大牛地气田致密砂岩气层的异常高孔隙带特征与成因

利用岩石薄片分析、扫描电镜分析及粘土矿物的X衍射资料，分析了鄂尔多斯盆地塔巴庙区块大牛地气田上古生界盒3段致密砂岩储层中异常高孔隙带的特征和成因。分析表明，异常高孔隙带具有高渗和低渗两种类型。其中，异常高孔渗带（孔隙度大于8％，渗透率大于0.5×10^－3μm²）的岩性主要为粗粒的岩屑石英砂岩和粗粒石英砂岩，杂基含量一般低于10％，孔隙多为残余粒间孔隙，中孔、中-粗喉的孔喉结构，绿泥石粘土包壳和古异常流体压力的发育是原生粒间孔隙被保护的主要原因；而异常高孔隙带（孔隙度大于8％，渗透率小于0.5×10^－3μm²）的岩性为粗-中-细粒岩屑砂岩和长石岩屑砂岩，杂基含量较高，孔隙多为各类溶蚀孔隙和交代溶蚀孔隙，孔隙主要为细孔，喉道主要为细-微喉，各类次生溶蚀孔隙的发育是形成异常高孔隙带的主要成因。

Characteristics and Origins of High-porosity Zones in Tight Gas Sand in Daniudi Gas Field, the Ordos Basin

The characteristics and origins of the high porosity zones in the tight sandstone reservoirs in the 3rd member of the Upper Paleozoic Shihezi Formation in Daniudi gas field of Tabamiao block in the Ordos Basin are analyzed by using various data, such as thin section, SEM and X diffraction of clay minerals. The high porosity zones can be divided into two types, one with low permeability and the other with high permeability. The high porosity and high permeability zones, with porosity over 8% and permeability over 0.5×10－3μm2, are dominated by coarse grained lithic quartz sandstone and quartz sandstone with matrix content generally below 10%. The pores are mainly of residual intergranular pore type, and the pore throat structure is characterized by medium pore and medium coarse throat. Clay coating of chlorite and the development of fossil abnormal fluid pressure are main factors leading to the preservation of the intergranular pores. In contrast, the high porosity and low permeability zones, with porosity over 8% and permeability below 0.5×10－3μm2, are coarse medium fine grained lithic sandstone and feldspar lithic sandstone with relatively higher matrix content. The pores are mainly of various dissolution pores and metasomatic dissolution pores, and the pore throat structure is characterized by fine pore and fine micro throat. The development of various secondary dissolution pores is the main cause of the high porosity zone.