深水油气井全生命周期环空圈闭压力预测模型

Prediction Model of Annular Trapped Pressure in the Whole Life Cycle of Deepwater Oil and Gas Wells

准确预测环空圈闭压力对维持油气井井筒完整性、延长油气井生命周期具有十分重要的意义。基于PVT状态方程,结合井筒瞬态传热模型与环空体积计算模型,建立了耦合环空体积-温度变化的深水油气井全生命周期环空圈闭压力预测模型。模型计算结果与试验数据的误差约为6.6%。实例井计算结果表明:环空圈闭压力与环空流体压缩系数、地温梯度及环空段长度等成正比关系,上述参数越大,则圈闭压力越高;圈闭压力与环空流体膨胀系数、套管的弹性模量与泊松比等呈负相关关系;圈闭压力随着生产时间与产量的增加,呈现先迅速增加后趋于稳定的趋势。因此,环空圈闭压力上升主要集中在油气井投产初期,应优选低膨胀系数的高压缩性环空流体、减小环空段高度,并尽可能采用弹性模量和泊松比较大的套管,以降低环空圈闭压力。研究结果可为深水油气井安全高效生产提供参考。

Accurate prediction of annular trapped pressure is great significance for maintaining wellbore integrity and prolonging life cycle of oil and gas wells. In the paper, based on PVT state equation, combined with wellbore transient heat transfer model and annular volume calculation model, a prediction model of annular trapped pressure in the whole life cycle of deepwater oil and gas wells coupling annular volume-temperature fluctuation was built. The error between the model calculation results and the test data is about 6.6%. The calculation results of an example well show that the annular trapped pressure is proportional to the annular fluid compression coefficient, geothermal gradient and annular segment length;the larger the above parameters, the higher the trapped pressure is;the trapped pressure has a negative correlation with annular fluid expansion coefficient, elastic modulus of casing and Poisson’s ratio;as the production time and yield increase, the trapped pressure first increases rapidly and then tends to be stable;therefore, the rise of annular trapped pressure is mainly concentrated in the early stage of production of oil and gas wells, the high compressibility annular fluid with low expansion coefficient should be optimized, the annular segment height should be reduced, and the casing with large elastic modulus and Poisson’s ratio should be used as far as possible to reduce the annular trapped pressure. The research results provide reference for safe and efficient production of deepwater oil and gas wells.