Separated Layer Water-flooding Long Rubber Packer Mechanics Analysis And Design Research

Most of the oil fields in China has entered into its middle or latter development period, water-cut in reservoir increases gradually and interlayer inconsistency is intensified. In order to increase oil production and enhance the oil field production efficiency, oil well stimulation method has turned into thin, poor oil layer exploitation in large and thick layer from interlayer exploitation. The existed layered water injection technology cannot meet the demand of fine separate layer water injection in poor, thin layer, mainly because the length of the separate layer water injection packer rubber is too short to determine the setting position of packer under the influence of the string extension and the magnetic positioning error. Therefore, to study a kind of long rubber packer used inside a big thick layer is necessary, to achieve effective packing for the setting layer by the reverse packer of thin interbedded layer; At the same time, as a result of the perforated setting packer zone, irregular pieces and even pieces stinging inside will appear on casing wall after perforating, and may cause rubber tube cut to seal failure when long rubber expansion setting. Therefore, it is necessary for us to study the stress of the packer rubber tube when using packer, analyze stress distribution law of rubber tube, to provide suggestions for oil field application of long rubber tube packer.In this paper, according to the principle of expanding the water injection packer, mainly for K344-112,720 mm and 970 mm two long hydrogenated nitrile rubber tube packer, the Mooney-Rivlin constitutive model and the finite element analysis method are utilized to do numerical simulation research on packer under normal condition and the condition of casing perforation packer setting according to the packer setting and water flooding two kinds of working conditions. The analysis results show that in the process of setting the bottom of long rubber tube packer first expands, then middle part and top part expands along with pressure increases, and rubber tube overall expansion is not uniform; Under normal conditions, the stress clusters of packer rubber tube after setting appear in the rubber tube shoulder; Among them, the stress concentration phenomenon on lower shoulder of the rubber tube is obvious, maximum equivalent stress value of rubber is within value of allowable stress, so rubber will not be damaged. When the packer setting is in the perforation section, stress concentration phenomenon occurred both in the shoulder and burr of rubber tube; Among them, when top part of rubber contacts with burr, maximum equivalent stress values appear in the lower shoulder of 720mm rubber and the upper shoulder of 970 mm rubber; when middle and bottom part of rubber contacts with perforation section respectively, the maximum equivalent stress values both appear in the lower shoulder; After packer setting, rubber tube will not be damaged only when water injection pressure is under the 8MPa-12MPa and rubber maximum equivalent stress value is within allowable stress.According to packer mechanics analysis under different conditions, no matter packer setting is in the perforation section or not perforated casing, stress concentration phenomenon both appear on the shoulder of rubber. It is the most obvious on lower shoulder, and the main cause of stress concentration is the impact of compensation structure. Thus, with rubber tube size optimization in order to reduce the stress concentration, the compensation structure should also be optimized. According to the result of optimization,720mm packer has optimal structure with contact angle of 31.127, rubber inner diameter of 75.472 mm, external diameter of 111.39 mm and the compensation structure of 0.0649 mm; After the optimization, maximum equivalent stress of rubber is 8.837 MPa and is 5.085 MPa lower than unoptimized structure and the overall packer structure optimization is good; 970mm 970 mm packer has optimal structure with contact angle of 38.44, rubber inner diameter of 75.925 mm, external diameter of 111.98 mm and the compensation structure of 0.0459 mm; After the optimization, rubber maximum equivalent stress is 11.272MPa and is 3.038MPa lower than unoptimized structure and the overall packer structure optimization is good.