Rock Physics SIG: RhoVe Method II: Empirical Velocity-Density-Temperature-Effective Stress Transform* - Oct 3rd
Sponsored by NER, CGG and Ikon Science
Event Location:
CGG
10300 Town Park Dr.
Houston, TX 77072
NOTE: You Must be Logged In to Register.
Speaker: Matt Czerniak, GCS Solutions, Inc.
The rhob-velocity-effective stress (RhoVe) method represents an empirical approach to pore pressure analysis and calibration that utilizes a series of model-driven, genetically-linked “virtual” rock property relationships. The method is fundamentally a two-parameter approach (a-term and alpha), which are used to construct a velocity-vertical effective stress (VES) and a density-VES family of curves that can be applied to a well of interest where convergence of the two transformed properties offers a robust solution. A sub-regional study of subsalt wells located in the south-central Deepwater Gulf of Mexico (DWGoM) confirmed the presence of a plateau, or upper limit in a-term relationships (sonic versus density cross plot space), in a narrow band that approximately coincides with Bowers published Gulf of Mexico “slow” trend for shales and is consistent with the effects of ongoing chemical compaction. When the a-term is set as a function of alpha, along with a delimiter function set to match the observed plateau, the RhoVe method is reduced to a single parameter (alpha’) that includes the effects of compositional changes related to clay diagenesis and the effects of ongoing chemical compaction. Once calibrated, the construct represents a fully-populated” petrophysical (shale-only) model volume that can be queried and interrogated to perform advanced calculations.
A new empirical approach for calculating pore pressure from temperature is presented that both frames the structural-stratigraphic history of fine-grained clastics in a sub-regional setting and allows for an interpretation of local diagenetic effects. Post-drill pore pressure analysis results for the initial subsalt study area were expanded to include other (non-subsalt) areas of DWGoM and Shelf, and the RhoVe method was extended to produce a family of velocity-VES and density-VES relationships applied as a function of temperature (RhoVe-T), that can seamlessly account for the effects of bound water expulsion related to compositional changes and other diagenetic factors related to load transfer and ongoing chemical compaction. The method utilizes a single master power law reference relationship between temperature (in degrees Fahrenheit) and alpha’ that is applied as an instantaneous series to wells that span the Gulf of Mexico Shelf and Deepwater. The temperature-alpha’ power law function transforms both sonic and density data for the entire stratigraphic section, including Plio-Pleistocene/Miocene/Oligocene and older Wilcox-equivalent Paleogene shales and mudstones.
Accounting for the effects of ongoing chemical compaction and diagenesis using alternate associations extends the predictability of high-velocity, high-density, low-effective stress rock types such as those found in the Deepwater Gulf of Mexico Miocene and Wilcox-equivalent Paleogene mudstones and older onshore unconventional shale-play reservoir sections.
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5:15pm Refreshments
5:30pm Presentation Begins
6:30pm Adjourn
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