基于渗流-温度双场耦合的油藏型储气库数值模拟

Numerical simulation of UGS facilities rebuilt from oil reservoirs based on the coupling of seepage and temperature fields

调峰保供是储气库的职能,建库指标的精确预测,事关新钻井数量和投资。复杂断块油藏改建储气库后,多周期高速注采过程均为油气水三相流动,油、气高压物性参数受温度影响极大,在进行复杂断块油藏型储气库数值模拟时,若忽略冷气注入温度场扰动和高速非达西附加压力损失,可能会导致储气库数值模拟指标预测精度降低。为提高指标预测精度,以复杂断块油藏型储气库为例,结合流体黏温及高速非达西实验,建立了渗流-温度双场耦合数学模型。基于有限体积法(FVM),在空间上采用两点通量近似方案(TPFA),在时间上采用后向(隐式)欧拉格式对模型进行离散求解。高精度拟合了衰竭开发阶段区块、单井物质平衡及压力,实例开展了储气库运行指标敏感性分析。结果表明:冷气注入温度场扰动、高速非达西效应分别是累产油、气量误差的主控因素;井控温度范围随注气速度增加呈对数上升,油气相渗流能力大幅下降时水相渗流能力反而上升,使得采出液量增多、地层压力下降;高速非达西附加压降造成天然气注入后部分采不出,随着储气库多周期运行,天然气储量及压力逐渐增加。

Peak shaving and supply guarantee are the functions of Underground Gas Storage(UGS).The accurate prediction of the UGS construction index is related to the number of new wells and investments.When a complex fault block reservoir is transformed into UGS,it encounters three-phase flow(oil,gas,and water)during multi-cycle and high-velocity operations.The petrophysical properties of oil and gas are greatly affected by temperature.Without considering the temperature disturbance after cold gas injection and the additional pressure loss of high-velocity turbulence,the index prediction accuracy of the existing numerical simulation methods for UGS is low.To improve the accuracy of index prediction for a UGS rebuilt from a complex fault block oil reservoir,combined with fluid viscosity-temperature and high-velocity turbulence experiments,a coupled mathematical model of seepage and temperature is established.The model is solved discretely using the Finite Volume Method(FVM),with a Two-Point Flux Approximation(TPFA)scheme for spatial discretization and a backward(implicit)Euler scheme for temporal discretization.The material balance and pressure of the reservoir and single well in the depletion development stage are matched with high precision.The sensitivity analysis of the UGS operation index is carried out in an example.The results show that the disturbance of the cold gas injection temperature field and high-velocity non-Darcy effect is the main controlling factors of accumulative oil production and gas volume error respectively.The well control temperature range increases logarithmically with the gas injection rate and the water-phase seepage capacity increases when the oil-phase and gas-phase seepage capacity decreases significantly,resulting in the increase of the produced liquid volume and the decrease of formation pressure.The additional pressure drop caused by high-velocity turbulent flow results in some injected natural gas not being produced,leading to an increase in natural gas reserves and pressure over successive cycles.