通过分析深水钻井气侵特点和现有气侵监测方法的不足,论证了在隔水管底部进行气侵早期监测的可行性,提出了基于隔水管底部超声波气侵监测的气侵程度实时定量描述方法。分析了多普勒超声波监测气侵方法存在的问题,设计了隔水管底部透射式超声波气侵监测实验装置,用于分析不同截面含气率条件下的声波衰减特性,给出了运用超声波监测隔水管处气侵情况的解决方案。结合深水钻井井筒环空气液两相流计算模型和含可信度的地层压力预测,建立了基于隔水管底部截面气侵监测数据的井筒气侵程度反算方法。该方法与常规方法相比可提前4min左右检测到气侵,并可根据隔水管底部声波响应数据准确确定气侵发生的时刻、气体到达井口所需时间、任一时刻的总溢流量及任一时刻不同井深处的截面含气率。
Through the analysis of gas-cut features in deepwater drilling and shortages of existing gas-cut detection methods, the feasibility of early detection of gas cut at the bottom of riser was demonstrated, and a method was proposed for quantitative description of gas-cut degree in deepwater drilling based on ultrasonic monitoring at the bottom of riser. The problems of Doppler ultrasound gas-cut detection method was analyzed and the experimental device of gas-cut monitoring at the bottom of riser based on the ultrasonic transmission was built, which was used to analyze the sound attenuation characteristics under different conditions of void fraction. The solutions for using ultrasound to monitor gas-cut situation at the bottom of riser was proposed. Combined with the gas-liquid two-phase model of wellbore annulus in deepwater drilling and the formation pressure prediction method with credibility, the inverse calculation method of gas-cut degree in wellbore was established, which was based on the monitoring data of gas cut at the bottom section of riser. This method could detect the gas cut about four minutes in advance compared with conventional methods, and the gas cut occurring moment, the time left for gas to reach the wellhead, the total overflow rate at any moment, and the void fraction in different depth could be accurately determined based on the acoustic response data of the bottom of riser.