东坪基岩气藏气水相对渗透率的确定方法

Determination of Gas-water Relative Permeability in Dongping Bedrock Gas Reservoir

罗沛 杨云 柴小颖 杨会洁 王炯

LUOPei YANGYun CHAIXiaoying YANGHuijie WANGJiong

重庆科技学院石油与天然气工程学院, 重庆 沙坪坝 401331 中国石油青海油田公司勘探开发研究院, 甘肃 敦煌 736202

College of Oil and Gas Engineering, Chongqing University of Science and Technology, Shapingba, Chongqing 401331, China Research lnstitute of Exploration and Development, Qinghai Oilfield Company, PetroChina, Dunhuang, Gansu 736202, China

东坪基岩气藏储层岩性差异大，非均质性强。孔缝发育区岩石松散，无法钻取完整的岩芯，而致密带几乎不渗透，无法通过驱替实验获取相对渗透率曲线，这成为困扰气藏动态分析和开发指标计算的难题。基于水驱气藏物质平衡原理，建立了不依赖水侵量的储层含水饱和度计算方法，避免了水侵量计算方法中的不确定因素，提高了含水饱和度计算的准确性。建立了基于储层孔隙结构分形维数和生产水气比历史拟合相结合的气水相对渗透率计算方法。根据该气藏毛管压力曲线的分类确定孔隙结构分形维数的界限，通过生产水气比拟合确定具有代表性的储层孔隙结构分形维数，进而计算气水相对渗透率曲线。该方法克服了因毛管压力曲线多样化而导致分形维数难以确定的难题，所获得的相渗曲线更能代表气藏的整体渗流特征。该方法为无法通过岩芯驱替获取相渗曲线的气藏提供了有效途径，对于其他基岩气藏及严重非均质气藏具有借鉴意义。

The lithology of the bedrock reservoirs in Dongping is different and heterogeneous. The rock is loose and complete core cannot be drilled in zones where pores and fractures are well developed, while the tight zone is almost impervious. So, the relative permeability curve cannot be obtained through displacement experiment. It has become a difficult problem for gas reservoir dynamic analysis and prediction. In order to solve this problem, a calculation method of water saturation of formation at different development time is established based on the principle of water drive gas reservoir material balance. This will improve the accuracy of water saturation by avoiding the uncertain factors in the calculation method of water influx. Based on the fractal dimension of the pore structure and the historical fitting of the water-gas ratio data, the gas-water relative permeability calculation method is established. The fractal dimension limit of pore structure is determined by classifying capillary pressure curve of this gas reservoir, the fractal dimension of reservoir pore structure was determined by historical water-gas ratio data fitting method, and the relative permeability curve of gas and water is calculated. This method can effectively overcome the difficulty in determining the fractal dimension due to the diversity of capillary pressure curves, and the obtained relative permeability curves can better represent the overall seepage characteristics of heterogeneous gas reservoirs. This method not only provides an effective way for gas reservoirs that cannot obtain relative permeability curve through core displacement, but also has reference significance for other bedrock gas reservoirs and seriously heterogeneous gas reservoirs.

10.11885/j.issn.1674-5086.2020.03.07.01