Reservoir Characterization of Confined Sheet Reservoirs using Borehole Images and Core, Tahiti Field, Gulf of Mexico, U.S.A

Stelting, Charles E.¹, William J. Schweller², Gigi Ellis³, Scott E. Turner⁴, Myrt E. Cribbs⁴, Freddy Yip⁴ (1) Chevron Energy Technology Company, Houston, TX (2) Chevron Energy Technology Company, San Ramon, (3) Chevron North America Exploration & Production, Houston, (4) Chevron North America Exploration & Production, Houston, TX

In the Tahiti Field, GOM, approximately 3250 ft of Oil Based Micro-Imaging (OBMI) data in nine wells were calibrated with nearly 400 ft of core from the two main reservoirs to improve characterization of confined sheet sands in a sub-salt basin with minimal seismic definition. Several reservoir units have been identified in four Early Miocene third-order sequences. Of these reservoirs, approximately 90% of the recoverable resources are in the M15 and M21 sands. Four depositional facies are defined in the cores and subsequently characterized in the OBMI data: 1) amalgamated, fine- to very fine-grained, massive sandstones; 2) Medium- to very thick-bedded, very fine- to fine-grained, massive to graded beds with preserved bed caps; 3) stratified mudstones and 4) chaotic mass-transport facies. Each facies type has distinct borehole image character.

The amalgamated, massive sandstone facies occupies greater than 90% of the M21B Sand. Bedded sands indicative of lower energy and mass-transport deposits are rare. The M21A Sand, a compensationally stacked complex, is composed of two massive sandstone lobes. The lower lobe thickens toward the basin center whereas the upper lobe thickens toward the basin edge. The M15A Sand is also dominantly massive sandstone (75%), but frequently occurring bedded sandstones, debrites and mudstones support an inference of lower lateral continuity and reduced connectivity relative to the M21 sands. Integration of the OBMI data and core was a critical component for the construction of reservoir models.