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ABSTRACT
Basalt appears to have geochemical advantages as a reservoir for
- Geology > Rock Type > Igneous Rock > Basalt (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Reservoir Description and Dynamics > Storage Reservoir Engineering > CO2 capture and sequestration (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Seismic (four dimensional) monitoring (0.92)
SUMMARY Seismic Interferometry is rapidly becoming an established technique to recover the Green’s function between receivers, but practical limitations in the source energy distribution inevitably lead to spurious energy in the results. Here we use a spurious wave we previously called the Virtual Refraction to estimate subsurface parameters. We extend our previous acoustic analysis to a two layer elastic model with attenuation and noise. We demonstrate that stacking crosscorrelation gathers in the presence of noise improves our ability to pick the stationary-phase point associated with the critical offset. Finally we discuss using multiple refraction modes to solve for subsurface parameters using only virtual refraction data. INTRODUCTION The Green’s function between two receivers is obtained by crosscorrelating the recorded wavefields at the receivers from sources located everywhere in the media (Lobkis andWeaver, 2001;Weaver and Lobkis, 2001; Roux and Fink, 2003; Derode et al., 2003; Snieder, 2004; Roux et al., 2005). Shapiro and Campillo (2004) and Sabra et al. (2005) use ocean noise to recover the surface wave part of the elastic Green’s function, while Malcolm et al. (2004) use the seismic coda to estimate the surface wave Green’s function between receivers. Wapenaar and Fokkema (2006) and van Manen et al. (2005) show that in media without attenuation, recovery of the Green’s function is exact when monopole and dipole sources surround the receivers on a closed surface. In real data these conditions cannot be met; although, even with limited source distributions it is possible to extract important medium parameters (Schuster et al., 2004; van Wijk, 2006; Bakulin and Calvert, 2006). Dong et al. (2006) use refracted energy in seismic interferometry to distinguish between head waves and diving waves. We recently showed the cause of spurious energy related to refracted acoustic waves in an application of Seismic Interferometry (SI) (Mikesell et al., 2009). We used crosscorrelation-type SI to show that when we break assumptions about the source type and source distribution we recover the Green’s function between receivers plus a spurious wave we call the Virtual Refraction. Figure 1 illustrates a simple acoustic model. We place monopole acoustic sources on a circle surrounding the receiver array. We perform crosscorrelations between r1 and all other receivers for each source on the circle. We then sum the cross-correlations between r1 and a particular receiver over all sources located on the circle. Placing the summed traces together we generate the virtual shot record shown in Figure 2 (Mikesell et al., 2009). The virtual refraction is the coherent event arriving before the direct wave. The velocity of the virtual refraction is that of the lower layer in the model in Figure 1, but the arrival time of the virtual refraction is too early. The path dr illustrates the travel path of the virtual refraction. The arrival time of the virtual refraction is associated with the path difference along the refracting layer between two receivers. We can see this if we consider a single receiver r26, which is 100 m from r1.
Introduction Summary We use seismic refraction interferometry to determine the relative depth to water table in a near surface seismic survey. By summing crosscorrelations of wavefields at two receivers from multiple sources we create a virtual shot record. The virtual shot record shows a refraction event that intercepts zero offset at zero time. We term this the virtual refraction, which has the velocity of the second layer. The virtual shot record allows for easier interpretation by suppressing uncorrelated noise, and easier picking of the refraction. Using the virtual shot record with the correlation gather and real shot record we can determine the velocity of the first layer and depth to the refractor. We show that the spurious refractor is present in field data and can be used to extract subsurface properties such as interface depth and seismic velocities. By crosscorrelating shot records at two receivers from multiple sources, we can determine the Green’s function between the two receivers. This method, called seismic interferometry, is used on passive seismic data to recover the surface waves using ocean noise (Shapiro & Campillo, 2004), as well as to circumvent near surface heterogeneity (Bakulin, 2006). Dong (2006) and Tatanova (2008) show that the arrival time of the virtual refraction also changes with differences in travel path through the upper layer to either receiver. A result of violating assumptions used in seismic interferometry is spurious energy in the virtual shot record. (Dong, 2006) and (Tatanova, 2008). Mikesell et al. (2009) show such energy related to refractions contains useful information about the subsurface. Because the spurious refraction has an intercept time of zero we can immediately estimate the velocity of the second layer. The critical offset and time can be determined from the stationary phase point and the real shot record. By using the information from the spurious refraction, Mikesell et al. (2009) were able to determine the model properties without other wave modes. While this works for numerical acoustic simulations, it has not been tested using real seismic data. In this work we apply the analysis developed by Mikesell et al. (2009) to field data collected at the Boise Hydrogeophysical Research Site to determine relative water table depth and seismic wave velocities. Background The Boise Hydrogeophysical Research Site (BHRS) is a research well field located 15 km southeast of Boise, ID. The BHRS was developed to study the permeability and other properties of heterogeneous aquifers. The stratigraphy contains layers of coarse sand, cobbles, and fluvial deposits on top a clay layer approximately 20 m deep. A local quarry exposure shows similar stratigraphy. These layers are significant for hydraulic conductivity profiles, but the water table has a much greater effect on seismic waves. At the BHRS the water table is approximately 4 m deep. In 1997 and 1998 18 wells were drilled to aid in collection of hydrologic, geophysical, and well log data. In 1998, Paul Michaels conducted a VSP survey at the BHRS. Velocities for P-waves above and below the water table are approximately 425 m/s and 2700 m/s respectively (P. Michaels, personal communication, 2008).
