A variety of geological and physical structural features of the oil and gas pools under development and the properties of the produced fluids predetermine the need to apply individual approaches to solve the problems of improving the operating efficiency of wells in difficult conditions. Currently, the tasks of integrated multiple-factor study of the processes of gas and liquid mixtures motion in the bottomhole zone – pump – wellbore system are relevant with the purposes of predicting the intensity of difficulties in oil production and optimizing the operating conditions of submersible pumping equipment. The drop in the bottomhole pressure below the oil bubblepoint pressure, which is forced to maintain the required oil recovery rate, ensures that a large amount of free gas enters the directional and horizontal wells with the liquid. The significant differences in reservoirs and formation fluids properties determine the need to sel ect the optimal well operating conditions with account of the specifics of the gas and liquid mixtures motion in the actuating elements of pumps and tubing and the intensity of the occurring complicating factors due to increased free gas content in the produced fluid.
The analysis of the operating conditions of the oil wells operated by Rosneft Oil Company has shown that, when producing a relatively water-free well stream, the free gas ratio at the pump suction may exceed permissible values even with a two-fold bottomhole pressure reduction in relation to the bubblepoint pressure of the produced liquid, which leads to the need to use gas separators as part of the ESP. In addition to being a difficulty on its own, a high gas-oil ratio contributes to the occurrence of associated difficulties such as the sedimentation of inorganic salts, paraffin, asphalt, resin substances, and solids. The article shows that the negative impact of the deposits of inorganic salts, paraffin asphaltene-resin-paraffin substances is most significant for the wells in the fields operated by RN-Purneftegas and RN-Vankor. Reducing the pressure at the pump intake below the oil bubblepoint pressure and the resulting free gas in the produced stream leads to intensive scaling in the flow channel of the ESP. When dismantling emergency pumps, salts were universally found in their lower stages while in deposits of inorganic salts were present in the upper stages only in 60% of the studied cases due to a decrease in the free gas as the gas and liquid mixture moves through the pump.
Application of the probabilistic approach and the reliability theory to the reviewing of more than 80,000 failures of the pumping equipment has shown that the probability of a failure-free operation for more than 400 days tends to zero for the wells with a high gas-oil ratio.
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