四川盆地安岳地区须二段气藏相态特征新认识

安岳地区须二段气藏储层低孔、致密,气水交织,含水饱和度高,油气分布不受构造与海拔控制,气井普遍产凝析油,平均生产油气比148 g/m³,为四川盆地凝析油含量最高的非常规凝析气藏。采用常规凝析气藏研究手段已无法正确确定气藏类型和准确评价气藏相态特征。为此,建立了高压物性实验、常规凝析气藏类型判别与生产静动态特征相结合的气藏类型判别方法,据此判定该气藏为局部带“油垫”的饱和凝析气藏;运用相态恢复理论准确地模拟了该气藏的流体特征,计算得到气藏平均凝析油含量高达249 g/m³,所预测的凝析油产量与实际相吻合。进而提出了提高凝析油采收率的相应开发措施,在考虑注入成本以及后期处理等因素后,建议单井采用“先衰竭后干气吞吐”的开采方式。针对安岳地区须二段气藏相态特征的认识和研究方法,对类似非常规砂岩凝析气藏相态特征的研究具有指导意义。

A new understanding of the phase behavior of gas reservoirs in the 2nd member of the Xujiahe Formation in the Anyue Block,Sichuan Basin

The gas reservoirs in the 2^nd member of the Xujiahe Formation of the Anyue Block, Sichuan Basin, are featured by low porosity, high tightness, gas/water co existence, high water saturation, and the oil/gas distribution free from structural & altitudinal limitations. Local gas wells with condensate oil commonly produced and the average oil gas rate of 148 g/m³ are thereby known as the most productive unconventional condensate gas wells in the Sichuan Basin. Such conventional methods are inadequate to correctly identify the said condensate reservoir and accurately assess its phase behavior. Thus, in combination with high pressure physical property testing and static/dynamic performance analysis, a new gas reservoir type identification method was thus developed. With this new method, the condensate gas reservoirs in this study area were identified as such a type partially underlain by oil rims. Then, the phase recovery theory was adopted to simulate the fluid characteristics of such reservoirs, the average condensate content of which were calculated to be up to 249 g/m³, a figure later proved to be approximate to the actual value. Finally, pertinent development techniques were proposed to enhance the condensate recovery. A recovery technology termed as "depletion followed by dry gas re injection" was suggested for enhancing the single well production when the re injection cost, post processing and other factors were taken into account. This study is of significance as a reference to research on the phase behavior of similar unconventional sandstone condensate gas reservoirs.