泡沫欠平衡钻井气液流量组合优选研究

Research on gas-liquid flow rate optimization in foam underbalanced drilling

泡沫欠平衡钻井过程中,气体、液体和固相岩屑混合在一起,沿井筒环空向上流动,属于典型的"气-液-固"多相流。为了保护储层,避免发生井壁失稳坍塌事故,在泡沫欠平衡钻井时,必须保证井底压力小于地层压力并高于地层坍塌压力,同时还要保证整个井段泡沫钻井液处于最佳泡沫质量区,以具有足够的携岩能力。针对工程施工实际情况,对井筒环空进行网格划分,利用欠平衡钻井井筒多相流模型分段求解井筒流态和流动压力,综合分析井底压力与注入气液流量组合的对应关系,从而将井底压力安全窗口转化为可直接控制的气液流量安全窗口,为安全施工提供依据。该研究成果在也门某区块泡沫欠平衡钻井中的钻井实效对比分析表明,该方法较为实用可靠。

In the process of foam underbalanced drilling, the mixture of gas, liquid and cuttings flows upwards through the annular, so it is a typical gas - liquid - solid multiphase flow. In order to protect the reservoir and avoid borehole wall collapsing during foam drilling, it is crucial to ensure that the bottom hole pressure is lower than the formation pressure and higher than the formation collapse pressure;in the mean time, foam drilling fluid in the whole wellbore should be in the best foam quality stage to have sufficient cutting -carrying capacity. In this paper, main relations between bottom hole pressure and gasliquid injection rate are analysed with the underbalanced multiphase flow models. In order to obtain precise flow pattern and flow pressure, the whole well bore is spatial meshed and 4terative method is used. So, a convenient safety window expressed by gas - liquid injection rate is obtained instead of that by bottom hole pressure. Finally, a foam drilling example from a block in Yemen is presented; the drilling results show that this method is reliable and practical.