From Discovery To Production In 18 Months: Evaluation and lntergration of Geotechnical Data in a Fast Track Development Strategy, Zafiro Field Offshore Equatorial Guinea
Authors: Blundell Lane C. , Famakinwa S. Bolaji , Stephens Andrew R. , Monson Gene D. 
Published: October 2008

The Zafiro Field, located in License Area B, offshore Bioko Island, Equatorial Guinea, was discovered by Mobil and partners United Meridian Corporation in March, 1995. The Field was the subject of a "fast track" development program with first production achieved less than 18 months after the initial discovery. This fast track development approach utilizes a Floating Production, Storage and Offloading vessel (FPSO) with subsea completion and tieback of wells. The decision to proceed with development followed limited appraisal drilling, no additional seismic data and limited reservoir and performance data which produced a large range of uncertainty in the estimate of recoverable reserves for the Zafiro Field.

The Zafiro reservoirs are oil and gas bearing sands that were deposited in a deep-water setting. Detailed examination of over 2000' of conventional core has led to an excellent understanding of the depositional processes and reservoir characteristics of these sands. The current seismic database comprises 2D and a recently acquired 3D survey. Workstation based amplitude extraction, together with other attribute analysis and 3D visualization techniques are being applied to delineate the main Zafiro reservoirs. Phase I development is complete with a total of 6 wells on line and production exceed 36,000 BOPD as of February, 1997. Peak production is expected to reach 80,000 BOPD in late 1997.

INTRODUCTION

The Zafiro Field is situated in License Area B (Block B), in the western offshore area of Bioko Island, Equatorial Guinea, adjacent to the international border with Nigeria (Figure I). The field lies approximately 36 kilometers (22.5 miles) southeast of Mobil's Edop Field in Nigeria and 68 kilometers (42 miles) west northwest of the island of Bioko. The License Area covers approximately 500,000 acres with water depths ranging from less than 300 feet to greater than 5000 feet. The License Area and the Zafiro Field are operated by Mobil Equatorial Guinea Inc. with a 75% interest and partner United Meridian Corporation who hold the remaining 25% interest. The Zafiro Field is divided into three primary areas, the main Zafiro area to the west, the Opalo area to the northeast and the Topacio area to the south. The field is approximately 12 by 10 kilometers in size with water depths over the Zafiro Field itself ranging from 450 feet to over 1900 feet.

FIELD HISTORY

Mobil farmed into the license area in May 1994. The first exploratory well drilled on Area B, offshore Bioko Island, Equatorial Guinea by the MobilILIMC group was the unsuccessful Delta- l well which targeted a pre Qua-lboe interval. The Zafiro Field was discovered with the drilling and testing of the Zafiro-l well in March 1995. The Zafiro-l well targeted shallower, Pliocene, Intra-Qua Iboe, amplitude-laden sedimentary packages. Drilled in 634' of water, the Zafiro- I well encountered excellent oil-bearing reservoir sands between 5000 feet and 5400 feet subsea. These high porosity-permeability reservoirs tested at over 10,500 BOPD on 2 3/8" choke. The discovery was followed in quick succession by the successful appraisal wells Zafiro-2, Opalo- 1 and Zafiro-3. These subsequent wells encountered similar sandlshale sequences although correlation between wells was difficult.