# Seismic Petrophysics Andy May April 14, 2014 Rock

Seismic Petrophysics Andy May April 14, 2014 Rock Physics Determine the in-situ acoustic properties of the reservoir and surrounding rocks and their fluids. Seismic Petrophysics 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 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 variability Slide - 3 How is it done? The engineers supply the production characteristics of the wells The petrophysicist uses the geophysical info to create synthetics with various rock and fluid characteristics, prompted by the engineers 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, determine accuracy and reliability Slide - 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 Mechanical Properties Construction Solid, Non-Porous Material (Matrix) Dry, Porous Material (Frame) Fluid Filled, Porous Material Fluid Only After Wally Souder, 2001 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 Gassmann 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 Petrophysical Rock Models Defining Shale on logs Correlation 5 0

Caliper (CAL) (in) Env Corr GR (GRCO) (API) 15 0 15 150 Raw Porosity Edited Sonic (DLTC) Deep Induction (RILD) 150 50 0.2 (ohmm) 20 RW Env Corr Neutron (PHIN) 0.02 (ohmm) 2 0.6 0 True formation resistivity (RT) 0.2 (ohmm) 20 Env Corr Density (RHOC) Apparent Rw (RWA) 1.7

(g/cc) 2.7 0.02 (ohmm) 2 Porosity Vshale PHIESS General Eng. -100 Static SP (SSP) (mV) Resistivity Depth (ft) 5 Bitsize (BITSZ) (in) VSHSP 0.5 0 0

1 OIL VSHND 0.5 0 0 BVW 0.5 0 BVXO 0.5 PAY 4 0 0 Effective Porosity (PHIE) 0.5 1 VSHKTH 0 0 35

36 37 38 39 RT = .85 GR = 100 12050 RHOC = 2.32 PHIN = 40 DT = 121 12050 1 1 Volume of shale (VSH) 0 0 34 GR = 47 VSHGR Shale

1 DOL LS SS SH Sonic when wet Correlation Resistivity Density Shear Compressional Bulk Moduli Effective Porosity Co mp HS SH Bound (KHS_SH) 0 Depth (ft) Env Corr Density (RHOC)

1.7 (g/cc) 2.7 RH OC ( water) (RH OC_GW) 1.7 0 Env Corr GR (GRCO) (API) True formation resistivity (RT) 150 40 40 PHIE unbounded (PHIEU) 0.5 0 40 0.5 Co mp HS SS Bound (KHS_SS) 0

0.2 (ohmm) 2.7 900 Modeled Density (RHOC _G) 20 1.7 200 Mud Rock Shear (DTS_CSTG) (g/cc) Shear theoretical (DTS_T) 2.7 900 (us/f) DLT (water) (DLT_TW) 50 0 Bulk Mod sand (K_SS) DLT theoretical (DLT_T) Bulk Mod of solid (KMOD_M) 70 200 (us/f) 50 0

40 70 200 Edited Sonic (DLTC) Bulk Mod shale (K_SH) (us/f) 50 0 40 0.5 0 PAY 4 BVW BVXO 0 0 Effective Porosity (PHIE) 0.5 0 SH SS VOLC LS DOL AN

Sonic when wet Density when wet 7450 7450 7500 7500 7550 7550 7600 7600 7650 7650 7700 7700 7750 7750

7800 7800 PHIEU The effect of bad hole Correlation Resistivity Bitsize (BITSZ) (in) 16 6 Caliper (CAL) (in) 16 0 Env Corr GR (GRCO) (GAPI) 150 Depth (m)

6 Density Shear Compressional Effective Porosity Measured shear 0.5 200 Env Corr Density (RHOC) 1.7 (g/cc) 2.7 900 DTSMC 70 200 True formation resistivity (RT) Modeled Density (RHOC_G) Shear theoretical (DTS_T) 0.2 (ohmm) 20 1.7 2.7 900 70 200 DLT (water) (DLT_TW) DLT theoretical (DLT_T) Edited Sonic (DLTC)

50 0.5 50 0.5 50 0.5 650 650 700 700 Caliper PHIE unbounded (PHIEU) BVW BVXO Effective Porosity (PHIE) 0 0 0 0 SH SS

VOLC LS DOL AN GOM Example Measured AI After Frederic Gallice GOM Example AI Model Insitu After Frederic Gallice Slide - 14 PSTM 120 BE Well tie Reverse Polarity 300 Slide - 15 CQI Stack, Reverse polarity

300 Slide - 16 Further Reading Keys and Xu, Geophysics, 2002. Xu and White, 1996. " Physical Model for Shear...", Geophysical Prospecting. This summarizes their theory pretty well. Note their model is a PHIE and 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. This approximation is robust and of high quality. 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 XuWhite 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.

Petrophysicists Conclusions Petrophysical velocity modeling can improve well ties to seismic Using Rock Physics and Seismic Petrophysics, well data can be compared in detail to the seismic Sonic and density logs are often bad due to borehole and invasion effects

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