High Capacity Artificial Lift Alternatives In The Offshore Environment
Authors: Cline William B. , Garford David W. 
Published: December 2007

This paper assesses some of the artificial lift needs of the offshore industry and endeavours to highlight those areas which are independently critical to functional simplicity, reliability, safety and economics. The importance of planning for artificial lift requirements at the onset of development can be shown to be vital to optimum field economic performance.

Introduction

In spite of improved early field application of pressure maintenance/secondary recovery techniques it is likely that a great many high capacity offshore fields will ultimately be obliged to rely heavily upon artificial lift to maintain their required production schedules and economic performance standards. As the industry moves out into deeper waters not only does proper predevelopment long-term artificial lift planning become more important but, with the increasing surveillance of the industry by Government and other regulatory bodies, continually higher standards of safety and reliability must be met. Not only must flow be maintained on fields entering their oil production decline phase but the benefits of enhanced productivity and production maintenance at productivity and production maintenance at relatively high levels from natural flow well systems during the crucial early debt retirement years invariably play a critical role in terms of project economics particularly where marginal reserve accumulations are concerned. There is clearly the necessity to integrate artificial lift into the very early stages of field planning, both in terms of surface and sub-surface equipment. Initial plans for well completion and platform design (bearing in mind the severe cost of load bearing deck space) must allow for anticipated future lift requirements. This is especially in the context of the inevitable prospect of handling water production at a time in the economic life of the project when significant incremental capital cost supplements are, at best, problematic.

PLANNING REQUIREMENTS PLANNING REQUIREMENTS While pre-development planning for artificial lift in the more difficult offshore areas is predominantly a capital and operating cost predominantly a capital and operating cost optimisation problem, comprehensive treatment of the best approach hinges very substantially on well production forecast assessments. These flow production forecast assessments. These flow performance predictions and the target design features performance predictions and the target design features that arise from them are all too often necessarily carried out with extremely limited productivity data relative to the producer's financial productivity data relative to the producer's financial exposure prospects. Thus the flexibility, reliability and resulting confidence in the system selected depends on a very practical assessment of the well performance sensitivity analyses specified to yield reasonable design targets.

Downhole equipment should be simplified wherever possible in the interest of suppressing the impact of very high offshore well servicing costs. In this context, single point injection gas lift can frequently be recommended where high kick-off pressures are preferred to lower pressure, multiple unloading valve string systems. Submersible electric pumping may one day be a dominant favorite choice for high volume offshore artificial lift systems but it currently falls behind in many application circumstances in terms of its ability to reliably accommodate high angle wellbores, solids in the produced fluids, and segregated multiple completions among other operational limitations. An operations research breakthrough simply in the areas of mudline and sub-seabed pack-offs along with reliable electric power cable junction splicing could in themselves power cable junction splicing could in themselves provide a basis for substantially broader provide a basis for substantially broader applications of submersible electric pumps to high volume oil production in the marine environment.

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