关键词: 川西坳陷, 须家河组, 致密气藏, 气水分布, 成因机理

Abstract:

Severe densification and complicated gas-water distribution of the Upper Triassic Xujiahe Formation reservoir have become the key issues to natural gas exploration and development of the Western Sichuan depression. Based on the research of geological characteristics of the gas reservoirs, fluids and gas-water distribution, combined the comprehensive analysis of the regional geological conditions and physical modeling experiments, the genetic mechanism of the complicated gas-water distribution is discussed in this paper. The results show that the natural gas in the second sector of the Xujiahe Formation is coal-type cracking gas, and the water is CaCl₂type belonging to the high-sealed environment. The gas testing and logging explanation results shows that the reservoir of the second sector of the Xujiahe Formation is primary gas layer or gasbearing layer that only a few wells show gaswater layers or water layer, and the water displays no layering and the characteristics of stringlike stratigraphic water. The stratigraphic water distribution is not controlled by structure, and not showing up gas and down water or up water and down gas. In the formation process of deep basin gas, due to strong heterogeneity, the gas driving water firstly enters the reservoir with relatively high porosity and permeability, but the stratigraphic water completely sealed in super tight sandstone is not easily expelled to form residual stratigraphic water. This genetic mechanism was approved by physical modeling experiments.

Key words: Western Sichuan depression, Xujiahe Formation, tight sandstone reservoir, gas-water distribution, genetic mechanism