Discovery of the Qijiang shale gas field in a structurally complex region on the southeastern margin of the Sichuan Basin and its implications

Following the discovery of the Fuling shale gas field, shale gas exploration in the Sichuan Basin has expanded into the structurally complex region on its southeastern margin, where the Qijiang shale gas field has benn discovered. The findings achieved in the study are as follows. (1) The Qijiang shale gas field is generally similar to the Fuling shale gas field in terms of geological features, as shown with high total organic carbon (TOC) content (average: 2.62 %), high porosity (average: 4.53 %), and high gas content (average: 5.43 m³/t). It is a typical self-sourced dry gas reservoir of continuity. Furthermore, the Qijiang shale gas field exhibits complex surface and subsurface conditions, including a large burial depth range involving moderately deep to deep layers with a medium depth of 3354 m, low geothermal gradients (average: 2.99 ℃/100 m), and extensive formation pressure coefficient in a range of 0.98 to 1.98 (average: 1.50) spanning normal to ultra-high pressure. (2) A shale gas enrichment model for basin-margin nose-like faulted anticlines in the structurally complex region is established featuring enrichment at deep burial areas as controlled by major fault zone, and this specifies that the shale gas enrichment in the anticlines, the critical features of shale gas sweet spots encompass high-quality shale, high fluid pressure, well-developed microfractures, and low in-situ stress. (3) Technologies applicable to deep shale gas reservoirs are developed, including sweet spot prediction technology and volume fracturing to form intricate fracture networks, providing a firm guarantee for high, stable gas flow in the Qijiang shale gas field. In November 2022, estimated shale gas in-place of 1459.68×10⁸ m³ from the Wufeng-Longmaxi formations in the Dingshan block was booked for the first time.