A Dynamic Braking Resistor (DBR) -Less Variable Speed Drive (VSD) Solution for the Rod-Lift Systems

Abstract

In 2022, extensive research conducted by Spears and Associates^[1 ] revealed that rod-lift spend accounts for 22% of the global artificial-lift expenditure, amounting to approximately $2.72 billion dollars. Seventy-five percent of this expenditure is concentrated in North America, due to the widespread installation of rod-lift systems in the region. Typically, when a well is initially drilled in conventional fields and a rod-lift system is installed, it remains in operation for the life of the well, which can extend for over 50 years. Although the size of the rod-lift pump may be reduced as the well's production declines, the overall type of lift system remains unchanged.

Furthermore, in unconventional playfields, the lift-system requirements may vary significantly due to the exceptionally high fluid output of these wells, surpassing daily averages of 1,000 barrels. In such instances, high-flow, artificial-lift systems such as electric submersible pumps (ESPs) or gas lift are utilized. Conversely, during the later stages of well life, when production rates decline or become uneconomical, more cost-effective, and lower-volume lift systems such as hydraulic lift, plunger lift, or rod lift are commonly employed. These latter systems generally become permanent installations until production rates decline further or become uneconomical. It is generally believed that when one considers how many total wells utilize rod lift vs ESP, the hands down winner is rod lift, possibly by something like a 10 to 1 margin. Rod lift is more reliable, cheaper, and more loved in the patch. It gets the most votes for the title king of the lift. According to research conducted by Spears and Associates more than 20% of all new wells drilled globally will incorporate rod lift. Within this context, this paper aims to investigate opportunities to enhance operational efficiency, reduce energy consumption, and achieve cost effectiveness—offering substantial advantages to businesses operating with rod-lift systems.

This paper introduces a new power-management technology that enhances the energy efficiency of typical rod-lift systems by consuming less energy for the same level of production, compared to conventional systems. The new approach is implemented where the regenerative energy is stored locally during the down stroke of the pump and recycled to the pump motor to reduce the power consumption requirements from the utility grid. This results in significant savings in utility costs for rod lift operations. The proposed technology is simple in design, having no moving mechanical components, and does not require additional electrical loads for operation, making this solution cost effective, reliable, and easy to install. Moreover, this technology proposes the elimination of the dynamic braking resistor (DBR), which is typically required in most rod-lift systems. By removing the DBR, the system becomes more reliable while also reducing costs. The implementation of a variable speed drive (VSD), coupled with this proposed DBR technology, delivers an overall reduction of operational costs and greater system reliability.