Study on Geometric Characteristics and Quantitative Description Method of Casing Deformation during Shale Reservoir Hydraulic Fracturing

Casing deformation is a common but serious problem experienced during hydraulic fracturing operations in shale reservoirs. The Multi-Finger Imaging Tool is used to measure the casing deformation where the casing inner diameter is the only parameter used to characterize the deformation. Many deformed casing geometric details are often ignored, and these geometric characteristics are helpful for revealing the casing deformation mechanism. In this study, we established a quantitative method to describe the casing deformation using methods of judging the similarity of curves. By comparing the field casing deformation sections and the initial casing section, we categorized the casing deformation sections into concave and elliptical types. Furthermore, using the centroid calculation, elliptical type was sub-divided into symmetric ellipse type and eccentric ellipse type. On the basis of the Weiyuan and Guandong oil field’s fault distribution maps, we demonstrated that the fault slip could be the main cause of concave type and eccentric ellipse type. A numerical study was then carried out to ascertain whether fault slip can cause concave type and eccentric ellipse type casing deformations and to establish the relationship between fault slip magnitude and casing deformation. The results support the idea that concave type and eccentric ellipse type casing deformation are caused by the fault slip. Sensitivity analysis showed that the shape of the casing section was largely influenced by the dip angle, while the change of the casing inner diameter was largely influenced by the strike angle. The method proposed herein presents a useful step towards the prediction of the causes of casing deformation and provides a relationship between casing inner diameter change and fault slip.