Roland Gritto - Academia.edu (original) (raw)

Papers by Roland Gritto

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Sep 26, 2018

We analyzed seismicity near the EGS development at The Geysers, CA Prati-32 injection well to eva... more We analyzed seismicity near the EGS development at The Geysers, CA Prati-32 injection well to evaluate the development and the physical attributes of a subsurface fracture network. The goals of our study include the ability to estimate the orientation and the activated fracture area, to estimate stress orientation and stress orientation changes as well as fluid saturation and spatio-temporal changes in fluid saturation. We compiled a 168-event waveform-based seismic moment tensor catalog for events 0.7≤Mw≤3.9 based on a semi-automated moment tensor analysis technique to be used for in-situ stress estimation during the injection phases. We found an approximate 15-degree counterclockwise rotation of the least compressive stress σ3, and a rotation of the maximum compressive stress σ1 toward the vertical as the injected volume of water increased. We developed a rupture-area magnitude scaling relationship of The Geysers earthquakes obtained from finite-source inversion for fault slip that reveals a very high correlation to published results. Based on the rupture area-magnitude relationship we mapped Mw from the LBNL earthquake catalog to estimate the activated fracture area and its location within the injection volume of Prati-32. Analysis of the Vp/Vs-ratio based on the double-difference Wadati technique revealed the development of an injection-derived steam plume during the early injection phase, particularly in the northern parts of the Prati-32 study area.

AGU Fall Meeting Abstracts, Dec 14, 2015

AGU Fall Meeting Abstracts, Dec 1, 2016

AGU Fall Meeting Abstracts, Dec 1, 2011

Lawrence Berkeley National Laboratory, Aug 28, 2002

Crosswell seismic and electromagnetic data sets taken before and during CO 2 flooding of an oil r... more Crosswell seismic and electromagnetic data sets taken before and during CO 2 flooding of an oil reservoir are inverted to produce crosswell images of the change in compressional velocity, shear velocity and electrical conductivity during a CO 2 injection pilot study. A rock properties model is developed using measured log porosity, fluid saturations, pressure, temperature, bulk density, sonic velocity and electrical conductivity. The parameters of the rock properties model are found by an L1-norm simplex minimization of predicted and observed compressional velocity and density. A separate minimization using Archie's law provides parameters for modeling the relations between water saturation, porosity and the electrical conductivity. The rock properties model is used to generate relationships between changes in geophysical parameters and changes in reservoir parameters. The electrical conductivity changes are directly mapped to changes in water saturation. The estimated changes in water saturation are used with the observed changes in shear wave velocity to predict changes in reservoir pressure. The estimation of the spatial extent and amount of CO 2 relies on first removing the effects of the water saturation and pressure changes from the observed compressional velocity changes, producing a residual compressional velocity change. The residual compressional velocity change is then interpreted in terms of increases in the CO 2 /oil ratio. Resulting images of CO 2 /oil ratio show CO 2 rich zones that are well correlated with the location of injection perforations with the size of these zones also correlating to the amount of injected CO 2. The images produced by this process are better correlated to the location and amount of injected CO 2 than are any of the individual images of change in geophysical parameters.

Geophysical Research Letters, Apr 4, 2003

The Energy Citations Database (ECD) provides access to historical and current research (1948 to t... more The Energy Citations Database (ECD) provides access to historical and current research (1948 to the present) from the Department of Energy (DOE) and predecessor agencies.

A series of time-lapse seismic cross well and single well experiments were conducted in a diatomi... more A series of time-lapse seismic cross well and single well experiments were conducted in a diatomite reservoir to monitor the injection of CO 2 into a hydrofracture zone, using P-and S-wave data. During the first phase the set of seismic experiments were conducted after the injection of water into the hydrofrac-zone. The set of seismic experiments was repeated after a time period of 7 months during which CO 2 was injected into the hydrofractured zone. The issues to be addressed ranged from the detectability of the geologic structure in the diatomic reservoir to the detectability of CO 2 within the hydrofracture. During the pre-injection experiment, the P-wave velocities exhibited relatively low values between 1700-1900 m/s, which decreased to 1600-1800 m/s during the post-injection phase (-5%). The analysis of the pre-injection S-wave data revealed slow S-wave velocities between 600-800 m/s, while the post-injection data revealed velocities between 500-700 m/s (-6%). These velocity estimates produced high Poisson ratios between 0.36 and 0.46 for this highly porous (~ 50%) material. Differencing post-and pre-injection data revealed an increase in Poisson ratio of up to 5%. Both, velocity and Poisson estimates indicate the dissolution of CO 2 in the liquid phase of the reservoir accompanied by a pore-pressure increase. The results of the cross well experiments were corroborated by single well data and laboratory measurements on core data.

