Abstract：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.
张智，向世林，冯潇霄，刘和兴，孟文波，李炎军，马传华. 深水油气井非稳态测试环空压力预测模型[J]. 天然气工业, 2020, 40(12): 80-87.
ZHANG Zhi, XIANG Shilin, FENG Xiaoxiao, LIU Hexing, MENG Wenbo, LI Yanjun, MA Chuanhua. An annulus pressure prediction model for deepwater oil & gas wells during unsteady-state testing
. NATURAL GAS INDUSTRY, 2020, 40(12): 80-87.
