鄂尔多斯盆地北部二叠系下石盒子组致密砂岩成岩作用及孔隙成因

鄂尔多斯盆地上古生界分布有大面积致密砂岩储层。鄂北地区杭锦旗探区和大牛地气田储层的埋藏—成岩作用具较大差异性。两者的对比性研究有助于深刻理解致密砂岩的成储过程。运用铸体薄片和扫描电镜观察等储层测试方法明确了两者储层成岩作用和孔隙发育特征。研究表明:埋深差异、断裂作用和后期抬升作用导致两者储层的成岩阶段分别为中成岩A₁期和中成岩B期。泊尔江海子断裂以北杭锦旗探区储层中发育广泛的高岭石胶结，长石含量约10%。孔隙以长石溶孔、铸模孔和粒间溶孔为主，加之张裂缝的沟通作用，孔隙条件较好，属“隆起区长石溶蚀增孔—张裂缝沟通孔隙”的形成机制。断裂以南的杭锦旗探区储层和大牛地气田相似。大牛地气田储层持续埋深，成岩演化程度高，长石溶蚀殆尽。孔隙条件较差，孔隙主要以岩屑溶孔和微孔隙为主，属“斜坡深埋区岩屑溶蚀增孔”的形成机制。

Diagenesis and Pore Formation of the Upper Paleozoic Tight Sandstone in the Northern Area of the Ordos Basin

Tight sandstones are well developed in the Upper Paleozoic in the Ordos Basin. Burial diagenesis in the reservoirs of the Hangjinqi area and Daniudi gas field are quite different. Their comparative study is helpful in understanding the formation process of the reservoir in tight sandstone. Their diagenesis and pore development characteristics are revealed by the observation of casting thin sections and scanning electronic microscopy. The study shows they are in Stage A₁ and B of Middle Diagenesis as a result of different burial depths， fracturing， and later uplift. Kaolinite cementation developed extensively in the reservoir of the Hangjinqi area where in the north of the Boerjianghaizi Fault， and the feldspar content is 10%. Within the feldspar， dissolution， moldic， and intergranular dissolution pores are the dominant types. With the connection of tension fissure， reservoir porosity is quite high， and its forming mechanism is “feldspar dissolution to improve porosity and tension fissure connection in the uplift area”. The reservoir of the Hangjinqi area north of the Boerjianghaizi Fault is similar to the Daniudi gas field. The reservoir in the Daniudi gas field is characterized by deep burial， a high degree of diagenetic evolution， and complete dissolution of feldspar. Reservoir porosity is low and rock fragment dissolution pores and micropores are dominant. Its forming mechanism is “rock fragment dissolution to improve porosity in the slope area”.