Marginal field development: the nigerian experience

With the limited frequency content of the seismic data, stratigraphic information from seismic was restricted to the identification of thick, sandstone-prone fairways that were mapped throughout the field area as architectural elements in the reservoir model. Tying to the low frequency inversion data placed the seismic tops and bases of these architectural elements in the shales above and below the corresponding sandstone unit in the well logs. This architectural element interpretation forms the basis for well-to-well correlation, field volumetrics, and reservoir modeling.

A channelized sheet system was selected as the most likely depositional model for the 17MY reservoir based on the available seismic and well data.  To fully capture the potential range of depositional systems and associated in-place volumes and connectivities caused by variable net-to-gross and reservoir architecture, four end-member models were also created:  isolated channel, isolated sheet, amalgamated channel, and amalgamated sheet. 

The resulting earth models (three hundred in all) were statically and dynamically ranked using streamline flow simulation to select low-, mid-, and high-case earth models for use within Experimental Design (ED) to supply probabilistic production forecasts.  In addition to a range of earth models, a range of other geologic and petrophysical parameters were supplied for use in ED, including permeability, permeability contrast, number of faults, and fault seal/transmissibility.

The limited number of wells and low resolution seismic data result in considerable uncertainty with respect to many elements of the geological model. To fully understand the range and impact of these uncertainties, probabilistic volumetric analyses were completed using Crystal Ball.  The P₅-P₅₀-P₉₅ in-place probabilistic volumes were used as a benchmark to verify that the range of in-place hydrocarbons in the earth models was reasonable.

This workflow provided a methodology for testing the Agbami field development plan against a wide range of key uncertainties.  Key challenges faced by the project team included:

         Finding suitable geologic analogs, including data on input parameters such as object geometries.

         Gaining consensus and buy-in with respect to input parameters and methodologies from a large subsurface team, peers, and partners.

         Building the framework, both structurally (i.e., properly modeling a thrust fault in close proximity to the wells) and stratigraphically (i.e., architectural elements that laterally pinch-out.)

         Model resolution (vertical and aerial) vs. model size.

 

Simulation and Results

Field data, laboratory data, and analog data were incorporated into a range of reservoir simulation models. The field data included appraisal well logs, cores, 3D seismic, fluid samples, pressure data, and drill stem tests. 

Experimental Design was used throughout the evaluation to obtain the maximum information with the minimum computational effort. The results from this process facilitated the identification of the key uncertainties and provided direct input into economic models for decision analysis. During each phase of the process key parameters of uncertainty were identified and ranked in terms of project impact. Field development options were evaluated in distinct phases over the full range of uncertainty.

In Phase Two of the evaluation, the pressure maintenance schemes were selected.  Crestal gas re-injection with peripheral water injection was chosen for the 17MY reservoir. Crestal gas re-injection only was selected for the 14MY and 16MY reservoirs. These approaches to pressure maintenance deliver an effective full life gas disposition strategy for the Agbami Field.  The facility capacity requirements were also selected during this phase.

In Phase 3 of the evaluation the well count parameter was investigated and the optimum number of 38 wells was selected. Production profiles were generated and presented in terms of P10, P50, and P90.

 

David Grimes began his career with Texaco in Houston in 1978 and joined ChevronTexaco in 2001 through their merger with Chevron. He is currently assigned as a Geophysicist on the Agbami Development Subsurface Team, a part of ChevronTexaco Overseas Petroleum Company’s Nigeria/Mid-Africa Strategic Business Unit. In addition to this current development assignment, he has worked international exploration projects in Nigeria and Angola and domestic exploration projects in the Rocky Mountains and in West Texas.  He began his career in seismic data processing and analysis and worked on projects from around the world. He served on Texaco’s Exploration Risk Committee in the year prior to the merger with Chevron. David has a B.S. Degree in Mathematics and Physics from Stephen F. Austin State University and is currently a member of the SEG. His email is grimesdl@chevrontexaco.com.

 

Elliott Ginger has worked for ChevronTexaco (via Getty Oil Company and Texaco) since 1981.  He is currently the Reservoir Characterization Team Leader for the Agbami Development Subsurface Team.  Previous assignments have included sixteen years as a reservoir geologist at Getty and Texaco’s Exploration and Production Research Center working on reservoir characterization/earth modeling projects on fields in the Middle East, Australia, Guatemala, China, Gulf of Mexico, Alaska, California, West Texas, New Mexico, and Alabama.  He also spent 1.5 years in Perth, Australia, as a secondee on behalf of Texaco to West Australia Petroleum Pty. Ltd. as a member of the Drilled Resources Team for the Greater Gorgon gas fields, Northwest Shelf, Australia.  Elliott has a B.S. Degree in Geology from Ohio University and is a member of AAPG.

SAN RAMON, Calif., Jul. 14, 2003 -- ChevronTexaco today confirmed the announcement by The Nigerian National Petroleum Corporation (NNPC) that an agreement has been reached by NNPC; Famfa Oil Limited; ChevronTexaco affiliate, Star Deep Water Petroleum Limited; and Petroleo Brasiliero Nigeria Limited (Petrobras) that will govern future operations on the petroleum concession covered by OPL 216, offshore Nigeria. The agreement clears the way for planned activities towards the development of the Agbami Field.

