Investigation and Application of High-Efficiency Network Fracturing Technology for Deep Shale Gas in the Southern Sichuan Basin.

Abstract

The Longmaxi Formations in the Luzhou block located in the Southern Sichuan Basin exhibit thick shale formations and huge shale gas resources and have become one of the significant blocks for large-scale production of shale gas. However, due to the natural fractures and high in situ stress and horizontal stress differences, proppants are broken and embedded severely, and complex network fractures are difficult to form, so traditional hydraulic fracturing technology cannot meet the need for profitable development of deep shale gas. In order to increase the stimulated reservoir volume and improve fracture complexity, large-scale hydraulic fracturing experiments and fracture propagation numerical simulations have been conducted based on the geology and engineering treatment difficulty of the Luzhou block to discuss the main factors influencing fracturing effectiveness. Meanwhile, two round field tests were conducted to evaluate the fracturing effectiveness, and the following study results were obtained. First, in situ stress and horizontal stress differences are the main mechanical factors, while cluster spacing and proppant injection intensity are the main fracturing parameters. Therefore, multi-cluster perforation, high-intensity proppant injection, and diversion are employed to improve fracture complexity and conductivity, thus increasing effective fracture volume. Furthermore, the second round of field tests gained remarkable results. The “short-cluster spacing + high proppant amount + variable viscosity slick water + diversion” high-efficiency fracturing technology was formed, and the average test production got to 28.6 × 104 m3/d, which represented a 64% increase over the first round. It concludes that the high-efficiency hydraulic fracturing technology contributes to increasing shale gas production, notably in the Luzhou block for deep shale gas, and provides reliable technology support and study direction for further technical optimization in this block.