鄂尔多斯盆地中部奥陶系顶盐溶作用及其储集孔隙成因

盐溶作用使碳酸盐岩孔隙性增加,同时在古代碳酸岩中由于渗－潜流水对已成孔隙产生沉淀,在滞流区又可形成致密性岩性遮挡。石盐结晶发生在沉积期,是被溶蚀的沉积易溶母质。盐溶孔的大量发育形成于后表生成岩期。天然气产量和岩石的物性取决于盐溶孔的开启程度。充填程度差异在区域上可导致储层孔隙空间的差异性和非均质性,正是由于岩石的这一自身“亏空”和“补偿”形成了区域上成岩圈闭或岩性遮挡。

Salt-dissolution and the Pore Genesis of the Reservoir on Top of Ordivician in the Contral Ordos Basin

The salt-dissolution refers to halite nuneral dissolution in the carbonate reservoir rock of the Ordos basin, which is the main factor to form secondary pores (here called as salt-dissolved pore). Reservoir rocks containning salt-dissolved pore are widely distributed on top of Majiagou Formation of Ordovician in the tentral Ordos basin, and ocarpied an area of more than 30,000 km2. On the bases of a large number of data obtained from core observation, thin section determination,cathodo luminescence, SEM, electron probe and so on, it can be seen that the gas-bearing bed of Majiagou Formation closely velated to salt-dissolution. The gas output and rock's physical properties dependon the openning extent of the salt-dissolved pore. The salt-dissolution caused an increase of porosity in carbonate reservoir, and at the same time, the fluid deposition in the previous porosity through leading-phreatic water.In water stagnant region the fight lithologic borrier can be formed. Halite}cry-stallization took place in sedimentary period, which was easily-dissolved substance in carbonate rock. And abundant salt-dissolved pores were produced in epidiagenesis. The vegional difference of pore filling lead to the difference and anisotropise of pore space in carbonate reservoir rock. It was the "loss" and "compensation" of rock itself that formed the vegional diagenetic trap or lithologic barrier.