气层厚度对井底压力的影响分析

Analyzing the Effect of Gas Layer Thickness on Bottom Hole Pressure

摘要: 在气井的钻井过程中，井底压力的变化对井控风险的影响是很大的。但目前在分析影响气层井筒井底压力变化的因素时，未考虑气层厚度对井底压力的影响。基于质量守恒和动量守恒定理，针对井筒气侵后的实际情况，首先建立了气侵后井底压力的计算模型，然后联合分相流方程，运用有限差分的方法，以工程实例数据为基础，讨论了打开气层厚度对井底压力的影响规律。分析结果表明，随着钻遇气层厚度的增大，井底压力稳定值较大，井底压差也愈大，最终导致井控难度加大，建议采用合理的手段尽早侦测气侵情况，采取措施能够减少地层气体的侵入量，达到安全井控的目的。该研究是对气侵、井底压力变化规律认识的完善，对现场实际井控安全操作策略的制定具有重要指导意义。

Abstract: In the process of drilling of gas wells, the change of bottom hole pressure has great influence on well control. However, the influence of gas layer thickness on the bottom hole pressure was not considered currently in analyzing the factors influencing the changes of bottom hole pressure. Based on mass conservation and principle of conservation of momentum, the mathematical model of bottom pressure after invading was established. And then based on the engineering case, com-bined with the phase separation equations, the finite difference method is used to discuss the in-fluential rules of gas layer thickness on the bottom hole pressure. The result shows that the bottom hole differential pressure and the stable value of B.H.P. increases while the thickness of drilling gas formation is large, which can increase the difficulty of well control. The suggestion is that rational measurement is used for early control of gas invasion to reduce the gas invasion and safe well control. The study is the completion to the understanding of gas invasion and regulation of the changes of bottom hole pressure, it provides guidance for setting up the strategy of well control.