Mechanics And Safety Analysis For Multi-packer Strings In Horizontal Well

In the process of well testing, well completion, production and so on in horizontal well,the successful tripping and lifting of multi-packer strings are the necessary security condition.Because of bent borehole which will create large friction resistance between strings andcasings, so there should be greater axial load to ensure the strings trip into the casingsuccessfully. Because of the existence of the multi-packer, the axial deformation of the stringswill be restrained. In order to understand the mechanical behavior for multi-packer strings,the specific research is done as follow:First of all, to make known the bending section of strings in the horizontal well, with theaccount of the influence of borehole curvature radius and radial interval between strings andcasings, the mechanical model of the curved strings was established. After the analysis ofbuckling critical load which is derived by the principle of minimum potential energy, it wasfound that buckling critical load increased with the radius of borehole curvature, whiledecrease with the increase of the radial interval between strings and casings. Considering theinfluence of the packer on curved section in the aspect of friction resistance, the packerstrings friction resistance formula can be inferred in the curved section. Secondly, consideringtwo cases whether the strings witch between different packers in contact with the casings inwall or not, two mechanical models are built respectively in different working conditions, andthen the transfer efficiency of axial force of horizontal section strings is derived. In addition,on the base of the working condition of set down and fracture, we consider temperature effect,ballooning effect, fluid friction resistance effect in the process of large capacity and highpump pressure reservoir reconstruction. Combining multi-packer strings residual axial force,we build multi-packer strings stress calculation model in the horizontal section. Based on thefourth strength theory which can check the strength safety of multi-packer strings in theprocess of fracture, the results showed that the differences of bottom temperature andpressure are the main factors affecting the safety of multi-packer strings. Finally, this paperwill provide a reasonable combination proposal for the safety of multi-packer stringsconstruction in horizontal well.