Research On Mechanical Behavior Analysis And Technical Evaluation Methods Of Casing Repair

Shengli Oilfield is currently in the development stage of ultra-high water cut,the development is more and more difficult and the number of casing damage wells increased year by year.By 2014,a total of 11294 wells were damaged,which seriously affected the oilfield production and caused huge economic losses.At the same time,as the development time increases,the remaining oil in the reservoir decreases year by year,and the cost of casing damage repair increases.Therefore,a correct understanding of the development effect and development status of the oilfield in the development stage of the ultra-high water cut,and developing a new method for the effective prediction of casing damage wells and on this basis,formulating and implementing an effective and comprehensive management plan are the top priorities for casing damage prevention and treatment,which has important practical significance to the oilfield capacity building and oilfield sustainable development.In this paper,according to the deformation law of underground casing,the stress and deformation process of casing is simulated,the optimal repairing dimensions of ?139.7mm(5.5in)casing with wall thickness of 7.72 mm and ?177.8mm(7in)casing with 9.19 mm wall thickness are determined for N80 steel grade in Shengli Oilfield.Taking the common remedial measures in oil field as the research object and combining with the numerical simulation and theoretical analysis,the calculation results are used as the technical support to establish the evaluation method for casing damage management,which has certain guiding significance for practical production.First of all,based on the actual stress of the casing,assuming that the casing is absolutely circular,the complete contact between the casing,cement ring and the formation is established,and a nonlinear contact mechanics model of casing,cement ring and formation is established.For determining the theoretical optimal repairing dimensions of the casing,the variation trend of casing deformation and the maximum equivalent stress in the casing is studied by applying inhomogeneous stresses on the outside of the model.Secondly,the simulation models of the three most commonly used subsidy methods in oilfield(cement subsidy,hydraulic reinforcement subsidy and expansion tube subsidy)are established.And the anti-load capacity of the above three types of subsidies are compared.The research shows that the casing-subsidized pipe assembly repaired by hydraulic reinforcement subsidy has better anti-axial pull,pressure and anti-internal pressure capacity,but the anti-external pressure capacity is relatively weaker.Thirdly,on the basis of the comparison results,under the condition of standard internal pressure of 25 MPa,the influence of casing length,width,number of cracks and location of cracks on the subsidized combination was further studied.The results show that the crack width is the most important factor that affects the ability of the combination to resist internal pressure.Finally,combined with the above research results,considering the construction conditions of on-site repairing work in oilfields,a set of damage well management technology evaluation index system is set up.Subsequently,the best repairing measure from the technical aspect is selected.Then,based on the evaluation of casing damage technology,the economic evaluation of casing damage repair is established.By establishing the economic evaluation model,it is judged whether the economic benefits of the optimal restoration measures meet the actual needs.The actual production is guided according to the judgment results and the sustainable development of oilfield enterprises is ensured.