渤海海域辽东凹陷东南缘沙二段优质储层差异及成因

Differences and Genesis of High-quality Reservoirs in the Second Member of the Shahejie Formation at the Southeastern Margin of the Liaodong Sag,Bohai Sea

渤海海域辽东湾凹陷东南缘沙二段储层中发现了油气,但物性差异较大、优质储层成因不明,严重制约了该区的勘探评价。利用岩心及常规物性、铸体薄片、全岩等分析化验资料,对该区沙二段储层差异及优质储层成因进行了研究。结果表明:1)研究区沙二段发育辫状河三角洲砂砾岩储层,其物性具有明显的差异性,由南向北储层物性逐渐变差;南部储层平均孔隙度为18.1%,以中—高孔为主;中部储层平均孔隙度为12.0%,以低—特低孔为主;北部储层平均孔隙度为7.7%,以特低孔—超低孔为主。2)研究区储层埋藏较浅(埋深小于3000 m),压实较弱,但储集空间类型迥异,南部储层储集空间以裂缝(粒内缝、粒缘缝、收缩缝)为主;中部以溶蚀孔和构造缝为主,局部见原生孔;北部以少量粒间溶蚀孔为主,局部见少量构造裂缝。3)母岩类型是造成区域上储层物性差异的主要控制因素,由南向北,母岩类型由中生界碎屑岩和元古界变质石英砂岩向元古界碳酸盐岩过渡,造成南部储层杂基含量高,胶结作用弱,但裂缝发育,物性好,而北部储层胶结作用逐渐增强,物性逐渐变差。4)不同构造形成的优质储层控制因素具有差异性,南部储层厚度小,但裂缝发育,优质储层厚度大,裂缝是形成优质储层的主要控制因素;而北部储层厚度大,但优质储层厚度小,呈薄层出现,胶结作用强,优质储层主要受早期大气淡水淋滤和成岩期溶蚀作用控制。

Oil and gas have been found in the reservoir of the second member of the Shahejie Formation in the southeastern margin of the Liaodongwan Sag,but the reservoir physical properties and genesis of the high-quality reservoirs were unknown,which seriously restricted the exploration evaluation of the area.,the reservoir differences and the genesis of high-quality reservoirs were studied based on analysis data of cores and conventional cast flake and whole-rock physical properties.The results show that:(1)A braided river delta glutenite reservoir was developed in the study area,with clearly different reservoir physical properties.The average porosity of the southern reservoir is 18.1%,and is dominated by medium-high pores.The average porosity of the central reservoir is 12.0%,and is dominated by low-to extra-low pores.The average porosity of the northern reservoir is 7.7%,and is dominated by extralow to ultra-low pores.(2)The reservoirs in the study area are shallow(buried depth less than 3000 m),and the compaction is weak,but the types of reservoir space are different.The reservoir space in the south is mainly composed of cracks(granular inner seam,grain-edge joints,shrinkage joints).The central dissolution pores and structural joints are predominant,and local primary pores are present.In the north,there is a small number of intergranular dissolution pores and a small number of structural cracks are seen locally.(3)The parent rock type is the main controlling factor for the difference in the physical properties of the reservoirs.From south to north,the parent rock type transitions from Mesozoic clastic rocks and Proterozoic metamorphic quartz sandstone to Proterozoic carbonate rocks,resulting in a high content of heterogeneous resources in the southern reservoir,with weak cementation and good physical properties.The cementation of the reservoir in the north was gradually increasing and cracks developed,and the physical properties gradually deteriorated.(4)The formation control of the high-quality reservoirs at each location was different.The thickness of the reservoirs in the south was small,but fractures have developed.The thickness of high-quality reservoirs was large,and the cause of the fractures was the main controlling factor.The thickness of the reservoir in the north was large,but the high-quality reservoir was present only in a thin layer,with strong cementation.The main control was early atmospheric freshwater forest filtration and diagenetic dissolution.