蜀南地区龙马溪组页岩气工业建产区游离气和孔隙度下限讨论

游离气作为页岩气重要赋存形式之一,决定了页岩气的开发潜力及经济效益.以蜀南地区龙马溪组页岩为例,结合X-射线衍射、岩石有机碳、储层物性、测井解释及生产测试等资料,对比分析了四川盆地及周缘页岩游离气含量与测试日产气量的关系,初步提出了工业建产区页岩游离气含量下限,并从烃源、储集及保存等方面对页岩游离气含量主控因素进行了系...

Cutoff of Free Gas and Porosity in Shale Gas Industrial Production Area of Longmaxi Formation in Southern Sichuan Basin

As an important form of shale gas, free gas determines the development potential and economic benefit of shale gas. Taking the Longmaxi Formation shale in southern Sichuan Basin as an example, and combining with X-ray diffraction (XRD), rock organic carbon, reservoir physical property, log interpretation and production test, we compared and correlated between free gas content and test daily gas production in Sichuan Basin and its periphery. We proposed the free gas content cutoff in industrial production area, and discussed the major controlling factors of shale free gas content from the aspects of hydrocarbon source, reservoir and preservation. Porosity cutoff was also discussed accordingly. The results show that it is easier to obtain industrial gas flow when the shale free gas content is above 2.5 m³/t. Free gas content of the Longmaxi Formation shale in southern Sichuan Basin is clearly positively correlated with TOC, porosity, siliceous mineral content, formation pressure coefficient, and fracture development, but negatively correlated with water saturation and carbonate mineral content. Fracture development, water saturation, siliceous minerals and carbonate can indirectly affect free gas content by correlating porosity, which are unlikely to be its major controlling factors. Major controlling factors of free gas content are TOC, porosity and formation pressure coefficient. The Monte Carlo simulation of free gas content indicates over 50% probability for 2.5 m³/t above free gas content when the shale porosity is > 4%. It is recommended to set porosity cutoff at 4% in shale gas industrial production area selection to control geological risk. Shale gas content should be evaluated systematically from three important aspects (i.e.TOC, porosity and formation pressure coefficient) with focus on free gas evaluation.