Abstract:

Shale gas exploration and development in China has turned to shales buried in more than 3 500 m deep, posing development challenges with their high-pressure, poor physical properties and reluctance to form complex fracture networks after stimulations. The Jiangdong block, one of the major blocks in the phase-Ⅱ productivity construction of the Fuling shale gas field in the Sichuan Basin, contains shale gas at or deeper than such depth in an area of 57.8 km², accounting for about half of the total block area. The main targets are the high-quality thin black shale layers (① to ⑤) in the Upper Ordovician Wufeng-Lower Silurian Longmaxi Formations that are rich in carbon, silicon, lamellation and pyrite. By applying an appraisal index system for deep shale gas blocks and an optimized horizontal well location selection method to the shales, we come to the conclusion that the major geological factors influencing the performance of deep shale gas wells are the burial depth, in-situ stress, fracture growth characteristics and dip angle of shale layers. It is therefore recommended that, during horizontal well drilling design, the angle between the wellbore and the minimum principal stress be less than 40° with a level difference between two designed target points (A and B) being kept as less than 300 m as possible. The exploration and development practices in the deep shale in the Jiangdong block have achieved relatively higher test production and recoverable reserves from single wells, which is of realistic guidance and reference for other similar deep shale gas exploration and development in the basin.

Key words: development potential, deep shale gas, Wufeng Formation, Longmaxi Formation, Jiangdong block, Fuling shale gas field, Sichuan Basin