Accumulation and exploration of continental shale gas resources of Cretaceous Shahezi Formation in Lishu fault depression, Songliao Basin, NE China

Abstract

Distribution characteristics, organic matter development characteristics, gas-bearing characteristics, reservoir characteristics, and preservation conditions of the Shahezi Formation shale of Lower Cretaceous in the Lishu fault depression, Songliao Basin, NE China, are analyzed using organic geochemical, whole rock, and SEM analysis data, and CO2 and N2 adsorption and high-pressure mercury injection experiment data in combination with the tectonic and sedimentation evolution of the region to reveal the geological conditions for enrichment and resource potential of continental shale gas. The organic-rich shale in the Lower Cretaceous of the Lishu fault depression is mainly developed in the lower submember of the second member of the Shahezi Formation (K1sh21 Fm.) and is thick and stable in distribution. The shale has high TOC, mainly types II1 and II2 organic matter, and is in the mature to the over-mature stage. The volcanic activity, salinization, and reduction of the water environment are conducive to the formation of the organic-rich shale. The shale reservoirs have mainly clay mineral intergranular pores, organic matter pores, carbonate mineral dissolution pores, and foliated microfractures as storage space. The pores are in the mesopore range of 10–50 nm, and the microfractures are mostly 5–10 μm wide. Massive argillaceous rocks of lowland and highstand domains are deposited above and below the gas-bearing shale separately in the lower submember of the K1sh21 Fm., act as the natural roof and floor in the process of shale gas accumulation and preservation, and control the shale gas enrichment. Based on the above understandings, the first shale gas exploration well in Shahezi Formation was drilled in the Lishu fault depression of Songliao Basin. After fracturing, the well tested a daily gas production of 7.6×104 m3 marking a breakthrough in continental shale gas exploration in the Shahezi Formation (K1sh Fm.) of the Lishu fault depression in Songliao Basin. The exploration practice has reference significance for the exploration of continental shale gas in the Lower Cretaceous of Songliao Basin and its periphery.