
1672-5107
eISSN
1995-8226
DOI
10.1007/s12182-013-0269-2
Publisher site
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Abstract

borehole instability occur frequently during drilling igneous formations, which is a serious impediment to oil and gas exploration and production. The lack of systematic understanding of the inherent instability mechanisms is an important problem. A series of experiments were conducted on several igneous rock samples taken from the sloughing formations in the Tuha area in an attempt to reveal the inherent mechanisms of wellbore instability when drilling in fractured igneous rocks. Research methods involved VOXUU\FKHPLVWU\DQDO\VLVRIPLFURJHRORJLFDOIHDWXUHV 0LFUR&7LPDJLQJ6(0 DQGURFNPHFKDQLFV testing. The experimental results indicated that clay minerals were widely distributed in the intergranular space of the diagenetic minerals, crystal defects, and microcracks. Drilling fluid filtrate would invade the rock along the microcracks. The invasion amount gradually increased over time, which constantly LQWHQVL¿HGWKHK\GUDWLRQDQGVZHOOLQJRIFOD\PLQHUDOVOHDGLQJWRFKDQJHVLQWKHPLFURVFRSLFVWUXFWXUH of igneous rocks. Primary and secondary microcracks can propagate and merge into single cracks and thus reducing rock cohesion and the binding force along cleavage planes. Based on this result the authors propose that a key towards solving wellbore instability in igneous formations is that specific micro-geological characteristics of the igneous rocks should be taken into consideration in the design of antisloughing drilling muds. Igneous rocks, microcracks, clay minerals, hydration, instability Key words: to suffer from borehole instability consist mainly of smectite, 1 Introduction whose physical and chemical properties present strong Borehole instability caused by clay mineral hydration GLVSHUVLELOLW\RUH[SDQVLELOLW\ %KX\DQDQG3DVVH\ during drilling is a major problem in the oil industry. This 6WMHUQHWDO7KRPVRQ5RKUPDQ :KHQ SKHQRPHQRQXVXDOO\RFFXUVLQWKHFOD\ULFKPXGVKDOH FRQWDFWHGZLWKLQFRPSDWLEOHGULOOLQJÀXLG¿OWUDWHWKHVHFOD\ however, with expansion of exploration, it is also found in minerals would be hydrated (in the forms of dispersion or WKHGULOOLQJRILJQHRXVIRUPDWLRQV 0LWVXKDWDHWDO H[SDQVLRQ WKXVOHDGLQJWRZHOOERUH,QLQVWDELOLW\WKH-LGRQJ Sahabudin and Darren, 2000). In recent years, borehole 2LO¿HOGWKHEDVDOWDQGIWXIIRUPDWLRQVLQWKH*XDQWDR*URXS collapse, hole enlargement, lost circulation, pipe sticking where borehole instability occurs contain a large number and other complex problems often emerge in most of oil of clay minerals, up to 36%-78%, with a relative content of and gas basins when drilling into igneous rocks (basalt, smectite of 90%-97%. The high content and wide distribution tuff-based), resulting in the expansion of the drilling cycle of opaline silica which also expands easily may also be one and increase in drilling cost. To reduce wellbore instability of the reasons for borehole instability (Yuan et al, 2007). problems in igneous rock formations, several researchers Tuff is easily to disperse, with a core recovery rate of less KDYHLQYHVWLJDWHGWKHIDFWRUVLQÀXHQFLQJERUHKROHLQVWDELOLW\ than 10%, while basalt and altered basalt have relatively low Researchers focusing on metasomatic