东营凹陷古近系红层储层成岩作用特征及形成机制

东营凹陷古近系孔店组一段（简称孔一段）-沙河街组四段下亚段（简称沙四下亚段）沉积时期发育了规模巨大的干旱气候条件下形成的红层沉积。综合利用钻井岩心、铸体薄片、物性及黏土矿物资料，并结合盆地埋藏演化史，对储层成岩作用特征及成因机制进行了系统研究。储层具有多重碱性成岩环境和酸性成岩环境作用特征。压实作用中等偏强，热压实效应明显。胶结物类型主要包括碳酸盐、铁碳酸盐、石膏、硬石膏和自生石英等，胶结作用在砂体边缘强，砂体内部较弱，砂体中部胶结物含量由断块下部向断块上部逐渐增加。溶解作用主要为碱性环境下形成的石英溶解和酸性环境下形成的长石、碳酸盐胶结物溶解，溶蚀孔隙含量由砂体边缘向砂体内部逐渐增加，由断块下部向断块上部逐渐降低。交代作用主要为碳酸盐、硫酸盐胶结物交代石英、长石颗粒及石英加大、铁碳酸盐交代碳酸盐。红层储层经历了早期碳酸盐及石膏胶结、早期石英溶解→长石及碳酸盐胶结物溶解、自生石英胶结→晚期碳酸盐及硬石膏胶结、晚期石英溶解→晚期少量碳酸盐胶结物、长石溶解的成岩演化序列。多重碱性及酸性成岩环境交替演化和上升流作用机制控制了储层的发育。

Diagenetic characteristics and formation mechanism of Paleogene red-bed reservoirs in Dongying sag

Red-bed deposits developed on a large scale during the Ek₁-Es₄^x stage of Paleogene in Dongying sag under arid climate. Integrated with analyses of burial and evolutionary histories of the basin, diagenetic characteristics and formation mechanism of red-bed reservoirs in the study area were systematically investigated based on data of drilling cores, casting thin sections, physical properties and clay minerals. These red-bed reservoirs are characterized by the formation in multiple alkaline and acidic diagenetic environments, moderate to strong compaction, and apparent thermal compaction. Cement types mainly include carbonate, ferrocarbonatite, authigenic quartz, gypsum and anhydrite. Cementation is strong at the boundary belt of sandstones but relatively weak at the middle part of sandstones, where cement contents increase gradually from the lower part to the upper part of fault blocks. Dissolution in red-bed reservoirs occurs mainly as quartz dissolution in an alkaline diagenetic environment or feldspar and carbonate cement dissolution in an acidic diagenetic environment. Dissolution plane porosity increases gradually from the fringe to the bosom of sand bodies but decreases gradually from the lower part to the upper part of fault blocks. Metasomatism occurs mainly in quartz and feldspar grains with carbonate and sulfate cements, authigenic quartz, and carbonate with ferrocarbonatite. The diagenetic sequence of red-bed reservoirs was specified from the early carbonate and gypsum cementation, early quartz dissolution to the feldspar and carbonate cement dissolution, authigenic quartz cementation to the late carbonate and anhydrite cementation, late quartz dissolution then to the late carbonate cement and feldspar dissolution. The alternate evolution of multiple alkaline and acidic diagenetic environments and the action mechanism of upwelling current have controlled the development of these reservoirs.