Carbonate Analogs Through Time: The CATT Hypothesis – A Different Approach to Predictive Model/Concept Development

James R. Markello* (ExxonMobil Upstream Research Company, Houston, TX, USA)
Richard B. Koepnick* (Qatar Petroleum, Doha, Qatar)
Lowell E. Waite* (Pioneer Natural Resources USA, Inc., Dallas, TX, USA)
Joel F. Collins* (Exxon Mobil Development Company, Houston, TX, USA)
Aus Al’Tawil* (Saudi ARAMCO, Dhahran, Saudi Arabia)
Julia Caldaro-Baird* (ChevronTexaco, Denver, CO, USA)
Michael C. Pope* (Washington State University, Pullman, WA, USA)
L. James Weber* (ExxonMobil Exploration Company, Houston, TX, USA)
Jan Golonka* (Institute of Geological Sciences, Jagiellonian University, Krakow, Poland)

* Authors and current locations; all were employees of Mobil E&P Technical Center, Dallas, TX where the research was completed.

Concept. The Carbonate Analogs Through Time (CATT) Hypothesis defines an approach for developing predictive models of carbonate systems and reservoirs. Simply stated, “insightful, high-confidence, age-specific predictive models and concepts for carbonate system and reservoir occurrence, composition, stratal attributes, and reservoir properties can be developed by summing the states or ambient conditions of the carbonate processes and global-scale Earth processes at any given geologic age or time-slice.” We term these models age-sensitive patterns or themes. This hypothesis is built upon the cumulative body of knowledge that demonstrates carbonate and Earth processes have differentially varied throughout Phanerozoic time.

This approach to predictive model development differs from previous attempts in that it integrates carbonate process-based facts, concepts/principles with the age-sensitive historical context of the state of the Earth for any specific geologic time period. Enormous volumes of excellent work over the past 100 years (we acknowledge but obviously cannot reference here) have resulted in understanding:

The ecologic, oceanographic, sedimentologic process-based controls on carbonate factory development;
The stratigraphic and accommodation process-based controls on carbonate stratal architecture;
The secular variation trends throughout Phanerozoic time of

evolution of carbonate-producing biota including assemblage acmes and extinctions,
carbonate biotic and abiotic grain mineralogy,
global tectonics (plate configuration, rifting and orogenic events, supercontinent cycle),
climate (greenhouse vs icehouse cycles; humid vs arid conditions),
eustasy (time-duration-based scales of sea level cycles from 1st to 5th-order),
ocean circulation (currents, storm tracts, and tides related to plate configuration),
ocean chemistry (isotopic and element/cation compositions);

The stratigraphic hierarchy and the constraint that 1st and 2nd-order Phanerozoic stratigraphic successions are age-fixed in geologic time and are named (Wilson Pangean Cycle; Sloss Sequences/Subsequences).

We have produced a set of products that encapsulate all of these facts, trends, and interpretations: an atlas containing present-day and paleogeographic maps with details of known carbonate systems and reservoirs, and a wall poster-size compilation of the secular varying geologic controls synchronized to the geologic time-scale.

Examples. Integrated, predictive CATT age-sensitive patterns/themes are multi-component, can vary between broad/general to narrow/specific, can be expressed in language that is predictive or simply sets expectations, and can include causal rationale or not. Here are examples that present the style and flavor of CATT themes.

Cambro-Ordovician (Sauk III) carbonate reservoirs in North America will be dominated by meter-scale peritidal muddy dolomite cycles with moderate reservoir quality due to dolomitization and/or karsting related to exposure during time of Middle Ordovician unconformity development.
In general, Late Devonian/Carboniferous isolated carbonate platform reservoirs of the North Caspian are Limestone and will have:
- mostly preserved primary porosity (calcitic mineralogy) in thick (rapid subsidence) Devonian (Kaskaskia I) coral/stromatoporoid platform-rimming framestones and well-connected platform-interior layers (greenhouse stacking) of skeletal grainstones;
- poor-quality reservoir to non-reservoir in Walsortian muddy buildups in Early Lower Carboniferous (Kaskaskia II) strata that overlie preceding Devonian rims; and
- higher-quality porosity/permeability moldic ooid grainstones (aragonitic mineralogy; frequent exposure) in thin (slower subsidence), less well-connected (icehouse stacking patterns) layers in Late Lower (top Kaskaskia II unconformity) and Early Upper Carboniferous (Lower Absaroka I) strata.
Late Jurassic (Zuni I) reservoirs of the Middle East:
- are skeletal and ooid lime grainstones
- were formed within the Arabian intrashelf basin (at the equatorial western margin of the gigantic Panthallasic/Neotethys ocean)
- have excellent reservoir quality because of the lack of depositional mud (macrotidal settings), and of preserved primary porosity (calcitic mineralogy; no marine and little burial cementation; rapid burial and little to no meteoric diagenesis), and
- have widespread and excellent layer connectivity (greenhouse stacking).
Middle Cretaceous (Zuni II) distally steepened carbonate ramps will have rudist mounds and rudist-dominated skeletal grainstones at the ramp hinge with mixed moldic and primary pore systems (metastable aragonitic rudist mineralogy within greenhouse climate and calcitic seas).
Late Tertiary (Tejas III) rimmed shelves and isolated platforms are constructed by aragonitic scleractinian communities with low connectivity platform-interior skeletal and ooid grainstone alternating with mudstones (icehouse stacking patterns) and will have dominantly moldic pore networks (frequent exposure and leaching of aragonitic grains in humid climate settings).

