Print this pageExploitation of Thin Oil Rims Using Horizontal Sidetracks at MC 194 (Cognac) Field
DANAHY, MICHAEL A. and JEFFREY R. SCHEIBAL
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 8200 and 9300 feet subsea. Cognac Field, discovered in July 1975, is a faulted downthrown rollover anticline developed by a 1260-foot 62-slot conventional platform in 1024 feet of water. Primary development drilling concluded in 1981 and a 3D 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 true vertical thickness. Unconventional slim-hole sidetracking techniques (6-3/4 inch and 4-3/4 inch hole) were employed by a workover-class platform rig to drill 11 oil rim horizontal wells with an average completed length of 1160 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 of 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.