鄂尔多斯盆地大牛地气田马家沟组古岩溶储集层特征

Characteristics of Majiagou Palaeokarstic Reservoir of Ordovician in Daniudi Gas Field of Ordos Basin

探讨了鄂尔多斯盆地大牛地气田奥陶系碳酸盐岩储集层的岩石学及地球化学特征。应用显微光学方法分析了岩溶储集层的微观特征,应用同位素地球化学方法研究了储集层的成岩作用特征,应用残余厚度法和印模法开展了古岩溶地貌恢复及其对储集层发育的控制作用研究。大牛地气田奥陶系马家沟组古岩溶储集层以岩溶角砾岩和泥粉晶白云岩为主,发育溶蚀孔、洞、缝以及晶间孔隙,储集层碳、氧稳定同位素明显偏负,87Sr/86Sr值明显偏高。岩溶地貌划分为3种地貌单元,其中岩溶斜坡的溶蚀作用强烈,是储集层发育的有利部位,其上覆铝土岩为有效盖层,封盖能力较强,是天然气聚集的有利区域。研究结果表明,稳定同位素地球化学方法是研究碳酸盐岩储集层岩溶作用的有效手段,溶蚀及白云岩化作用是控制岩溶储集层发育的重要因素。

The petrographic and geochemical characteristics of carbonate reservoirs of the Ordovician in Daniudi gas field in Ordos basin are presented in this paper,including the micro-characteristics of the palaeokarstic reservoir by using microscopic optical method,the diagenetic properties of the reservoir by using isotopic geochemical methods and the palaeokarstic landform restoration by using residual thickness and impression approaches and its control of the reservoir development.The palaeokarstic reservoir of Majiagou formation is dominated by karst breccias and micritic dolomite,with developed caves,fractures and intergranular pores,and the carbon-oxygen isotope is negative,the 87Sr/86Sr is higher,obviously.The palaeokarstic landforms can be divided into 3 types,of which the karstic ramp underwent strong karstification,being the favorable domain of developed reservoirs;the bauxites above the karstic ramp are effective cap rocks with well sealing ability,being the favorable area for gas accumulation.The studied results show that stable isotope geochemistry is an effective tool to study karstification of carbonate reservoirs,the dissolution and dolomization are the key factors controlling the palaeokarstic reservoir development.