alteration petrology dispersibility, but still expand easily with an expansion ratio pointed out that the neutral or basic igneous rocks, especially XSWR =KDQJHWDO pyroclastic rocks under hydrothermal conditions (contact In addition, the particular petrological structure of igneous ZLWKWKHIRUPDWLRQÀXLGXQGHUKLJKWHPSHUDWXUHFRQGLWLRQV rocks is also a potential factor of borehole instability (Sato would be vulnerable to argillization. Plagioclase is often HWDO.DZDPRWRDQG6DWR-HUUDPHWDO altered to kaolinite and smectite minerals. Numerous studies .DUDNXODQG8OXVD\DQJ:HWDO HDN:SODQHV show that clay minerals in igneous rock formations tending and non-homogeneous structure greatly weakens the strength RIIRUPDWLRQURFN0RUHRYHUWKHPLFURVWUXFWXUHVRILJQHRXV rocks also have an impact on the deformation mode (Crosta *Corresponding author. email: liuxiangjunswpi@163.com HWDO+RVVDLQDQG6HVKDJLUL/XW]HWDO Received August 31, 2012 Pet.Sci.(2013)10:212-218 213 so that the traditional Hoek-Brown instability criterion is QRORQJHUDSSOLFDEOH 0DVRXPLDQG'RXJODV 7KH hardness of amygdaloid differs substantially from that of the basalt matrix drilled in amygdaloidal basalt in the Tahe 30 Oilfield (the amygdaloid are composed of calcite, opaline silica, and chlorite). The released stress, surge pressure, drilling tool collision, and other mechanical factors during drilling make it easy to produce stress concentration at the amygdale, which results in sloughing of surrounding rock and lost circulation in basalt with abundant pores (Li et al, 2011). S-1-2 S-22 S- 3 S-30 S-48 S-5 S- 8 S-23 52 51 5 &DYLQDWRHWDO%DXHUHWDO IRFXVHGPRUH Sample number on investigating the factors affecting the geo-mechanical Fig. 1 Whole-rock mineral analysis of clay content in tuff specimens properties of rocks and the relationship with acoustic parameters, but they did not pay attention to understanding the mechanisms of borehole instability in igneous formations. The understanding obtained from the studies on drilling IOXLGVXVHGLQLJQHRXVIRUPDWLRQVDQ 7HWDO$EXUWR DQG&O\GH&KHQHWDO ZDVWKDWWKHRULJLQDO collapse pressure of the igneous rock was high and wellbore stabilization was achieved by continuously adjusting the drilling fluid density. But so far, when wellbore instability occurs in newly drilled igneous rocks (such as Yubei), it is still necessary to take a lot of time and effort to come up 0 36 35 S-33 27 S-17 S-21 S-25 S-31 S-34 S-37 S-28 with countermeasures. The fundamental reason is the lack of Sample number a clear and systematic understanding of the mechanisms of wellbore instability in igneous rock formations. Fig. 2 Whole-rock mineral analysis of clay content in basalt specimens In view of the above problems, which are related to Table 1 lists the clay mineral composition of some test physical and mechanical properties of igneous rocks under samples. It can be seen from Table 1 that in all test samples, specific geological and engineering conditions, a series of WKHGRPLQDQWFOD\PLQHUDOLVVPHFWLWHLQWKHIRXUPDLQFOD\ experiments were conducted on several igneous rock samples minerals (kaolinite, chlorite, illite, and smectite), the relative taken from the sloughing formations in the Tuha area, to percentages of smectite is generally more than 50%, except attempt to reveal the inherent instability mechanisms of these samples S-32 and S-28, even exceeding 95%. The relative fractured igneous rocks. contents of smectite in samples S-32 and S-28 are 19% and 32%, respectively. 