川西坳陷中段上三叠统须二段气水分布特征及成因机理

川西坳陷深层上三叠统须家河组储层致密化严重,气水分布十分复杂,已经成为制约天然气勘探和开发的关键问题。在对须二段致密气藏地质特征、流体特征和气水分布特征研究的基础上,结合研究区实际地质条件,综合物理模拟实验的结果,揭示了该区复杂的气水分布成因机理。研究结果表明,川西坳陷须二段天然气主要为煤型裂解气,地层水型主要表现为CaCl2型,属于高封闭环境下的地层水。试气资料和测井解释结果表明,川西坳陷深层须二段主要以气层和含气层为主,局部井为气水同层和纯水层,地层水无成层性,水的分布表现出串珠状残留地层水的特点。孤立的地层水不受构造的控制,水的产出并不表现出上水下气或上气下水的特点,由于储层非均质性强,在深盆气形成过程中,气驱替水首先通过相对疏松的高孔高渗的储集空间,而对超致密砂体内已封存完好的水体则无力驱替,形成"残留地层水",物理模拟实验结果也证实了这一点。

Gas-water Distribution Characteristics and Genetic Mechanism of the Second Sector of the Upper Triassic Xujiahe Formation in the Middle of the Western Sichuan Depression

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.