Commenting on the announcement, George L. Kirkland, President, ChevronTexaco Overseas Petroleum Inc., said: "This agreement marks an important stage in the development of the Agbami Field, itself an important component of ChevronTexaco's growth strategy in West Africa. With our partners, we can now move forward in earnest towards our targets of first oil by 2007 and adding an eventual 250,000 barrels of oil per day to Nigeria's output during peak field production."

The Agbami partners will now move ahead immediately with the project bidding process, which will lead to the award of contracts for the provision of a Floating Production, Storage and Off-loading vessel and the construction and installation of sub-sea production facilities.

The Agbami Field ranks among the largest single discoveries in deepwater West Africa, with a structure spanning an area of 45,000 acres that straddles OPL 216 and OPL 217. The initial discovery well, announced in January 1999, encountered 420 feet of net pay in multiple zones. Produced hydrocarbons from the reservoir are light (45 degree API gravity) and sweet with no contaminants.


http://www.chevron.com/news/press/2005/2005-02-22.asp



ChevronTexaco and Partners Sign Agbami FPSO Construction Contract

ABUJA, Feb. 22, 2005 -- Star Deep Water Petroleum Limited, an affiliate of ChevronTexaco Corporation today signed the agreement for the award of the contract for the construction of the Floating Production, Storage and Offloading (FPSO) vessel for Agbami Field to Daewoo Shipping and Marine Engineering (DSME) Corporation of South Korea. The Managing Director of ChevronTexaco Nigeria and Mid-Africa Business Unit, Mr. Jay Pryor, signed on behalf of the Agbami Unit while the President and Chief Executive Officer of DSME Mr. S. L. Jung signed on behalf of the contractor.

The signing of the $1.1 billion FPSO construction contract is a key milestone in the development of the Agbami field scheduled to come on stream in 2008 with a daily production of about 250,000 barrels of oil.

"We are excited by today’s ceremony which represents for us, and our partners in the Agbami project, a major milestone in our efforts to bring the giant Agbami field into production on schedule. We are deeply appreciative of the tremendous amount of effort by all partners to get us to this point in our plan for the Agbami Field development," said Mr Pryor who also congratulated Daewoo Shipping and Marine Engineering (DSME) for winning the bid to build the FPSO for the Agbami Field.

In addition, Mr. Pryor said that the project will emphasize ChevronTexaco’s core values in the area of Safety, Environmental Stewardship, Transparency, Local Content Development and Community Engagement. "We are aware that many people regard Agbami as remarkable for its reserves," Pryor noted, "but we want the project execution to show that it has more to offer Nigeria and its other stakeholders than production figures." In reference to the company’s commitment to environmental stewardship, the MD added that "our goal is to leave very minimal impact on the environment as we produce the Agbami Field."

Engineer Kupolokun, the Group Managing Director of NNPC, said that with the signing of the FPSO construction contract, the country is again set to extend the frontiers of success in the industry and create further opportunities for growth and development for Nigeria. "Apart from the production and reserves addition that this project brings, it will also set the standard for Local Content participation in Nigeria’s Deepwater Projects," he said. "We project that up to an astonishing 6,500 Tons of fabrication and 300,000 man-hours of engineering and services will be performed by Nigerians on this FPSO contract alone. This is significantly more than has ever been done on any Deepwater Project in Nigeria," Engineer Kupolokun added.

ChevronTexaco, through its affiliate – Star Deep Water Petroleum Limited is the operator of the Agbami Unit. Located in water depth of about 4,500 feet, the field straddles OMLs 127 and 128. Other partners in the project include Texaco Nigeria Outer Shelf Inc. (a ChevronTexaco affiliate), Petroleo Brasileiro Nigeria Limited, Statoil Nigeria Limited, Famfa Oil Limited and the NNPC. The Field is located about 70 kilometres offshore in the central area of the Niger Delta.

http://www.searchanddiscovery.com/documents/abstracts/2004regional_west_africa/abstracts/pearce.htm
Developing World Class Deepwater Capabilities: Value Creation through Partnerships

James Pearce¹, Nita Nautiyal², and Tad Schirmer^1
1 ChevronTexaco Nigeria Limited, Lagos, Nigeria
² ChevronTexaco Nigeria Limited, Houston, TX

ChevronTexaco's deepwater portfolio in Nigeria is robust covering 11 production sharing contract blocks, representing the largest deepwater acreage holding in the country. ChevronTexaco is either operator or technical adviser in half of these blocks. Several discoveries have been made and development is proceeding on the billion barrel Agbami field in 5000 feet of water about 70 miles offshore in Nigeria.

Continuing with an aggressive exploration and appraisal program, while developing known discoveries, will require extensive in-country capacity building, national employment and new business generation. A critical success factor for this program will be the development of "deepwater organizational capability" or "OC". This will include recruiting of university graduates and some experienced hires, identification of key skills needed for deepwater exploration, development and operations, skills assessment for new hires and experienced hires, a focused development program to provide skills enhancement, and finally a comprehensive post-training evaluation program.

