泥质岩盖层对水溶相天然气封闭能力的综合评价方法及其应用

为了研究泥质岩盖层对水溶相天然气封闭能力,在泥质岩盖层对水溶相天然气封闭机理分析的基础上,利用达西定律建立了一套单位压差下水溶相天然气通过泥质岩盖层相对渗滤速度的研究方法,根据水溶相天然气通过泥质岩盖层渗滤速度的相对大小,建立了泥质岩盖层对水溶相天然气封闭能力的综合评价指标———CSWI。CSWI既可以反映泥质岩盖层本身特征对水溶相天然气封闭能力的影响,又可以反映地层水特征对水溶相天然气封闭能力的影响。将CSWI应用于大庆长垣以东地区泉一、二段泥质岩盖层对水溶相天然气封闭能力的综合评价中,结果得到该区泉一、二段泥质岩盖层在西部具有好的封闭水溶相天然气能力,向东部其封闭能力逐渐降为中等。评价结果与该区西部天然气相对富集的地质条件吻合,这表明该方法用于泥质岩盖层对水溶相天然气封闭能力的综合评价是可行的。

A Comprehensive Evaluation Method on Seal Ability of Mudstone Caprock to Gas in Water-Dissolving Phase and its Application

To study seal ability of mudstone caprock to gas in water-dissolving phase, based on seal mechanism analysis of the mudstone caprocks to gas in water-dissolving phase, a research method of calculating relative percolation velocity, by Darch's law, of the gas in water-dissolving phase through mudstone caprocks under unit pressure difference was proposed. Based on the relative percolation velocity of gas in water-dissolving phase through mudstone caprocks, a comprehensive evaluation index (CSWI)for seal ability of mudstone caprock to gas in water-dissolving phase was established. CSWI can reflect not only the influence of the characteristics of mudstone caprock itself on its seal ability to gas in water-dissolving phase, but also the influence from the characteristics of the formation water to the seal ability of mudstone caprock to gas in water-dissolving phase. It is a comprehensive evaluation index for the seal ability of mudstone caprock to gas in water-dissolving phase. It was applied in evaluating comprehensively the seal ability of Kq_ 1 2 mudstone caprocks to gas in water-dissolving phase to the east of the Daqing Pacanticline. The result reveals a good seal ability of Kq_ 1 2 mudstone caprocks in water-dissolving phase in the west of research region, with a decreasing trendency in seal ability from west to east. The evaluation results are in accord with the actual geological conditions of gas accumulation in the west of research region, revealing the effectiveness of the evaluation.