The HEP Pumping Unit: Performance Characteristics, Potential Applications And Field Trial Results
Authors: Laidlaw R.N. , Jespersen P.J. 
Published: March 2010

Abstract
The HEP pumping unit, which is the result of a four-year development program by Canadian Foremost Ltd., constitutes an alternative to the familiar beam pumping, unit as a means of transferring energy from the prime mover to the sucker rod string of a pumping well. This paper will address some basic concepts which are part of the HEP system design and will describe some of the resultant unit performance characteristics, The potential for enhancement of pumping well operations utilizing the high degree of control over rod string motion attainable with the HEP system is discussed, together with the results of a number of field trials in the Lloydminster area and some plans for further unit evaluation and development. A cost and capacity comparison with conventional beam pumping units is also included.

Introduction
Work which led to the development of the HEP pumping unit commenced in late 1975, Canadian Foremost became involved in early 1976 and to? date funding of the HEP' development program has amounted to approximately two and one half million dollars. The HEP unit does not represent a single specific technological breakthrough. It is best described as an engineered system which links together a number of components representing the state of the art in several areas of technology.
The use of Hydraulics to transmit energy to the sucker rod string, Electronics to control the polished rod motion and Pneumatics for counterbalance effect is the source of the acronym HEP, Early field testing of the unit was carried out in late. 1976 and early 1977. Certain operational problems were identified and, after some design improvements, a more extensive field testing program was commenced during the fall of 1978, Although a portion of this field evaluation program still remains to be completed, encouraging results have been experienced in application of the unit to the lifting of highly viscous crude oil. Substantial production rate 4tcreases have been attained on wells with rod fall problems. At the time of writing, fifteen units were under lease or had been sold to various operators in Alberta and Saskatchewan.

Basic Concepts
The primary objective of the work which led to the development of the HEP unit was to eliminate the gearbox on a conventional beam pumping unit in favour of a high-torque / low-speed motor. Various types of hydraulic motors were known to exhibit this type of characteristic. Efforts to optimize system efficiency and control capabilities led to a unit geometry considerably different from that of conventional units (Fig. 1). The concept of using unit geometry to cause conversion of rotary motion in reciprocating motion was abandoned. The originally conceived high-torque/low-speed motor was replaced by a double-acting piston and cylinder motor, mounted above the wellhead, with the piston rod connected to the polished rod by means of a carrier bar and rod clamp. In this manner, it is possible to convert hydraulic power directly into reciprocating rod string motion (Fig. 2).