Introduction

Early pumping units were powered by steam engines, and then the slow-speed gas engines became standard. The use of electric motors gained wide acceptance during the late 1940s, and nowadays the majority of pumping units is run by electricity. Originally, the main advantages of electric power were the low cost of electric power, lower investment costs due to low price of electric motors, and the easy adaptation of motors to intermittent pumping. Some of these advantages still exist, although the cost of electricity has substantially increased through the years.

The choice between electric or gas power is based on several factors. The availability of gas or electricity at the wellsite has prime importance, but the proper decision cannot be reached without an analysis of the operating costs involved. The investment cost of a gas engine is much higher than that of an electric motor, but, on the other hand, gas engines have a much longer service life. The energy costs when using electric motors have steadily increased during the last years due to increased power costs. Gas, if available, can turn out to be more economical and can even cost nothing if it was vented before. In summary, to decide on the type of prime mover to be used in a given installation, a comparison of the anticipated operating costs is required.

Internal Combustion Engines

Internal combustion engines usually run on gas which can be dry separator gas or, more frequently, wet wellhead gas led from the...