January, 2019: Bill Drake

Bill Drake




Organic matter (OM)-hosted porosity can be the dominant contributor to total hydrocarbon storage in unconventional source-rock reservoirs.  These secondary organic pores form as a function of thermal maturation, and accurate characterization of their spatial variability is critical to petroleum exploration and play assessment.  However, measuring OM porosity and mapping its areal distribution remain a challenge.  For example, using direct visual evidence to measure OM porosity has been contentious, and source rock data needed for mapping are commonly sparse in frontier areas of basins.  One approach to overcoming these issues is to resourcefully apply organic carbon mass-balance analysis as a tool to estimate and delineate OM porosity where well control is lacking.  We introduce a methodology to calculate all mass-balance elements in map form rather than at well points in order to incorporate known geologic complexities and effectively highlight a source-rock reservoir fairway in map view.  In our example from the Woodford Shale of the Permian Basin, we provide first-order quantification of OM porosity and reveal its geographic extent within a regional petroleum system.  Our results suggest that mass-balance calculation of OM porosity in map form can be used as a regional exploration tool for assessing resource potential of source rocks in frontier areas.

There are several implications to mapping variations in OM porosity for exploration purposes.  For example, assumptions of the wettability of the inorganic pore system may need to be revisited when OM porosity dominates the total porosity. In addition, the larger the difference between OM-porosity OOIP and total OOIP (from all porosity types), the less optimal a horizontal landing zone in a high TOC source-rock interval may be.  The largest sensitivities to the regional analysis are the TOC and thermal maturity maps and the choice of a kinetics curve.  These and other limitations should be considered when relating imaged OM-porosity characteristics to TOC richness, thermal maturity, kerogen types, associated mineralogy, and compaction.


Bill holds a B.S. in Geological Science from the University of California, Santa Barbara, and his M.S graduate research at Northern Arizona University focused on extensional tectonics, structural analysis, stratigraphy, and isotope geochronology in Baja California Sur, Mexico.  Following stints in environmental consulting in California and Arizona, and as a geologist with the Arizona Geologic Survey, he spent seven years with Pioneer Natural Resources in Denver involved with exploration of Cretaceous and Paleozoic systems in the Rockies and western Midcontinent.  Bill is currently a geologist with QEP Resources in Denver working on a variety of petroleum systems in the Permian Basin.