What Have We Learn from the Most Prolific Pad of Shale Gas in the Sichuan Basin?

Abstract

Abstract There are more than 1300 horizontal wells in the Sichuan Basin shale reservoirsthat produce more than 20 billion cubic meters of gas in 2021. A test production of best-performing shale gas pad,so far in China, consisting of 8 horizontal wells, is over 4.7 × 106 m³/d (167.7 MMcf/d). The average EUR per well is estimated to exceed 2.0 × 108 m³(7.0 bcf).The underlying geological controlling factors including TOC content, porosity, gas saturation and brittle mineral content for these prolific wells were analyzed. The length of the well laterals drilling into the sweetest pay zone was characterized by well logging. The strategies of optimizing drilling and completion strategies used in these wells are discussed. In addition, the solutions to deal with the frequent occurrence of casing deformation are also proposed and adopted. Rate transient analysis was performed on these wells to assess the stimulation efficiency, which was further compared with those wells treated by conventional stimulationstrategies. It was found that the thickness and length of the completion in the highest quality pay zone are the two main geological controlling factors for the prolific wells. Different from the conventional stimulation strategies, the eight wells in one pad were all treated using higher intensity stimulation strategies. The average spacing between treated stages ranges from 85 m to 91 m, with tighter cluster spacing. Fracturing was temporarily plugged to passively treat sever deformation in two laterals consisting of 29 stages (total length of 2068m). Compared with the neighboring offset wells, the average bulk linear flow parameter of these eight well is 72% higher. Integration of geological designs (like sweet spot optimization) and engineering designs (such as tighter cluster spacing within longer stages, temporarily plugging fracturingand using more proppants), created a high-productivity template for the next stage of efficient developments of shale gas. The findings obtained in this study are also beneficial to unlock unconventional resources including shale oil and tight gas in China.