Deformation mechanism of horizontal shale gas well production casing and its engineering solution: A case study on the Huangjinba Block of the Zhaotong National Shale Gas Demonstration Zone

In the Huangjinba Block of the Zhaotong National Shale Gas Demonstration Zone in the periphery of the Sichuan Basin, two horizontal shale gas wells suffer severe casing deformation. In this paper, the geological and engineering characteristics of the strata around the deformed casing interval were analyzed based on the 24-arm caliper measurement of casing deformation, open-hole caliper, electrical resistivity, drilling time and gas logging, cementing CBL∖VDL and CBL imaging. Then, 24-arm caliper measurement data were analyzed and 3D imaged by 3D imaging analysis software, to figure out the morphologic characteristics of deformed casing. It is shown that severe casing deformation tends to occur where structural fractures are developed. Besides, casing deformation is mainly in the form of “S”-shape bending vertically. The severely deformed casing is also characterized by obviously transverse shear deformation caused by the high-angle sliding compression of rocks. Therefore, some suggestions were proposed correspondingly. First, the countermeasures in this block shall focus on shear casing deformation caused by the sliding of rocks along the fracture face. Wellbore trajectory shall be designed based on the structural contours map of pay zones to bypass the “ridge” and “valley bottom” area in the local high and steep structural zones. Second, the distribution information of fractured zones shall be predicted based on the ant-tracking attribute volume distribution map of pay zones, so that the wellbore trajectory can run along the strike of fractured zone. And third, it is recommended to use plug-drilling free big bore bridge plug or full-bore infinite stage completion technique, so that the conventional bridge plug milling operation after fracturing can be omitted and each fractured layer can be put into production after fracturing.