低渗透油藏混相气驱生产气油比预测

Prediction of produced GOR of miscible gas flooding in low permeability reservoirs

生产气油比是气驱油藏开发设计的一项关键指标。在明确气驱全生命周期产出气具有5种来源基础上,提出了与3个开发阶段相匹配的低渗透油藏气驱生产气油比预测公式。从注气到见气前阶段生产气油比主要受油藏流体初始溶解气油比控制,给出了水溶气等效气油比确定方法;从见气到气窜前阶段的生产气油比主要受气驱“油墙”的溶气能力影响,可借鉴低渗透油藏气驱“油墙”物理性质描述系统方法确定气驱“油墙”溶解气油比;气窜后阶段的生产气油比变化情况由游离气形成的气油比决定,其预测基于“采出液腾出的空间被注入气和水充满”朴素认识,联合应用油气渗流分流方程、Corey模型和Stone方程、低渗透油藏气驱增产倍数,以及交替注入的水气段塞比等概念进行计算。“3段式”气驱生产气油比预测油藏工程方法得到了低渗透油藏CO2混相驱矿场试验的验证,可用于注气开发方案设计,采油工艺优化或注气埋存潜力评价。

The produced GOR is a key index for the development and design of gas flooding reservoirs. On the basis of confirming that there are five sources of gas production in the whole life cycle of gas flooding, the prediction formula of produced GOR in low permeability reservoirs matching with three development stages is proposed. From gas injection to pre-gas production, the pro. duced GOR is mainly controlled by the initial dissolved GOR of the reservoir fluid, and method of determining the equivalent GOR of water-soluble gas is given. The produced GOR in the stage from pre-gas production to gas channeling is affected by the gas dis. solved capacity of ″oil bank″. The method of describing the physical property of gas flooding″oil bank″ in low permeability reser. voirs can be used for reference to determine dissolved GOR of gas flooding″oil bank″. The change of produced GOR after gas chan. neling is determined by the GOR formed by free gas, and its prediction based on the understanding that the pore space released by the produced liquids would be filled with the injected gas and water. It is calculated by oil and gas fractional flow equation, Corey's model and Stone's equation combined with concepts of gas flooding increasing multiple in low permeability reservoir, and slug size ratio of water-gas during water alternating gas injection. The reservoir engineering method of produced GOR prediction taking the form of ″three-stages″ has been verified by the field test of CO2 miscible flooding. It can be used in gas injection development plan. ning design, optimization of oil production process or gas injection storage potential evaluation.