AUTHOR=Shen Cheng , Zeng Bo , Wu Jianfa , Song Yi , Guo Xingwu , Zhou Xiaojin , Li Junfeng 

TITLE=Casing Deformation Response and Controlling Technology Based on Diagnostics of Shale Gas Fracturing Curve

JOURNAL=Frontiers in Energy Research

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2022.958040

DOI=10.3389/fenrg.2022.958040

ISSN=2296-598X

ABSTRACT=Casing deformation has a serious impact on the operation progress and stimulation effect of shale gas fracturing. Taking 105 gas wells in a typical shale gas reservoir in Luzhou in southern Sichuan as an example, the method of diagnostics of fracturing curve was introduced to establish a prediction model of casing deformation, and evaluation of real-time net pressure and fracture stimulation mode and analysis of controlling factors that induce casing deformation during the fracturing process were realized. According to the diagnostic results of the fracturing curve, the real-time net pressure of the stages with fluctuated pressure is characterized by a gradual decrease, and the duration for fluid leak-off and fracturing propagation blockage gradually increases. The real-time net pressure of stages with casing deformation is slightly higher than stages with fluctuated pressure, during which fluid leak-off and fracture propagation occur. It is concluded that due to development of natural fractures, strata curvature, and lateral trajectory penetrating reservoirs, the changes of net pressure and fracture propagation mode are coupled. Under the influence of connection with natural fractures and bedding plane, the high-intensity fracturing treatment of the prior stages causes high-energy activation of fractures and bedding plane. Moreover, due to multiple penetration into interlayer within the fracturing stages, local stress torsion occurs, resulting in a continuous drop in net pressure and strike-slip in transition to reverse faulting, and significantly increasing duration of fluid leak-off and fracture propagation blockage. These are main factors for fracturing-induced casing deformation. According to the response induced by casing deformation, a casing deformation controlling mode was established, and a technology of casing deformation pre-control was established to quantitatively assess risks in the borehole and optimize fracturing treatment sequence, reducing the previous casing deformation rate from 56% to 20%, and realizing borehole integrity of 100%. The method has good applicability in the field and can be promoted.