Sichuan Basin Longmaxi Shale Gas Stimulation and Completion Case Study

Abstract

The shale gas buzz in China continued in 2012. The Longmaxi Silurian age formation is one of three main target marine shales in China, the others being the Cambrian age Qiongzhusi and Niutitang. The Longmaxi serves as the more likely completion target for attempting to reach the production goals set forth by the government and state owned enterprises (SOEs). The Longmaxi is an interbedded mudstone/siltstone formation with an organic-rich carbonaceous interval at its base. It experienced widespread deposition and is predominantly found in what is currently known as the Sichuan basin in Sichuan province and the Chongqing municipality, with some evidence of its occurrence farther south and east into Guizhou and Hunan provinces. The lower organic-rich interval is the target for completion as it serves to store more hydrocarbon, which also lends itself to effective hydraulic fracture stimulation and flow capacity enhancement. This paper is a case study of one Longmaxi horizontal well and the efforts that were made to benchmark the formation deliverability from a horizontal wellbore with multiple stages of completion. An analog formation was identified from the vertical pilot well logs to guide the stimulation design. A diagnostic fracture injection test (DFIT) was performed and analyzed, as well as some stimulation-related core testing being completed to further refine the proposed hydraulic fracture treatment. A summary of the treatments are presented, followed by conclusions and paths forward for further efforts with completing the Longmaxi. A previous paper (Lv et al. 2012) cited completion of the first Cambrian age Qiongzhusi horizontal completion. This paper picks up from there, further detailing the shale gas development that is likely to be a major contributor to China's evolving energy mix.

New Insight into Enhancing Organic-Rich Shale Gas Recovery: Shut-in Performance Increased through Oxidative Fluids

“…Shale matrix is crushed as much as possible to improve the density of fracture networks, which contributes to a high gas production and consequent high gas recovery [13,14]. Currently, in order to improve the density of the fracture network, a small amount of acidic fluids usually was pumped into the formation prior to the fracturing operation, which can decrease the fracture pressure of the rock through the dissolution of carbonate minerals or other rock cements [71][72][73][74][75]. This has proven to be a good process according to the reported field data of shale gas wells from either the ones in north America, such as Bakken and Engle Ford formation, or the ones from the Sichuan basin in China [76,77].…”