基于井筒-地层置换效应的页岩油钻井环空流体温度分布

Distribution of annular fluid temperature due to fluid displacement between wellbore and formation during shale oil drilling

为了准确掌握井筒钻井液与地层页岩油置换条件下的环空流体温度分布规律,基于流体流动与传热理论,充分考虑置换后环空混合流体流动方式和热物性参数的变化,建立页岩油钻井环空流体温度分布预测模型,探究置换条件下环空流体温度分布规律,并分析置换位置、置换流体类型、置换速率对环空流体温度的影响规律。结果表明:置换条件下的环空流体温度高于正常循环条件下的温度;置换发生在井底时,环空流体温度分布曲线无明显拐点,而置换发生在非井底时,曲线存在明显拐点,且拐点位置与置换点位置一致;与低比热容的地层页岩油相比,高比热容的地层水与井筒钻井液发生置换时环空流体温度更高;当地层页岩油侵入速率大于井筒钻井液漏失速率时,置换速率越大,置换后的环空流体温度越高,反之越低。

The temperature distribution of annular fluid during shale oil drilling with oil-based drilling fluid can be affected by the fluid displacement condition between wellbore and near-wellbore rock formation.In this study,a prediction model of the annular fluid temperature distribution in shale oil wells was established based on fluid flow and heat transfer theory.The influence of the fluid displacement on the flow mode of the annular mixed fluid and the thermal physical parameters of the fluid were considered in the model.Based on the model,the annular fluid temperature distribution under different displacement conditions was investigated.In addition,the influence of the displacement location,fluid type,displacement flow rate on the annular fluid temperature were analyzed.The results show that,when fluid displacement occurs,the fluid temperature in the annulus is higher than that under the normal drilling fluid circulation condition.If the fluid displacement occurs at the bottom of the well,there will be no obvious inflection point on the annular fluid temperature distribution curve.While the displacement occurs at other locations,there will be an obvious inflection point on the curve,and the location of the inflection point on the temperature disdribution curve is well corresponded to the displacement occurrence location.Furthermore,compared with shale oil with low specific heat,the annular fluid temperature will be higher when drilling fluid is displaced by formation water with high specific heat.In addition,when the intrusion rate of the formation fluids is greater than the leakage rate of the drilling fluid in wellbore,the higher the displacement rate,the higher the annulus fluid temperature.