鄂尔多斯盆地大牛地气田马家沟组储层类型成因及其主控因素

Reservoir Types and Genesis of the Majiagou Formation Daniudi Gas Field,Ordos Basin

鄂尔多斯盆地大牛地地区奥陶系马家沟组油气勘探持续获得突破,实践表明马五段整体含气,但储层类型多,成因复杂。为系统归纳该段储层成因类型,通过岩心观察、薄片鉴定、阴极发光薄片观察、全岩X射线衍射分析、碳氧同位素分析等方法,对储集空间类型和储层发育主控因素进行了研究。结果表明,研究区马家沟组储层发育晶间孔、晶间溶孔、微裂缝、残余粒间孔和粒内溶孔等。储层发育的有利沉积相为局限台地藻云坪和蒸发台地膏云坪,并受回流渗透白云石化机制控制。表生岩溶作用对马五5亚段储层无明显控制作用。研究区储层根据成因可分为四种类型:膏溶型储层、弱改造破裂型云岩储层、粉晶白云岩储层和同生溶蚀颗粒型储层。膏溶型储层和粉晶白云岩储层是主要的储层类型,膏溶型储层与沉积环境盐度和表生期岩溶作用有关,主要发育膏模孔;粉晶白云岩储层主要受海平面下降期的回流渗透白云石化控制,以晶间孔为主。以上四类储层成因类型的认识,对下一步鄂尔多斯盆地马五段的优质储层预测具有指导意义。

Oil and gas exploration of the Majiagou Formation in the Daniudi area,Ordos Basin,continues to make breakthroughs.Practice has shown that the whole Fifth member of the Majiagou Formation(Ma5)contains gas,but its multiplicity of reservoir types and complex genetic backgrounds have not been conducive to classification prediction.To systematically summarize the reservoir genetic types in this study,the reservoir space types and main influences on reservoir development were investigated by core observation,thin section identification,cathodoluminescence thin section observation,whole-rock X-ray diffraction analysis and carbon and oxygen isotope analysis.These demonstrate that,in the study area,the Ma5 reservoirs contain intercrystal pores,intercrystal dissolution pores,microcracks,residual intergrain pores and intragrain dissolution pores.The reservoir developed in a confined evaporative platform as a result of seepage-reflux dolomitization.Epigenetic karstification had no obvious influence on the reservoir in the Ma_(5)^(5) submember.Genetic analysis in the study area suggests four types of reservoir:gypsum-dissolved,weakly re-formed fractured dolomite,powder-crystal dolomite and syngenetic dissolution granular reservoirs,with gypsum-dissolved reservoirs and powder-crystal dolomite reservoirs being the main types.Gypsum-dissolved reservoirs are related to the salinity of the sedimentary environment and karstification during the supergene period,and contain mainly gypsum mold pores.Powder-crystal dolomite reservoirs are the result of seepage-reflux dolomitization during the period of sea-level decline,and the reservoir space consists of intercrystal pores.This summary is significant as a guideline for subsequent high-quality reservoir predictions in the Ma5 member in the Ordos Basin.