Techno-Economic Evaluations of Deepwater Marginal Field Developments
Authors: Chitwood J.E. , Wanvik L. , Chin Y. Doreen , Sheets B.J. 
Published: October 2008

In Systems Engineering CTR 6901, DeepStar developed a process to identify technologies that have good economic impact on 3 typical deepwater tie-back marginal reservoirs. This is accomplished with a life-cycle economic analysis which establishes benchmark economics using standard technologies. New technologies were then incorporated into these scenarios and the economic impact was compared to the benchmark field development results. Use of this process provides insights, for the conditions studied, into new technologies' ability to have commercial impact on deepwater marginal fields. This paper provides an overview of this work and findings.

Introduction:

DeepStar System Engineering CTR 6901 evaluated the life cycle economic aspects of three long offset marginal tie-back fields identified as Cottontail, Coyote and Hyena (all are scavenger names). The characteristics of these fields are given in Table 1. The evaluation was performed in two parts.

The first part applied currently available technology to these 3 fields to establish the current industry capability and related commercial performance. Four of these "base cases" were established for each of the three reservoirs.

The development scenario alternatives used in this evaluation were:Subsea tiebacks with heated flowlinesVertical well access (Dry Tree in 5,000 fsw)In-field processing system on structure.Subsea Processing System. Graphically, these 12 scenarios are illustrated in Figure 1.

Each scenario was evaluated using a typical project economics approach which accounts for all CAPEX, OPEX, production profile, etc over the life of the field. An Excel spreadsheet developed by AkerKvaerner was used for this purpose to make all data visible and easy to understand. This is an important feature since this work only has value to a large and diverse group if the details can be understood, challenged & ultimately believed. This evaluation identified the "benchmark" scenario for each field with the most avorable economics from the Operator's perspective. These were:Cottontail - Case 1: A standard 4-well tie-back using an electrically heated flowline for flow assurance in 5,000 fsw with a 30 mile offset to the Host facility.Coyote - Case 14: This 10,000 fsw 50 mile offset field performed best with a 3-phase subsea processing system.Hyena - Case 6: For this 5,000 fsw West of Africa Field, a satellite structure with dry tree production wells gave the best economic results.

This best economic scenario for each field became the "benchmark" example against which all other development alternatives and technologies may be compared.

The second part of CTR 6901 evaluated the 10 selected technologies listed in Table 2 as if they were commercially mature and technically viable as projected by their sponsors.

Each emerging technology was individually evaluated in the respective benchmark development scenario (or other scenario where appropriate) and the economic results were evaluated. None of these technologies generated an economic step change in the field life cycle economics for the tie-back field conditions evaluated.

The technologies yielding (small) positive economics were consolidated together to determine their collective impact on these marginal tie-back field economics. The result identified a combination of emerging technologies, which together, have potential to improve the field's life-cycle economics.