2 Microstructure and clay mineral analysis of igneous rocks Table 1 Clay mineral content and composition The mechanical properties of rocks are affected by Relative content, % Total clay mineral mineral composition, rock texture, clay content and clay type. Sample content, % Kaolinite Chlorite Illite Smectite Therefore, analysis of mineral component, rock texture, and clay type and content of igneous rocks may greatly contribute S-3 39 0.1 0.2 3.8 96 to understanding the borehole instability mechanisms. S-47 13 0.3 0.2 0.8 99 2.1 Whole-rock mineral analysis by X-ray diffraction S-9 15 0.0 0.1 0.3 99 (XRD) S-22 22 0.1 0.2 0.6 99 IUDFWLRQDQDO\VLVLVDIDVWUHOLDEOHDQGFRQYHQLHQW;UD\GLI S-26 26 21.2 14.2 0.0 65 method for determining clay mineral type and content. Several rock samples taken from the sloughing formations S-32 16 31.2 15.6 34.7 19 LQWKHVWXG\DUHDZHUHJURXQGWR¿QHSRZGHUDQGWKHQ;5' S-28 32 50.3 16.8 0.5 32 was applied to determine the total clay mineral content in S-23 23 0.3 0.2 0.8 99 the powder. Compared with the intercrystalline distance and intensity of diffracted ray for different types of clay 52 26 0.1 0.2 0.4 99 minerals, the types and relative contents of clay minerals 36 23 0.0 22.7 6.1 71 ZHUHLGHQWLILHG7KHUHVXOWVRI;5'DQDO\VLVVKRZHGWKDW both types of igneous rock samples had high clay contents (see 5 10 0.3 0.2 46.6 53 Figs. 1 and 2). The average clay content of the tuff samples 53 39 0.6 0.7 2.0 97 was 18% and that of the basalt samples was 23%. Clay content, % Clay content, % DOHW7]LDOODV6RWKFRWWDQG $VVHIDUHVHDUFKHUV6HYHUDO 214 Pet.Sci.(2013)10:212-218 6FDQQLQJHOHFWURQPLFURVFRS\ 6(0 LVDQH[WUHPHO\ useful technique commonly used to observe the microscopic structure of clay minerals and their occurrence modes. Fig. 3 shows the morphological characteristics of clay minerals in a EDVDOWVDPSOH,WFDQEHVHHQIURPWKH6(0LPDJH )LJ D that clay minerals in the basalt samples were well developed. 6PHFWLWHZDVLGHQWL¿HGLQWKHVFDQQLQJHOHFWURQPLFURJUDSKV DWDPDJQL¿FDWLRQRIXSWRWLPHV )LJ E Fig. 4 shows the morphological characteristics of clay PLQHUDOVLQDWXIIVDPSOH7KH6(0UHVXOWVVKRZHGWKDW a large number of clay minerals were observed in the intergranular space, crystal defects and the micro-cracks of the diagenetic minerals, in both types of specimen. The main mineral occurred as a small flaky texture, which was LGHQWL¿HGDVVPHFWLWH Fig. 40LFURVFRSLFPRUSKRORJ\RIFOD\PLQHUDOVLQPLFURSRUHVDQG microcrack present in a tuff sample (S-32) indicated that the underground igneous rocks exhibited a strong heterogeneity, and weak planes were well developed, most of which were filled with other minerals, showing banded mineral filling characteristics (Fig. 5(c), 5(d)). However, there were also developed a small number of XQ¿OOHGFUDFNV )LJ D Fig. 6 shows the microscopic structures of basalt and tuff samples obtained with the scanning electron microscope. A small number of pores were observed in both basalt and tuff samples. They were mainly intergranular micropores, which were connected by microcracks and