Page 157 - Geology of Carbonate Reservoirs

138 DEPOSITIONAL CARBONATE RESERVOIRS

Debrite Coarse Turbidite

Figure 5.13 Slope - toe successions are characterized by debrites and coarse (proximal) tur-

bidites or grain flows. Fine (distal) turbidites, rhythmites, and laminites occur farther from

the slope and are more typical of basinal deposition. Debrites and coarse turbidites are gen-
erally absent on ramps owing to the absence of steep slopes that may be unstable and subject
to collapse or shedding during storms, earthquakes, or other “ events ” that trigger slope
failure.
basic task of the geoscientists and engineers who must decide where to drill the next
well and how to develop a field in the most cost - effective manner. Identifi cation and

classification of porosity is the first step in determining the geological origin of a

reservoir, predicting its 3D size and shape, and ultimately, in identifying and ranking

individual flow units, baffles, and barriers.

The following checklist includes some of the basic methods for identifying and
exploiting depositional carbonate reservoirs.

1. Determine the platform type and standard depositional succession or succes-

sions that make up the reservoir in order to predict depositional anatomy of
the reservoir body. Next, identify and classify genetic pore types by examin-
ing rock samples from full - diameter or sidewall cores, or cuttings. Determine
which pore types — depositional, diagenetic, fractures, or hybrids of those end
members — dominate the reservoir interval. It they are depositional pores or
hybrids with dominant depositional attributes, use facies maps as substitutes
(proxies) for porosity. For hybrids with diagenetic attributes dominant, iden-
tify the diagenetic processes and timing of diagenetic changes in order to

map the size and shape of flow units. For example, moldic porosity in a
grainstone – packstone reservoir may or may not occupy the entire facies
volume, in which case the portion of the facies that was affected by
dissolution has to be determined by identifying stratigraphic characteristics
such as unconformities, caliche surfaces, karst features, or other evidence of