Shale wellbore stability and well trajectory optimization: a case study from Changning, Sichuan, China
Chao Fang, Qian Wang, Hongwei� Jiang, Zhaowei Chen, Ying Wang, Wenbao Zhai, Shaoyun Chen
Abstract
Horizontal well drilling is one of the effective methods to develop shale gas in Longmaxi Formation. The main challenge when drilling wells is to maintain wellbore stability especially across the weak plane of shale formations. In order to solve this problem, a comprehensive geomechanics study was carried out to understand the causes of the wellbore failure and to optimize the most appropriate drilling strategy. In the study, the geomechanical model was conducted by constructing calibrated drilled well profiles using field and laboratory data for the Longmaxi Formation. For the horizontal wells, logging data were used to estimate the rock mechanical properties, overburden pressure, pore pressure and in-situ principal stresses. The results indicated that compared with Mohr-Coulomb, Modified Lade (ML) combined with weak plane (WP) failure criteria are suitable for analyzing the wellbore stability problems to determine optimum mud weight and safe wellbore trajectory for future successful drilling in the study area. Both mud weight and well trajectory affect the wellbore safety, it is recommended to comprehensively consider the influence of mud weight and well trajectory on wellbore instability, which provides practical guidance for drilling engineering and geological design and greatly improve the wellbore safety.