深井井筒-地层传热传质环境下井筒温度压力时变特性研究

One of the most key problems for deep oil and gas exploration and development is narrow safety window of formation which likely leads to mass and heat transfers between wellbore and formation under the bottom hole pressure fluctuations conditions, thus resulted in the occurrence of complicated problems in down-hole. Nowadays, great attentions are focused on studying the law of wellbore pressure evolution under mass exchange condition for deep well. However, when drilling is applied to deep well or high geothermal gradient formation, the change of down-hole temperature generated by mass exchange between wellbore and formation has an important effect on wellbore fluid rheological properties, pressure profile, mass exchange capacity, which should be deep studied. Therefore, the transient heat transfer models during circulation and shut-in stages are developed under different mass exchange conditions by analyzing the heat transfer mechanism between wellbore and formation among control volumes. Meanwhile, the coupled flow model and computation model of wellbore multiphase flow are also established under the heat-mass transfer of wellbore and formation conditions by studying the law of wellbore fluid flow characteristic and pressure evolution, followed by solving the model by using the fully implicit finite difference method. Furthermore, combining with experimental and field data, the models are modified to accurately obtain the evolvement law of temperature and pressure of wellbore, which can not only further improve the wellbore multiphase flow theory system, but also facilitate the theory and technology development of deep well drilling.

深层油气资源勘探开发面临的关键难题之一为“窄安全窗口”地层在井底压力波动下易造成井筒-地层间发生质量与热量交换，导致井下复杂情况频繁发生。目前学术技术界较多关注于深井质量交换条件下井筒压力演变规律研究，但对于深井或高地温梯度地层钻井时，井筒与地层间发生质量交换所引起井下温度变化会给钻井液性能、井筒压力剖面及质量交换量等带来的重要影响仍待深入研究。为此，本项目通过分析井筒与地层各控制体之间及其内部的复杂热交换机理，建立不同质量交换条件下流体循环与停止循环期间井下瞬态传热模型；通过研究传热传质耦合条件下井筒流动特征与压力演变规律，建立井筒与地层间传热传质耦合流动模型与井筒多相流计算模型，并采用全隐式有限差分法求解；结合实验与现场实测数据修正模型，以精确获得井筒温度压力实时演变规律，完善高温深井井筒多相流理论体系，促进深井钻井理论与技术发展。

深层油气资源勘探开发面临的关键难题之一为“窄安全窗口”地层在井底压力波动下易造成井筒-地层间发生质量与热量交换，导致井下复杂情况频繁发生。精细评价井筒-地层传质传热耦合条件下温度压力演变特性对高温深井安全钻进具有重要的理论与现实意义。为此，本论文基于传热学、流体力学及渗流力学相关理论基础，并借助于大型实验台架开展了该前沿热点方向的研究，取得如下诸多重要成果与认识：1)在建模过程中，井筒-地层三维瞬态传热模型可简化为井筒一维、地层二维传热模型；2）钻进过程中溢流或漏失对井筒温度产生较大影响，溢流深度点以上，井筒温度高于原始地层温度；漏失深度点以上，井筒温度低于原始地层温度；在溢流和漏失深度点以下，井筒温度与正常钻进条件下井筒温度几乎相等；同时，流体停止循环期间对原始地层温度扰动距离大于循环期间；3）随着管底开始注气，管内压力先增大再减小；管路下部比上部先达到压力峰值，压力波动程度随着管深的增加而减小；模型数值仿真结果与实验数据吻合程度较高，误差范围在均控制在10%以内；4）气液分界面由井筒端向地层端可分为三段，迅速下降段，平缓段，下降段；流体粘度、裂缝宽度及欠压值影响着气液界面的边缘走向。本项目从理论和实验方面揭示了深井钻井过程中井筒-地层质量交换引起热量传递的内在机理，阐述了井筒温度压力可控的影响因素。深化了对井筒温度压力演变规律的认识，丰富了复杂工况钻井的水力学模型。