AGU Fall Meeting Abstracts, Dec 1, 2002

A series of time-lapse seismic cross well and single well experiments were conducted in a diatomi... more A series of time-lapse seismic cross well and single well experiments were conducted in a diatomite reservoir to monitor the injection of CO2 into a hydrofracture zone, based on P- and S-wave data. A high-frequency piezo-electric P-wave source and an orbital-vibrator S-wave source were used to generate waves that were recorded by hydrophones as well as three-component geophones. The injection

AGU Fall Meeting Abstracts, Dec 1, 2013

Lawrence Berkeley National Laboratory, Apr 29, 2003

A series of time-lapse seismic cross well and single well experiments were conducted in a diatomi... more A series of time-lapse seismic cross well and single well experiments were conducted in a diatomite reservoir to monitor the injection of CO 2 into a hydrofracture zone, using P-and S-wave data. During the first phase the set of seismic experiments were conducted after the injection of water into the hydrofrac-zone. The set of seismic experiments was repeated after a time period of 7 months during which CO 2 was injected into the hydrofractured zone. The issues to be addressed ranged from the detectability of the geologic structure in the diatomic reservoir to the detectability of CO 2 within the hydrofracture. During the pre-injection experiment, the P-wave velocities exhibited relatively low values between 1700-1900 m/s, which decreased to 1600-1800 m/s during the post-injection phase (-5%). The analysis of the pre-injection S-wave data revealed slow S-wave velocities between 600-800 m/s, while the post-injection data revealed velocities between 500-700 m/s (-6%). These velocity estimates produced high Poisson ratios between 0.36 and 0.46 for this highly porous (~ 50%) material. Differencing post-and pre-injection data revealed an increase in Poisson ratio of up to 5%. Both, velocity and Poisson estimates indicate the dissolution of CO 2 in the liquid phase of the reservoir accompanied by a pore-pressure increase. The results of the cross well experiments were corroborated by single well data and laboratory measurements on core data.

Geophysics, Jun 13, 2023

We analyze results of high-resolution seismic imaging at The Geysers geothermal reservoir in nort... more We analyze results of high-resolution seismic imaging at The Geysers geothermal reservoir in northern California, USA, using a dense seismic network to image the spatial heterogeneity of the reservoir structure and flow paths. The project uses 92 seismic stations spaced at approximately 500 m over a 5 km × 5 km study area. Microseismic data for more than 17,000 earthquakes have been acquired over a period of 13 months and automatically processed for P- and S-wave phase arrival times. The data are subsequently inverted using a joint inversion approach to image the spatial heterogeneity of the reservoir including the 3D P- and S-wave velocity structure and [Formula: see text]/[Formula: see text] ratio, and to locate earthquake hypocenters. The resulting tomographic images are appraised by integration into The Geysers’ 3D reservoir model and by a spatial correlation to the injection and production wells. Spatial correlation of P-wave velocity images to water injection and steam production wells reveal higher velocities below injection wells, due to higher water saturation, and lower velocities in the vicinity of steam-producing wells, due to the presence of steam in the surrounding reservoir rocks. The spatial correlation of [Formula: see text]/[Formula: see text] to steam in the reservoir indicates decreased estimates in the vicinity of steam production wells. In contrast, the [Formula: see text]/[Formula: see text] ratio reveals high values in the reservoir for regions near water injection wells and along the potential flow path of water through the reservoir. The estimates of shear modulus indicate high values in a region of competent graywacke, which is known for a lack of fractures and steam production, and low values in a region that is dominated by water flow, suggesting that fractured rock created a pathway for the water through the reservoir. The heterogeneity observed in the S-wave velocities indicates a compartmentalized reservoir, which correlates spatially with fault projections in the 3D reservoir model.

