辽河油田热采井套管瞬时安全系数计算及优选

Calculation and Optimization of Instantaneous Safety Factors for Casing in Thermal Recovery Wells of Liaohe Oilfield

辽河油田稠油热采井套管损坏现象频发,注汽过程中套管热应力过高是套管损坏的主要原因,考虑稠油热采工程地质参数对套管规格进行优选是解决该问题的关键。针对此,考虑高温条件下套管屈服强度以及弹性模量变化规律,采用有限元方法建立了温度-压力耦合作用下套管应力计算及分析数值模型,分析了热采过程中套管-水泥环-地层温度场变化规律,并且对该模型进行了验证,计算了温压耦合作用下套管应力动态变化规律,研究了套管规格参数(钢级、壁厚)和工程地质参数(注汽压力、地层力学特性)对套管应力的影响,得到了不同条件下套管安全系数变化规律。研究结果表明:当注汽温度升高时,套管的热应力会显著增加,导致安全系数降低。为了满足更高温度的热采环境,可以采用更高级别和厚度的套管钢材,并根据不同工程场景选择不同的套管钢级和壁厚。在热采井地层弹性模量下降时,套管内壁所受的热应力会减小。为了减小套管所受的热应力,可以调整注汽压力以降低其与地应力之间的压差。研究结果可为辽河油田热采井的套管优选和高温状态下套管的安全性评估提供依据。

Casing failure frequently occurs in thermal recovery wells of heavy oil in the Liaohe Oilfield due to high thermal stress in the casing during steam injection.To solve this problem,it is necessary to optimize the casing depending on engineering geology parameters for thermal recovery of heavy oil.In this paper,considering the changes in yield strength and elastic modulus of casing under high temperature conditions,a numerical model for calculating and analyzing casing stress under the action of temperature-pressure coupling was built using finite element method,and was verified.The casing-cement sheath-formation temperature field changes during thermal recovery were analyzed,and the dynamic changes in casing stress under the action of temperature-pressure coupling were calculated.The influences of casing specification parameters(steel grade,wall thickness)and engineering geology parameters(steam injection pressure,formation mechanical properties)on casing stress were identified.The variation of casing safety factor under different conditions was obtained.The research results show that as the steam injection temperature increases,the thermal stress of the casing significantly increases,leading to a decrease in safety factor.In order to meet higher temperature thermal recovery environments,higher grades and thicknesses of casing steel can be used,and different casing steel grades and wall thicknesses can be selected according to different engineering scenarios.When the elastic modulus of the formation in thermal recovery wells decreases,the thermal stress on the inner wall of the casing decreases.In order to reduce the thermal stress on the casing,the steam injection pressure can be adjusted to reduce the pressure difference between it and the ground stress.The research results provide a basis for the optimal selection of casing for thermal recovery wells in Liaohe Oilfield and the safety evaluation of casing under high temperature conditions.