深水油基钻井液钻井溢流压井期间井筒环空非稳态多相流动规律研究

The probability of drilling abnormal high pressure reservoir is big when the oil and gas exploration area move to deep or ultradeep water, leading to the inevitable gas kick. So the early detection is very important. However the detection methods in deepwater drilling based on oil-based mud are different from the methods on the land or shallow water due to the complicated phase behavior of the oil-based mud, which has been widely used in the deepwater drilling. Understanding multiphase flow in wellbore annuli during gas kick in deepwater drilling based on oil-based mud clearly is necessary and of great significance for preventing the gas kick and blow out. Based on the gas and oil-based mud two phase flow experiment, the flow pattern transitions are obtained, the prediction models of gas void fraction and pressure drop for each flow pattern are established. Then the gas and oil-based mud two phase flow are studied. Based on this, the dissolution and precipitation of gas and oil-based mud are researched. Then the phase behavior of oil-based mud, the variation of transient temperature during gas kick are studied, and the unsteady state multiphase flow model in wellbore annuli considering the effect of phase transition are established. The solving method and verification is given. Based on this, the effect of well type, reservoir parameter and the size of choke line are researched. Then the variation of pit gain, well bottom hole pressure, gas void fraction, shut-in pressure and choke pressure are obtained. Then the occurrence, evolution mechanism of gas kick during deepwater drilling will be clearly understand. The theoretical guidance will be given for the early detection of gas kick, the optimization of well kill method and the design of well control parameters.

深水油气开发钻遇异常高压油气层的机率较大，溢流不可避免，对其监测十分重要。油基钻井液已广泛应用于深水钻井，由于其复杂的相态特征，使得溢流早期识别与陆上及浅水有较大差异。清楚掌握深水油基钻井液溢流规律对于防止溢流及井喷至关重要。本项目通过进行油基钻井液—气体两相流动实验，研究流型间过渡准则，建立相应流型下的含气率及压降预测模型，得到油基钻井液—气体两相流动规律。基于此，研究油基钻井液中气体的溶解、析出规律，得到气侵后油基钻井液的相态特征。研究环空流体非稳态传热机理，建立考虑油气相变的深水井筒环空油基钻井液非稳态多相流动模型，给出求解方法并进行验证。基于此，分析井型、储层参数、节流管线尺寸等参数的影响，得到泥浆池增量、井底压力、含气率、关井压力及节流压力等井控参数的变化规律，使人们对深水井溢流的发生演变的机理及过程有一个清楚的认识，为深水井溢流早期监测、压井方式的优选及参数设计提供理论指导。

深水油气藏已经成为油气勘探的热点，钻遇异常高压油气层的机会也就越来越大，溢流不可避免。而深水油基钻井液钻井溢流规律与陆上有较大区别，侵入气体在一定条件下可能全溶解于油基钻井液中，井筒为液相；随着压力、温度的降低，又会析出，形成游离气，出现气液两相。油基钻井液复杂的相态特征，不利于溢流的早期监测。因此，研究深水油基钻井液溢流压井期间井筒多相流动规律问题很有必要，对于实现我国深海油气勘探开发技术的跨越式发展，具有重要意义。.本课题首先研究了环空气液两相流动的特性，然后以液膜区域为控制单元，研究了钻杆膜、套管膜及气芯区域存在液滴对质量、动量传递的影响，建立了适合于直井、斜井的环空段塞流水动力学模型，得到了段塞流向分散泡状流、泡状流及环状流的流型过渡评价准则。并与前人气-煤油两相流实验结果进行了对比，持液率及压降梯度预测误差在±15%以内，较好的描述了段塞流及泡状流情况下的水动力性质，可以应用于溢流情况下的环空多相流动规律研究。其次研究了深水钻井钻进期间井筒传热的形式，分析了流型对水动力参数的影响、钻杆膜及套管膜对传热的影响，建立了环空段塞流、环状流及泡状流流型下的环空流体温度计算模型。在此基础上，建立了环空气液两相瞬态传热模型，较为真实的反映了溢流后井筒内流体温度的实际变化过程，为井筒流体相态特征研究及多相流动计算提供相对准确的温度分布数据。.再次研究了甲烷与油基钻井液混合流体相态变化特征，考虑了温度、压力的影响，得到了溢流后井筒环空中的相态变化特征，即井筒环空不脱气、井筒环空部分脱气及井筒环空全脱气三种情况。最后基于环空气液两相流理论及闪蒸理论，考虑了井筒环空相态变化的影响、环空结构对流动参数的影响及流型对传热的影响，建立了油基钻井液钻井溢流期间井筒环空多相流动模型。通过模型求解，得到了相态变化对环空流体温度及压力的影响，得到了泥浆池液面、井底压力、含气率随溢流时间的变化规律，为深水油基钻井液钻井溢流早期监测及压井参数设计提供了理论依据。