cleavage planes widely distributed in the samples. The existence of abundant micropores, microcracks and cleavage planes greatly reduced the mechanical properties of igneous rocks, so the rock Fig. 3 0LFURVFRSLFPRUSKRORJ\RIFOD\PLQHUDOVLQDEDVDOWVDPSOH 6 mass may be easily damaged by external force along the PLFURFUDFNVDQGFOHDYDJHSODQHV¿QDOO\UHVXOWLQJLQZHOOERUH instability. On the other hand, these micropores, microcracks 2.2 Weak structural plane and microscopic pore and cleavage planes also provided channels or passages structure description for the water phase of the drilling fluid penetrating into the The development of cracks, cleavage, and weak structural formation and interacting with clay minerals (especially the planes directly determine the rock mechanical properties. smectite), increasing the possibility of the invasion of drilling This also affects the permeability in vicinity of the wellbore. ÀXLG¿OWUDWHVGHHSLQWRWKHIRUPDWLRQ'XULQJGULOOLQJLQWKLV Analysis of drill core samples from the study area (Fig. 5) DUHDZKHQGULOOLQJÀXLG¿OWUDWHVSHQHWUDWHLQWRWKHIRUPDWLRQ Pet.Sci.(2013)10:212-218 215 Fig. 5 Weak planes in full-size drilling cores DORQJWKHPLFURFUDFNVRUFOHDYDJHSODQHVWKH¿OWUDWHVRIWHQ it split along the cleavage planes or microcracks, finally exacerbate the hydration, expansion and dispersion of clay resulting in wellbore instability. When the filtrate loss of minerals, thereby reducing the bonding strength of the rock the drilling fluid gets higher, it can easily lead to borehole and the binding force between cleavage planes, then causing sloughing and sticking. Fig. 6IVDPSOHV6(0LPDJHVRIEDVDOWDQGWXI 216 Pet.Sci.(2013)10:212-218 It can be seen from Fig. 7(b) that both the mass and 3 Mechanical properties of rock samples density of the core samples increased with soak time. This VRDNLQJLQWKHGULOOLQJÀXLGDIWHU indicated that the amount of drilling fluid filtrate invading the core samples gradually increased over time and the core To further investigate the instability mechanisms of the IHFWHGE\WKHGULOOLQJÀXLGZLWKLQVDPSOHZDVQRW\HWIXOODI fractured igneous rocks, the mechanical properties of rock h. samples were measured after soakng in the drilling fluid Previous research indicated that the acoustic velocity (Table 2). Triaxial compression tests were conducted to increased with an increase in fluid saturation (Pujol and analyze the dynamic characteristics of rock samples after 6PWKVRQDQJ:DQG'DL=KXHWDO ,Q VRDNLQJLQWKHGULOOLQJÀXLGIRUIHUHQWGLIRWLPHV7JXDUDQWHH WKHVHWHVWVWKHGULOOLQJÀXLG¿OWUDWHLQYDGHGWKHFRUHVDPSOH the comparability of the experimental results, from the as it was soaked, so the fluid saturation increased in the same lithologic type of core samples, we selected integrated sample and the effective pore space with gas decreased due samples with similar initial density and initial acoustic travel to swelling of clay minerals which are sensitive to water. This time as experimental core samples (Table 3). resulted in a reduction in acoustic travel time (i.e. increase Table 2'ULOOLQJÀXLGIRUPXODWLRQ in wave velocity) of the core samples (Fig. 7(a)). Thus even ZLWKRXWH[WHUQDOSUHVVXUHIHUHQFHGLIWKHGULOOLQJÀXLG¿OWUDWH Component Content, % Component Content, % may invade the core sample and react