蠕变地层与油井套管相互作用力学模型

Mechanics model for interaction between creep formation and oil well casing

在油井生产过程中,地层的蠕变使套管承受的外部挤压载荷逐渐接近于上覆岩层压力。当套管的外部挤压载荷大于套管的抗挤强度时,套管将产生屈服、变形甚至破裂。目前采用的蠕变地层与套管相互作用的力学模型存在理论上的错误,无法正确计算套管的外部挤压载荷。根据实际建井过程和力学原理,建立了正确的蠕变地层与套管相互作用的力学模型。如果地层不具有蠕变性,地应力不会作用在套管上;如果地层具有蠕变性,且持续时间比较长时,套管所受的外挤载荷为地层的上覆岩层压力。现场检测到的套管非轴对称形变主要是由套管壁厚不均匀、材质不均匀、套管受到刮伤及套管一侧黏土膨胀等因素所致,而不是地层的非均匀地应力造成的。

Formation creep will make the external pressure on the casing get up to the overburden pressure in the process of well pro duction. When the external extrusion load exceeds the casing compressive strength, the casing will be yielded and deformed or even cracked. The prevalent interaction model between creep formation and casing has some theoretical mistakes and can not be used for calculating the external pressure of casing. Based on the well construction procedure and mechanics principle, a correct interaction model between creep formation and casing was established. If the formation is rigid or elastic, earth stresses can not exert on the cas- ing. If the formation is of creep property, the external pressure on the casing will be the overburden pressure after a long time. The non-axisymmetry deformation of casing detected from well site is mainly resulted from non uniform thickness,non-uniform material of casing, scraping damage on casing and clay swelling in one side of casing, but not from the non-uniform earth stresses.