Bryan DeVault

Multicomponent AVO analysis, Vacuum field, New Mexico

Shear‐wave amplitude variation with offset (AVO) analysis can be used to map changes in density, shear‐wave velocity, and fracturing at reservoir scale by allowing the influence of each factor to be separately extracted from the observed seismic response. Weighted least‐squares inversion of the anisotropic reflection coefficients was implemented to find the shear‐wave splitting coefficient and velocity‐contrast parameters. A time‐lapse nine‐component, 4‐D seismic survey acquired over Vacuum field in Lea County, New Mexico, was used to test our methodology of shear‐wave AVO analysis and to compare the results with well production and azimuthal P‐wave AVO analysis.Weighted least‐squares shear‐wave AVO stacks of the splitting parameter were found to be excellent predictors of well fluid‐production performance, implying a strong link between seismically inferred fracturing and reservoir‐scale permeability of the San Andres dolomites at Vacuum field. Analysis of the shear‐wave velocity contrast indicated the p...

Identification of lithology in the Gulf of Mexico

In a small town outside of Houston, a local rancher was overheard saying, “Do you have any 3-D seismic across your place? You ought to get some, because it tells you exactly what’s down there and where to drill.” Yes, the transfer of technology has been accelerated by new electronic media such as the Internet, but is it possible that it bypassed the geophysicists?

Prestack 9‐C joint inversion for stratigraphic prediction in the Williston Basin

We have successfully applied the multicomponent prestack elastic waveform inversion methodology proposed by Agullo et al (2004) to 9-C 3D data from North Dakota. The objective of the survey was to image grainstone shoals which form stratigraphic traps for oil using the P and shear modes. The shoals are a difficult exploration target as they are characterized by a subtle, nonunique P-wave seismic response. Prestack joint elastic inversion of the P and SH modes delineates both the shoal itself and the updip seal facies that act as the trap in this part of the play. Elastic attributes were particularly successful at characterizing the dolomite fraction at the reservoir, which allowed mapping of trap geometries.

Poststack, prestack, and joint inversion of P- and S-wave data for Morrow A sandstone characterization

AbstractExploration for oil-bearing Morrow sandstones using conventional seismic data/methods has a startlingly low success rate of only 3%. The S-wave velocity contrast between the Morrow shale and A sandstone is strong compared with the P-wave velocity contrast, and, therefore, multicomponent seismic data could help to characterize these reservoirs. The SV and SH data used in this study are generated using S-wave data from horizontal source and horizontal receiver recording. Prestack P- and S-wave inversions, and joint P- and S-wave inversions, provide estimates of P- and S-wave impedances, and density for characterization of the Morrow A sandstone. Due to the weak P-wave amplitude-versus-angle response at the Morrow A sandstone top, the density and S-wave impedance estimated from joint P- and S-wave inversions were inferior to the prestack S-wave inversion. The inversion results were compared with the Morrow A sandstone thickness and density maps obtained from well logs to select the final impedance an...

Shear‐wave azimuthal velocity anisotropy in a Williston Basin 9‐C 3‐D survey

We have observed significant azimuthal variation in shearwave stacking velocities in a recently-acquired 9-C 3-D survey in the Williston Basin of North Dakota. While not uncommon for P-wave data, we are unaware of any previous observations of this phenomenon on shear-wave 3-D data. The amount of azimuthal anisotropy (not to be confused with the difference in vertical shear-wave velocities that gives rise to shear-wave splitting) observed in the stacking velocities of the slow shear mode (>10% in the deep subsurface) is somewhat larger than for the fast mode. Interestingly, no measurable azimuthal P-wave velocity anisotropy is present, and the total amount of shear-wave splitting from the surface to the target reservoir is less than 1%. Inconsistencies between the values of measured from splitting and inferred from azimuthal variation in the moveout lead us to conclude that the subsurface here displays weak orthorhombic symmetry.

Investigation of HFVS Technology Applied to 9-Component 3D Seismic Exploration

A 3D experiment was conducted in October of 2003 in Southeast Colorado to investigate the application of the High Fidelity Vibratory Seismic (HFVS) technology to a 9-component seismic acquisition (9C). The HFVS method allows data from multiple vibratory sources to be simultaneously collected during the acquisition phase and separated in the processing stage. The concurrent recording of the required source components, P, Si and Sx has the potential to increase the production rate of the 9C survey by a factor of three. The time saved can be used to acquire additional seismic data, improve the seismic image quality or reduce acquisition expense. This experiment is concerned with the fidelity of the extracted source component data from the simultaneous recordings. The separated data must be of sufficient quality for the subsequent stages of component rotation and data processing.

Multicomponent AVO analysis at Vacuum Field, New Mexico, Part I: Theory and Data Processing

Summary Shear-wave AVO analysis is a powerful tool for separating the contributions of changes in density, velocity, and fracturing to the observed seismic amplitude response. Shear-wave AVO analysis can be used to map variations in each of these quantities and to thereby characterize both fracturing and porosity in hydrocarbon reservoirs. Weighted least squares solution of linearized anisotropic plane-wave reflection coefficient equations for the fracture density and shear-wave velocity contrast parameters has been used to analyze lateral variations in fracture density in San Andres carbonates in the Central Vacuum Unit using a multicomponent 3-D seismic survey. The use of weighted least squares techniques also allows computation of standard deviations for each of the AVO attributes and, therefore, estimation of the reliability of the resulting interpretations.

Azimuthal anisotropy: Is it really ubiquitous?

Following the groundbreaking work of Crampin (1985), Alford (1986), Lynn and Thomsen (1990) and Lewis et al (1991), it quickly became conventional wisdom in the industry that substantial shear-wave azimuthal anisotropy is nearly ubiquitous in the subsurface. Crampin and Zatsepin (1995) made theoretical arguments that implied that most of the subsurface is azimuthally anisotropic. As industry’s ability to measure and quantify azimuthal anisotropy at a variety of scales has grown, this assumption has remained largely unexamined. Looking at over a dozen datasets, including surface 9-C seismic, 9-C VSPs, and dipole sonic logs at a number of locations in the Western US and Alberta, I have seen little unambiguous evidence of azimuthal shear-wave anisotropy despite polarization analysis of each dataset.