The elastohydrodynamic lubrication model for the ellipsoid contact considering three-dimensional crack effect is established and solved with an under-relaxation algorithm. In doing so, the fluid field is divided into the two computation domains, in which the usual Reynolds equation and its reduced form are solved for the film pressure with the crack effect. Meanwhile, a fast Fourier transform method is adopted to accelerate the deformation calculation. Simulation model is verified. Numerical results show that the crack can cause jumps for the film pressure and film thickness. Increasing the crack length along the rolling direction and the depth at the crack's open end, and decreasing the crack tip inclined angle all result in an increment in the maximum film pressure. In addition, increasing the crack width can make the film pressure within the crack shift towards both ends of the crack width. The crack close to the contact center brings out a large film pressure.

No abstract

For the “three-high” gas wells in Sichuan Basin which are often regulated for production rate and shut-in for maintenance, annular pressure by temperature effect is a kind of wellbore safety threat that cannot be ignored. In this work, the wellbore temperature and pressure calculation model of gas–liquid two-phase flow with non-hydrocarbon correction and the prediction model of annular pressure by temperature effect is developed. Moreover, the judgment chart of annular pressure type is established through a large number of simulation calculations with different gas production rates and water production rates. Example calculation shows that whether water production and non-hydrocarbon components are considered in the prediction model has a non-negligible influence on calculation results. The predicted annular pressure is compared with that obtained from the actual measurement showing a good agreement. Meanwhile, the judgment chart realizes the valid determination of annular pressure type for three “three-high” gas wells in Sichuan Basin. Influential factors analysis indicates that reducing the thermal expansion coefficient of annulus fluid, adding the hollow glass spheres or injecting highly compressible protective liquid into the annulus and installing compressible foam material on the inner wall of casing are effective methods to control the annular pressure by temperature effect. To reserve partial annulus space can effectively reduce the annular pressure by temperature effect. For most of “three-high” gas wells in Sichuan Basin, the optimum height of annulus air cavity is 100 m.