考虑应力敏感的致密气井压裂前后变泄气半径及产能研究

致密气井的泄气半径和产能会受到应力敏感和启动压力梯度的影响,利用边界压力梯度极限法,考虑应力敏感和启动压力梯度,建立了气井压裂前后的泄气半径及产能计算公式。通过实例验证了公式的准确性;同时分析了应力敏感、启动压力梯度、井底流压、裂缝长度对泄气半径和产能的影响。结果表明:泄气半径随井底流压、应力敏感系数、启动压力梯度的增加而降低;随裂缝长度的增加而增加,其中启动压力梯度的影响比应力敏感大。应力敏感对产能的影响大于启动压力梯度,变泄气半径下的产能随应力敏感系数的增加而降低,随裂缝长度的增加而增加;但产能变化幅度均小于定泄气半径。研究对致密气井泄气半径和产能的准确预测及提高采收率具有重要的意义。

Variable Drainage Radius and Productivity of Tight Gas Well Before and After Fracturing Considering Stress Sensitivity

The gas drainage radius and productivity of tight gas wells can be affected by stress sensitivity and threshold pressure gradient. Using pressure gradient boundary limit law, considering stress sensitivity and threshold pressure gradient, the drainage radius and productivity formulas of gas wells and fractured gas wells were established respectively. Example shows the accuracy of the formula, and the influences of stress sensitivity, threshold pressure gradient, bottom hole flowing pressure and fracture length on the gas drainage radius and productivity were analyzed. The results show that gas drainage radius decreases with increasing bottom hole flowing pressure, stress sensitivity coefficient, starting pressure gradient, and it increases with increasing fracture length. The influence of threshold pressure gradient on gas drainage radius is greater than stress sensitivity. The impact of stress sensitivity on productivity is greater than that of threshold pressure gradient. In the case of variable gas drainage radius, productivity decreases with the increase of stress sensitivity coefficient, but the reduction is less than that of a given gas drainage radius. It increases with increasing fracture length, but the increase is less than that of the predetermined drainage radius. This study has an important significance to predict the gas drainage radius and productivity of tight gas reservoirs, and to improve the recovery of tight gas reservoirs.