深井超深井井筒多相瞬态流动模型及压力演变规律研究

With the exploration and development of deep oil and gas reservoirs, a growing number of deep and ultra-deep well has been drilled int the world. Deep well and ultra-deep drilling is faced with many challenges because of its complicated geological conditions. Wellbore pressure control is one of the bottlenecks that restrict the safety of drilling in deep and ultra-deep Wells. This research project focuses on the study of multi-phase transient flow model and dynamic variations of wellbore pressure in deep and ultra-deep wells. Firstly, the mechanism of gravity displacement will be revealed based on the experiment and numerical simulation, and then the formation-wellbore coupling flow model will be also established. On this basis, based on the drift model, a mathematical model for simulating the wellbore multi-phase transient flow behaviors in deep and ultra-deep wells will be established. The model takes into account the formation-wellbore coupling flow in the case of gravity displacement blowout and gas kick and the density and effective viscosity of drilling fluid behaviors under high-temperature and high-pressure. Experiments will be carried out to verify the model. Besides, the numerical simulation will be carried out based on the mathematical model to investigate the multi-phase transient flow and dynamic variations of wellbore pressure under complicated conditions such as gravity displacement and gas kick in deep and ultra-deep well drilling. This research can provide the core theoretical support for wellbore pressure control in deep and ultra-deep well drilling.

随着深部油气资源的勘探开发，深井超深井的数量大幅增加。深井超深井钻井工程地质条件复杂，钻井工程面临诸多挑战。井筒压力控制问题是制约深井超深井钻井安全的瓶颈难题之一。本项目围绕深井超深井井筒多相瞬态流动模型及压力演变问题开展研究。首先，基于实验和数值仿真揭示重力置换式漏喷同存发生的机理，建立地层-井筒耦合流动模型。然后，在此基础上，基于漂移模型建立深井超深井钻井井筒多相瞬态流动模型，模型考虑重力置换、气侵情况下的地层-井筒耦合流动及高温高压钻井液密度及流动性动态变化，并开展实验完成模型验证和修正完善。最后，基于数学模型开展数值仿真，研究深井超深井钻井重力置换、气侵等复杂工况下井筒多相瞬态流动及压力演变规律。开展此项研究，能够为深井超深井钻井的井筒压力控制提供核心的理论支撑。

随着深部油气资源的勘探开发，深井超深井的数量大幅增加，目前我国陆地钻井最深井已达到9026米，刷新亚洲最深直井记录。深井超深井钻井工程地质条件复杂，钻井工程面临诸多挑战，特别是钻遇裂缝性地层时易发生气侵、重力置换等井下复杂，井控风险大。井筒压力控制问题是制约深井超深井钻井安全的瓶颈难题之一。本项目围绕深井超深井井筒多相瞬态流动模型及压力演变问题开展研究。首先，基于系统的室内实验和基于井下高温高压环境的数值仿真研究揭示了重力置换式漏喷同存发生的机理和主控因素，研究发现，气液两相存在显著的密度差和裂缝提供了大尺度的流动空间是重力置换发生的主要机理，重力置换主要受裂缝宽度、井底压差、钻井液密度、地层压力等因素控制，并根据大量的实验数据和数模结果归纳出了框架性规律，进一步建立了实用化的地层-井筒耦合流动模型，形成了模型关键参数的获取方法。然后，基于漂移模型建立深井超深井钻井井筒多相瞬态流动模型，并形成了高精度的数值求解算法与程序，模型考虑重力置换、气侵情况下的地层-井筒耦合流动及高温高压钻井液密度及流动性动态变化，并开展实验完成模型验证，瞬态流动模拟误差＜±10%。最后，基于数学模型开展数值仿真，研究深井超深井钻井重力置换、气侵等复杂工况下井筒多相瞬态流动及压力演变规律。研究表明，单股气侵时，井筒内气塞上部液体流量会随着气体上升而增大，井口出气的时间长于于井底产气的时间，井底压力在环空气体完全排出后逐渐恢复至出气前状态；连续气侵时，随着气体不断进入环空并向井口运移井底压力逐渐降低，当气体靠近井口时井底压力快速降低，随后缓慢趋于稳定，套压则在气体到达井口后急剧上升随后逐渐恢复稳定，井底处于一个稳定的状态，若不科学控压，气侵现象不会缓解；重力置换发生时，井筒两相流参数变化与纯气侵过程相似，但井筒流动规律更加复杂。本研究取得的成果具有重要理论价值，可为深井超深井钻井井筒压力控制提供核心理论支撑。