with clay minerals $0.3 0.3 NaCOOH 5 under capillary pressure when the core sample was soaked in HV-PAC 0.5 WD801 1 WKHGULOOLQJÀXLG7KLVLVDQLPSRUWDQWIDFWRUIRUWKHUHGXFWLRQ ;& 0.3 BST-II 0.5 of rock strength. Triaxial compression test results showed NaHPAN 1.5 &0&+9 0.5 that the compressive strength of igneous rock sample was VLJQL¿FDQWO\ORZHUDIWHUVRDNLQJWKDQLWVLQLWLDOYDOXHDQGWKH LYDF 3.0 SPNH 2 overall elasticity modulus also decreased (Fig. 8). Table 3 Basic parameters of core samples The experimental results showed that drilling fluid LQYDVLRQVLJQL¿FDQWO\UHGXFHGWKHPHFKDQLFDOVWUHQJWKRIWKH Sample Density Acoustic time Porosity Permeability 3 -2 igneous rocks. However, the reduction of the rock mechanical number g/cm ȝVP % ×10 mD properties is only the representation in macro physics, which 2 2.52 225.4 3.6 1.5 cannot reveal the intrinsic yield failure of rocks. This cannot 10 2.57 232.3 2.9 5.1 describe the relationship between the internal structure of 11 2.58 233.1 3.8 6.2 the rock and its mechanical properties (Sulukcu and Ulusay, 12 2.58 252.0 4.7 6.8 2001). The question is: how does the interaction between the drilling fluid and the microcracks and the clay minerals 45 2.53 242.5 4.2 2.2 change the rock structure, affect the propagation of the 46 2.46 229.5 3.7 2.6 internal cracks, and then reduce the stability of the igneous 47 2.53 237.7 4.1 1.7 rock? In our laboratory, a micro-CT scanner was used to 53 2.54 238.5 3.9 1.6 image the igneous core samples before and after soaking in the drilling fluid to record visually the subtle evolution The core samples were soaked in the drilling fluid for of microcracks in core samples, thus revealing the intrinsic 24, 48, and 72 h, respectively, at atmospheric temperature failure mechanism. and pressure. During soaking, the acoustic travel time, and The microcracks were found to present an increasing mass, and densities of core samples measured at certain time trend with soak time (Fig. 9). With the continuous invasion intervals. Finally, triaxial compression tests were conducted RIWKHGULOOLQJÀXLG¿OWUDWHSURSDJDWLQJPLFURFUDFNVWHQGHG XQGHUWKHVLPXODWHGIRUPDWLRQFRQ¿QLQJSUHVVXUH to bifurcate in the core samples until full communication 2.49 66.30 66.15 2.48 66.00 Core mass 65.85 Core density 2.47 65.70 2.46 65.55 0.0 5.0 10.0 15.0 20.0 25.0 30.0 020 40 60 80 100 Soak time, h Soak time, h (a) (b) Fig. 7 Petrophysical properties of core sample S-12# after different times of soaking Acoustic travel time, s/m Core mass, g Core density, g/cm Pet.Sci.(2013)10:212-218 217 Fig. 8 IHFWRIGULOOLQJÀXLGLQYDVLRQRQPHFKDQLFDOSDUDPHWHUV(I occurred. The depth of crack propagation was related to the Fig. 10 shows the photos of specimens S-9 and S-7 degree of development of the initial cracks. Filtrate invasion ZKLFKZHUHVRDNHGLQWKHGULOOLQJÀXLGIRUK&UDFNVDQG and the corrosion and erosion of clay minerals in weak disintegration of rock were observed on the end portion of planes would decrease the friction strength of the surface of the specimen under atmospheric pressure. Combined with weak planes and lead to the microcracks being interconnected CT scan analysis, we drew the conclusion that continuous with the main crack, resulting in macroscopic damage. propagation and evolution of