砂岩储层致密化与油气充注耦合关系——以渤海湾盆地霸县凹陷沙三—沙四段为例

Coupling relationship between sandstone reservoir densification and hydrocarbon charging:taking the 3rd to 4th member of Shahejie Formation in Baxian Depression of Bohai Bay Basin as an example

以渤海湾盆地霸县凹陷沙三—沙四段为例,利用岩心观察、铸体薄片鉴定、流体包裹体分析等方法,基于计算机图像分析技术和“反演回剥”原理,研究砂岩储层的岩石物性、成岩作用和致密化过程,分析砂岩储层致密化与油气充注成藏的时序关系。结果表明:目的储层岩石类型以细粒岩屑质长石砂岩为主,成分成熟度和结构成熟度低,主要为中、低孔—低、特低、超低渗储层;主要经历压实、胶结、溶蚀、交代等成岩作用,具有多期溶蚀、多期胶结的特征;孔隙度演化整体呈原生孔隙减少→次生孔隙增加→次生孔隙减少→次生孔隙弱增加的趋势;明化镇组沉积中后期储层达到致密化,压实和胶结作用是储层致密化的主要因素,晚期碳酸盐胶结是储层致密化的直接原因。储层经历东营组沉积末期(27.8~25.2 Ma)、馆陶组沉积末期至明化镇组沉积期(10.6~6.2 Ma)两期油气充注,分别发生在储层致密化前后,分别对应“先成藏后致密型”和“先致密后成藏型”两种成岩—成藏耦合关系。在第二期油气充注时期,岔—高—鄚构造带的孔隙度整体高于苏桥—文安斜坡带的,苏桥—文安斜坡带的孔隙度低于成藏物性下限,难以发生油气充注。该结果为渤海湾盆地霸县凹陷致密砂岩储层的油气勘探提供参考。

Taking the 3 rd to 4 th member of Shahejie Formation in Baxian Depression of Bohai Bay Basin as an example,the petrophysical properties and diagenetic evolution of the sandstone reservoirs were systematically studied by core observation,cast thin section identification and fluid inclusion analysis,the densification process of the reservoir was established based on computer image analysis technology and the principle of " back-stripping inversion",and the time sequence relationship between sandstone reservoir densification and hydrocarbon charging was analyzed.The results show that the target reservoir rock type is dominated by fine-grained lithic feldspar sandstone with low component maturity and structural maturity,mainly medium-to-low porosity and low to ultra-low permeability reservoirs.The reservoir mainly experienced diagenesis such as compaction,cementation,dissolution and metasomatism,with the characteristics of multi-stage dissolution and multi-stage cementation.The overall porosity evolution shows a trend of primary pores decrease from secondary pores increase to secondary pores decrease to weakly increase secondary pores.The reservoir reached densification in the middle and late depositional stages of the Minghuazhen Formation.Compaction and cementation are the main factors of densification,and the late carbonate cementation is the most direct reason for the densification of the reservoir.The reservoir experienced two stages of oil and gas charging,which occurred at the end of Dongying Formation(27.8-25.2 Ma)and from the end of Guantao Formation to Minghuazhen Formation(10.6-6.2 Ma),respectively.The first phase of the hydrocarbon charging occurred before densification of reservoirs belonging to the type of densification after hydrocarbon accumulation.The second phase of the hydrocarbon charging occurred after densification of reservoirs,belonging to the type of densification before the hydrocarbon accumulation.In the second stage of hydrocarbon charging,the porosity of Cha-Gao-Mao Structural Belt is higher than that of Suqiao-Wen’an Slope Belt,and the actual porosity of Suqiao-Wen’an Slope Belt was lower than the lower limit of reservoir-forming physical property,making it difficult for oil and gas charging to occur.The research results provide a reference for oil and gas exploration of tight sandstone reservoir in Baxian Depression of Bohai Bay Basin.