渤海湾盆地济阳坳陷渤南洼陷沙四下亚段红层有利储层成因机制

Formation mechanism of favorable reservoirs in red beds in lower submember of fourth member of Shahejie Formation, Bonan Subsag, Jiyang Depression, Bohai Bay Basin

孟涛

MENG Tao

中国石化 胜利油田分公司 勘探开发研究院, 山东 东营 257015

Research Institute of Exploration and Development, Shengli Oilfield Company, SINOPEC, Dongying, Shandong 257015, China

渤海湾盆地济阳坳陷渤南洼陷沙四下亚段红层经历了较长时期的沉积和成岩改造作用，原生孔隙保留机制、次生孔隙演化规律不清，制约着勘探进展。运用岩心观察、铸体薄片鉴定及扫描电镜分析等技术手段，在储层特征分析基础上，开展了红层有利储层受控因素分析，总结了有利储层成因机制，预测了有利储层分布。该区沙四下亚段红层沉积存在冲积扇-辫状河-辫状河三角洲-湖泊和扇三角洲-湖泊2大沉积体系；砂岩类型以岩屑长石砂岩为主，储集空间由残留原生孔隙、次生溶蚀孔隙及裂缝构成，储层物性较差，属于特低孔特低渗储层。储层在机械压实作用以及碱、酸流体的交替影响下，储集空间经历了原生孔隙保留、次生孔隙形成及储层致密化3个阶段；埋深与有利相带决定原生孔隙保存程度，有机酸、上覆地层异常高压与断裂展布决定次生孔隙发育程度。原生孔隙发育的有利储层类型为3 000 m以浅的冲积扇扇端储集体，分布于南部盆缘，呈裙带状展布；次生孔隙发育的有利储层类型为沙四上亚段压力系数大于1.2且沙四下亚段断裂体系发育的辫状河和辫状河三角洲储集体，分布在洼陷带，呈带状、叠合连片状展布。

The red beds in the lower submember of the fourth member of Shahejie Formation (Es4) in the Bonan Subsag of the Jiyang Depression of the Bohai Bay Basin have undergone a long period of sedimentation and diagenesis. The mechanism of primary pore retention and the evolution constraints of secondary pores are not clear, which restricts exploration progress. The controlling factors of favorable reservoirs in the red beds were analyzed by means of core observation, casting thin section identification and scanning electron microscopy and combined with reservoir characteristics analysis. The formation mechanism of the favorable reservoirs was summarized, and their distribution was also predicted. There are two major sedimentary systems in the red bed sediments of the lower Es4 submember of Bonan Subsag, including alluvial fan-braided river-braided river delta-lake and fan delta-lake. Sandstones are mainly lithic feldspars. Reservoir porosity is composed of residual primary pores, secondary dissolution pores and fractures. Reservoir physical properties are poor. The reservoir belongs to the category of ultra-low porosity and ultra-low permeability. Under the influence of mechanical compaction and the alternation of alkali and acid fluids, the reservoir porosity in the study area experienced three stages: primary pore retention, secondary pore formation and reservoir densification. Burial depth and favorable facies zones determine the preservation degree of primary pores, while organic acid, abnormally high pressure in overlying strata and fracture distribution determine the degree of secondary pore development. The favorable reservoirs with primary pore development are fan-terminal reservoirs of alluvial fan buried less than 3 000 m, which are distributed as belts on the southern basin margin. The favorable reservoirs with secondary pore development are braided river and braided river delta reservoirs with pressure coefficient greater than 1.2 in the upper submember of Es4 and fault system develop in the lower submember of Es4, which are distributed in sag zones and show strip-like and overlapping sheet distribution.

中国石化胜利油田分公司科技攻关项目"渤南洼陷缓坡带沉积-成藏再认识及勘探潜力评价" YKK1911

https://doi.org/10.11781/sysydz202001019