深水油气井非稳态测试环空压力预测模型

为了解决深水油气井测试时各环空压力上升而破坏井筒完整性的问题，针对气井测试的短期非稳态过程，建立了井筒非稳态传热模型；然后，根据流体等压膨胀系数、等温压缩系数与密度的函数关系，建立考虑流体性质非线性变化的环空压力预测模型；在此基础上，以南海西部某深水高温高压气井为例，采用所建立的模型预测了不同测试制度下的环空温度与压力，根据最小安全系数对井筒管柱强度进行校核，进而确定井筒各环空最大允许压力，并且绘制出不同测试制度下的安全诊断图版。研究结果表明：①环空温度随着测试产量和测试时间的增加而升高，但井口和井底的温度差减小，在同一测试产量和测试时间下，环空2温度始终高于环空3，并且环空之间的温度差较大；②环空2、3的压力随着测试产量和测试时间的增加而升高，但上升的趋势变缓，并且在同一测试产量和测试时间条件下，环空2的压力大于环空3；③若不考虑流体性质非线性变化的影响，将会低估环空压力值，并且随着测试产量和测试时间增加，相对误差会继续增大；④随着测试产量和时间的增加，环空2的压力值会率先超过环空最大允许压力，因而在深水高温高压井测试作业中应重点关注不同测试制度下环空2的压力变化情况。结论认为，基于所绘制的诊断图版，可以方便、快捷地判断深水气井测试制度的设计是否合理，最大限度地保证测试过程中的井筒完整性。

An annulus pressure prediction model for deepwater oil & gas wells during unsteady-state testing

In order to solve the problem of wellbore integrity damage due to annulus pressure increase during deepwater oil & gas well testing, this paper established a wellbore unsteady-state heat transfer model for the short-term unsteady state process of gas well testing. Then, the annulus pressure prediction model considering the nonlinear change of fluid properties was established according to the functional relationship between the isobaric expansion coefficient, isothermal compression coefficient and density. Finally, the established model was applied to predict the annulus temperature and pressure under different testing systems by taking a certain deepwater high temperature and high pressure (HTHP) gas well in the western South China Sea as an example. In addition, the strength of the wellbore string was checked according to the minimum safety factor. And based on this, the maximum allowable pressure of each annulus in the wellbore was determined, and the safety diagnosis chart under different testing systems was plotted. And the following research results were obtained. First, with the increase of testing production rate and testing time, the annulus temperature increases, but the temperature difference between the wellhead and the bottom hole decreases. At the same testing production rate and testing time, the temperature of annulus 2 is always higher than that of annulus 3, and their temperature difference is larger. Second, with the increase of testing production rate and testing time, the pressure of annulus 2 and 3 increase, but the rising trend slows down. The pressure of annulus 2 is higher than that of annulus 3 at the same testing production rate and testing time. Third, if the influence of the nonlinear change of fluid property is not taken into consideration, the annulus pressure will be underestimated, and the relative error will increase continuously with the increase of testing production rate and testing time. Fourth, with the increase of testing production rate and testing time, the pressure of annulus 2 will first exceed the maximum allowable annulus pressure. Therefore, during the testing operation of the deepwater HTHP well, more attention shall be paid to the pressure change of annulus 2 under different testing systems. In conclusion, the proposed safety diagnosis chart can conveniently and quickly judge whether the testing system of a deepwater gas well is designed reasonably, so as to ensure the wellbore integrity in the testing process to the maximum.