裂缝油藏回注溶解气混相驱替特征及影响因素

裂缝油藏回注溶解气混相驱油机理较为复杂。以实际裂缝型挥发油藏为例基于双孔双渗组分模型研究了回注溶解气的驱替特征和原油驱动方式;分析了扩散作用、窜流能力、压敏效应、采油速度和回注气比例的影响规律。结果表明:回注溶解气混相驱替时,原始弹性能量、原油溶解膨胀和注气波及同时存在;地层压力逐渐下降,溶解气油比逐渐增高;储层原油轻质组分和饱和压力逐渐增加,黏度和密度逐渐减小。扩散作用和裂缝者质窜流有利于减小注入气沿裂缝的突进同时降低基质原油黏度和密度,但减弱了注气波及作用;压敏效应可以增加岩石的弹性能量,有利于提高原油采出程度;适当地提高采油速度和回注气比例有助于增强波及作用其中1.2的回注比可以实现注采平衡。

Miscible Displacement Characteristics and Influencing Factors for Solution Gas Re-injection in Fractured Reservoir

Miscible displacement mechanism for solution gas re-injection in dual media is complex. On the basis of a dual-porosity and dual-permeability compositional model, this paper took a real fractured volatile reservoir for example, studied the miscible displacement characteristics and drive mechanism for solution gas re-injection, and analyzed influencing factors including diffusion, cross flow between fracture and matrix, pressure sensitivity, oil recovery rate and gas re-injection fraction. The results show that in the process of miscible displacement by solution gas re-injection, the drive mechanism is composed of the original volume expansion by depletion, swelling and displacement; the reservoir pressure drops and solution gas-oil ratio increases; for oil in place the light components and saturation pressure gradually increase while the viscosity and density decrease. The diffusion and cross flow between fracture and matrix can help reduce the fingering along fracture and decrease the viscosity and density of oil in matrix, however, weaken the sweep efficiency of injected gas; the pressure sensitivity intensifies the shrinkage of porosity, which benefits to enhancing recovery; maintaining the oil recovery rate and re-injection fraction at proper high level can improve sweep efficiency, and an injection-production voidage balance can be achieved at the re-injection fraction 1.2.