internal microcracks would This resulted in a decrease in rock strength at the borehole communicate themselves with the cracks on the core surface, wall with weak planes and then borehole sloughing during which reduced the binding force between layers, then caused drilling. For the basalt block with higher hardness, even more WKHHQGSRUWLRQWRIÀDNHWKHRIEORFN7KHUHIRUHEDVHGRQWKH complicated conditions such as sticking would occur. micro-geological characteristics analysis in this paper, we CT-scan images Fig. 9 summarized a failure mechanism of borehole instability in IUDFWXUHGLJQHRXVURFNVIRUPDWLRQV7KHGULOOLQJÀXLG¿OWUDWH can penetrate along the cracks and microcracks and react with some clay minerals (swelling and hydration), which causes a decrease in cohesion of mineral particles. Therefore, primary or secondary microcracks may continuously propagate and merge into single cracks until partial or total collapse occur in the core samples. 4 Conclusions ;5'DQG6(0DQDO\VHVLQGLFDWHWKDWFOD\PLQHUDOVDUH common in the intergranular space of the diagenetic minerals, crystal defects, and microcracks. The dominant clay mineral is smectite. 2) Triaxial compression test results show that the 218 Pet.Sci.(2013)10:212-218 Hong Kong, China compressive strength of an igneous rock sample is -6'X6/L0DR+7HWDO5HVHDUFKDQGDSSOLFDWLRQRIGULOOLQJÀXLG significantly lower after soaking in drilling fluid filtrate technology in igneous rock formation of deep exploration wells in than its initial value, and the overall elasticity modulus also Tuha. Petroleum Geology and Engineering. 2011. 25(Suppl.): 49-52 (in decreases. Chinese) 0LFUR&7LPDJLQJLQGLFDWHVWKDWSULPDU\DQG ]6-/XW&OLQH(-DQG0DUWLQ-:5RFNPHFKDQLFDOWHVWLQJIRUWKH secondary microcracks may propagate and merge into single desert peak enhanced geothermal system (EGS) project, Nevada. FUDFNVGXHWRLQYDVLRQRIWKHGULOOLQJÀXLG¿OWUDWHOHDGLQJWR $PHULFDQ5RFN0HFKDQLFV$VVRFLDWLRQ-XQH6DOW/DNH partial collapse of the rock. City, Utah 4) The inherent instability mechanism of fractured igneous 0DV RXPL+DQG'RXJODV.-([SHULPHQWDOVWXG\RIVL]HHIIHFWVRI rocks is revealed. The presence of weak planes, microcracks URFNRQ8&6DQGSRLQWORDGWHVWV$PHULFDQ5RFN0HFKDQLFV and cleavage planes in the igneous rock exacerbates the $VVRFLDWLRQ-XQH&KLFDJR,OOLQRLV VXKDWD0DWVXR<0LW.DQG0LQHJLVKL00DJQHWRWHOOXULFVXUYH\IRU hydration and swelling of clay minerals, and thereby changes exploration of a volcanic rock reservoir in the Yurihara oil and gas the mechanical properties of rock in the vicinity of the ¿HOG-DSDQ*HRSK\VLFDO3URVSHFWLQJ borehole. This eventually causes borehole instability. RO-DQG6PWKVRQ66HLVPLFZDYHDWWHQXDWLRQLQYROFDQLFURFNVIURP3XM VSP experiments. Geophysics. 1991. 56(9): 1441-1455 Acknowledgements UPDQ05RK3URVSHFWLYLW\RIYROFDQLFEDVLQVUDS7GHOLQHDWLRQDQG acreage de-risking. AAPG Bulletin. 2007. 91(6): 915-939 The authors are grateful for financial support from the Sah abudin S and Darren E. Reducing well costs by optimizing drilling National Natural Science Foundation of China (Grant No. including hard/abrasive igneous rock section offshore Vietnam. U1262209). 