Study on Influence of Mud Pollution on Formation Fracture Pressure
1 Chongqing Key Laboratory of Complex Oil & Gas Fields Exploration and Development, Chongqing University of Science and Technology, Chongqing, China
2 Research Institute of Shaanxi Yanchang Petroleum (Group) Co., Ltd, Xi’an, Shaanxi, China
3 Southwest Oil/gas Field Co. Gas Production Engineering Research Institute, CNPC, Guanghan, Sichuan, China
The mud pollution may change the mechanical properties of rock during oil and gas drilling process, which affects the prediction of fracture pressure, leads to the failure of hydraulic fracturing treatment. Therefore, it is necessary to study influence of mud pollution on formation fracture pressure to improve the forecasting accuracy. The mud pollution has influences on the modulus of elasticity and the Poisson’s ratio of rock by the mud pollution experiment, the core microstructure is observed around the mud pollution. Based on the experiment and research, the effects of mud pollution on the fracturing pressure are studied by finite element software system ANSYS, the factors such as pollution depth, perforation length and Poisson’s ratio of polluted area are taken into account. The result of the experiment indicated that the modulus of elasticity of rock is reduced and the Poisson’s ratio of rock is increased by the mud pollution. Through computing and analyzing, it can be concluded that increases in pollution depth and Poisson’s ratio can lead to a vast increase in formation fracturing pressure. A calculation example is presented and the results show that the results of this research can provide valuable guidance to the designers of hydraulic fracturing treatment.
Key words: rock mechanics / pollution zone / fracturing pressure / finite element / hydraulic fracturing
© Owned by the authors, published by EDP Sciences, 2015
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