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The Role of Basin Modeling in Supporting the Evaluation and De-Risking of Business Opportunities in the Deepwater Section of the Gulf of Mexico

Klaus Leischner¹, Brad Prather², and Jan Harrell²
¹Shell International Exploration and Production Inc., Houston, TX
²Shell Exploration and Production Company, Houston, TX

In order to support the evaluation of exploration opportunities in the pre-salt deepwater section of the Gulf of Mexico, several sub-regional and larger regional basin models have been constructed, using SHELL’s in-house basin modeling platform BPA-Cauldron. These models provide critical input for portfolio ranking, risking of individual prospects as well as a thorough volume to value (V2V) assessment in Shell.

Additionally, after the large oil spill caused by the Macondo incident in the Gulf of Mexico, the worst case discharge - the maximum amount of oil which can flow through a well bore to the seafloor in case of an un-constrained flow - requires the calculation of fluid and rock properties in the formation, as well as a good estimate of the formation temperatures and pressures.

In this context basin models have the advantage of allowing the calculation of the required variables consistently, applying basic geological constraints and taking into account the specific geological boundary conditions for a given prospect. Particularly in the pre-salt of the Gulf of Mexico it is critical to take into account the laterally rapidly changing sub-surface conditions.

Over the last 5 years the confidence level in the basin modeling approach has increased considerably, since the model outcomes have been confirmed repeatedly with well data. A look-back analysis confirms that pore pressures can be predicted within 500 psi, and temperatures are predicted within ca. 10oF. Porosities and permeabilities are usually predicted based on Touchstone models and in many instances porosities were predicted within 2 porosity units. The key uncertainty is related to poor seismic imaging below the salt and the often limited understanding of the evolution of the salt canopy through time.

The calculation of fluid properties is generally more difficult, but for the few data points which are available at this stage for the pre-salt section, API and GOR's are generally within 20% of the predictions. Fluid property predictions are based on outputs from CAULDRON, but also empirical relationships related to the source rock maturity within the drainage area of a given prospect and assumptions about the source rock facies are incorporated.

A workflow and outputs will be shown to illustrate the significance of basin modeling in the opportunity evaluation process and de-risking of business opportunities in the Gulf of Mexico within SHELL.

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