大型致密砂岩气田采收率计算方法

大型致密砂岩气田储层物性差,含气面积大,非均质性强,气田储量与产量规模大,采收率与最终采气量是指导气田长期稳定生产、制定开发技术对策以及衡量气田开发效果的关键指标。致密砂岩气田孔喉小,渗流机理复杂,常规的实验室模拟方法难以得到准确的采收率数据。以苏里格大型致密砂岩气田为研究对象,优选中区、东区、西区、南区等典型区块进行精细解剖,根据地质特征及开发效果将投产井分成3类;以辫状河体系带为沉积相带约束,确定各类井区的面积比例;选取生产时间较长、基本达到拟稳态的井为分析样本,利用产能不稳定分析及生产曲线积分等方法,评价各类井的井均动态储量及最终累积产量;结合储层规模、结构与生产动态特征,论证单井控制范围;对各类井区以面积比例加权,模拟预测井网足够完善时区块的技术极限采气量及采收率。研究表明,气田各区技术极限采收率为26.8%~75.5%、平均为57.0%,远低于常规气藏的80%~90%。气田技术极限采气量为2.18×10¹²m³,目前经济极限采气量为1.27×10¹²m³,可通过技术进步降低开发成本,未来增产潜力大。

Recovery factor calculation method of giant tight sandstone gas field

Giant tight sandstone gas fields are characterized with poor reservoir property, large gas bearing area, strong heterogeneity and enormous scale of reserves and production. Recovery factor and ultimate gas production are the key indicators to guide the long-term stable development of gas field, formulate development technical strategies and evaluate the development effect of gas field. Due to the small pore-throat and complex porous flow mechanism of tight sandstone gas field, it is difficult to obtain accurate recovery data using conventional laboratory simulation methods. Taking Sulige giant tight sandstone gas field as the research object, typical blocks selected from the central, east, west and south zones are detailedly analyzed, and production wells are classified into three types according to geological characteristics and development effect. The area ratios of various well blocks are restricted by braided-river sedimentary facies belts. A large-output well with long production history and basic quasi-steady state is selected as the analysis sample. The productivity instability analysis and production curvilinear integral methods are applied to evaluate the average dynamic reserves and ultimate accumulated production for each type of well. The single-well control scope is validated comprehensively using reservoir scale, structure and production dynamic characteristics. Using area proportional weight method, the gas production rate and recovery factor restricted by technological level are predicted in case of enough complete well pattern. The research result shows that the aforesaid recovery factor in each large block of gas field is 26.8%-75.5%, averaged at 57.0%, far lower than the conventional gas reservoirs of 80%-90%. Based on the current technology, this gas field has the limited production of 2.18×10¹²m³, and the maximum economic production is 1.27×10¹²m³. In the future, with the technology improvement, development cost will be reduced to achieve the large potential of output increase.