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.