1. A Petrophysically valid Xu- White Velocity Model Andy May March 19, 2014

2. Rock Physics Determine the in-situ acoustic properties of the reservoir and surrounding rocks and their fluids. Use the properties to create an ideal seismic response, both compressional and shear. How does the seismic response change with porosity, permeability, fluid content, bed thickness, mineral content, etc.? Slide - 2 Seismic Petrophysics

3. How is it done? Do a full petrophysical interpretation of the wells in the area Use the interpretation to create a velocity (Rock Physics) model Geophysicist supplies a depth tie of the wells to the seismic volume, a wavelet and sections through the wells The geologist supplies the tops and info on rock variablity The engineers supply the production characteristics of the wells The petrophysicist uses the geophysical info to create synthetics with various rock and fluid characteristics Together the geophysicist and the petrophysicist compare the synthetics to the seismic to help decide what can be seen and how to display it Crossplots and cross sections are made comparing seismic properties to production and geological characteristics to quantify/verify the results Slide - 3

4. Goals for the velocity (Rock Physics) model Borehole and invasion correct the compressional and shear sonic logs Borehole and invasion correct the density Compute the acoustic properties and the density of the borehole and formation fluids Compute a shear log when one was not measured Fill gaps in both shear and compressional sonic

5. Solid, Non-Porous Material (Matrix) Dry, Porous Material (Frame) Fluid Filled, Porous Material K 0 bulk modulus U 0 shear modulus K d bulk modulus U d shear modulus K bulk modulus U shear modulus Fluid Only K f bulk modulus U d (U f =0) shear modulus Mechanical Properties Notation After Wally Souder, 2001

6. Processing Steps Compute “Solid Rock” density, compressional ITT, and shear ITT using volumetric sum of petrophysical results. The “theoretical values.” Add effective porosity to the solid values using Kuster-Toksoz Add borehole and formation fluids to theoretical compressional sonic using the Gassman equation and Sxo Iterate to best pore aspect ratios by converging the difference between theoretical sonic and measured sonic compressional values. Add formation fluids to best theoretical dry frame sonic values

7. Porosity and Vshale Definitions PHIT = PHIE + PHISH*VSH Assumes that porosity is distributed proportionately between sand and shale, that is, RHOMA of shale = RHOMA of sand. Volumetric equation Xu and White, “Poro-elasticity of Clastic Rocks”

8. Petrophysical Rock Models

9. Defining “Shale” on logs

10. Greenberg and Castanga, 1992 “V Clay ” is not the actual volume of clay, mineral or otherwise. It is an abstraction of dry Vsh. It has the Rhoma of sand and the velocity of dry shale.

11. DLT_TW Sonic when wet DLT_TW RHOC_GW

12. Sonic when wet Density when wet PHIEU

13. Caliper Measured shear

14. Measured AIGOM Example After Frederic Gallice

15. AI Model Insitu GOM Example After Frederic Gallice

16. Example well China Example After Gordon Marney wireline

17. Conclusions Petrophysical velocity modeling can improve well ties to seismic The wet shale and effective porosity method is superior to the total porosity and dry clay method Sonic and density logs are often bad due to borehole and invasion effects

18. Further Reading Keys and Xu, Geophysics, 2002. This paper incorporates all of the discussion, criticism, and corrections to the Xu and White model that had accumulated since its introduction in 1995. The analytical model presented in this paper is very good. As Leiknes, et. al. discusses the exact Kuster and Toksoz effective medium solution in Xu and White, 1995 is flawed. The approximation is robust and of high quality. Xu and White, 1996. " Physical Model for Shear...", Geophysical Prospecting. This summarizes their theory pretty well. Note their model is a PHIE and VSH model, ignore the references to Vclay. The equations make this clear, the text is a bit sloppy. Leiknes, Pedersen, and Nordahl. "Examination and Application of the Sand-clay..." This paper discusses and summarizes all of the criticism of the Xu-White model in a fair way. These issues are dealt with in the Keys and Xu paper. Batzle and Wang, 1992, “Seismic Properties of Pore Fluids.” This paper gives the equations for oil, gas, water acoustic properties. I used these in the model. The equations I use in the model for OBM are from Dr. Han and are not published.

19. Petrophysicists