Research on Wellbore Stability in Formation with Anisotropic Strength

Abstract:

As most of sedimentary rocks are anisotropic, it is significant to research the impact of the anisotropy of strength on wellbore stability in drilling engineering. Particularly, in the Kuqa piedmont exploration area, the anisotropy of strength caused by various jointed surfaces, fracture surfaces and fault planes in formation cause the formation of several groups of weak low-intensity planes traversing borehole . These weak planes will become failure earlier than the rock body in the context of strong stress and high pore pressure, causing chipping, breakouts and sticking. If fractures have good permeability and drilling fluid column pressure is greater than pore pressure, loss may occur. The loss pressure would not be controlled by fracturing pressure and horizontal minimum principal stress, but it depends on the relationship between fracture occurrence and triaxial stress state. In the event of loss, the drilling fluid will flow into these weak structural planes, causing the decrease of friction between rocks and increase of wellbore instability. As a result, for strongly anisotropic formation, the collapse pressure and leakage pressure of weak planes are key factors for evaluating well drilling stability. In this study, according to the stability evaluation on the transversely isotropic rock mechanics in Keshen zone of Kuqa piedmont, the impacts of fracture development on wellbore instability is analyzed; relevant suggestions on engineering geology for the special pressure window in strong anisotropic formation are also put forward.

• Periodical: Advanced Materials Research (Volumes 765-767)
• Pages: 3151-3157
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.765-767.3151
• Online since: September 2013
• Authors: Hui Zhang, Fang Jun Ou, Guo Qing Yin, Jing Bing Yi, Fang Yuan, Bing Xie, Chao Li, Wei Zhao
• Keywords: Anisotropy of Strength, Borehole Trajectory, Collapse Pressure, Fracture, Leakage Pressure, Mud Performance, Wellbore Stability

References

[1] Mark D. Zoback ., Reservoir Geomechanics [M] Cambridge: Cambridge University Press, (2007).

[2] Chen Mian, Jin Yan, Zhang Guangqing, et al. Rock Mechanics for Petroleum Engineering [M] Beijing: Press of Science and Technology, (2008).

[3] Liu Xiangjun, Luo Pingya et al; Rock Mechanics & Petroleum Engineering [M]. Beijing: Petroleum Industry Press, (2004).

[4] Donath, F.A. Experimental study of shear failure in anisotropic rock[J]. Bulletin of Geological Soc. America., 1966(72): 985-990.

DOI: 10.1130/0016-7606(1961)72[985:esosfi]2.0.co;2

[5] Jaeger, J.C., Cook, N.G.W. Fundamentals of Rock Mechanics. 2nd edn New York, Chapman and Hall, (1979).

[6] Willson, S.M., Last, N.C. et al. Drilling in South America: A wellbore stability approach for complex geologic conditions, SPE 53940. 1999, 6th LACPEC Conference, Caracas, Venezuela, Society of Petroleum Engineers.

DOI: 10.2118/53940-ms

[7] Finkbeiner, T., D. Moos, W. DeRose, Wellbore stability evaluation for horizontal hole completion – A case study, SPE 64409, (2000).

DOI: 10.2118/64409-ms

[8] Liu Xiangjun, Ye Zhongbin, Chen Yijian; Influence of Rock Weak Plane Texture on Wellbore Stability [J]. Natural Gas Industry, 2002, (2): 41-42.

[9] Jin Yan, Chen Mian, Liu Gonghui et al. Analysis on Wellbore Stability of Weak Plane Formation in Inclined Wells. Journal of the University of Petroleum, China (Natural Science Edition), 1999, (4)33-35.

[10] Zhang Fuxiang, Wang Xinhai, Li Yuanbin, et al.; Contribution Rate of Fractured Sandstone Gas Fracture In Kuqa Piedmont Area On The Formation Permeability; Journal of Petroleum and Natural Gas, 2011, (6): 149-152.

[11] Application of Adding Sand Fracture Treatment Tech in Yeyin2 Well [J]. Well Testing; 2005, (2): 65-66.

[12] T., and M. D. Zoback, Fracture permeability and in situ stress to 7 km depth in the KTB scientific drillhole [J]., Geophys. Res. Let., 2000(27): 1045–1048.

DOI: 10.1029/1999gl011068

[13] Lian Zhanghua, Kang Yili, Xu Jin, et al. Stress Analysis on Fracture Plane and Near Borehole [J]. Journal of Southwest Petroleum Institute, 2001, (3)37-39.