The Combination Relationship And Gas Bearing Character Of Cracks And Positive Rhythm, Inverted Rhythm Sand Body

In this thesis, the author analyzes the compositional characters of cracks and positive rhythm, inverted rhythm sand body, the transforming ability of sandstone and the gas bearing character of positive rhythm, inverted rhythm sand body of Neopaleozoic in Ordos Basin by using core, well log, conventional permeability test and simulative experiments data on base of regional geology knowledge.(1) In the positive rhythm and inverted rhythm sand body of Neopaleozoic, plane-parallel cracks and low-angle declinate cracks often appear in the lithologic interface and sandstone with developed stratal configuration. Subvertical cracks often appear in the sandstone where stratal configuration is not developed, possibly the sand is tight or homogeneous.(2)When cracks develop in the positive rhythm and inverted rhythm sand body, the porosity of sandstone with cracks is about 2 percents higher than that without cracks, the porosity contributed by cracks is 20% to 30% of sand porosity, and the permeability of cracks is dozens to hundreds thousand times of sandstone's. When cracks are not considered, the porosity and permeability in the bottom of positive rhythm sand body are usually higher, while they are lower in the bottom of inverted rhythm sand body.(3) In the positive rhythm sand body with undeveloped subvertical cracks, the bottom of the sand body is the advantageous gas-bearing position. In the positive rhythm sand body with developed subvertical cracks, where the nature gas is prone to float upward under buoyancy, the upper part of the sand body is the advantageous gas-bearing position. In the inverted rhythm sand body, no matter subvertical cracks are developed or not, the upper part of the sand body is the advantageous gas-bearing position.