Alex Martinez

Understanding geophysical responses of shale-gas plays

Unconventional resources such as shale gas are becoming increasingly important exploration and production targets. To understand the geophysical responses of shale-gas plays, we use a rock physics relationship, which is constrained with geology and formation-evaluation analysis, to calculate effective properties such as impedance and VP / VS . Numerical studies suggest that in-situ rock para-meters such as mineral composition (e.g., clay, quartz, and calcite) and TOC, as well as the interaction among them, can significantly influence the geophysical responses of the organic-rich rocks, thus providing the basis for the geophysical characterization of shale-gas plays.

Correction for NMO stretch and differential attenuation in converted-wave data: A key enabling technology for prestack joint inversion of PP and PS data

In many parts of the world, P- or S-wave impedance (I P or I S or seismic velocities ( V P or V S ) are not good indicators of lithology. In these cases, estimation of density or V P / V S is essential for reservoir characterization. Conventional inversion of PP-mode data is known to yield I P and I S , but a reliable estimate of density requires prestack inversion of very large-angle PP data (Roy et al., 2008). Such large-angle PP data sets necessitate acquisition and true-amplitude processing of unusually large offsets.

Characterization of spatially varying surface waves in a land seismic survey

Summary We present several methods for analyzing surface waves in a highly sampled 3-C, 3D survey, and report the most important characteristics derived from those analyses. In particular, we demonstrate the spatial variability of surfacewave velocities and polarization properties. We also show that surface-wave velocities are correlated with other seismic and nonseismic properties of the near surface, such as shear-wave statics and surface texture derived from satellite imagery.

Joint PP-PS angle-stack analysis and AVA inversion in Grane Field, offshore Norway

Eleven years ago, publication of the UK North Sea Alba Field OBC converted-wave (PS) image examples by MacLeod et al. caused quite a stir. The authors provided convincing evidence that “the Alba survey is the first 3D OBC survey in which successful converted-wave imaging of the reservoir has created significant economic benefit.” Most of us with an interest in multicomponent seismology know it well, as Alba has become one of the classic examples of a “stealth” reservoir (Rape et al., 2005), having low P- but high S-impedance contrast. The Alba reservoir and others like it are difficult to recognize on conventional P-wave images, but they stand out quite nicely when viewed on their PS equivalents.

Study Geophysical Response of Middle East Carbonate Reservoir using Computational Rock Physics Approach

Summary Development of carbonate rock physics model is difficult because pore systems are more complex in carbonate than they are in clastics. The best way to describe pore structure is through 3D µCT image of rock pore space. Instead of traditional effective medium based modeling by taking assumption of pore geometry, we adopt computational rock physics approach in this study. Multi-resolution µCT images are taken for carbonate cores belonging to different facies from middle east carbonate reservoir. Electrical conductivity and elastic properties (Vp, Vs) are computed on 3D rock micro-tomographis using finite difference (FD) and finite element method (FEM). To further extend predicting capability, a family of 3D model granular porous media with different porosity, pore (grain) aspect ratio, pore (grain) size distribution, pore connectivity and spatial arrangement are built to represent different carbonate petrophysical pore types. Modeling results compare well with core, log measurements. Direct link between rock microstructure and its elastic, electrical behavior is built up using computational rock physics. Finally, AVO forward modeling is built to quantify porosity, fluid saturation and lithology (facies) effect on seismic response for middle east carbonate reservoir.