Study On Influencing Factors And Rules Of Pressure-bearing Capacity Of Fuzzy-ball Workover Fluid In Fractured Formation

The fracture formation has good connectivity,so the workover fluid leakage is serious in the workover operation,which could bring safety,economy,environmental protection and other problems.Fuzzy-ball workover fluid is a kind of plugging control fluid developed based on fuzzy plugging theory,which has been successfully applied to the temporary plugging workover operation in fractured formation.The pressure-bearing capacity of fuzzy-ball workover fluid has been verified.But the influencing factors and rules of the pressure bearing capacity are unclear.So experience design can not achieve the purpose of temporarily plugging workover.The pressure-bearing capacity is related to the size of leakage,which affects the success or failure of workover.Therefore,it is necessary to study the influencing factors and rules of the pressure-bearing of fuzzy-ball workover fluid in fractured formation,and improve the pressure-bearing capacity value by optimizing the operating parameters to solve the problem of fluid loss in fractured formation.Based on the investigation and analysis of the influencing factors of the pressure-bearing capacity of fractured formation,this paper carries out the laboratory simulation experiment of pressure-bearing capacity on fractured core,looking for the relationship between the pressure-bearing capacity and influencing factors.Multiple regression analysis is used to establish a mathematical model of pressure-bearing capacity,and the results show that: fracture width,formation pressure,formation lithology/transformation method have a greater impact on pressure-bearing capacity,followed by the apparent viscosity and injection speed,and the effect of formation temperature and density is small.In order to verify the accuracy and applicability of the mathematical model,the field data of fuzzy-ball workover fluid are used for verification.The influence rule obtained by the single factor analysis is consistent with the model.The relative error between the fitting value and the actual value of pressure-bearing capacity is 0.5%～35.3%,and the model is optimized according to the field data to improve the accuracy of the optimized model.The relative error is reduced to 0.1%～5.5%,the average is 2.3%.The analysis shows that the pressure-bearing capacity is positively related to the formation depth,formation pressure,apparent viscosity and dosage of the workover fluid,and negatively related to the formation lithology,density,dynamic plastic ratio,open flow rate and pumping displacement.The pressure bearing capacity of carbonate rock is smaller than that of sandstone.On the site,pressure-bearing capacity of fuzzy-ball workover fluid can be improved by increasing the apparent viscosity,properly reducing the displacement and increasing the dosage of the workover fluid.The influencing factors and rules obtained from the study are used to guide the field operation.Pressure-bearing capacity of fuzzy-ball workover fluid can reach 35.3MPa,which is only 3.7% different from the mathematical model fitting value,which effectively reduce the workover fluid leakage and have field applicability.The research results can be used to guide the temporary plugging and workover operation in fractured formation,improve pressure-bearing capacity of fuzzy-ball workover fluid,control the loss of workover fluid during workover,and effectively improve the development process and economic benefits of oil and gas resources in fractured formation.