Geology Reference
In-Depth Information
PRACTICAL USE OF MICROFACIES
The third part of the topic provides insights into applied aspects of microfacies studies. Chapter 17 considers the
role of microfacies in reservoir rock analyses of hydrocarbon reservoirs and carbonate-hosted base metal depos-
its. Chapter 18 deals with carbonate resources and rock properties and their depositional and diagenetic controls.
Chapter 19 emphasizes a very promising approach, the use of microfacies in archaeology.
17 Reservoir Rocks and Host Rocks
Reservoir rocks are characterized by petrophysical
properties favoring the capacity for the migration and
storage of fluids, gas and minerals. Microfacies analy-
sis has been strongly triggered by the exploration and
development of hydrocarbon reservoirs and source
rocks in limestone and dolomites and is still of interest
in understanding depositional controls, facies hetero-
geneities and reservoir property distribution.
Carbonates can also be host rocks for ore deposits.
Patterns of syn- and epigenetic mineralizations become
more understandable from the use of microfacies data.
sheets on shelves and ramps (Smackover Forma-
tion, USA),
•
reefs and mounds formed on platforms, ramps and
shelves, and platform-margin reefs (Malampaya,
Philippines),
•
downslope debris and allochthonous platform and
reef material intercalated within basinal sediments
(Poza Rica, Golden Lane, Mexico), and
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chalks formed on deeper shelves and basins (Creta-
ceous Chalk, North Sea).
Carbonate reservoirs linked strongly to
diagenetic
processes
are related to
•
subunconformities, subaerial exposure and karst,
often associated with leaching processes (Camposta,
Spain),
17.1 Carbonate Hydrocarbon
Reservoirs
•
early and late diagenetic dolomitization (Arab ABC
Formation, Middle East),
Estimations of the proportion of carbonate rocks to the
total of world's hydrocarbon production vary between
about 40% and more than 60%. Carbonate rocks con-
tain the world's largest reservoirs in the Middle East
(e.g. Ghawar Field, Saudi Arabia) and Kazakhstan (e.g.
Kazagan Field). Facies analysis is a critical explora-
tion tool. The objective of reservoir studies is to con-
struct reservoir models that describe or predict poros-
ity and permeability distribution.
•
fracturing (Maracaibo Platform, Venezuela), and
•
burial diagenesis (Devonian, Alberta).
Being able to recognize both the depositional fa-
cies and the diagenetic history is essential in under-
standing the creation and preservation of carbonate res-
ervoirs. Facies analysis helps in identifying environ-
ments and establishing depositional models including
prediction of reservoir extent and rock types.
Carbonate reservoirs can be grouped according to
their depositional setting or diagenesis (Roehl and
Choquette 1985). Common reservoirs tied to
deposi-
tional settings
are located in
•
The
theme of volume 83/11 (1999) of the AAPG
Bulletin was 'Carbonate Reservoirs: Strategies for the
Future'. The papers in this issue highlight the work
required for understanding the external envelope and
internal architecture of carbonate reservoirs as well as
the spatial distribution of porosity and permeability
dolomitized platform interior or ramp sequences
(e.g. Williston Basin, Dakota),
•
oolitic and bioclastic sand bodies forming shoals and
