Stratigraphic Organization and Predictability of Mixed Coarse- and Fine-Grained Lithofacies Successions in a Lower Miocene Deepwater Slope Channel Complex System, Angola Block 15

M.L. Porter¹, A.R.G. Sprague², M.D. Sullivan³, D.C. Jennette⁴, R.T. Beaubouef⁵, T.R. Garfield⁵, C. Rossen¹, D.R. Sickafoose⁵, G. N. Jensen¹, S.J. Friedmann⁶, and D.C. Mohrig^7
1 ExxonMobil Development Co, Houston, TX
² ExxonMobil Upstream Research Co, Houston, TX
³ Chevron Oil, Houston, TX
⁴ Apache Oil, Houston, TX
⁵ ExxonMobil Exploration Company, Houston, TX
⁶ Lawrence Livermore Laboratory, Livermore, CA
⁷ M.I.T, Boston, MA

Regional seismic mapping identified Lower- and Middle Miocene Slope Channel Systems as significant exploration targets for Angola Block 15. Seventeen exploration wells, followed by four appraisal wells established these slope channel complexes as a world-class development opportunity. ExxonMobil's current development activity targets stacked turbidite-dominated reservoirs in long-reach, high-angle wellbores tied back to Tension Leg Platform (TLP) and close-moored FPSO facilities.

One of the major development targets in Block 15 is Burdigalian-aged (Bur1) slope channel reservoirs. This slope channel system traverses across the block in an east-west direction and can be continuously mapped on adjacent seismic datasets over a 30-40 km reach. Map patterns of the Bur1 system show distinctive changes in sinuosity, channel confinement and degree of amalgamation broadly related to concurrent growth of salt-related structures. Channel complex confinement is more pronounced and lateral amalgamation better developed in segments that cross structural highs. The Bur1 channel system shows higher sinuosity, weaker lateral amalgamation and less erosional confinement in synclinal lows.

The episodic fill of the Bur1 slope channel system can be better understood by a hierarchical arrangement of unconformity-bounded stratal units. Within these unconformity-bounded channel sets, nested channels form composite channel complexes that show distinctive trends in lithofacies type and vertical facies succession. Conventional cores calibrated to well-logs and high-resolution seismic data show the lower portions of the channel complexes are dominated by sandy-muddy debrites, slumps and injected sandstones. These facies are typically overlain by coarse-grained, gravelly and well-amalgamated sandy turbidites. The overlying facies succession is more variable, but commonly consists of interbedded sandy and muddy turbidites, injected sandstones, and a range of both muddy and sandy debrites.