How to Solve the Problem of Anti-collapse of Oil Casing

Crush failure of oil casing pipe is a common form of casing damage. The anti-collapse performance of casing has always been the focus of attention, and the prediction and application of OCTG for special oil pipelines has always been a research focus. According to the tube blank extrusion failure form, according to the J55 petroleum casing diameter ratio D≤S, it can be divided into two types: instability failure and strength failure. The APIBull5C3 standard divides it into four failure modes according to the pipe diameter ratio: yield extrusion strength PY, plastic extrusion strength PP, transition extrusion strength PT and elastic extrusion strength PF.

The K-T model better predicts the anti-fragmentation performance of the current oil casing, but its formula coefficient depends on the level of each enterprise. It can be seen from the model that when D/S is in the plastic collapse and transitional collapse zone, the ellipticity is very obvious, and the ellipticity becomes the process control factor that affects the main size and quality of the anti-pressure value; when D/S is in the elastic collapse zone or yield collapse When the residual stress is not obvious, the nominal yield strength I should be controlled as much as possible.

In deep wells, not only the influence of high temperature on the strength of the oil casing, but also the influence of high temperature on the elastic modulus and Poisson's ratio of the pipe material must be considered. These factors will eventually affect the collapse resistance of the pipeline under service conditions. Ultra-thick-walled casing is an effective method to solve the problem of abnormally high pressure formation collapse in deep wells.

The anti-collapsing oil casing should adopt the temperature adjustment heat treatment process, try to increase the tempering temperature to meet the yield strength requirements, increase the straightening temperature, and reduce the residual stress. The quenching depth and uniformity of the tube body.

Due to the directionality and anisotropy of formation pressure, the stress environment of J55 oil casing is very harsh, and casing collapse damage is more serious. It is recommended to increase the safety factor of oil casing pipes against collapse, but the casing collapse resistance is an inherent engineering attribute and cannot be changed with the characteristics of formation stress distribution.