"RhoVe Method - A New Empirical Pore Pressure Transform"
Matt Czerniak (GCS Solutions, Inc.)
A new empirical pore pressure transform has been developed using modifications to methods first proposed by Alberty and McLean, 2003, and Alberty, 2011. The rhob-velocity-effective stress (Rho-V-e) method produces a model-driven, stand-alone set of “virtual” rock properties, which at intermediate positions are consistent with Bowers method default values for the Gulf of Mexico (Bowers, 1995, 2001). The RhoVe method uses a single transform to convert both compressional sonic and bulk density to common estimates of effective stress and pore pressure where convergence of the two transformed properties offers a robust solution.
Velocity-density conversion functions (of the form proposed by Bowers, 2001, and Raymer, Hunt, and Gardner, 1980), are mathematically linked to a continuous series of velocity-depth normal compaction trend functions. The calculations are limited by bounding end-member curves that provide a basis for intermediate (fractional) solutions of velocity-effective stress and density-effective stress relationships that are applied to a well of interest.
Paired velocity-depth compaction trends were iteratively solved by using published theoretical porosity trends for smectite and illite (Lahann and Swarbrick, 2011), and published velocity-depth normal compaction trends (Ebrom and Heppard, 2010). By using the comparative velocity-density functions that match the offset well data in cross-plot, normal effective stress for each end-member and intermediate solutions can be calculated by integrating the discrete velocity-depth profile - now converted to density-depth. The method produces robust solutions as tested on multiple deep water Gulf of Mexico wells, and extends the predictability of high-velocity, low-effective stress rock types such as those found in the Deepwater Gulf of Mexico Wilcox-equivalent Paleogene and older section. The velocity-effective stress trend curves can also improve pore pressure characterization of the overlying overburden section extending to the mud line. Advantages of the RhoVe method are that it can be made interactive and fast, relative to the application of other acoustic transform methods.
This talk attempts to build on previous efforts by other workers to include the role of clay type, clay volume and diagenesis on altering velocity-effective stress relationships and presents a technique in which the effects of clay diagenesis and other factors may be captured and utilized empirically for pore pressure analysis and prediction.
Matthew Czerniak is the Director of GCS Solutions, Inc., The Woodlands, TX. He received his B.S. in Geology from Michigan State University and M.S. in Geology and Geophysics from Louisiana State University. He has worked as a professional geologist for 33 years, with about 20 years of work specializing in pore pressure analysis and prediction. He has worked for BP, Mobil Oil Exploration, Chevron, Hess, BHP and ConocoPhillips.