Dissection and Causation Classification of Luzhou Shale Gas Casing Deformation

[Objective] China possesses abundant shale oil and gas resources, but frequent casing deformation (CD) during hydraulic fracturing in horizontal wells has become a critical constraint on the economic development of these resources. The industry gradually reaches an agreement on geomechanical mechanism of the casing shearing deformation of shale oil and gas, but lacks further knowledge on specific cause of CD (such as ‘pre-fracturing CD’) and predictive method for determining wellbore cleanout tool’s maximum diameter. [Methods] To solve these problems, by taking the Luzhou block deep shale gas reservoir as an example, (1) a predictive method for determining wellbore cleanout tool’s maximum diameter based on multi-perspective and quantitative confirmation of 3D CD morphology using 24-arm multi-finger logging tool (MIT) is proposed, and, (2) by comprehensive analysis of information from geological-engineering aspects, such as CD features, subseismic fault and large fracture location, fracturing events of specific stage, micro-seismic data and so on, [Results] specific causes of 225 CD sections in Luzhou are confirmed, and then new classification of four CD causes are proposed: objective-well-near CD, objective-well-far CD, offset-well-caused CD, and pre-fracturing CD. [Conclusion] (1) 3D imaging of CD intervals using non-centralized MIT logging not only reveals the true deformation morphology but also quantitatively characterizes shear displacement. (2) In deep shale gas development, the proportion of CD points caused by offset-well fracturing (55%) exceeds that caused by objective-well fracturing (45%). [Significance] (1) The propose of the predictive method for maximum wellbore cleanout tool diameter provides critical technical parameters for post-CD tool selection (e.g., bridge plug size). (2) The novel CD causation classification establishes a theoretical basis for optimizing fracturing sequence and scale of CD wells’ pad and adjacent pads, and CD-integrated mitigation strategies. This study has significant practical implications for shale oil and gas development.