东营凹陷沙河街组近岸水下扇低渗储层成因

Genesis of low permeability reservoirs of nearshore subaqueous fan in Shahejie Formation in Dongying Sag,Bohai Bay Basin

为了阐明渤海湾盆地东营凹陷北部陡坡带近岸水下扇低渗储层成因,应用岩心和储层分析资料,通过储层岩石特征、成岩作用、成岩序列和孔隙演化及其控制因素分析,指出东营凹陷北部沙河街组近岸水下扇砂体由长石砂岩、长石质岩屑砂岩等构成,储层经历了较强机械压实作用、碳酸盐胶结作用、碳酸盐和长石溶解作用等成岩作用,现储层埋深1 700~3 500 m,处于中成岩演化阶段,总体形成了中低孔低渗（孔隙度平均为11.3%,渗透率平均为23.12×10-3μm2）储层。储层中低孔低渗主要受控于较强的压实作用和较强的碳酸盐胶结作用,但溶蚀成岩作用对于改善储层质量起到了重要作用。主要在2 900~3 200 m深度段,有机酸对砂岩长石颗粒的溶蚀,形成的粒间和粒内孔隙不仅增加了孔隙度,而且提高了储层渗透率,改善了储层质量（孔隙度可达到25%,渗透率达到1 000×10-3μm2）。显然,发现溶蚀作用及其形成的次生孔隙发育深度段对于预测有利储层是非常重要的。

In order to demonstrate the genesis of low permeability reservoir of nearshore subaqueous fan in northern steep slope of Dongying sag,abundant cores and reservoir analysis data were utilized to conduct the research on lithological characters of reservoir,diagensis,diagenetic sequence and porosity evolution as well as their controlling factors. The sandbodies of nearshore subaqueous fan of the Shahejie Formation consist of arkose and feldspathic lithic sandstone and the reservoirs have experienced strong compaction,carbonate cementation,dissolution of calcite and feldspar in the burial diagenetic evolution. The reservoirs are at the middle diagenetic stage now,have a burial depth in the range of 1 700-3 500 m and mid-low porosity（ mean porosity 11. 3%） and low permeability（ mean permeability 23. 12 × 10-3μm2）. The strong compaction and carbonate cementation reduced the porosity and permeability of the reservois,while dissolution contributed to the improvement of reservoir quality. The intergranular pores and intragranular pores resulted from dissolution of calcite and feldspar at the depth of 2 900-3 200 m are constructive to reservoir quality（ porosity up to 25% and permeability up to 1 000 × 10-3μm2）. Obviously,identification of dissolution and intervals with well-developed secondary pores is extremely important for predicting favorable reservoir.