致密气藏压裂水平井气水两相产能求解新方法

A NEW SOLUTION FOR GAS-WATER TWO-PHASE PRODUCTIVITY OF FRACTURED HORIZONTAL WELLS IN TIGHT GAS RESERVOIRS

致密气藏由于其裂缝发育程度不好,地层渗透率过低等原因,通常采用水平井钻井并结合压裂增产技术对其进行开采。调研发现,在此类气藏中,一般存在储层应力效应,启动压力现象,甚至出现气水两相流动;目前对该类气藏的气水两相流动产能求解模型还较少。基于常规裸眼完井压裂水平井模型,同时考虑应力敏感,启动压力梯度以及裂缝间的干扰,引入新型气水两相拟压力的定义,并运用势的叠加原理和等值渗流阻力法,推导了致密气藏压裂水平井气水两相稳态产能模型,为非常规气藏气水两相流动的产能求解提供了新的方法。通过实例分析,随着渗透率模量和裂缝渗流率的增加,气井产能逐渐增加;随着水气体积比的增大,产能则逐渐降低;启动压力梯度则对产能的影响并不十分明显。因此,在低渗透致密气藏的开发过程中,需要着重对裂缝的参数进行优化,减小地层中因气水两相流动对产能造成的影响,以便达到更好的开发效果。

Due to poor fracture development and low permeability, most tight gas reservoirs are usually exploited by horizontal drilling combined with fracturing stimulation. Research shows that, in these reservoirs, there exists generally stress effect, starting pressure, and even gas-water two-phase flow. At present, reports about the productivity solution model for gas-water two-phase flow are very seldom. Based on a conventional fractured horizontal well model of open-hole completion, considering the stress sensitivity, starting pressure gradient, and mutual interference among fractures, we define the gas-water two-phase pseudo pressure. And through the superposition principle of potential and the law of equivalent percolation resistance, a gas-water two-phase steady-state productivity model is derived, which provides a new method for productivity solution.Case study indicates that(1)productivity increases gradually with increasing permeability modulus and fracture percolation rate;(2)productivity decreases with an increase of water-gas volume ratio; and(3)starting pressure gradient has no obvious effect on productivity. Therefore, during a development of tight gas reservoirs, it is necessary to optimize fracture parameters to reduce the impact of gas-water two-phase flow on productivity.