Michael Davidson

Analysis of passive surface-wave noise in surface microseismic data and its implications

Tight gas reservoirs are projected to be a major portion of future energy resources. Because of their low permeability, hydraulic fracturing of these reservoirs is required to improve the permeability and reservoir productivity. Passive seismic monitoring is one of the few tools that can be used to characterize the changes in the reservoir due to hydraulic fracturing. Although the majority of the studies monitoring hydraulic fracturing exploit down hole microseismic data, surface microseismic monitoring is receiving increased attention because it is potentially much less expensive to acquire. Due to a broader receiver aperture and spatial coverage, surface microseismic data may be more advantageous than down hole microseismic data.

Effect of near-surface anisotropy on a deep anisotropic target layer

Summary Near-surface anisotropy can distort P-wave traveltime and amplitude analysis from deep target layers. When the target layer is azimuthally anisotropic, the traveltime/velocity variation with azimuth (VVAZ) or amplitude variation with azimuth (AVAZ) from the target layer may show anomalous behavior due to the influence of the near-surface anisotropy. This study uses two synthetic cases to analyze the effect of near-surface anisotropy on a deep anisotropic target. Our results suggest that the traveltime data (or VVAZ signals) from the target layers can be distorted significantly due to the presence of near-surface anisotropy; but the near-surface anisotropy influence may be negligible on the AVAZ signals from the deep target layer.

A robust workflow for detecting azimuthal anisotropy

Summary The prestack analysis of amplitude variation with offset/angle (AVO/AVA) has been a useful hydrocarbon exploration tool for a number of years. As this technology matured, forward modeling became an important tool to understand the seismic response, to ensure acquisition parameters were adequate for its detection, and to calibrate and validate the data processing sequence and analysis tools. There has been significant recent interest in using azimuthal variations in seismic amplitudes to detect high productivity sweet spots related to in situ natural fractures. The role of forward modeling has not been as significant in azimuthal AVO as in conventional AVO. We describe a robust azimuthal processing analysis workflow based on a series of 1D and 3D elastic modeling exercises designed to validate the azimuthal processing flow and extracted azimuthal attributes. Our results indicate that forward modeling is necessary to understand the offset range that might exhibit an azimuthal amplitude variation and the magnitude of the variation, and its detectability in the presence of noise.

Vibroseis Source Signature Uncertainty and its Impact on Simultaneous Sourcing

Knowledge of the source wavelet in a controlled source seismic experiment significantly improves our ability to extract information from the resulting seismic data. The radiated source signature in Vibroseis field experiments is found to deviate from the pilot sweep and the ground force estimate (GFE) signal put out by the controller, especially at higher frequencies. The Vibroseis source signature uncertainty is a problem for simultaneous sweeping techniques that require reliable phase control and an accurate GFE in order to separate simultaneous sweeps.

High-resolution automatic microseismic source detections

Kirchhoff summation is one of the robust techniques to automatically scan for microseismic source locations. It does not require manual picking of P- and S-wave phase arrivals, but assumes the source location to have the largest stacked energy from all receivers. The energy focusing can be ambiguous if data have low signal-to-noise ratio or contaminations from undesirable phase arrivals such as scattered or converted waves. We propose a new high-resolution Kirchhoff summation to sharpen the focusing of the stacked energy objective function. This new approach divides the receiver array into a number of receiver groups. Each receiver group performs a conventional Kirchhoff summation (partial summation image) to improve the signal-to-noise ratio. The final stacked image is a multiplication of all partial summation images. Multiplication of partial images is the key to sharpen and to focus the stacked energy. We have successfully applied this new method on synthetic and microseismic field data and it outperforms conventional Kirchhoff summation by improving focusing and better differentiating overlapping or multiple events.

Seismic depth imaging in an integrated regional framework — innovating in the deepwater gulf of Mexico

Regional geologic context is an important factor in the effective assessment of exploration risk in frontier areas such as the ultra-deep waters of the Gulf of Mexico. The use of regional frameworks has been reported during the prospect evaluation and discovery phases of several large deepwater fields in the Gulf of Mexico. This paper describes a new, fully integrated, region-wide seismic framework that addresses this need. The approach incorporates: • Long offset, long record length, high resolution data acquisition • Integrated, area-wide subsurface model-building incorporating salt interpretive experience, seismic velocity estimation, and guidance from 3D gravity control • Pre-stack depth imaging techniques.