Abstract
When coiled tubing is applied in high oil–gas wells, buckling load of a coiled tubing under the injector is the key for functionality. The coiled tubing is curved, but it is simplified to straight tubing for buckling load solved in the past. These calculations were not sufficient for the problem. In this article, buckling load of a bent coiled tubing is discussed based on the actual details of the exploitation. First, the coiled tubing curvature changes during the working period reaching the shape presented in analysis of the article. To determine the distribution of stress and the zones to failure, a coiled tubing was studied using the theory of curved beam moment, and buckling load of the bending coiled tubing was derived. The study has indicated that the gooseneck curve radius and the yield strength enable to determine the residual curvature of coiled tubing. The axial stress along the convex and concave sides is a half periodic sine and cosine distribution along the length of the coiled tubing, and the maximum axial stress is on the middle of the concave side of the outside diameter of the coiled tubing. There is an inversely proportional relationship between buckling load and length of the tubing, and a proportion of buckling load and the diameter–thickness ratio. Moreover, buckling load was more sensitive to the tubing length than its wall-thickness.
Highlights
Coiled tubing (CT) is called flexible pipe; it is twined around the roller
After the CT is the strain e3 1 is pushed out from the injector, it rebounds due to the material elastic energy, and the direction of rebound is opposite to the direction of loading, the strain e3 1 changes to e!14, and the cros s section 1-1 is rotated to section 4-4
As we can see from equation (15), the residual curvature radius is affected by the radius of gooseneck, the diameter of CT, yield strength, and Young’s modulus of material
Summary
Coiled tubing (CT) is called flexible pipe; it is twined around the roller. When it is deployed, the CT is pulled out of the roller and pushed into the well by the injector. Keywords Coiled tubing, residual curvature, buckling load, bending, injector Following the emulation results and using the theory of a bent beam, a new buckling load equation for CT residual bending is derived.
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