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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Exploitation of Thin Oil Rims Using Horizontal
Sidetracks at MC 194 (Cognac) Field
By
Shell Offshore Inc., New Orleans, LA
Horizontal wells have been utilized in Cognac Field (GOM Mississippi Canyon 194) to deplete remaining oil rims in five Pliocene age deltaic sand reservoirs between 8,200 and 9,300 feet subsea. Cognac Field, discovered in July 1975, is a faulted downthrown rollover anticline developed by a 1,260-foot 62-slot conventional platform in 1,024 feet of water. Primary development drilling concluded in 1981, and a 3-D seismic survey was shot in 1987 resulting in a successful 20-well redevelopment program to address bypassed oil.
In early 1993, evaluation of remaining
economic potential strongly indicated
the need to accelerate the recovery of
remaining oil reserves prior to gas cap
blow
-down. Pulsed neutron logs,
combined with conventional production
surveillance, delineated rims of
60 to 100 feet of m e vertical thickness.
Unconventional slim-hole sidetracking
techniques (6-3/4" and 4-3/4"
holes) were employed by a workover-class
platform rig to drill 12 oil rim
horizontal wells with an average completed
length of 1,160 feet.
Recognition and detailed mapping of
depositional environments were
important in planning and steering
sidetracks. Over an average producing
life of 12 months, a favorably
positioned oil rim horizontal well produces
at rates 3 to 10 times that of a
conventional completion. Thin oil
rims, originally classified as economically
marginal, have contributed a
robust 41% (5.2 MMBO) of the field's
oil production since the beginning of
the sidetrack program in January
1994.
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