低渗气藏初始产水定量评价新方法——以东海盆地西湖凹陷为例

A new method for quantitative evaluation on initial water production in low permeability gas reservoirs: A case study from Xihu sag in East China Sea basin

针对东海盆地西湖凹陷不同物性气藏出水差异大、低渗气藏出水缺乏定量、系统的判别方法的问题,以半渗透隔板曲线代替传统的压汞曲线,经J函数处理将有限的实验数据拓展到任意物性条件,实现了含水饱和度垂向表征;利用稳态法测得7条低渗岩样相渗曲线,经实验曲线端点规律统计得到了不同物性气藏气、水相对渗透率预测关系式,进而实现了初始生产水气比的计算。综合不同物性、不同气柱高度计算的含水饱和度、初始生产水气比,形成定量的、系统的初始产水评价图版。依据本文评价图版将研究区气藏由上到下依次划分为5个区带:Ⅰ纯气区、Ⅱ近气区、Ⅲ气水同产区、Ⅳ近水区、Ⅴ纯水区。西湖凹陷实际气藏出水状况与图版预测结果相吻合,验证了本文评价图版的可靠性和实用性。从本文评价图版可以看出,储层物性和气柱高度决定了西湖凹陷气藏的出水状况,有效产气区深度下限随渗透率降低而急剧升高,不同物性的气藏同处于气柱高度相近的气水过渡区内,但常规气藏以产气为主,特低渗气藏则以产水为主。

For problems that there is large difference in water production from different physical properties gas reservoirs and there is no effective quantitative and systematic methods to distinguish water production of low permeability gas reservoirs in Xihu sag,East China Sea basin,the porous diaphragm curve is used instead of the traditional mercury injection curve,and the limited experimental data are extended to arbitrary physical property conditions by J-function processing to realize the vertical characterization of water saturation. Seven relative permeability curves of low permeability rock samples are measured by steady-state flow method. The relationship between relative permeability of gas and water in gas reservoirs with different physical properties is obtained by making statistical analysis on experimental curves endpoint law,and the calculation of the initial production water-gas ratio can be realized. A quantitative and systematic evaluation chart of initial production water is formed by calculation of water saturation and initial production water-gas ratio under different physical properties and different gas column heights. According to the evaluation chart of this paper, the gas reservoirs in the study area are divided into five zones from top to bottom: pure gas zone I,approximate gas zone II,gas-water production zone III,approximate water zone IV and pure water zone V. The actual water production situation of Xihu sag gas reservoir coincides with the result of chart prediction,which verifies the reliability and practicability of the evaluation chart in this paper. From the evaluation chart of this paper,it can be included that reservoir physical property and gas column height determine the water production situation of gas reservoir and the lower limit of depth in effective gas production regions increases sharply with the decrease of permeability. Although gas reservoirs with different physical properties are in the gas-water transition zone with similar gas column heights,gas production is dominant in conventional gas reservoirs and water production is dominant in ultra-low permeability gas reservoirs.