Tahiti: Development Strategy Assessment Using Design of Experiments and Response Surface Methods
- Patricia Elva Carreras (Chevron Energy Technology Co) | Scott Edward Turner (Chevron North American E&P) | Gwendolyn Tharp Wilkinson (Chevron USA Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Western Regional/AAPG Pacific Section/GSA Cordilleran Section Joint Meeting, 8-10 May, Anchorage, Alaska, USA
- Publication Date
- Document Type
- Conference Paper
- 2006. Society of Petroleum Engineers
- 2.3 Completion Monitoring Systems/Intelligent Wells, 5.7.5 Economic Evaluations, 5.1.1 Exploration, Development, Structural Geology, 5.6.4 Drillstem/Well Testing, 5.4.1 Waterflooding, 1.6 Drilling Operations, 5.7.4 Probabilistic Methods, 5.3.1 Flow in Porous Media, 2 Well Completion, 7.3.3 Project Management, 4.1.2 Separation and Treating, 2.4.3 Sand/Solids Control, 7.1.9 Project Economic Analysis, 5.5 Reservoir Simulation, 4.5 Offshore Facilities and Subsea Systems, 5.1.2 Faults and Fracture Characterisation, 7.1.10 Field Economic Analysis, 4.1.5 Processing Equipment, 4.3.4 Scale
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Tahiti field in deepwater Gulf of Mexico is a three-way anticlinal structure trapped against salt, with primary hydrocarbon-bearing turbidite sands ranging from 24,000 to 27,000 ft TVD. The discovery well was drilled in 2002, and two appraisal wells were drilled soon afterwards. Due to significant uncertainties remaining after appraisal, probabilistic methods were used to assess development alternatives.
In this study the classical experimental design method was applied and reasonable P10, P50 and P90 reservoir simulation models were designed. Next, we looked upon the development plan by performing a second round of design of experiment runs with uncontrollable uncertainties and decisions as factors. The goal was to validate that the previously selected models reasonably represented P10, P50 and P90 oil recoveries and net present value after including decisions in the design. The validation worked out properly reinforcing the confidence in the model selection. Finally, the polynomial response models were used to explore multiple scenarios by varying decisions across the whole range of uncontrollable uncertainties.
The proposed workflow enhances the use of experimental design by combining the technique with response surface methods and rational engineering judgment. The approach is recommended for the evaluation of greenfields when a new perspective of the economic analysis of project decisions is desired.
Tahiti field is located in more than 4,000 ft of water in the Green Canyon area of the Gulf of Mexico, about 190 miles southwest of New Orleans as shown in Fig. 1. The field was discovered in April 20021 with the drilling of well GC 640 #1. Results from the exploratory well indicated the presence of high quality reservoir sand with total net pay of over 400 ft essentially distributed in three main Miocene turbidite sheet sands at depths ranging from 24,000 to 27,000 ft TVD. In 2003 two appraisal wells were drilled simultaneously using two rigs. One of the appraisals encountered more than 1,000 ft of net pay in high-quality sandstones, confirming one of the most significant net pay accumulations in the history of the deepwater Gulf of Mexico.[2-4] A successful test5 of the discovery well was performed in the second quarter of 2004. The field will be developed in phases. The first phase of development was fully sanctioned in August 2005 by Tahiti joint venture partners Chevron, Statoil and Shell at a cost of more than $1.8 billion.6 Total capital costs for the project are anticipated to be approximately $3.5 billion. Chevron is the operator and holds a 58% working interest. Statoil holds a 25% interest, and Shell holds a 17% interest (Total E&P USA, Inc. purchased Shell's working interest effective January 20067). The field is expected to come on-line in mid-2008.
Due to significant uncertainties remaining after appraisal, probabilistic methods were used to assess development alternatives during Phases 2 and 3 of Chevron's project management process. Phase 2 work (select preferred alternative) was presented in another paper.8 The main purpose of this study, part of Phase 3 (develop preferred alternatives), was to assess a mature predevelopment strategy. The proposed workflow enhances the use of design of experiments (DOE) by combining the technique with response surface methods and rational engineering judgment. The approach is recommended for the evaluation of greenfields when a new perspective of the economic analysis of project decisions is desired.
In consideration of the highly confidential nature of the project, field characteristics are described in very general terms and normalized results are presented.
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