Wednesday, May 11th, 2011

Well log and seismically derived impedance of clay-rocks for higher resolution of pore pressure prediction

Stephanie B. Nowak and Philip D. Heppard, ConocoPhillips

Abstract

In this paper we discuss how acoustic impedance can be utilized for pore pressure prediction.  Acoustic impedance, the product of velocity and density, of normally pressured shales behaves in a predictable manner of increasing impedance with increasing burial depth as shale compacts.  Overpressure in clay rocks is noted by a deviation from the normal compaction trend to lower values.  The minerology of clay rocks affects the impedance in a manner similar to other log responses of velocity, resistivity and density and must be considered when evaluating for pore pressure.  Previous applications of seismically derived impedance for pore pressure have used it to modify migration-derived velocities to improve resolution.  In this application we use a calibrated inversion of seismic data for shale impedance and directly convert to pore pressure.  This process reduces the effects from other rock types, improving resolution and potentially accuracy.  This is in contrast with seismic migration velocities which include an average property of all rocks over relatively thick sections. This negatively affects pore pressure predictions since almost all pore pressure calculations are based on the predictability of shale and clay rocks, not sandstone, siltstone, marl, limestone and other rock types.

Speaker Biography

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, and his M.S. in geology from the University of Akron, Ohio, some time ago.  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 team within the Subsurface Technology group in Houston.

Stephanie B. Nowak is a senior geophysicist currently working at Noble Energy in Houston but was very recently a member of ConocoPhillip's Upstream Technology group in Houston. Her research focuses have been on pore pressure prediction, seal evaluation and shale properties derived from seismic data. She was with ConocoPhillips from 2005 to 2011 working in exploration and development roles as well as a specialist in AVO and attribute analysis. Stephanie received her BS in Engineering Physics from Miami University, her MS in Geophysics from Wright State and her PhD in Geophysics from Virginia Tech.