HGS North American Dinner: Compaction & Overpressure in Shales

Compaction and Overpressure in Shales:
Theory and Practice

Pressures in the subsurface control the migration of fluids, including hydrocarbons, and hence are of interest not only to drillers (whose wells must deal with these pressures) but also to explorationists generally. Away from well control, the most common source of pressure information are P-wave seismic velocities. Converting shale velocities to pressures requires an understanding of the normal (hydrostatic) compaction curve for shales in a given region. Absent a normal compaction curve, it is impossible to state whether a given shale velocity represents normal pressure, overpressure, or underpressure. We will show the expected range of normal compaction curves, and discuss the driving factors that influence compaction. A quantitative model of shale compaction has been developed that accounts for many of the features of shale porosity evolution with depth, including predictions of P-wave and S-wave velocities. We conclude with a big picture review of the place of pressure analysis in hydrocarbon exploration.

 

 

Philip D. Heppard is a principal geologist with ConocoPhillips in Houston, Texas. Since 1988 Philip has been a pore pressure expert supporting worldwide exploration and development efforts encompassing most known petroleum basins and has been a lecturer on pore pressure for AAPG and related professional organizations. In 2003 he won the AAPG best international poster award for “Using shear and Vp/Vs to predict overpressure in petroleum basins” with his four co-authors. His interest has been the integration of well and seismic data to predict overpressure in the subsurface for well planning and the evaluation of seal quality, as well operational support for drilling wells. He has worked as a development geologist for the Permian Basin, Texas, and Trinidad, West Indies. Philip received his B.S. in geology from Juniata College, Pennsylvania, in 1977 and his M.S. in geology from the University of Akron, Ohio, in 1984. He joined Amoco Production Co. in 1979 and then BP after the merger of the two in 1999. He joined ConocoPhillips Company in February 2006 to become a leading member of their GeoPressure network within the Subsurface Technology group in Houston. 

Dan Ebrom is a senior geophysical advisor with StatoilHydro's Exploration Technology Group inside their Global Exploration division. His most recent work has been on the forward modeling of P-wave and S-wave velocities in mudrocks, given at the October 2008 GCAGS meeting. Along with Phil Heppard and Martin Albertin, he won BP's Helios Innovation Prize in 2005 for a novel method of predicting pressure beneath salt. Prior to StatoilHydro, Dan worked for BP, and earlier worked at Texaco Research. He holds a doctorate in geology and geophysics, and a master's in exploration geophysics, both from the University of Houston. Dan has just finished a term as treasurer of the Society of Exploration Geophysicists (SEG), and is a past president of the Geophysical Society of Houston (GSH). He is a co-organizer (along with Ali Mese) of this fall’s SEG Workshop “Shales as reservoirs, shales as seals”.

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