Abstract

Worldwide more than two thirds of the oil wells are placed on some kind of artificial lift, mostly on sucker-rod pumping, ESP, or gas lift. Because of the great number of installations it is extremely important that they operate under optimum conditions. Even small changes in operational efficiencies can significantly increase operational expenditures, so optimization of the energy efficiency has a great impact on profitability of oil production. The presentation deals with establishing the most energy-efficient operation of artificial lift installations. The aim of the optimization is finding the minimum operational costs while producing a prescribed liquid rate from the well, i.e. attaining the maximum power efficiency. Three forms of artificial lifting are studied: sucker-rod pumping, ESP, and gas lifting.

The power efficiency of any artificial lift system is defined by the relation of the useful power used for fluid lifting and the total input power. The useful hydraulic power is defined by the change of potential energy of the produced fluid, while the total input power can be calculated. Analysis of the power flow in rod pumped wells shows that maximum efficiency is reached with the proper combination of pump size, polished rod stroke length, and pumping speed. The installation's power efficiency is primarily determined by the choice of the pumping mode. The power efficiency of ESP installations is shown to reach a maximum when using a motor and a pump with the maximum efficiency while minimizing the power losses in the electric cable. Optimum design of continuous flow gas lift installations involves NODAL analyses and finds the combination of tubing size, injection and wellhead pressures, and flowline size that ensures the minimum compressor power requirements.

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