Pumping Well Optimization Techniques
Authors: Ejckmeier James R. , Eng P. 
Published: March 2010

Abstract
In recent years there have been a number of papers published dealing either with computer diagnosis of downhole pumping conditions (1,5) or with the results of optimization programs(13,14) based on computer analysis of pumping conditions. This paper can be considered a follow-up to previous papers inasmuch as it discusses techniques and presents guide lines which can be used when analyzing gear box and rod string loading situations, when attempting to establish connected horsepower requirements when reviewing mechanical pumping performance, and when calculating pump intake pressures and producing well capabilities. Consideration is given to the manner in which these inter-related factors affect optimization efforts.

INTRODUCTION
SURFACE LOADING CONDITIONS on a pumping installation can be determined from dynamometer measurements. Downhole conditions can be established using computer Programs(1) which mathematically simulate the pumping system. This paper discusses techniques and presents guidelines which can be used when analyzing wells for the purpose of obtaining optimum pumping performance.
Optimization may be defined as those courses of action which result in minimum operating costs consistent with maximum production. Pumping well optimization recommendations should take into account the operating problems which are peculiar to any one pumping area. Consideration must be given to gearbox, motor and rod string loading. These loading situations are, however, quite often a direct result of the downhole conditions. It is therefore necessary to examine pump mechanical performance, and to establish the pump intake pressure and total well producing capability. Consideration must also be given to the interrelated manner in which each of the above factors contribute to tire performance of the pumping systems.

DISCUSSION

Torque Loading

Torque Calculations
Torque may be defined as "force acting at a distance." The loading on a gear box results from two forces, as shown on Figure 1; i.e. the well load and the counterbalance effect. The well load at any displacement position can readily be established from surface dynamometer measurements. The counterbalance effect is determined by either "clamping off" or "chaining off" at the polish rod with the crank arm in the horizontal position. Torque loading over a full pumping cycle can be calculated using the API recommended procedure(2).
Manual torque calculations are time-consuming and consequently computer-calculated results are to be preferred. Example results showing the well load torque, counterbalance torque and net gear box torque are presented in Figure 2.
Counterbalance Moment
For a properly balanced condition the net torque, peaks should both be positive and be about equal in magnitude. As illustrated in Figure 3, when a pumping installation is either overbalanced or underbalanced a severe overload situation can occur. On pumping units the maximum counterbalance moment is often two to three times the gear box rating. Consequently, if a unit is overbalanced or underbalanced by 20 per cent the increase in gear box loading may be in the 40 to 60 per cent range.

Gear Box Backlash
Occasionally a severe "backlash" may be encountered.