改进的低渗透底水气藏压裂井见水时间预测公式

A modified prediction equation of water breakthrough time for fractured wells in low permeability gas reservoirs with bottom water

低渗透底水气藏中的气井在实际生产中需通过压裂改造获得工业产能,预测压裂井见水时间对合理开发该类气藏具有重要指导意义。针对低渗透底水气藏压裂井的渗流特征,将渗流场划分为射孔段及其下部两个部分,以稳态渗流理论为基础,分别建立了符合各区渗流状态的产能方程,结合水锥顶点的运动方程建立了低渗透底水气藏压裂井见水时间预测公式。实例计算表明,压裂井能显著延缓气井见水时间,利用本方法计算的见水时间更接近实际。敏感性分析表明,随气藏打开程度增加,气井见水时间先增大后减小;增大裂缝半长及裂缝导流能力都将延缓气井见水,但增加幅度逐渐降低,存在最优值。

Jeopardized by poor reservoir properties, gas wells in low permeability reservoirs with bottom water should be fractured in order to acquire industrial capacities. Therefore, a modified equation for predicting well＇s water breakthrough time is studied for effectively developing low permeability gas reservoirs with bottom water. Based on the characteristics of seepage flow in fractured wells, the seepage field is divided into two parts, the perforation interval and its lower section. With the aid of steady state seepage theory, productivity equations for all fields are derived respectively. Eventually, a modified prediction equation is established by means of utilizing the motion equation of water cone apex. Case study shows that fracturing will postpone the process of water breakthrough and the time calculated by this article has less error as compared with the value gained by practical production data. The analysis on sensitive factors reveals that each parameter has its optimal value. With the increase of perforation degree, water breakthrough time will increase at first and then decrease. And the larger the fracture half-length and conductivity are, the longer the water breakthrough time will be. However, the increasing rates tend to be reduced gradually.