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Application of the SourceRER modeling system (Source Retrodiction & Environmental Reconstruction) to Unconventional Reservoirs: Estimating Mudstone Character and Distribution using Paleo-Environmental Factors

Kevin M. Bohacs¹, Brian P. West², and George J. Grabowski, Jr.²
¹ExxonMobil Upstream Research Company, Houston, TX, USA
²ExxonMobil Exploration Company, Houston, TX, USA

Source rocks are the essential foundation to all hydrocarbon systems and most ‘shale’ reservoir units are, or are closely associated with, source rocks. The potential of these rocks are a strong function of their content of biogenic and organic matter. The Source Retrodiction* & Environmental Reconstruction (SourceRER) modeling system uses many aspects of the depositional environment of organic-matter-rich rocks (ORRs) as input to make quantitative reconstructions of the key proximate controls of Production, Destruction, and Dilution and of the consequent source-rock quality. These inputs include key states of the ocean and atmosphere as well as such geological contingencies as geological age, paleogeographic setting, and climate mode. A Bayesian network is used to model this system, honoring various non-linear interactions among natural controls, mechanisms, processes and contingencies, and tracking their probabilistic relations. The output parameters quantifying source-rock quality comprise both ORR character and source rock potential attributes. SourceRER analyses have been conducted on 37 time horizons spanning the Phanerozoic (based on ExxonMobil global paleogeographic reconstructions). The analyses accurately match > 88% of calibration data, with significant mismatches for only a few time slices (3 of 37). Potential users include: explorers evaluating source adequacy and play-element distribution, explorers and assessors estimating risk of source presence and adequacy, and basin modelers addressing source and reservoir character, generation timing, hydrocarbon yields and unconventional reservoirs.

The processes that control source rock occurrence have been well studied and documented for decades. Many of these studies are locale specific, although a number of recent studies have attempted to describe underlying principles and provide a framework for source-rock prediction.

If the characteristics of a particular source occurrence are known, it is possible, in theory, to relate those characteristics to the inferred paleoenvironment of their deposition. Sophisticated tools are currently available to forward model many aspects of the Earth’s paleoenvironmental processes (climatic, biotic, oceanographic); however, few methods or workflows exist that combine all these aspects to predict source-rocks. Those workflows that do exist are generally linear, ‘if-then’ conditional type constructions-- these do not attempt to determine fully a dependent probability of source-rock presence and character that accounts for inherent uncertainty of input factors and non-linear feedbacks. SourceRER was developed to provide a framework for robust and systematic prediction of likelihood of source presence and character based on fundamental processes and contingencies, expert opinion, and observations. This system does not require detailed quantitative input (e.g. paleoclimate estimates from a GCM) and is not a traditional forward model. SourceRER is a tool for modeling fundamental relations that combine to result in source-rock deposition.

AAPG Search and Discovery Article #120098©2013 AAPG Hedberg Conference Petroleum Systems: Modeling the Past, Planning the Future, Nice, France, October 1-5, 2012