Abstract:

Based on the outcrop observation, profile survey and sample analysis of Devonian dark shale, this paper studied the accumulation condition of Devonian shale gas in Dian-Qian-Gui Basin. The results show that two sets of dark shales of intraplatform depression facies were deposited in Dian-Qian-Gui Basin during the Early to Middle Devonian, and the single layer thickness of Devonian shale is 10-55 m; the accumulative thickness is generally between 100 m and 450 m. The TOC values are mainly in the range of 1.0% to 2.5%, and the organic matter type is Ⅰ-Ⅱ₁, and the vitrinite reflectance values indicate high to over mature thermal evolution stages. As an effective reservoir, the porosity and permeability of Devonian shale in Dian-Qian-Gui Basin are similar to those of Jiulaodong Formation in well Wei-201, and various reservoir space types well developed in the shale, and the content of brittle minerals is averagely up to 67%. The gas preservation conditions of southwestern Qiannan Depression and middle-west Guizhong Depression are relatively better because of the relative flat strata, low fault density and erosion thickness, and thrusting and transpressional faults. Overall considering of the dark shale thickness, buried depth, organic matter content, thermal evolution degree and preservation condition, it can be predicted that the favorable intervals of Devonian shale gas are Tangding Formation and Luofu Formation, and the favorable areas mainly distribute in Tian’e-Nandan-Hechi area and Luzhai-Laibin-Heshan-Dahua area of middle Guizhong Depression. By using the analogy method of geological resource abundance, it can be calculated that the geological resources of Devonian shale gas is 0.66×10¹² m³ to 1.09×10¹² m³ .

Key words: shale gas, resource potential, Devonian, Dian-Qian-Gui Basin