Abstract: Exploration of the Haute Mer Block, Offshore Congo

MAURIAUD, P., D.DRAPEAU, M.VESSERON, and A.KOTHE

The block covers 2275 km2 in the southeast part of the coastal Congolese basin. Bathymetry ranges from 100m to 1100m, 60% being deeper than 500m. Since 1983, 12 exploration wells have been drilled leading to 2 major discoveries: Nkossa where production started in June 1996 and Moho which is still under appraisal.

The geological setting is controlled by the opening of the South Atlantic ocean; three phases are classically recognized: (1) a rift phase of Neocomian age characterized by lacustrine organic rich sedimentation and tilted blocks tectonics; (2) a post-rift phase characterized at the base by Aptian salt deposits followed by a mixed clastics and carbonates sedimentation from Albian to Cenomanian; structuration during this phase is related to the gravity sliding of Albian carbonates on ductile salt deposits; and (3) the margin phase beginning in Senonian-Turonian is marked during the Neogene by a western tilt of 3 to 4 degrees, erosion of the African craton and deposition of a thick prism of deep sea terrigenous series.

Two petroleum systems are recognized: in the north, a presalt source rock generating hydrocarbons trapped in pre and post salt reservoirs; in the south source rocks and reservoirs are post-salt deposits. The exploration is focused on 3 main plays: presalt sandstones of the gres de base formation around the Likouala high, postsalt mixed platforms carbonates of Albo-Cenomanien age (Nkossa and Moho) and slope and basin sandstones deposits of Tertiary age. The two last plays are considered to have the best potential.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria