渤海湾盆地车镇凹陷陡坡带沙河街组近岸水下扇低孔低渗储层成岩序列

Diagenetic Sequence of Low Porosity and Permeability Reservoirs from Nearshore Subaqeous Fan of Shahejie Formation in the Steep Slope Zone of Chezhen Depression,Bohai Bay Basin

根据大量岩芯、薄片、扫描电子显微镜（SEM）和镜质体反射率等储层资料,探讨了渤海湾盆地车镇凹陷陡坡带沙河街组近岸水下扇砂体岩石学特征、储层物性特征、成岩作用类型及其特征、成岩阶段与成岩序列、储层孔隙类型与次生孔隙发育特征,分析了低孔低渗储层中次生孔隙（＂甜点＂）的形成条件及控制因素。结果表明：车镇凹陷陡坡带沙河街组近岸水下扇砂体由岩屑质长石砂岩构成,在埋藏过程中,储层经历了压实、胶结、溶解和交代等成岩作用,现今储层埋深2 000～3 800m,储层处于中成岩阶段,总体上形成了低孔低渗储层;溶蚀作用对于改善储层质量起到了重要作用;主要在2 300～3 100m深度段的有机酸对长石颗粒的溶蚀以及形成的粒间和粒内孔隙不仅增加了储层孔隙度,而且提高了储层渗透率,改善了储层质量,孔隙度可达25%,渗透率达到50×10-3μm2,为油气富集高产提供了储集空间。总之,溶蚀作用及其形成的次生孔隙发育带对于预测有利储层是非常重要的。

Based on the core,thin section,SEM and vitrinite reflectance data,the characteristics of lithology,physical properties,diagenesis,diagenetic stage and sequence,pore type,secondary pore for sand bodies of nearshore subaqueous fan of Shahejie Formation in the steep slope zone of Chezhen depression were discussed;formation condition and controlling factor of secondary pores（＂sweet spot＂）in reservoir with low porosity and permeability were analyzed.The results show that the sand bodies of nearshore subaqueous fan of Shahejie Formation in the steep slope zone ofChezhen depression are consisted of feldspathic sandstone,mainly experiencing compaction,cementation,dissolution and metasomatism in the burial diagenetic evolution,and the reservoir is in the middle diagenetic stage now with the burial depth of 2 000-3 800m,and the reservoir has the characteristics of low porosity and permeability;the dissolution plays a significant role in improving reservoir quality during the burial diagenetic evolution in the mainly depth;the feldspar dissolution by organic acid in the depth of 2 300-3 100 mand the intergranular and intragranular pores increase the porosity and permeability of reservoir and improve the reservoir quality,and the porosity is up to 25%and the permeability is up to 50×10-3μm2,so that the reservoir spaces contribute to petroleum accumulation and high yield.In general,dissolutions and secondary pore development zone are very important for predicting favorable reservoir.