6HSWHPEHUHFKQRORJ\$VLD3DFL¿F'ULOOLQJ7,$'&63( 0DOD\VLD 63( .XDOD/XPSXU References R.6DW: ULJKW&$DQG,FKLNDZD03RVWIUDFDQDO\VHVLQGLFDWLQJ UWR0DQG$EX&O\GHU57KHHYROXWLRQRIURWDU\VWHHUDEOHSUDFW LFHVWR multiple fractures created in a volcanic formation. SPE India Oil and drill faster, safer and cheaper deepwater salt sections in the Gulf Gas Conference and Exhibition, 17-19 February 1998, New Delhi, RI0H[LFR63(,$'&'ULOOLQJ&RQIHUHQFHDQG([KLELWLRQ India (SPE 39513) 06 $PVWHUGDP1HWKHUODQGV 63(0DUFK Stj ern G, Agle A and Horsrud P. Local rock mechanical knowledge $VV HID6DQG6RWKFRWW-$FRXVWLFDQGSHWURSK\VLFDOSURSHUWLHVRI improves drilling performance in fractured formations at the Heidrun VHDÀRRUEHGURFNV63()RUPDWLRQ(YDOXDWLRQ   ¿HOG-RXUQDORI3HWUROHXP6FLHQFHDQG(QJLQHHULQJ (SPE 37164) 96 HU6%DX- )ULHGPDQ0DQG+DQGLQ-(IIHFWVRIZDWHUVDWXUDWLRQRQ Sul ukcu S and Ulusay R. Evaluation of the block punch index test with strength and ductility of three igneous rocks at effective pressures particular reference to the size effect, failure mechanism and its WR03DDQGWHPSHUDWXUHVWRSDUWLDOPHOWLQJ$PHULFDQ5RFN HIIHFWLYHQHVVLQSUHGLFWLQJURFNVWUHQJWK,QWHUQDWLRQDO-RXUQDORI &DPEULGJH$VVRFLDWLRQ-XQH±-XO\0HFKDQLFV 5RFN0HFKDQLFV 0LQLQJ6FLHQFHV Bhu yan K and Passey Q R. Clay estimation from GR and neutron- &,QWHJUDWHG3DQ7URFNPHFKDQLFVDQGGULOOLQJÀXLGGHVLJQDSSURDFK density porosity logs. The 35th Annual Logging Symposium WRPDQDJHVKDOH63(,6505RFN0HFKDQLFVLQ3HWUROHXP Transactions. Society of Professional Well Log Analysts, 1994 URQGKHLP1RUZD\ 63( 7(QJLQHHULQJ-XO\ &DY LQDWR*3&UDYHUR0,DELFKLQR*HWDO*HRVWUXFWXUDODQG Tho mson K. Extrusive and intrusive magmatism in the North Rockall geomechanical characterization of rock exposures for an endangered Trough. Petroleum Geology. 2003. 2(10): 6-9 DOSLQHURDG$PHULFDQ5RFN0HFKDQLFV$VVRFLDWLRQ-XQH Tzi allas G P, Tsiambaos G and Saroglou H. 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Estimating anisotropic parameters from PS WKHVWUHQJWKSURSHUWLHVRIFU\VWDOOLQHURFNV,650,QWHUQDWLRQDO FRQYHUWHGZDYHGDWD-RXUQDORI6HLVPLF([SORUDWLRQ 6\PSRVLXPWK$VLDQ5RFN0HFKDQLFV6\PSRVLXP 1-3 November 2008, Tehran, Iran 5DQ4;X=6HWDO<6WUDWHJ\QRI6KLJKHI¿FLHQF\GHYHORSPHQWXD< UDP'$6LQJOH-HU57+REEV5HW:DO8QGHUVWDQGLQJWKHIVKRUHRI for volcanic gas reservoirs. Acta Petrolei Sinica. 2007. 28(1): 73-77 flood basalt sequence using onshore volcanic facies analogues: An (in Chinese) H[DPSOHIURPWKH)DURH6KHWODQGEDVLQ*HRORJLFDO0DJD]LQH QJ/=KD:/L-+X<+<HWDO&KDUDFWHULVWLFVDQGGLVWULEXWLRQ 146: 353-367 prediction of lithofacies of Carboniferous igneous rocks in Dixi Kaw amoto T and Sato K. Geological modelling of a heterogeneous $FWD3HWURORJLFD6LQLFD   LQDUHD(DVW-XQJJDU volcanic reservoir by the petrological method. SPE Asia Pacific Chinese) &RQIHUHQFHRQ,QWHJUDWHG0RGHOOLQJIRU$VVHW0DQDJHPHQW +/=KX/LX;-DQG/LX+([SHULPHQWDOUHVHDUFKRQIHFWVHIRIJDV RNRKDPD-DSDQ 63( <$SULO saturation on acoustic wave velocity of carbonate rock. Chinese Kar akul H and Ulusay R. Evaluation of strength anisotropy and -RXUQDORI5RFN0HFKDQLFVDQG(QJLQHHULQJ 6XSS empirical models for estimating strength of rock materials with 2784-2789 (in Chinese) LQFOLQHGZHDNQHVVSODQHVXVLQJEORFNSXQFKLQGH[WHVW,650 ,QWHUQDWLRQDO6\PSRVLXPRQ5RFN0HFKDQLFV0D\ (Edited by Sun Yanhua)

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Petroleum Science – Springer Journals

Published: May 18, 2013

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