Lesson Learned from an Unsuccessful Multi-Stage Fracturing Case and an Improved Completion Design in Thin-Interbed Reservoirs in Tarim Basin, China

Abstract Horizontal wells with multi-stage fracturing have been proved to be an efficient technology to exploit thin-interbed reservoirs. However, problems were encountered during multi-stage fracturing of horizontal wells in the Silurian reservoir in Ta-zhong Oilfield, western China. This paper mainly discussed the causes of these problems and the optimized completion and fracturing designs to avoid these problems. Ta-zhong Silurian reservoir is a thin-interbed, low-permeability reservoir with buried depth from 4000 to 4500m. The sand distribution is heterogeneous both vertically and horizontally. A horizontal well in this reservoir was fractured twice using two different multistage fracturing technologies, firstly hydraulic jetting fracturing and then packer-segregated fracturing. Abnormal pumping pressure and difficulties to add proppants were encountered in both of the two operations. The causes to these failures will be analyzed comprehensively, based on which an optimized multi-stage fracturing design of this well will be proposed through numerical modeling and analysis. According to the analysis, defective completion and fracturing design is the main cause of the failures experienced in the two operations. The ill-considered jetting parameters caused the difficulties of fracture propagation and proppant placement during the hydraulic jetting fracturing treatment, whereas inappropriate perforating intervals led to simultaneous initiation of multiple fractures in each stage during the packer-segregated fracturing treatment. These fractures interfered with each other and led to great near-wellbore pressure losses and fracture reorientation, and then resulted in abnormally high pumping pressure and challenges of proppant placement. Several changes to avoid these problems are proposed and incorporated in a new multi-stage fracturing design. The jetting parameters, fracture spacing, fracture geometries as well as perforation parameters are all optimized by numerical modeling in the new design of well A and other horizontal wells in Ta-zhong Silurian reservoir, which is expected to avoid the above-mentioned problems and obtain better results. Nowadays, horizontal wells with multi-stage fracturing are a common-used technology in tight thin-interbed formations. However, the design of segregated completion and multi-stage fracturing is still a challenge for such formations. This paper introduced the lessons learned from a failure case and proposed an optimized completion and fracturing design, therefore provided a good reference for completion design of the wells in Ta-zhong Silurian reservoir as well as similar reservoirs in the world.