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- Title
Study on failure characteristics and in situ stress inversion of brittle shale under complex loading.
- Authors
Liu, Houbin; Cui, Shuai; Meng, Yingfeng; Wang, Jiajun; Lv, Bin
- Abstract
Aiming at the frequent occurrence of borehole wall collapse and other accidents in the drilling process of deep shale horizontal wells in the Luzhou block, the effects on mechanical properties of brittle shale were studied and analyzed by carrying out plugging test of drilling fluid and loading and unloading test of confining pressure. Considering the weak plane of bedding fracture and according to the shape of borehole caving, a mathematical model of ground stress inversion was established. The research results show that the deep shale in the Luzhou block has a high content of brittle minerals, and the bedding and microfractures are relatively developed. The plugging performance of the drilling fluid has a significant impact on the compressive strength and elastic modulus of deep brittle shale. The good sealing performance of drilling fluid can effectively improve the failure strength of borehole wall rock. In a complex downhole pressure environment, a too fast tripping speed will cause the effective bottom hole pressure to drop, reduce the effective support of the drilling fluid on the wellbore, and induce the damage of the wellbore rock along the bedding and microfractures. Under the condition of formation heterogeneity, the collapse shape of the wellbore is no longer the ideal round or oval shape but more of a four-leaf shape. With the known shape of the borehole after the collapse, a mathematical model of inverse in situ stress was established, and the accuracy of the mathematical model of inverse in situ stress was verified through the true triaxial test. The research results provide a certain theoretical basis for the safe and efficient development of deep shale gas.
- Publication
Arabian Journal of Geosciences, 2022, Vol 15, Issue 9, p1
- ISSN
1866-7511
- Publication type
Article
- DOI
10.1007/s12517-022-09951-1