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The Carbonate Analogs Through Time (CATT) Hypothesis – A Systematic and Predictive Look at Phanerozoic Carbonate Reservoirs:
Extended Abstract*
By
James R. Markello1, Richard B. Koepnick2, and Lowell E. Waite3
Search and Discovery Article #40185 (2006)
Posted February 6, 2006
*Editorial Note: Modified from extended abstract prepared for presentation at
AAPG Annual Convention,
1ExxonMobil Upstream Research Company, Houston, TX ([email protected])
2Qatar Petroleum, Doha, Qatar ([email protected])
3Pioneer Natural Resources USA, Inc., Dallas, TX ([email protected])
Introduction
The Carbonate Analogs Through Time (CATT) Hypothesis defines an approach for developing systematic evaluations and predictive models of Phanerozoic carbonate systems and reservoirs for use in upstream exploration, development, and production businesses. Three applications are illustrated in this extended abstract: 1. age-based pattern development, 2. comparative reservoir analysis, and 3. analog selection.
Exploration
geoscientists employ a host of established and successful concepts, tools, and
data
to develop predictive models for field/reservoir occurrence and quality.
However, as exploration successes decrease, alternative approaches are needed to
refresh the exploration mindset. We present the CATT approach as a hypothesis
and as an alternative mindset for carbonate reservoir exploration. The geologic
age-based concepts and products provide thought-provoking perspectives on known
carbonate reservoir occurrences and offer a different way of thinking about
predicting where undiscovered carbonate reservoirs may exist. At the very least,
our Carbonate Analogs Through Time hypothesis provides a framework or context
within which to insightfully and schematically organize all of the concepts,
facts, and carbonate reservoir case studies/examples one encounters throughout a
career, and it can be used as an approach for comparative analysis of systems.
Reservoir engineers require detailed geologic-based reservoir parameters for
simulations of reservoir/field performance. Such simulations form the bases for
field development/depletion plans that invoke huge capital and operating
expenses. Thus, it is imperative to provide the best possible input to
simulation so that capex and opex investments are optimal. Typically, the input,
if not derived directly from data collected within a field under development,
has been gathered or derived from “analog” fields. Thus, choosing the most
appropriate analog is a critical task. We contend that the CATT approach
provides the conceptual basis for choosing the most appropriate analogs.
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CATT HypothesisThe CATT hypothesis simply stated is: “Insightful, high-confidence, age-specific predictive models for carbonate systems and reservoir occurrence, composition, stratal attributes, and reservoir properties can be developed by summing the ambient conditions of the carbonate processes and Earth processes at any geologic age.” We term these models age-sensitive patterns or themes.
The hypothesis is built upon the cumulative body of knowledge that demonstrates carbonate and Earth processes have differentially varied throughout Phanerozoic time. These carbonate and Earth processes include: 1) ecologic, oceanographic, sedimentologic process-based controls on carbonate-factory development; 2) stratigraphic and accommodation-process-based controls on carbonate stratal architecture; 3) secular trends of evolution, grain mineralogy, tectonics, climate, eustasy, ocean circulation, and ocean chemistry; 4) the stratigraphic hierarchy and the constraint that first- and second-order Phanerozoic stratigraphic successions (Sloss Sequences) are age-fixed in geologic time (mybp). Two key products of this research are: 1) a poster compilation of secular varying geologic controls synchronized to the time-scale (Figure 1) and 2) a global atlas containing 29 present-day and paleogeographic map pairs with details of known Phanerozoic carbonate systems/reservoirs with age-based carbonate themes (Figure 2).
Age-Based Pattern DevelopmentAn example of developing an “age-sensitive pattern” or “time-based theme” is when the map-view configuration and spatial relationships of carbonate systems depicted on a paleogeographic map are convolved with the ambient states of the carbonate and earth processes for that time period (Figure 3). In this case, the key carbonate systems/reservoirs that form the basis for this time-based theme are in the Ellenberger Formation of West Texas. Articulation or characterization of the theme can be made with simple declarative statements that capture key system and/or reservoir attributes (Figure 3 bullet points). The validation of this age-sensitive pattern or theme is whether other coeval carbonate systems that formed on the other margins of Laurentia, Baltica, and Siberia can be characterized similarly.
Comparative Reservoir Analysis
Sometimes there are significant differences between carbonate systems
and reservoirs within a geologic time period or age. We propose that the
CATT Hypothesis and the Atlas products (paleogeographic, paleoclimate
and paleo-oceanographic maps) provide an approach for comparative
analysis between systems within a geologic age that gives meaningful
understanding for the causes of the differences. Since 2003, we have
developed additional maps of paleoclimate and paleo-oceanography based
on recent publications from National Geographic for each of the 29
Phanerozoic time slices. These maps were empirically developed based on
present-day trends. Another ExxonMobil in-house project completed
parametric modeling of various time slices to evaluate these
empirically-based maps. There is very good agreement, and this increases
confidence for comparative analysis between coeval systems with
dramatically different attributes. An interesting case in point is
contrasting Late Jurassic systems/reservoirs of the Arabian Basin (Arab
Formation fields) with those of the northern Gulf of Mexico (Smackover
Formation Fields) (Figure 4). Many key
attributes that control reservoir properties are compared between the
Analog Selection
Demonstration of the utility of these tools for analog selection is
illustrated by explaining the heritage-Mobil example of farming-into
Tengiz
Our rationale was that better similarities existed between age
equivalent systems due to similar biota, mineralogy, long term climate
(Late Devonian greenhouse to Mississippian transitional to Pennsylvanian
icehouse), carbonate factory and profiles – isolated platforms, and
diagenesis – exposure meteoric processes rather than overwhelming
dolomitization. Although Arun is a Miocene (icehouse climate) isolated
platform, it consists of Neogene scleractinian-dominated framework
biota, with abundant microporosity. Also, reservoir fluids are
gas-condensate. Tengiz is also an isolated platform, but is Mid-Late
Paleozoic (greenhouse to icehouse conditions) and consists of tabulate,
rugosan corals and stromatoporoids, similar to the Late Devonian
reservoirs in Caroline and the Rainbow fields of western Canada. The
Lower Pennsylvanian section contains abundant ooids with moldic
porosity. This is very similar to the Salt Creek
Research IdeaThis research idea was conceived in 1991 at Mobil Research. Many Mobil geoscientists contributed to the maturing of the idea and to the development of the CATT products, especially the Mobil Global Themes Project team (detailed Global Paleogeographic Time-Slice maps), and members of the MEPTEC Carbonate Research Team. The project completed in late 1999 just before the ExxonMobil merger in 2000 . |
