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ABSTRACT: Field and Modeling Studies of Cyclic Carbonates: A Predictive Tool for Petroleum Exploration

James Frederick Read

Stratigraphic modeling conducted by the Virginia Tech group has concentrated on understanding how 1- to 30-m thick (fourth- and fifth-order) carbonate cycles are arranged to make up Vail sequences of carbonate platforms. In carbonate sequences containing large numbers of 1- to 10-m carbonate cycles, lack of well-defined markers generally prevents construction of detailed stratigraphic cross sections showing detailed facies changes. Fischer plots that graph cumulative cycle thickness corrected for linear subsidence using average cycle period can be used to correlate sections, and to show relation of individual cycle types to third-order sea levels. Interaction between simple or complex sea level curves defined by various frequencies and amplitudes, the sediment-surface, wa er-depth dependent sedimentation rate, lag-time, and subsidence through time can be shown using one-dimensional models. Isostatically balanced two-dimensional models that incorporate the above variables, plus initial platform slope and antecedent topography, thermotectonic subsidence (divided into rotational and regional components), sediment and water loading using an elastic beam model, and erosion can be used to construct synthetic cyclic facies cross sections of carbonate platforms. These can be used to define regional relations between cycles, likely vertical and lateral facies changes, distribution of disconformities, conformities and tidal-flat caps, and relative water depths of facies likely to be developed on the platform, as well as likely location of early diagenesis. The inte ration of field and modeling studies provides a rigorous analysis of cycle deposition that could be of great predictive value in the exploration and development of petroleum reservoirs.

AAPG Search and Discovery Article #91001©1989-1990 AAPG Distinguished Lecture Tours 1989-1990