ChevronTexaco has developed and began implementation of the initial OC program for deepwater development. Sixteen critical skills area have been identified, a skills assessment program developed, and hiring initiated. A follow-up program covering deepwater operations is now being implemented targeted on providing a strong Nigerian-based operations group for Agbami field operations. The Agbami field is now scheduled to go on production in late 2007. Within four years of operation, the workforce will be 90% Nigerian. Further, ChevronTexaco is working closely with NAPIMS, the commercial arm of the Nigerian National Petroleum Corporation, on the implementation of this program for the Agbami field with NAPIMS professionals will be participating in the OC program.

This paper will describe the elements of the ChevronTexaco deepwater OC program, progress to date in the areas of development and operations, and future plans in Nigeria.

http://www.spe.org/elibinfo/eJournal_Papers/spe/2005/EREE/12/SPE-91012-PA/SPE-91012-PA.htm
Incorporating Uncertainties in Well-Count Optimization With Experimental Design for the Deepwater Agbami Field
Paper Number 91012-PA

Authors Narahara, G.M.; Spokes, J.J.; Brennan, D.D.; Maxwell, G.; Bast, M. Journal

SPE Reservoir Evaluation & Engineering Issue, Volume 8, Number 6, December Pages pp. 548-560

Cross-Ref DOI10.2118/ 91012-PA

Copyright 2005. Society of Petroleum Engineers Preview

Summary

This paper describes a methodology for incorporating uncertainties in the optimization of well count for the deepwater Agbami field development. The lack of substantial reservoir-description data is common in many deepwater discoveries. Therefore, the development plan must be optimized and proven to be robust for a wide range of uncertainties. In the Agbami project, the design of experiments, or experimental design (ED) technique, was incorporated to optimize the well count across a wide range of subsurface uncertainties.

The lack of substantial reservoir-description data is common for many deepwater discoveries. In the Agbami project, the uncertainty in oil in place was significant (greater than a factor of 2). This uncertainty was captured in a range of earth (geologic) models. Additional uncertainty variables, including permeability, fault seals, and injection conformance, were studied concurrently. Multiple well-count development plans (high, mid, and low) were developed and used as a variable in ED. The ED technique allowed multiple well counts to be tested quickly against multiple geologic models. With the net present value (NPV) calculated for each case, not only was the well count for the overall highest NPV determined, but discrete testing of each geologic model determined the optimum well count for each model. The process allowed for testing the robustness of any well count vs. any uncertainty (or set of uncertainties).

A method was demonstrated quantifying the difference between perfect and imperfect knowledge of the reservoir description (geologic model) as it pertains to well locations.

The Agbami structure is a northwest/southeast-trending four-way closure anticline and is located on the Niger delta front approximately 65 miles offshore Nigeria in the Gulf of Guinea (see the map in Fig. 1). The structure spans an area of 45,000 acres at spill point and is located in 4,800 ft of water. The Agbami No. 1 discovery well was drilled in late 1998. The appraisal program was completed in 2001 and included five wells and one sidetrack drilled on the structure, with each encountering oil pay. These five wells and a sidetrack penetrated an average of approximately 350 ft of oil.

In this phase (Phase 3) of the development process, the key objectives are to construct a field-development plan and to obtain sanctioning. With drilling depths of up to 10,000 ft below mudline in 4,800 ft of water, well costs at Agbami will be at the high end of typical deepwater costs. Therefore, an important optimization parameter in the field development is the total well count.

Agbami is typical of many deepwater developments in that the seismic is less than perfect and the appraisal well data are sparse relative to the area coverage. Therefore, subsurface uncertainty is high. In fact, the 5% probable oil in place is more than two times the oil in place at the 95% probability. As a result, the development process is challenged with determining the optimum well count for the field development across the wide range of subsurface uncertainty.

Several key development decisions were determined in the previous phase (Phase 2) of the development process. These decisions were taken as givens in this study and are listed as follows:

• The recommended pressure-maintenance scheme and gas-disposition strategy for the 17 million-year (MY) units is a combination of crestal gas injection with peripheral water injection.

• The recommended pressure-maintenance scheme and gas-disposition strategy for the 14MY/16MY units is crestal gas injection only.

• The facility design capacity recommendations are:

- 250,000 stock-tank bbl per day (STB/D) oil.

- 450,000 thousand cubic ft per day (Mcf/D) gas production.

- 250,000 STB/D water production.

- 450,000 STB/D liquid production.

http://www.nigeriasaotomejda.com/PDFs/JDZ%20Brochure.pdf Regional Geology and Petroleum Prospectivity   REGIONAL GEOLOGY The Gulf of Guinea is one of the most prolific hydrocarbon provinces of the world. Intensive exploration efforts over the last 35 years in and around the Niger Delta in particular has led to a succession of significant discoveries, notably the Bonga, Agbami/Ekoli and Akpo discoveries in Nigeria and Zafiro and Alba in Equatorial Guinea. However, the full potential of the continental slope and rise seaward of the shelf break is only recently becoming apparent, with a number of exploration programs having resulted in world-class discoveries being made in recent years.