EXPLORATION SEISMOLOGY

Early Days (ASU)


1. Looking at the orange box in the back of my still-unscratched Explorer during a VSP test in Phoenix, 1995.
2. Chris Skiba (ASU) prepares Thor, a homemade 300-kg weight drop, for a seismic test.
3. Thor lurking near Picacho, AZ, earth fissures. Jim Pfeiffer (now at Blackhawk Geoservices) found from analysis of surface waves that strength and/or porosity have been affected in a broad region (~100 m) around the expressed fissure.

Seismic Anisotropy in Fractured Gas Reservoirs

Low-permeability ("tight") natural-gas reservoirs, especially in the Rocky Mountain region, are an important resource base for US domestic energy production. Natural fractures provide important permeability pathways for efficient well yield. Subvertical fracture zones can be detected from anisotropy of seismic attributes. We coordinated and analyzed a large 3D seismic survey in Wyoming; my immediate colleagues and others also participated in several other studies sponsored by DOE.

Heloise Lynn (Lynn, Inc.) and colleagues produced this anisotropy map early in our analysis of a large three-dimensional P-wave shoot in Wyoming.The dominant fracture direction is east-west; zones that are slow perpendicular to this direction (red) indicate enhanced local fracturing and are positively correlated with well yield. Richard Bates, Dave Phillips, and Michele Simon also made substantive contributions to this work.


Prospectivity map generated by neural-network analysis of fracture-parallel reflectivity, fracture-parallel frequency, fracture-perpendicular velocity, and structural altitude, compared to gas yields at 19 control wells. Most-prospective regions are associated with changes in fault strike and may be associated with enhanced local fracturing due to distributed strain accommodation at fault bends or between faults on relay ramps.

Three-Dimensional Seismic Refraction Surveying


Elevation of overburden-bedrock interface from three-dimensional seismic-refraction tomography.Each of 86 shots was received along five parallel lines with an average of 118 receivers per shot.Contour interval 1 ft; coordinates are in feet. RMS data misfit is 3.5 ms and RMS misfit of surface with drilling results from eight wells (posted crosses) is 1.2 ft. Prominent bedrock channel (blue) may serve as conduit for heavier-than-water contaminants.

Crosswell Sonic Logging (CSL)


Three-dimensional crosshole sonic logging (CSL) in a drilled shaft with pre-engineered defects. Four tubes are placed into the rebar cage before the concrete is poured, allowing intrashaft access for acoustic sources and receivers.Velocity distribution from tomogram shows a low-velocity tail due to the defects. Natasa Mekic (formerly of Blackhawk Geoservices) generated this display. From Jalinoos et al., Defect Identification, Definition, and Characterization in Drilled Shaft Foundations, Federal Highways Admin. Contract DTFH68-03-P-00116