The Gunnison Discovery—Garden Banks Block 668, Gulf of Mexico

Jeff Gee-shang Pan¹ and Jim Fulcher^2
1Kerr-McGee Oil and Gas Corporation, 16666 Northchase Drive, Houston, Texas 77060
²Nexen Petroleum U.S.A., 12790 Merit Drive, Suite 800, Dallas, Texas 75251-1270

In April 2000, Kerr-McGee Oil and Gas Corporation and its partners Nexen Inc. and Cal Dive International drilled the discovery well of the Gunnison Field in Garden Banks Block 668. Garden Banks Block 668 is located about 155 miles southeast of Galveston, Texas and it is in 3,200 feet of water. The Gunnison Field 2P reserves are estimated to be up to 120 MMBOE.

The Gunnison Field is located on the south side of a ramped-minibasin created by the loading of allochthonous salt in Garden Banks blocks 667, 668 and 669. The original prospect generation and evaluation of the 3 "shallow" objectives in the Gunnison minibasin was primarily based on the regional geological work and study of the 2D seismic data prior to 1998. In mid-1998, 3D seismic data became available. Mapping of the re-processed GPI 3D data in 1999 produced 5 new levels of amplitude-supported targets in a deeper interval. The pre-drilled age prognosis of the eight targets ranged from Lower Pleistocene to Upper Pliocene. Several of the amplitudes conformed to down-dip structural limits and exhibited positive amplitude with offset response in good trapping configurations. The features of amplitude conformance and positive amplitude with offset significantly reduced the risk of the prospect. Geopressure analysis further mitigated the seal risk factor of the shallow targets; however, due to the difficulty of seismic imaging near salt flank, trap element remained the primary risk for the deep targets.

Due to the risk of the deeper objectives, poor imaging, low oil price (average $12) and budget issues, the two original partners opted not to participate. Kerr-McGee, as-the operator, presented the prospect 33 times to 16 different companies in order to subscribe new partners. The Gunnison discovery well GB 668 #1 was spudded in April 2000, with KMG 50%, CXY Canadian OXY, now Nexen 30%, and Cal Dive International 20%. The Gunnison Field was discovered just before midnight on Easter Sunday as the drill bits penetrated the first of twelve field pays (5 in the "shallow" and 7 in the "deep").

After 10 well penetrations, the Greater Gunnison Field was sanctioned for development in October 2001. The ups and downs of field size, extent of area, column heights, thickness and fluid quality were all addressed by the exploration and development teams. Thirty-two months after the discovery, on December 11, 2003, Gunnison Field achieved first production from the first of three sub-sea wells. The field is now ramping up to its projected peak daily production rate of approximately 30,000 barrels of oil and 180 million cubic feet of gas.

AAPG Search and Discovery Article #90080©2005 GCAGS 55th Annual Convention, New Orleans, Louisiana