马海东地区下干柴沟组下段砂岩储层孔隙结构特征及控制因素

Pore structure characteristics and their controlling factors of sandstone reservoirs in the Lower Xiaganchaigou Formation in Mahaidong area

马海东地区下干柴沟组下段砂岩储层具有良好的油气勘探前景。基于铸体薄片、扫描电镜和核磁共振T2谱曲线分析,研究了马海东地区下干柴沟组下段砂岩储层孔隙结构特征及主控因素。研究表明:下干柴沟组下段4砂组储集岩发育残余粒间孔、粒内溶孔、成岩缝和孔隙缩小型喉道,孔隙结构以Ⅰ类大孔中喉型和Ⅱ类中孔细喉型为主,中—大孔比例较高,孔隙连通性较好;2砂组储集岩发育残余粒间孔、粒内溶孔和弯片状、管束状喉道,孔隙结构以Ⅲ类细孔微喉型为主,小型孔隙占据主体,孔隙连通性较差。指出沉积环境是储集岩孔隙结构形成的前提条件,机械压实和胶结作用封堵、缩小孔喉,构造作用和溶蚀作用连通、扩大孔喉,导致4砂组与2砂组储层孔隙结构存在明显差异。研究成果为马海东地区下干柴沟组下段砂岩储层评价与预测提供了依据。

The sandstone reservoirs in the Lower Xiaganchaigou Formation of Mahaidong area have a great hydrocarbon exploration potential. Based on the analyses of the cast thin sections, scanning electron microscope and NMR T2 spectrum curves, the pore structure characteristics and their main controlling factors of the sandstone reservoirs were studied. The study shows that the residual intergranular pores, intragranular dissolved pores, diagenetic fractures and pore-narrowed throats are well developed in the fourth Sands Groups in the Lower Xiaganchaigou Formation. The pore structure is mainly composed of Type I macro pore-middle throat and Type II medium pore-fine throat with a high proportion of medium-large pores and good pore connectivity. The residual intergranular pores, intragranular dissolved pores, bent sheet and tube-shape throats are developed in the second Sands Groups.The pore structure is dominated by Type III fine pore and micro throat with small pores accounting for the main part and poor pore connectivity. It is pointed out that the sedimentary environment is the prerequisite for the formation of the pore structure in the reservoir rocks. Mechanical compaction and cementation block and narrow the pore throat, while the tectonic action and dissolution connect and expand the pore throat, resulting in significant differences in the pore structures between the fourth and the second Sandstone Groups. This study achievements provide the evidences for the evaluation and prediction of the sandstone reservoirs in the Lower Xiaganchaigou Formation in Mahaidong area.