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AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment

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Rhove Method - A New Empirical Pore Pressure Transform


A new empirical pore pressure transform has been developed that includes many of the advanced, state-of-the-art concepts that are useful in today’s pore pressure estimation and theory. The rhob-Previous HitvelocityNext Hit-effective stress (Rho-V-e) method produces a model-driven, stand-alone set of “virtual” rock property relationships, which at intermediate positions are consistent with Bowers method default values for the Gulf of Mexico. 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. Previous HitVelocityNext Hit-density conversion Previous HitfunctionsNext Hit are mathematically linked to a continuous series of Previous HitvelocityNext Hit-Previous HitdepthNext Hit normal compaction trend Previous HitfunctionsNext Hit. The Previous HitcalculationsNext Hit are limited by bounding end-member curves that provide a basis for intermediate (fractional) solutions of Previous HitvelocityNext Hit-effective stress and density-effective stress relationships that are applied to a well of interest. Paired “virtual” Previous HitvelocityNext Hit-Previous HitdepthNext Hit compaction trends were iteratively solved by Previous HitusingNext Hit published theoretical smectite and illite porosity trends and Previous HitvelocityNext Hit-Previous HitdepthNext Hit normal compaction trends. By Previous HitusingNext Hit the RhoVe-derived Previous HitvelocityNext Hit-density Previous HitfunctionsNext Hit that match the well of interest in cross-plot, normal effective stress for each end-member and intermediate solution can be calculated. Effective stress is calculated by taking the difference between the integrated density-Previous HitdepthNext Hit virtual overburden profile, converted from Previous HitvelocityNext Hit-Previous HitdepthNext Hit, and the inclusion of hydrostatic pressure. The method produces robust solutions as tested on multiple deep water Gulf of Mexico wells, and extends the predictability of high-Previous HitvelocityNext Hit, low-effective stress rock types such as those found in the Deepwater Gulf of Mexico Wilcox-equivalent Paleogene and older section. The Previous HitvelocityNext Hit-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 paper attempts to build on previous efforts by other workers to include the role of clay type, clay volume and diagenesis on altering Previous HitvelocityTop-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.