碳酸盐岩气藏储层非均质性对水侵差异化的影响

Influence of reservoir heterogeneity on water invasion differentiation in carbonate gas reservoirs

碳酸盐岩气藏因储层孔隙、溶洞、裂缝的尺度和分布密度不同易产生多样化的非均质性,使得气藏水侵规律的差异性较大。为了深入认识碳酸盐岩储层非均质性及其对气藏水侵的影响,进而对气藏水侵动态进行预判,基于全直径岩心数字化处理分析改进了定量描述孔、洞、缝搭配关系的方法,根据逾渗理论分析图版建立了评价微裂缝对储层渗流能力贡献的新方法,并通过开展气藏实际压力、温度条件下气水渗流及流固耦合应力敏感实验,获得气水相对渗透率和岩石压缩系数数据,据此分析不同类型裂缝、溶洞对气藏水侵的影响,结合四川盆地典型碳酸盐岩气藏水侵特征建立了不同储渗类型储层水侵影响差异化特征的预判方法。研究结果表明:(1)不同类型碳酸盐岩储层在广义上均属三重介质,裂缝发育使气藏水侵影响显现快,而溶洞均匀发育使水侵影响显现相对较慢;(2)微裂缝发育是特低孔隙度储层具备视均质中高渗透能力的必要条件,对应的水侵规律与沿大裂缝水窜或网状小裂缝发育带水侵明显不同;(3)水区储层孔隙度应力敏感是地层水侵能量的主要来源,异常高压气藏在开采初期这一特征更加突出。该研究成果已应用于四川盆地多个碳酸盐岩气藏的水体能量评估、水侵影响预测及治水措施有效性预判,为复杂气藏水侵影响的治理提供了有效的技术导向,同时也深化了对水侵差异化规律的认识。

Diversified heterogeneities tend to occur in carbonate gas reservoirs due to different scales and distribution densities of pores, caves and fractures in reservoirs, and consequently the water invasion laws of gas reservoirs are more different. In this paper, the methods quantitatively describing the matching relationships between pores, caves and fractures were improved based on full-diameter core digital processing and analysis so as to understand the heterogeneity of carbonate reservoirs and its influence on the water invasion laws of gas reservoirs and then predict the water invasion dynamics of gas reservoirs. Firstly, a new method to evaluate the contribution of microfractures to reservoir seepage capacity was established according to the analysis chart of percolation theory. Then, gas-water relative permeability and rock compression coefficient were measured by conducting gas/water seepage and fluid-solid coupling stress sensitivity experiments under the conditions of actual gas reservoir pressure and temperature. And accordingly the effects of various fractures and caves on the gas invasion laws of gas reservoirs were analyzed. Finally, the method to predict the differentiation characteristics of water invasion influence of the reservoirs with different types of physical properties was developed based on the water invasion characteristics of typical carbonate gas reservoirs in the Sichuan Basin. And the following research results were obtained. First, in a broad sense, different types of carbonate reservoirs are classified as a triple continuum. The development of fractures speeds up the appearance of water invasion in gas reservoirs while the uniform development of caves slows down the appearance of water invasion effect. Second, the development of microfractures is a prerequisite for ultra-low porosity reservoirs to possess the ability of medium permeability or high permeability. The water invasion law in this case is obviously different from the channeling along large fractures or the water invasion in the network small fracture development belt. Third, the stress sensitivity of reservoir porosity in aquifer is the main source of formation water invasion energy. This characteristic is more prominent in the early stage of the exploitation of abnormal high pressure gas reservoirs. The research results have been applied to water invasion energy assessment, water invasion performance forecast and water control measure effectiveness prediction in a number of carbonate reservoirs in the Sichuan Basin. And they provide effective technical guidance for water invasion control in complex gas reservoirs and further understanding of water invasion differentiation laws.