考虑应力敏感的致密气多级压裂水平井试井分析

根据致密气藏应力敏感实验数据和试井理论,建立了渗透率随有效应力呈幂律形式变化的多级压裂水平井三维数值试井模型。采用混合单元有限元方法对模型进行求解,得到了不同应力敏感条件下的试井理论曲线。研究了应力敏感不可逆性对试井曲线特征的影响,以及应力敏感系数、开关井次数及产量大小等因素对测试曲线形态的影响。研究结果表明,应力敏感不可逆性会造成储层渗透率的永久性伤害,应力敏感系数越大、开关井次数越多、产量越大对储层渗透率的伤害越大,其试井双对数曲线表现为压力及压力导数曲线上升,全历史压力曲线表现为压力下降幅度随开关井次数增加而增加。存在多次开关井的致密储层试井资料实例解释结果表明,若忽略应力敏感不可逆性的影响,会造成解释得到的原始储层渗透率偏小且全历史压力曲线后期很难拟合。

Well test analysis for multistage fractured horizontal wells in tight gas reservoir considering stress sensitivity

Based on the stress-sensitive experimental data and well test theory of tight gas reservoirs, this study establishes a three-dimensional numerical well test model for multistage fractured horizontal wells, in which the permeability varies with effective stress in a power law model. Well test log-log type curves under different stress-sensitive conditions are obtained using the finite element method with hybrid elements for model solution. The influences of stress sensitive irreversibility on the characteristics of well test curves are studied as well as the effects of other factors, such as stress sensitivity coefficient, opening and closing times and flow rate on the test curve morphology. The results show that the irreversibility of stress sensitivity can cause permanent damages to formation permeability. The greater the stress sensitivity coefficient is, the more the opening and closing times are, the larger the flow rate is, the more damages to formation permeability will occur. The well test log-log type curve is manifested as a rising pressure and pressure derivative curve, respectively. The full-history pressure curve shows a pressure drop amplitude upgraded with the increase of opening and closing times. For wells in tight reservoir after multiple closing and opening, the test data interpretation results indicate that if the influence of stress-sensitive irreversibility is neglected, the permeability of original formation is small, difficult to match the full-history pressure curve.