深水油气井开采过程环空压力预测与分析

深水油气井投入生产后受到地层高温流体的影响,井筒内温度场会重新分布引起环空压力上升,威胁油气井管柱的安全服役和井筒完整性。为确保深水油气井井身结构和管柱强度符合长期安全稳产的要求,建立了基于能量守恒定律和多层圆筒壁传热原理的深水油气井井筒温度分布计算模型,根据深水油气井井身结构复杂、环空层次多的特点,遵照体积相容性原则提出了计算环空压力的迭代方法,实现了对井筒内温度分布和环空压力的预测与分析。利用温度预测模型和压力计算方法对相关影响因素进行了分析。结果表明:环空温度、压力的上升主要集中在油气井投入生产的初期,随生产时间的增加变化逐渐变缓;产量较低时,井口产出流体的温度与环空温度、压力随产量的上升迅速增加,当产量到达一定数值以后井口产出流体的温度与环空温度、压力趋于稳定;环空温度和压力随着地温梯度的增加线性上升。

Prediction and analysis on annular pressure of deepwater well in the production stage

Deepwater oil and gas wells are under the influence of high-temperature formation fluid after put into production, so that the shaft temperature field is redistributed to cause a rise in annular pressure, threatening the safety service of well string and shaft integrity. The calculation model of shaft temperature distribution in deepwater wells was established on a basis of energy conservation law and multi-cylinder heat transfer discipline, thus assuring the well structure and string strength of deepwater wells can satisfy the demands for long-term safety production. According to the characteristics of deepwater wells such as complex well structure and multiple annular hierarchies in line with the principle of volume compatibility, the iterative method was proposed to calculate annular pressure, so as to predict and analyze the shaft temperature distribution and annular pressure. Relevant influence factors were analyzed using the temperature distribution model and pressure calculation method. The results have indicated that annular temperature and pressure mainly ascend in the initial production stage of oil and gas wells, and the changes become gentle over production time; in case of lower output, the wellhead fluid temperature, annular temperature and pressure will rise rapidly as output increase, but tends to be stable when the output reaches a certain value; annular temperature and pressure presents a liner rise with the increase of geothermal gradient.