Abstract: Petroleum exploration technologies are constantly evloving towards deep and complex formations. In response to the gas kick that is prone to occur during the drilling process of deep and complex oil and gas reservoirs, the key for well control is to accurately and quickly invert the formation pressure at the time of gas kick, allow the bottom hole pressure to quickly return to the safety window, and suppress the influx of gas from the formation to the wellbore. In traditional drilling processes, most of the formation pressure inversion during gas kick relies on the well shut-in pressure recovery curve, but it is highly time-consuming and less timely to obtain formation pressure during well shut-in. For this reason, a method is proposed to invert formation pressure under back-pressure stimulation without well shut-in. Firstly, a simplified two-phase flow model was established to simulate the gas-liquid two-phase flow behavior in the annulus. The comparison with the OLGA multiphase flow simulator shows that the simplified two-phase flow model has high computational accuracy and can be used to provide real-time annulus data required for formation pressure inversion algorithms. Secondly, considering the relationship between the volume of each component during gas kick, a formation pressure inversion formula was derived by use of the reservoir model. This method requires applying back-pressure at the wellhead to stimulate the changes in gas kick response parameters (bottom hole pressure and outlet flow rate). The formation pressure is reversed using the ground measurement data obtained from the managed pressure drilling system after back-pressure stimulation and the annular data calculated by the simplified two-phase flow model. The results of simulation experiment show that the back-pressure excitation method provides higher inversion accuracy when compared with the recursive least squares algorithm. Finally, taking into consideration errors in drilling fluid density and outlet flow rate, a robustness analysis was conducted on the back-pressure excitation algorithm. The experimental results show that despite of the errors in drilling fluid density and outlet flow rate, the back-pressure excitation algorithm still presents accurate inversion results and good robustness.

Key words: gas kick, formation pressure inversion, reservoir model, managed pressure drilling, two-phase flow model

摘要： 随着石油勘探技术不断向深层复杂地层发展,深层复杂油气藏钻探过程中易发生气侵现象,准确、快速地反演出气侵发生时的地层压力,使井底压力快速回到安全窗口内,抑制更多气体从地层流入井筒是井控的关键。传统钻井过程中,大多数气侵发生时的地层压力反演依靠关井压力恢复曲线得到,但关井求取地层压力需耗费大量时间,时效性差,基于此提出了一种无需关井的回压激励下地层压力反演方法。首先,建立简化两相流模型模拟环空内气液两相流动行为,通过与OLGA多相流模拟器对比,验证了简化两相流模型具备较高的计算精度,可用于提供地层压力反演算法所需的实时环空数据;其次,考虑到气侵过程中各组分体积关系,结合油藏模型,推导出地层压力反演公式,该方法需要在井口处施加回压激励气侵响应参数(井底压力、出口流量等)的变化,利用回压激励后控压钻井系统获得的地面测量数据和简化两相流模型计算的环空数据,反演出地层压力。仿真实验结果表明,回压激励法与递推最小二乘算法相比反演精度更高;最后,考虑钻井液密度、出口流量存在误差的情况,对回压激励算法进行鲁棒性分析。实验结果表明,钻井液密度、出口流量存在误差时,回压激励算法的反演结果仍准确,算法的鲁棒性好。

关键词: 气侵, 地层压力反演, 油藏模型, 控压钻井, 两相流模型