The Economics of Coiled Tubing Deployed ESP Completions in the North Sea. A Field Life Cycle Perspective
Authors: Tovar D. Juan J. , Callander Jeffrey S. 
Published: December 2007

As the North Sea continues its transition to a "mature area" status, new technologies are required to make new and existing fields more cost effective to develop and produce. Electrical Submersible Pumps(ESPs) are a considered option to increase production. However, this technology is expensive to implement in its conventional form. Other technologies such as Coiled Tubing(CT) are also being considered for use along with ESPs. During 1995 two(2) such installations were completed in the United Kingdom(UK). It was the first time (outside the US) that these two technologies have been used to complete oil wells in a new and innovative manner. There are however significant technical differences between both systems and it remains unclear as to what their individual and combined economic benefits and constraints are. This paper defines the economics of implementing these technologies in existing fields in the UK. For comparison purposes, the financial considerations are presented for a life-cycle of the installation that represents a 5 year period in the life of the field. The advantages of CAPEX and OPEX options are discussed. A comparison between the two(2) CT/ESP completions installed in the UK and a conventional tubing conveyed alternatives are also included. Finally, economic guidelines are proposed for utilisation of these new technologies in existing fields of the UKCS.

Background

Very little is known of the long term economics of CT/ESP completions. Initial attempts to define their economic aspects were limited and based on one(1) operation only, comparing equipment and services cost on an individual basis without considering long term performance and financial gains realised over the life of the installation. There are two(2) systems in use and both are technically quite different; one utilises the electrical power cable attached to the outside of the CT string in a similar manner as with conventional tubing conveyed systems. The second one has the electrical power cable installed inside the CT string with production of fluids taking place in the annular space between the CT string and the existing tubulars (casing or tubing). Sub-surface configurations for each CT alternative are presented in Figures 2 and 3. Table 1 illustrates the main operational characteristics for both installations.

Inherent potential economic benefits to ESP installations using CT technology can be outlined as follows–Potential for rigless operations.–Reduction in time for deployment/retrieval of the completion.–Possibility to lower the completion under live well conditions (2nd system only).

However, each of them introduce new constraints due to the individual technical solutions adopted. For instance, the system with an external power cable can not be installed under live well conditions but it still offers a reduction on the overall operational time hence a reduction in cost. The system with the power cable inside the CT string can be used to lower the completion under live well conditions hence reducing operational time and associated cost. This however, being new technology, might at this point have a level of acceptable risk that still is too high for consideration particularly for an area such as the North Sea. All these considerations have a major impact on the economics of the installation and the field.

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