低渗透油藏气驱注采比和注气量设计

Design of injection-production ratio and gas injection rate of gas flooding in low-permeability reservoirs

注采比合理性对气驱生产效果影响较大。基于物质平衡原理、达西定律和油气分流理论、气驱增产倍数和气驱油墙描述等概念与成果,考虑并量化了注入气溶解、油藏流体膨胀、注入气成矿固化、储层压敏效应、天然裂缝疏导和干层吸气、注气井组和外部液量交换、气油比构成等因素,分别建立了基于采出油水两相地下体积的气驱注采比计算公式(2P公式)和基于采出油气水三相地下体积的气驱注采比计算公式(3P公式),给出了单井日注气量计算方法。应用新方法,研究代表性特低渗透油藏二氧化碳驱项目注采比变化情况,连续注气气窜后应按照3P公式计算的气驱注采比进行配注;水气交替注入按照2P公式计算的气驱注采比进行配注基本可行。

The rationality of injection-production ratio is important to the production performance of gas flooding. According to concepts and research results of the material balance principle,Darcy’s law,fractional flow theory,oil production rate multiplier due to gas flooding;and"oil wall"description of gas flooding,and by considering the quantified factors including gas injection dissolution,reservoir fluid expansion,mineralization and solidification of injected gas,reservoir pressure-sensitive effect,natural fracture drainage and dry layer suction,liquid exchange between gas injection areas and external environment,and the composition of produced gas oil ratio,the formula of injection-production ratio based on underground two-phase volume of the produced oil-water(2 P formula)and underground three-phase volume of produced oil-water-gas(3 P formula)are proposed,respectively,and the calculation method of daily gas injection rate is proposed as well.The new method is applied to study the injection-production ratio change of representative CO2 flooding projects in extralow permeability oil reservoirs. It is found that it is feasible to allocate injection rate according to the injection-production ratio estimated by the 3 P formula after continuous gas injection(CGI),and to allocate injection rate of water-alternatinggas(WAG)injection according to the injection-production rate estimated by 2 P formula.