征沙村地区三工河组低渗透砂岩储层成岩特征

Diagenesis characteristics of low permeability reservoir in Sangonghe Formation of Zhengshacun area

通过对征沙村地区三工河组岩石样品镜下观察和各种微观测试结果分析,开展了深层低渗透砂岩储层成岩特征研究。结果表明,三工河组低渗透储层主要为长石质岩屑砂岩和岩屑砂岩,成分成熟度、结构成熟度均较低;压实作用较强烈,常见颗粒定向排列、压裂,塑性岩屑、片状云母弯曲变形等特征;方解石、绿泥石膜以及石英加大等胶结物充填孔隙,胶结作用较强烈;常见长石、岩屑沿颗粒解理面、压裂缝的条带状溶蚀和易溶组分筛状或点状溶蚀;发育多种类型自生矿物对碎屑颗粒的交代作用;储层处于中成岩阶段A期。压实作用是造成孔隙度损失和砂岩低渗的最主要因素,成岩晚期碳酸盐、硬石膏胶结物使孔渗进一步降低,溶蚀作用对孔渗改善效果不大。纵向上,随埋深增加,压实作用、胶结作用增强,渗透率显著降低;平面上沿北西-南东方向(沉积物源方向)压实作用、胶结作用增强,渗透率降低。成岩特征及差异性对三工河组低渗透砂岩的形成及分布具有重要作用。

Diagenetic characteristics of deep low permeability sandstone reservoir of Sangonghe Formation in Zhengshacun area were studied based on microscopic observation of rock samples and various microscopic test methods.The results showed that low permeability reservoirs of Sangonghe Formation are mainly feldspar lithic sandstone and lithic sandstone,compositional maturity and structural maturity are relatively low.Plastic rock debris,mica flake bending deformation filling intergranular pores are common in Sangonghe Formation and comprehensive performance shows strong deep compaction.Pores are filled with cements such as calcite,chlorite film and quartz enlargement which show strong cementation.Banded dissolution of feldspar,rock debris particles along cleavage planes,fractures and sieved or dotted dissolution of soluble components are common,and metasomatism of multi-type authigenic minerals on clastic particles are developed.The reservoir is generally in intermediate diagenesis stage A.Compaction is the most important factor which makes porosity loss and sandstone low permeability,further reduction of porosity and permeability caused by carbonate and anhydrite cements in late diagenesis.Dissolution has little improvement on porosity and permeability.In vertical directions,with increase of buried depth,compaction and cementation both increase,permeability significantly decreases.In horizontal directions,along NW-SE direction(sediment source direction),compaction and cementation increase,permeability decreases.Diagenetic characteristics and differences play an important role in the formation and distribution of low permeability sandstone in Sangonghe Formation.