EXPLORATION OF DEEP BASIN GAS POOL IN THE ORDOS BASIN

摘要

The Carboniferous-Permian System of the upper Paleozoic in Ordos Basin is a set of sedimentary formation with wide-coverage coal series. The gas-bearing reservoir is a set of compact sandstone with low porosity and permeability, of which the average porosity is less than 8%; and the permeability is less than 0.42 x I0~(-3)mm~2. The hydrocarbon source rock of coal series is in the period of high maturity-over mature wet gas-lot of dry gas generation, the gas generation amount coming to 539.83 x 10~(12)m~3. Through the research of the gas-water relations and the pressure features as well as exploration experiences, we determine that there exists the obvious phenomenon of gas-water inversion in the Carboniferous-Permian System of the upper Paleozoic, in the section ofP2hg-P|$2, from south to north, develops large areas of deep basin gas pool. Yet, after the Yanshanian Movement, with the rising of east part of the Ordos Basin, the deep basin gas pool lies in a reconstructive state now. Meanwhile, the speed of the hydrocarbon generation out of the source rock slowed down greatly. Although there is the supply of the desorption gas from coal-bearing rock, the amount is likely less than the lost, which made the early boundary of gas-water shrink back toward south. It is predicted that the distribution range of the deep basin gas in Ordos Basin will get to 12 x 10~4km~2, and the prospect total resource amount exceeds 42.27 x 10~(12)m~3, and the current resource amount exceeds 4.27 x 10~(12)m~3.