China Petroleum & Chemical Corporation's ("Sinopec") has announced that the first phase of the Qijiang shale gas field has uncovered a major discovery in Sichuan Basin with a proven geological reserve of 145.968 billion cubic meters. The discovery, delivered by Sinopec Exploration Company and Sinopec Southwest Oil & Gas Company, is a major breakthrough in Sinopec's "Project Deep Earth – Natural Gas Base in Sichuan and Chongqing."
The Qijiang shale gas field is the first shale gas field discovered in medium-deep and deep strata in a complex tectonic zone on the margin of the basin. Shale gas buried at the depth of over 3,500 meters is defined as deep shale, and the burial depth of Qijiang's shale formations ranges from 1,900 to 4,500 meters, with the majority being deep shale. With complex overlying strata, the project faced great challenges such as a significantly greater depth and variable ground stress.
To tackle the question of how a shale gas reservoir was formed in the basin margin with such complex surface and underground conditions, Sinopec's team conducted more than 10,000 lab analysis tests on the core at the depth of 1,320 meters. This revealed the development and maintenance mechanism of deep shelf shale pores and identified the deep shale can develop vast reservoirs with high porosity, and also revealed the "sweet spots" of projecting the deep shale targets.
The team collected high-precision 3D seismic data of deep shale gas covering an area of 3,662 square kilometers in the complex zone of the southeastern margin of the Sichuan Basin as well as drilling data of existing wells in southern Sichuan. After repeated discussion and screening, Sinopec has innovated a deep shale gas seismic prediction technology with pressure coefficient and gas content, fracture prediction and horizontal ground stress difference as the core – the equivalent of performing a CT scan of the strata to achieve the breakthrough in predicting the "sweet spots" of deep shale gas.
Sinopec also developed a three-dimensional fracturing technology with "precision cutting, pressurization and expansion, balanced expansion and guaranteed filling" for deep shale, which has improved the daily shale gas production of a single well to break the 300,000, 400,000 and 500,000 cubic meters marks in succession.