页岩油气井复杂压裂工况下套管载荷研究

Research on Casing Load under Complex Fracturing Conditions in Shale Oil and Gas Wells

页岩油气井多级压裂过程中井筒温度变化剧烈及井筒内压频繁交替升降,导致其水平段套管处于复杂的力学环境中,该部位的套管容易出现变形。建立了包括温度效应的套管应力分布有限元模型,计算分析了油气井多级压裂过程中井筒温度变化趋势及对井筒受力的影响,确定了多级压裂过程中套管承受的应力变化规律。对SY1井多级压裂过程中井筒温度变化趋势及套管承受的应力等进行了计算分析。结果表明,一次压裂过程中井筒内温度由147℃下降至77℃,在120 min的压裂过程中,在500 s内温度由77℃快速上升至140℃,然后缓慢上升至145℃。温度效应模型中套管承受的Mises应力随多级压裂级数的增加呈现增大的趋势(压裂压力+热效应),在43.18 h后达到最大值,套管内壁和外壁承受的Mises应力分别为457.7 MPa和417.79 MPa,该内壁应力比无温度效应条件下套管内壁承受的应力增加了24.72%。因此,对复杂压裂工况下的套管强度进行设计时,应分析井筒内温度效应对套管承受的应力的影响。

During the multi-stage fracturing process of shale oil and gas wells,the temperature of the wellbore changes dramatically and the internal pressure alternates frequently,resulting in the horizontal section of the casing being in a complex mechanical environment,and the casing in this area is prone to deformation.A finite element model of casing stress distribution considering temperature effect was established,and the trend of wellbore temperature variation and its impact on wellbore stress during multi-stage fracturing of oil and gas wells were calculated and analyzed.The stress variation law of the casing during multi-stage fracturing was determined.The trend of wellbore temperature changes and the stress borne by the casing during the multi-stage fracturing process of SY1 well were calculated and analyzed.The results show that the temperature inside the wellbore decreases from 147℃to 77℃during a single fracturing process.During the 120 min fracturing process,the temperature rapidly increases from 77℃to 140℃within 500 s,and then slowly increases to 145℃.For the temperature effect model,the casing Mises stress shows a cumulative increasing trend with the increase of multi-stage fracturing stages(fracturing pressure and thermal effect),which reaches its maximum value after 43.18 h.The Mises stress borne by the inner and outer walls of the casing is 457.7MPa and 417.79MPa,respectively,which is 24.72%higher than the internal wall stress without considering temperature effects.Therefore,when designing the strength of casing under complex fracturing conditions,the effect of temperature needs to be considered.