These are but a few of the possible themes that can be generated using the CATT Hypothesis. Although the examples may be trivial to experienced carbonate workers, they may be enlightening and/or new understandings for workers unfamiliar with some specific time period, region, basin and/or carbonate system/reservoir. One of our principle goals is to provide a time-based and spatial global framework (conceptual/factual not a commercial software database system) that every geoscientist can use throughout a career of investigation. This framework can be used to intelligently and insightfully compile, store, and retrieve data and interpretations of carbonate systems/reservoirs, derived either from personal experience or literature.

Methodology. The backbone or organizational framework for the CATT Hypothesis is the low-order hierarchical scales of stratigraphy. These 1st and 2nd-order stratigraphic successions are age-dated or fixed in geologic time (Sloss, 1963; 1988). They record the secular variations, key tectonic, climatic, and eustatic events, and important changes of the carbonate and global Earth processes. The framework consists of 32 age-specific 2nd-order supersequences, and these are based on definitions and stratal subdivisions from Haq et al (1987), Ross and Ross (1988), and Harlan et al (1990). Minor modifications were made to assemble a contiguous and consistent Phanerozoic time scale framework. Global paleogeographic plate reconstructions were developed for each of the 32 time slices. Because the time duration for a supersequence ranges from 5-20 my, and because we were working with carbonate systems, the decision was made that each reconstruction would be at the time of 2nd-order maximum sea level. Almost 8300 carbonate fields were identified from in-house and commercially purchased databases. Each field was assigned to a time-slice corresponding to the depositional age of its carbonate reservoir facies. For each time slice, its age-assigned fields were mapped on present-day geography and on the its plate reconstruction paleogeography. Composite presented-day maps of all fields and histograms of carbonate field numbers and sizes through time were made. The modern and ancient maps and the histogram distributions demonstrate that carbonate reservoirs are neither uniformly nor randomly distributed in time and space, but rather are causally distributed (Fig1).

Another key CATT product that was built based on the time framework is the Phanerozoic Carbonate Trends Chart (prepared by J.Collins). It is a compilation of the secular varying trends of the carbonate system controlling variables: tectonics (including Pangean stages, magnetic strip dating, igneous events), climate, eustasy, source rock intervals, OAE,’s, ooid occurrences, mineralogy, marine water isotopic composition, reef and non-reef timing, and biotic evolution (including acmes and extinctions; reef-builders). This compilation facilitates summation of the states or ambient conditions of the carbonate and Earth processes at any given geologic time by simply reading across the chart. By integrating and convolving the paleogeographic maps and the data from the Phanerozoic Carbonate Trends Chart, we derived 9 age-sensitive themes for the major Phanerozoic time intervals containing abundant carbonate reservoirs. Further, as outgrowths of this work, refinements and additions were made to carbonate process-based predictive models that enhanced our understanding of the causal mechanisms controlling carbonate system and reservoir distribution through geologic time.

The CATT Research Project – the Historical Perspective. This research idea was conceived by the three lead authors in 1991, and was proposed and funded in 1992 by heritage Mobil Research and Development Corporation. There were two principle objectives. First was to provide for the company a new methodology for appropriately selecting reservoir analogs and simulation-input data for carbonate fields that had been newly discovered, were being assessed for commerciality, and/or were under depletion planning. Second was to provide a body of knowledge and set of tools from which a global perspective of carbonate reservoirs could be derived and used to guide geo technical decision-making. The project completed in late 1999 coinciding with the ExxonMobil merger of 2000.

We gratefully acknowledge ExxonMobil Research Company management for granting approval and providing support to make these materials public.

References.

Haq, B. U., J. Hardenbol, and P. R. Vail, 1987, Chronology of fluctuating sea levels since the Triassic, Science, v. 235, p. 1156-1167.

Harland, W.B., et al., 1990, A Geologic Time Scale 1989; Cambridge University Press, 263p.

Kiessling, W, E. Flugel, and J. Golonka (eds.), 2002, Phanerozoic Reef Patterns; SEPM Sp. Pub. 72, 775p.

Ross, C.A. and J.R.P. Ross, 1988, Late Paleozoic transgressive-regressive deposition; in SEPM Sp. Pub. 42, Sea Level Changes: An Integrated Approach, C.K. Wilgus et al. (eds.), p.227-247.

Sloss, L.L., 1963, Sequences in the cratonic interior of North America; GSA Bulletin, v.100, p.1661-1665.

Sloss, L.L., 1988, Tectonic evaluation of the craton in Phanerozoic time; in Sloss, L.L (ed.), Sedimentary Cover – North American Craton, U.S.; Boulder, GSA, the Geology of North America, v.D-s, p. 25-51.

Wilson, J.T., 1966, Did the Atlantic close and then reopen? Nature, v. 207, p. 676-681.

Wilson, J.T., 1988, Convection Tectonics; some possible effects upon the Earth’s surface of flow from the deep mantle: Canadian Journal of Earth Sciences, v. 25, p. 1199-1208.

Figure 1. Representative products from our Global Atlas of Carbonate Fields. 1A. Modern-day distribution of 8276 carbonate fields. 1B. Late Permian global paleogeography with distribution of Guadalupian age carbonate reservoirs (black dots). 1C. Frequency distribution of carbonate fields by age.