This paper describes the steps taken in the planning, design, and field implementation of an enhanced artificial lift system to address the common challenges of conventional ESP installations. A set of case studies, in two basins, reviews the field installations and sequential optimization to achieve an improvement in ESP performance.
Unconventional horizontal wells have the complexity of depth, temperature, fluid composition, and rapidly declining production rates. Most artificial lift systems struggle and inadequately cope with inconsistent slug flows from a horizontal wellbore, foamy fluids, damaging solids and gas interference. In ESPs, gas interference frequently overheats the motor resulting in excessive shut downs and/or premature failures. The root cause of gas interference is flow from the horizontal wellbore that tends to be sluggy with inconsistent mixtures of gas and liquid. A downhole flow conditioning artificial lift technology designed to smoothen and suppress slug flows prior to the ESP dramatically improved ESP performance. Field implementation revealed that the technology conditioned the flow and successfully reduced slug flow behaviour showing consistent rates and pump intake pressures.
With the slug flow issue resolved, this revealed an unaddressed problem not previously noted with conventional ESP installations caused by liquid lifting in the small annular space adjacent the pump. With high enough gas rates, liquid lifting past the ESP can occur, starving the pump of liquid, overheating the motor, resulting in shutdowns. In initial field trials, this problem limited the ability to drawdown past 800 psi intake pressure. Subsequent field trials solved the problem by manipulating pump intake pressure or reducing equipment size for higher gas rate wells resulting in significantly lower pump intake pressures and improved ESP reliability. The paper describes consecutive cases that implement stepchange modifications to resolve both slug flows to the ESP and annular liquid lifting past ESPs. The optimized design resulted in an extended range of pump operability, improved reliability and enhanced control and reservoir management.