Electric submersible pumps (ESPs) have historically been limited when operating in gassy conditions. Studies and evidence gathered during failure analysis confirm the effects of gas on the performance of ESPs. Gas locking, mechanical wear, and low efficiency due to challenging environments have made operators change from a standardized string to a string that can mitigate the effects of gas, which can help maximize the production and increase the pump's run life.
The impellers of the centrifugal pump require a minimum amount of liquid mass in the impeller vanes to transfer the kinetic energy to the fluid mixture. This energy will be transformed to potential energy in the diffuser, but if the mass mixture in the impeller cannot perform an efficient energy transfer for the mixture, only the liquid phase will be pushed out the vanes of the pump and most of the gas will stay behind, filling the vanes of the impeller and creating a gas-lock condition.
In environments with a high presence of gas, additional equipment such as rotary gas separators are used to remove as much gas as possible before the fluids enter the pump. Gas separators have been proved as effective. However, when the conditions are extreme, such as in unconventional reservoirs, additional devices will be required to maintain a stable operation of the ESP, pump as much as possible a homogenous fluid, and minimize the downtime due to unnecessary trips to maximize the overall performance and run life of the ESP system, and optimize production and total cost of ownership for artificial lift operations.
This paper presents the comparative results of the performance of a group of ESPs installed in unconventional wells of a leading Midland basin operator with challenging conditions to operate an ESP. It will analyze the performance of the ESPs and compare the trends of the downhole parameters while operating with a standard string with a single gas separator and gas-handling system with those of an upgraded string that includes a tandem gas separator, an advanced gas-handling system, and a multiphase gas-handling system equipped with helico-axial-flow stages. This change in designs and configuration has improved the run life of the ESPs for unconventional wells with high gas volume fractions.