Borehole logs from the German Continental Deep Drilling Project (KTB) are analyzed to study the s... more Borehole logs from the German Continental Deep Drilling Project (KTB) are analyzed to study the small scale structure of the upper crust. An exponential function is found to best fit the autocorrelation function of the high frequency log data, with a correlation length of about 2 m. We separate the low frequency trend in the P wave velocity log, representing distinct geological lithology, emplaced by either original deposition processes or later tectonic activity, and investigate its power spectrum to determine a possible power law. A consL:wt slope of approximately-2, indicating fractal dimensions over a scale length nmging from 3.5 km to 100 m, best fits the spectrum. The power spectrum of the high frequency residual of the log revealed st.'ltionar

Rayleigh Scattering and Nonlinear Inversion of Elastic Waves

Seismological Research Letters, Aug 4, 2021

The recovery of seismic source parameters requires the use of calibrated velocity models. Althoug... more The recovery of seismic source parameters requires the use of calibrated velocity models. Although at long periods it is possible to use relatively simple plane-layered models, calibration is still needed to better constrain source parameters. For the Democratic People’s Republic of Korea (DPRK) nuclear tests, this is particularly true when considering the use of seismic stations in Japan where paths cross the Sea of Japan. In this study, we perform forward waveform modeling to calibrate velocity structures. We show that we can arrive at a set of models that minimizes Rayleigh group-velocity anomaly at stations located in China, South Korea, and Japan. Overall moment tensor capability with the new models is improved such that cross-correlation analysis of the 20–50 s period waveforms recovers the true time alignment of the data, enabling better automated source analysis. We performed source-type inversions for the moment tensor jointly for long-period regional waveforms and regional and teleseismic P-waves polarity data for the latest and largest DPRK nuclear test and examine event discrimination/screening capability, scalar moment, and yield estimates with uncertainty. We present the models for improved seismic source modeling of the region.

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Sep 26, 2018

We analyzed seismicity near the EGS development at The Geysers, CA Prati-32 injection well to eva... more We analyzed seismicity near the EGS development at The Geysers, CA Prati-32 injection well to evaluate the development and the physical attributes of a subsurface fracture network. The goals of our study include the ability to estimate the orientation and the activated fracture area, to estimate stress orientation and stress orientation changes as well as fluid saturation and spatio-temporal changes in fluid saturation. We compiled a 168-event waveform-based seismic moment tensor catalog for events 0.7≤Mw≤3.9 based on a semi-automated moment tensor analysis technique to be used for in-situ stress estimation during the injection phases. We found an approximate 15-degree counterclockwise rotation of the least compressive stress σ3, and a rotation of the maximum compressive stress σ1 toward the vertical as the injected volume of water increased. We developed a rupture-area magnitude scaling relationship of The Geysers earthquakes obtained from finite-source inversion for fault slip that reveals a very high correlation to published results. Based on the rupture area-magnitude relationship we mapped Mw from the LBNL earthquake catalog to estimate the activated fracture area and its location within the injection volume of Prati-32. Analysis of the Vp/Vs-ratio based on the double-difference Wadati technique revealed the development of an injection-derived steam plume during the early injection phase, particularly in the northern parts of the Prati-32 study area.

