东海低渗气藏渗流机理及产能评价研究

Study on Seepage Mechanism and Productivity Evaluation of Low Permeability Gas Reservoir in East China Sea

低渗气藏具有低孔渗、高束缚水饱和度等特点,受滑脱、高速非达西效应等因素影响,气-水两相渗流规律复杂,常规产能评价方法存在局限性。针对这一问题,以东海低渗气藏Y为靶区,研究不同含水饱和度、不同压力下气-水两相渗流规律,建立气相渗透率与含水饱和度关系图版,分析气-水两相相对渗透率随地层压力衰竭的变化规律;在此基础上,建立低渗气藏动态产能评价方法,并通过实际应用来检验其可靠性。结果表明:低渗气藏含水饱和度存在使气相渗透率加速下降的临界值,且该临界值随岩心渗透率的减小而降低;在气藏衰竭开发过程中,气-水两相渗流能力均随地层压力降低而减小。气-水两相渗流动态产能评价方法在矿场应用效果良好,对低渗气藏产能评价及动态预测具有借鉴意义。

Low permeability gas reservoirs have the characteristics of low porosity and permeability,high irreducible water saturation,etc.Due to the influence of slippage,high-speed non-Darcy effect and other factors,the gas-water two-phase seepage law is complex,and the conventional productivity evaluation method has limitations.Aiming at this problem,taking the low permeability gas reservoir Y in the East China Sea as the target area,the gas-water two-phase seepage law under different water saturations and different pressures is studied,and the relationship chart between gas permeability and water saturation is formed.The change law of gas-water two-phase relative permeability with formation pressure depletion is analyzed.On this basis,the dynamic productivity evaluation method of low permeability gas reservoir is established,and the reliability of the method is tested by practical application.The results show that there is a critical value of water saturation in low permeability gas reservoirs to accelerate the decline of gas-phase permeability,and the critical value decreases with the decrease of core permeability.In the process of gas reservoir depletion development,the gas-water two-phase seepage capacity decreases with the decrease of formation pressure.The established dynamic productivity evaluation method of gas-water two-phase seepage has good field application effect,which has important guiding significance for productivity evaluation and dynamic prediction of low permeability gas reservoirs.