致密气藏边界流晚期定流压产量递减模型研究

Research of Production Decline Model Dominated by Late-boundary Flow for Tight Gas Reservoir Under a Constant Flowing Pressure

开展定容性致密气藏边界流晚期产量递减模型研究,为致密气藏动态分析及指标预测提供理论依据。依托致密气藏渗流机理实验,在致密气藏渗流微分方程描述的基础上,以定容致密气藏边界流晚期拟稳态由定产的生产方式转为定流压生产方式为研究对象,结合物质平衡方程,建立定容致密气藏边界流晚期产量递减微分方程,并推导求解产量递减模型。研究结果表明:(1)与常规气藏相比,致密气藏非达西流压力损耗由3部分组成,为流体内摩擦力、启动压力和紊流效应的消耗,其中,启动压力也是造成二项式产能方程异常的重要原因;(2)因为紊流效应及启动压力的存在,定容致密气藏边界流晚期,时间-产量关系不再遵循Arps递减模型,启动压力梯度和紊流效应对气井产量递减具有减缓作用,当紊流系数和启动压力梯度趋于0时,再以拟平衡时间为时间轴的产量-时间递减曲线遵循指数递减模型;(3)实例分析表明,引入启动压力项可有效消除二项式产能方程异常现象,新模型可以实现气井动态储量、启动压力梯度等地层参数的计算。基于渗流机理的新模型的建立,为致密气藏二项式产能方程异常处理、产量递减主控因素特征提取、地层参数反演以及动态指标求取奠定了理论支撑,具有较强的实用性和前瞻性。

To study production decline model dominated by late-boundary flow for constant volume tight gas reservoir,and to provide a theoretical basis for gas reservoir performance analysis and index prediction.Based on experimental results of seepage mechanism for tight gas reservoir,after analyzing and establishing the seepage differential equation of tight gas reservoir,focusing on the late stage of boundary flow of constant volume tight gas reservoir,combined with material balance equation,a new equation and its differential equation were both proposed for the gas production vs time,and based on which,the quantitative model of initial decline rate and geological factors was determined.The results show that:(1)compared with conventional gas reservoirs,the non-Darcy flow pressure loss in tight gas reservoirs consists of three parts,which are derived from fluid internal friction,turbulence effect and start-up pressure,which is also an important reason for the anomaly of binomial productivity equation.(2)Because of turbulence effect and start-up pressure,Arps′s decline model was not followed for gas wells of constant volume tight gas reservoir,and the existence of start-up pressure gradient and the turbulence effect slows down the production decline rate of gas wells,and the gas well production decline model follows exponential decline,only when the turbulence coefficient tends to 0,without start-up pressure gradient,and the pseudo time is used instead of time.(3)The example shows that the binomial productivity anomaly can be effectively eliminated by introducing the start-up pressure term,and the reservoir parameters such as gas well dynamic reserves and start-up pressure gradient can be calculated by using the new model,which lays a theoretical foundation for the analysis of main controlling factors of production decline,formation parameter inversion and dynamic index calculation of constant volume tight gas reservoir,abnormal treatment of binomial equation in tight gas reservoir included,so it has strong practicability and foresight.