Optimizing Downhole Fluid Production of Sucker-Rod Pumps With Variable Motor Speed

Abstract

Summary Reciprocating oil pumps are operated traditionally by prime movers rotating at a constant speed. This paper demonstrates that by changing motor speed rapidly within a single stroke, pump production can be increased while stresses in the sucker rod and motor energy consumption are reduced. The optimal motor-speed profile is determined by representing the motor speed with Fourier series and searching for Fourier coefficients that maximize the production while satisfying the imposed constraints on stresses in the rod and on energy consumption. The pump-performance parameters required in the optimization process, such as fluid production, stresses in the rod, and motor torque resulting from a given variable motor speed, are calculated by predictive analysis. The analysis is based on a comprehensive dynamic model of the entire pumping system, comprising surface and downhole equipment. During, and beyond, a minimum 6-month field-validation period, the calculated optimal speed profile has been applied to control the movement of more than 20 pumps currently operating in Alberta, Canada. The resulting increased production and lower operating cost confirmed clearly the benefits of implementing a variable speed of the prime mover to improve pump performance. Presented examples demonstrate an increase of up to 133% in production without increasing energy consumption or loads in the system. Results similar to those with beam pumps can be achieved for hydraulically actuated pumps by applying variable flow rate or pressure to induce the calculated optimal polished rod velocity.