河套盆地临河坳陷古近系临河组深层—超深层碎屑岩储层物性差异成因

Origin of differences in physical properties of deep and ultra deep clastic reservoirs in the Paleogene Linhe Formation of the Linhe Depression, Hetao Basin

河套盆地临河坳陷临河组在6 000 m以深仍发育优质储层且高产工业油流,但相似埋深碎屑岩储层物性存在明显的差异性。为明确储层物性差异成因,降低深层—超深层油气勘探的风险,以临河坳陷临河组为研究对象,综合岩心、铸体薄片、扫描电镜和黏土矿物等资料,以岩石学、物性及成岩特征研究为基础,开展储层特征及物性差异成因研究。结果表明:临河组储层岩石以富含石英为主要特征,石英含量平均值为72%,填隙物含量介于1%~28%之间。储层孔隙度介于1%~29.2%之间,储集空间主要为原生粒间孔。储层压实作用和胶结作用强度总体较弱,局部较强。储层主要发育富胶结物砂岩、富泥杂基砂岩和低填隙物砂岩3类岩石相类型。富胶结物砂岩粒度较细,胶结作用强,物性致密;富泥杂基砂岩塑性碎屑含量较高且分选差,压实作用强,物性较差;低填隙物砂岩富含刚性颗粒且分选好,压实和胶结作用弱,原生孔隙发育,物性好。临河坳陷临河组储层物性受沉积和成岩作用共同控制,沉积水动力强弱决定了砂岩的粒度大小、分选好坏和泥质含量高低,进一步控制储层压实强度和物性成岩演化。砂体厚度控制了储层中胶结物含量及分布,进而影响储层物性。

The Linhe Formation in the Linhe Depression of Hetao Basin still develops high-quality reservoirs and produces high industrial oil flow at depths of over 6000 m,but there are significant differences in the physical properties of clastic rock reservoirs with similar burial depths.In order to clarify the causes of reservoir physical property differences and reduce the risk of deep to ultra deep oil and gas exploration,the Linhe Formation in the Linhe Depression was taken as the research object.Based on comprehensive data such as core,cast thin sections,scanning electron microscopy,and clay minerals,petrology,physical properties,and diagenetic characteristics were studied to study reservoir characteristics and the causes of physical property differences.The results show that the reservoir rocks of the Linhe Formation are mainly characterized by rich quartz,with an average quartz content of 72%and a filling material content ranging from 1%to 28%.The porosity of the reservoir ranges from 1%to 29.2%,and the storage space is mainly composed of primary intergranular pores.The reservoir has differential diagenetic characteristics of overall weak compaction weak cementation,and partial strong compaction strong cementation.The reservoir mainly develops three types of rock facies:Rich cementitious sandstone,rich mud mixed sandstone,and low interstitial sandstone.Rich cementitious sandstone has a finer particle size,strong cementation,and dense physical properties;Rich mud mixed sandstone has a high content of plastic debris and poor sorting,strong compaction,and poor physical properties;Low porosity sandstone is rich in rigid particles and well sorted,with weak compaction and cementation,developed primary pores,and good physical properties.The physical properties of the Linhe Formation reservoir in the Linhe Depression are jointly controlled by sedimentation and diagenesis.The dynamic conditions of sedimentary water determine the particle size,sorting,and mud matrix content of the sand body,which in turn affects the later compaction strength and physical property evolution of the reservoir.The thickness of the sand body controls the content and distribution of cement in the reservoir,which in turn affects the reservoir properties.