Prediction Method of Casing Deformation Risk Based on Geology-Engineering Integration Model and Its Application

The change of stress around the well will induce casing deformation of different degrees, resulting in insufficient completion of volume fracturing in shale gas horizontal wells, which seriously affects the efficient development of gas wells. Therefore, aiming at the geological engineering conditions of small fault development, fracture development, lithology difference of each small layer, rock mechanics anisotropy, and complex well path traversal in Longmaxi Formation shale reservoir in southern Sichuan, a high-precision geological engineering integrated model was established, and the spatial contact relationship between the wellbore and stratum, fault, and fracture in the whole underground well section was restored. Then, with stress changes leading to fracture and bedding slip as the main research objects, the characteristics of nearly 70 bedding slip points were analyzed and three types of high bedding slip risk patterns and identification methods were proposed. The study showed that: ① nearly one-third of the bedding slip is caused by a composite factor of high dogleg degree, bedding slip, and bedding slip, with the proportion of bedding slip caused by single factor high dogleg degree, bedding slip, and bedding slip being 5%, 57%, and 38%, respectively; ② The phenomenon of layer slip induced casing deformation often occurs in pairs, and the degree of layer slip induced casing deformation is relatively mild when the wellbore incidence angle is less than 10°; ③ The probability of malignant casing deformation induced by fracture slip is high, with nearly one-third of wells experiencing a 30% reduction in inner diameter after deformation in the casing deformation points caused by fracture slip. The data validation of nearly 50 actual casing change points on site shows that the casing change risk prediction method is reliable, and the risk assessment can provide guidance for the casing change risk control decision of shale gas well fracturing design.