Analysis And Research On The Mechanics Of Stratified Water Injection String In Halfaya Oil Field

The production time of the Halfaya oil field in Iraq is short.Due to the decrease of reservoir pressure,the production rate is relatively low,so the oil production engineering team uses water injection to improve well pressure and improve the recovery rate.The general water injection at the bottom of the reservoir plays a certain role in a short time.Shortly afterwards,there were problems such as water flooding,and so on.In order to achieve the orderly development of oil reservoirs and solve the problem of low production rate caused by low oil pressure,stratified water injection of the oil layer is needed.The structure of its water injection string is different from the common structure of water injection string in China.In order to ensure the effective process of water injection,it is necessary to analyze the string's force in the whole process of water injection,which provides reference for the structure design and process design of the pipe column.Based on the theory of fluid mechanics,elasticity and differential geometry,the stress of string's microelement is analyzed.According to Euler beam theory,the force differential equation of string is given,and the calculation model of axial force,axial displacement and strength of separate injection string is given.Based on the assumption of interaction between casing wall and pipe support reaction,the differential equation of string's buckling and critical load for sinusoidal buckling and helical buckling are given.The influence of section change,packer,expansion joint and slips on continuity of variables is analyzed.The packer element is numerically simulated by ABAQUS,and the Mooney-Rivlin constitutive model of rubber material is adopted.With the increase of load,the contact area and contact stress of casing tube wall increase.When approaching set-down load,the stress distribution inside the rubber cylinder is no longer symmetrical,and the maximum contact stress area is downward shifted.The maximum equivalent stress value is basically linear with the compression distance,and the main factor affecting the equivalent stress is the deformation of the rubber cylinder.With the increase of load,the deformation of the rubber barrel is aggravated.When the load is close to set-down load,there is a larger stress area inside the rubber cylinder.The bottom rubber cylinder will be the most likely component due to fatigue damage.The friction force of the middle rubber cylinder increases following power function curve with the compression moment,and the fitting formula of the maximum static friction force is given,which provides the mechanical boundary reference for subsequent pipe string mechanics analysis.Based on the theory of stratified injection string and the analysis of the continuity of variables,Mechanical analysis software for separate injection string is worked out,and its module structure and function are designed.It is applied to the mechanical analysis of actual water injection wells,and the calculated results are compared with the field logging data,and the error is within a reasonable range.Aimed at the analysis of string mechanics in Halfaya injection wells: The structure of layered water injection string adopted by M325 well meets the requirements;Under the limiting condition of upper water injection 100%,the pipe string may yield and there is a potential safety hazard,and in other working conditions,the safety factor is greater than 1,and the pipe string is reliable;When the water is leaking,and the lower layer is injected 100% and the upper layer is injected100%,the pipe may yield.M279 well: The structure of the stratified water injection pipe column neglecting the slips is unreasonable.The research in this paper provide technical support for the design and verification of water injection string in Hafei oilfield.