考虑储层与井筒特征的高温高压水平井溢流风险评价

Assessment of gas kick risk for high temperature and high pressure horizontal wells considering reservoir and wellbore characteristics

关键词:  水平井  气侵  储层特征  井筒环空多相流  溢流风险评价

Key words:  horizontal well  gas kick  reservoir characteristics  multiphase flow in wellbore annulus  overflow risk assessment

摘要:

考虑气体物性的影响,优选适用于高温高压水平井的气侵模型,分析储层渗透率、裸眼段长度、负压差等储层参数对气侵量的影响。基于建立的井筒环空瞬态多相流动模型,研究高温高压水平井溢流期间的含气率、泥浆池增量、井底压力的变化规律。基于此,评价储层渗透率、水平段长度、负压差对溢流风险的影响,与直井溢流风险进行对比分析。基于模拟结果发现:储层渗透率较低(小于2×10-3 μm²)、负压差较低(小于2 MPa)、水平段长度较小(小于10 m)、钻进储层厚度较小(小于5 m)时,气侵速度小,井底压力及溢流体积变化小,溢流风险小,不易发生井喷;相同条件下,直井溢流风险要高于水平井;在长水平段、厚度大、渗透率大的情况下,溢流风险较大,需优化配置钻井液密度、及时监测钻井状态才能显著降低目标井溢流井喷事故风险,为安全、经济、高效的开发高温高压油气藏提供理论依据。

Abstract:

In order to evaluate the gas kick risk of high temperature and high pressure horizontal wells, a gas intrusion model suitable for high temperature and high pressure horizontal wells was proposed, and the influences of various fluid and reservoir parameters were considered, such as gas property, reservoir permeability, open hole length and negative pressure difference. And then based on an established transient multiphase flow model in wellbore annulus, gas void fraction, mud pit gain level and bottom hole pressure during a gas kick in high temperature and high pressure horizontal well can be obtained. The effects of reservoir permeability, horizontal section length and negative pressure difference on the gas kick risk were evaluated, and compared with the overflow in vertical well. The simulation results indicate that, in the cases with low reservoir permeability (<2×10-3 μm²), low negative pressure difference (<2 MPa), short horizontal section length (<10 m) and thin reservoir thickness (<5 m), the variations of the bottomhole pressure and pit gain level is very small during a gas kick, so the overflow or blowout risk is small. Under the same conditions, the overflow risk of a vertical well is higher than that of the horizontal wells. In the case of long horizontal section, large thickness and high permeability, the risk of overflow becomes large. It is necessary to optimize the density of drilling fluids and timely monitor the drilling status, so as to significantly reduce the risk of gas kick and blowout in order to maintain a safe, economical and efficient drilling process.