Characterization of a Geothermal System In the Upper Arkansas Valley, CO
Blum, Thomas (Boise State University) | van Wijk, Kasper (Boise State University) | Liberty, Lee (Boise State University) | Batzle, Michael (Colorado School of Mines) | Krahenbuhl, Richard (Colorado School of Mines) | Revil, André (Colorado School of Mines) | Reynolds, Robert (Denver Museum Of Nature and Science)
SUMMARY The past four years, geophysics students and faculty from Colorado School of Mines and Boise State University have studied the subsurface in the Upper Arkansas Valley, Colorado, using a combination of geological and geophysical methods. Here, we present and integrate their results from seismic, self-potential and gravity data, as well as water temperature measurements in local wells to ascertain the overall basin structure and investigate a geothermal system in the Mt. Princeton area. We conclude that a shallow orthogonal fault system in this area appears to be responsible for the local geothermal signature at and near the surface. The extent to which high temperatures exist throughout the deeper basin is still under investigation. INTRODUCTION Geological background The Upper Arkansas basin is the northernmost extension of the Rio Grande Rift. This rift system starts near Leadville, Colorado and extends southward to Socorro, New Mexico, over a distance of 700 kilometers (Halley, 1978). The north-trending rift consists of a series of four en echelon basins. From north to south these basins are the Upper Arkansas, San Luis, Espanola, and Albuquerque Basins. The Upper Arkansas Basin is the least understood of the basins as deep drill hole studies are not available, and deep seismic profiles have only become available in the last five years. An overview of the basin and its main features is presented Figure 1. This basin is assumed to be the youngest expression of an Eocene collapse of the Laramide uplift (Tweto, 1979), with the rifting beginning around 25 to 30 Ma. It consists in a north-northwest-trending half-graben, dipping westward, bounded between the Mosquito range on the east and the Sawatch range on the west. It is about 100 km long and 5 to 10 km wide, and can be split in a northern part close to Leadville, and a main part spanning from Poncha Springs to the north of Buena Vista. The main faults associated with the rift system are mostly of north-northwest trend, and are older faults that were reactivated during the Oligocene and early Miocene (Tweto, 1979). The basin is thought to be from 1000 to 3000 m deep, and is filled with Tertiary sedimentary deposits known as the Dry Union formation. They are overlayed by Quaternary glacial and fluvial deposits, as shown in the cross-section on Figure 2. Large Dry Union outcrops are located west of Salida, at the southern end of the basin. A sample of volcanic ash was collected in the upper part of an outcrop and has been processed according to Ramezani et al. (2007), and dated at 10.23±0.024 Ma using single-grain U-Pb zircon geochronology. In the surroundings of Buena Vista, the fault plane of the west bounding fault, or Sawatch fault, lies at the interface between the Precambrian basement, assumed to be around 1500 m deep, and an igneous intrusion, the Mount Princeton batholith, dated at 36.6 Ma. The base of Mount Princeton presents faceted spurs dipping 50 with a strike of approximately 335º, and are the typical expression of a normal fault.
- North America > United States > Arkansas (1.00)
- North America > United States > Idaho > Ada County > Boise (0.25)
- North America > United States > New Mexico > Socorro County > Socorro (0.24)
- North America > United States > New Mexico > Bernalillo County > Albuquerque (0.24)
- Phanerozoic > Cenozoic > Neogene > Miocene (0.54)
- Phanerozoic > Cenozoic > Paleogene > Eocene (0.35)
- Geology > Geological Subdiscipline > Volcanology (1.00)
- Geology > Structural Geology > Fault > Dip-Slip Fault > Normal Fault (0.89)
- Geology > Structural Geology > Tectonics > Extensional Tectonics (0.87)
- Geology > Sedimentary Geology > Depositional Environment > Continental Environment > Fluvial Environment (0.54)
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Gravity Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- (2 more...)
- North America > United States > Arkansas > Arkansas Basin (0.99)
- North America > United States > New Mexico > Espanola Basin (0.94)
- North America > United States > New Mexico > Albuquerque Basin (0.94)
- North America > United States > Colorado > San Luis Basin (0.94)