密闭环空热膨胀压力全尺寸模拟实验

为了验证多层密闭环空热膨胀压力预测模型的准确性和适用性,更深入地探究油气井筒传热与环空压力之间的关系,有必要开展全尺寸环空压力模拟实验研究.通过设计符合油气井身结构特点和现场工况的双环空井段实验装置,模拟高温热流体在不同循环温度、循环流量和循环时间的条件下对密闭环空温度和压力造成的影响,分析实验中环空压力随温度增量的变化关系,验证理论模型结果的适用性.结果表明:双环空升温阶段,A环空比B环空升温增压速率更快,温度压力峰值更高;由于环空流体中含有部分无法消除的可压缩溶解气体,导致环空压力上涨幅比环空温度要小;提出环空压温比的概念来评估环空流体产生压力的能力大小,其中纯水受热膨胀产生的环空压温比最高,自然散热前期环空压温比更能反映流体产生热膨胀压力大小;实验测试数据与模型计算结果偏差均在10％以内,满足理论和现场实际需求.可见在实际计算中应该参考实验数据,考虑环空流体特性和气体压缩性质,提高预测精度.

Research on full-scale simulation experiment of trapped annular thermal expansion pressure

In order to verify the accuracy and applicability of the prediction model of multilayer trapped annular thermal expansion pressure, and to further explore the relationship between heat transfer and annular pressure in oil and gas wellbore, it is necessary to carry out the full-size simulation experiment study of annular pressure. The double-layer annulus section experiment device, which conforms to the structure characteristics of oil and gas well and field working conditions, is designed to simulate the influence of high temperature fluid on the temperature and pressure of trapped annulus under the conditions of different circulating temperature, circulating flow rate and circulating time, and the relationship between thermal expansion pressure and temperature increment is analyzed to verify the theoretical model results. The results show that the rate of heating and pressurization in A annulus is faster than that in B annulus and the peak temperature pressure in A annulus is higher in the heating stage of double-layer annulus. The annulus pressure rise is less than the annulus temperature because the annulus fluid contains part of the compressible dissolved gas which cannot be eliminated. The concept of pressure/temperature ratio was introduced to evaluate the pressure generation capacity of annular fluid, of which the annular pressure/temperature ratio generated by pure water heated expansion was the highest, and the annular pressure/temperature ratio in the early stage of natural heat dissipation could better reflect the thermal expansion pressure generated by the fluid. The deviation between experimental test data and model calculation results is less than 10%, which meets the theoretical and practical requirements. It is concluded that the experimental data should be referred and the annular fluid characteristics and gas compression properties should be considered in the actual calculation to improve the prediction accuracy.