Source Rock Evaluation Technique: A Probabilistic Approach for Determining Hydrocarbon Generation Potential and In-Place Volume for Shale Plays
The hydrocarbon generation potential of a source rock is a calculated volume that utilizes multiple rock properties including gross rock volume, total organic carbon, kerogen type, and pyrolysis parameters. Here we detail a probabilistic workflow to the generation potential calculation, using Monte Carlo simulation of the modified Schmoker, 1994, equation with a distribution of values for each input parameter. This methodology can be an important component in identifying prospective shale plays for oil and gas production, and can be compared against traditionally calculated hydrocarbons-in-place as a screening tool for ranking prospects. Specifically, traditional oil-in-place calculations for shale plays, due to uncertainties in porosity and fluid saturation, may overestimate available resources that can be estimated independently by calculating oil generation potential. The comparison of the two calculations can provide valuable insight into the volume of oil that can be generated and stored within a source rock interval and adjacent reservoirs.
In a test of the probabilistic workflow, we use source rock data from the Upper Cretaceous Niobrara Formation and evaluate the results in comparison to horizontal Niobrara production at Silo Field, Wyoming, USA. The simulation outputs show that the Niobrara formation in Silo Field has the potential to generate a mean resource of 29 million barrels of oil equivalent (MMBOE) of hydrocarbons per square mile, and store a mean of 21 MMBOE per square mile. A calculated net resource of 140 thousand barrels of oil equivalent per well closely approximates historical production for unstimulated, horizontal Niobrara wells at Silo Field.
We then apply the methodology to Ordovician and Silurian source rocks in Poland to determine source rock quality, and compare calculated generation potential against traditional volumetric in-place calculations. The results indicate the potential for significant resources in shale plays and can be used as screening criteria for ranking various acreage positions.
Determining generation potential provides a first step in understanding resource distribution by validating traditional in-place calculations. An integrated, probabilistic approach is crucial in areas where individual rock properties are inadequate indicators of source rock quality. To be truly robust, this method must incorporate resource preservation, migration, and flow characteristics to determine ultimate recoverability.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California