Mechanical Analysis Of Underground Pipe String Of Injection Water Well

As an economical and technically simplistic measure, water injection is widely used in the exploitation process of most of oilfield. For the sake of supplying the formation energy and maintaining the reservoir pressure, some clean water or sewage that meets certain standards will be injected into formation through the injection tubing strings when water injection progresses. Water injection tubing strings play an important role in bearing loads and transmitting power in the process of oil wells production and operation. Not only will the tubing strings bear internal pressure, external pressure, axial force and bracing force from the wells, but also many different types of load such as external bend torque, external torsion torque and so on during the production or operation. Mechanical behaviors of tubing strings may be extraordinarily different under the performance of these different load. Especially in the deep wells or high temperature and high pressure wells where tubing strings tend to in different equilibrium states or convert between different equilibrium states because of the change of pressure and temperature downhole or the different density of fluid inside or outside the tubing strings. By consulting and researching relevant domestic and international literatures of mechanical analysis and calculation, combining with the practical example, an analysis of force and deformation in water injection tubing strings has been done in this paper. The obtained conclusions have great significance for avoiding mutual interference between fluid and pressure of operation target strata caused by sealed section of tubing string moving out of sealed cauity of packer and preventing difficulties in running and pulling downhole tools caused by permanent helix bending and even preventing damage of packer and wellbore. Such results have been achieved from research in this paper:Firstly, the change of downhole pressure will lead to the change of forces and deformation of tubing strings caused by piston effect, expansion effect and buckling effect. The change of temperature will lead to the change of forces and deformation of tubing strings caused by temperature effect. As to tubing strings that could move partly or can not move, the initial mechanical force will also affect their forces and deformation.Secondly, combining with three different relationships between packer and tubing strings, calculating models of forces and deformation of mono-size tubing strings and multi-size tubing strings and multi-packer tubing strings under different circumstances are built. Calculating models of forces and deformation of bending part and horizontal part for horizontal well are discussed.Thirdly, mechanics analysis of water injection tubing string software is written according to built calculating models of forces and deformation. This software can not only calculate the deformation and forces of water injection tubing strings after the change of temperature and forces so that accidents such as failure of packer and fracture of tubing strings will be predicted, but also analyze how the influence factors that decide the deformation and forces of water injection tubing strings affect the deformation and forces so that reasonable tube combinations and operation parameters may be determined.At last, influence factors that affect the deformation and forces of water injection tubing string are analyzed by the written software.1)The increase of radial clearance between tubing and casing and diameter of sealed cavity of packer and depth of packer will lead to the increase of deformation of the whole tubing strings.2) With the increase of initial mechanical force, the force of tubing strings that can not move will increase after decrease.3) By exerting initial mechanical force on tubing strings that could move partly before the setting of packer, extraordinarily large deformation will be prevented after the change of pressure and temperature.4) With the increase of radius of curvature and radial clearance between tubing and casing, buckling critical load of bending part of horizontal well will decrease.