AGU Fall Meeting Abstracts, Dec 14, 2015

AGU Fall Meeting Abstracts, Dec 1, 2016

AGU Fall Meeting Abstracts, Dec 1, 2011

Lawrence Berkeley National Laboratory, Aug 28, 2002

Crosswell seismic and electromagnetic data sets taken before and during CO 2 flooding of an oil r... more Crosswell seismic and electromagnetic data sets taken before and during CO 2 flooding of an oil reservoir are inverted to produce crosswell images of the change in compressional velocity, shear velocity and electrical conductivity during a CO 2 injection pilot study. A rock properties model is developed using measured log porosity, fluid saturations, pressure, temperature, bulk density, sonic velocity and electrical conductivity. The parameters of the rock properties model are found by an L1-norm simplex minimization of predicted and observed compressional velocity and density. A separate minimization using Archie's law provides parameters for modeling the relations between water saturation, porosity and the electrical conductivity. The rock properties model is used to generate relationships between changes in geophysical parameters and changes in reservoir parameters. The electrical conductivity changes are directly mapped to changes in water saturation. The estimated changes in water saturation are used with the observed changes in shear wave velocity to predict changes in reservoir pressure. The estimation of the spatial extent and amount of CO 2 relies on first removing the effects of the water saturation and pressure changes from the observed compressional velocity changes, producing a residual compressional velocity change. The residual compressional velocity change is then interpreted in terms of increases in the CO 2 /oil ratio. Resulting images of CO 2 /oil ratio show CO 2 rich zones that are well correlated with the location of injection perforations with the size of these zones also correlating to the amount of injected CO 2. The images produced by this process are better correlated to the location and amount of injected CO 2 than are any of the individual images of change in geophysical parameters.

Geophysical Research Letters, Apr 4, 2003

The Energy Citations Database (ECD) provides access to historical and current research (1948 to t... more The Energy Citations Database (ECD) provides access to historical and current research (1948 to the present) from the Department of Energy (DOE) and predecessor agencies.

A series of time-lapse seismic cross well and single well experiments were conducted in a diatomi... more A series of time-lapse seismic cross well and single well experiments were conducted in a diatomite reservoir to monitor the injection of CO 2 into a hydrofracture zone, using P-and S-wave data. During the first phase the set of seismic experiments were conducted after the injection of water into the hydrofrac-zone. The set of seismic experiments was repeated after a time period of 7 months during which CO 2 was injected into the hydrofractured zone. The issues to be addressed ranged from the detectability of the geologic structure in the diatomic reservoir to the detectability of CO 2 within the hydrofracture. During the pre-injection experiment, the P-wave velocities exhibited relatively low values between 1700-1900 m/s, which decreased to 1600-1800 m/s during the post-injection phase (-5%). The analysis of the pre-injection S-wave data revealed slow S-wave velocities between 600-800 m/s, while the post-injection data revealed velocities between 500-700 m/s (-6%). These velocity estimates produced high Poisson ratios between 0.36 and 0.46 for this highly porous (~ 50%) material. Differencing post-and pre-injection data revealed an increase in Poisson ratio of up to 5%. Both, velocity and Poisson estimates indicate the dissolution of CO 2 in the liquid phase of the reservoir accompanied by a pore-pressure increase. The results of the cross well experiments were corroborated by single well data and laboratory measurements on core data.

AGU Fall Meeting Abstracts, Dec 1, 2002

A series of time-lapse seismic cross well and single well experiments were conducted in a diatomi... more A series of time-lapse seismic cross well and single well experiments were conducted in a diatomite reservoir to monitor the injection of CO2 into a hydrofracture zone, based on P- and S-wave data. A high-frequency piezo-electric P-wave source and an orbital-vibrator S-wave source were used to generate waves that were recorded by hydrophones as well as three-component geophones. The injection

AGU Fall Meeting Abstracts, Dec 1, 2013

Lawrence Berkeley National Laboratory, Apr 29, 2003

A series of time-lapse seismic cross well and single well experiments were conducted in a diatomi... more A series of time-lapse seismic cross well and single well experiments were conducted in a diatomite reservoir to monitor the injection of CO 2 into a hydrofracture zone, using P-and S-wave data. During the first phase the set of seismic experiments were conducted after the injection of water into the hydrofrac-zone. The set of seismic experiments was repeated after a time period of 7 months during which CO 2 was injected into the hydrofractured zone. The issues to be addressed ranged from the detectability of the geologic structure in the diatomic reservoir to the detectability of CO 2 within the hydrofracture. During the pre-injection experiment, the P-wave velocities exhibited relatively low values between 1700-1900 m/s, which decreased to 1600-1800 m/s during the post-injection phase (-5%). The analysis of the pre-injection S-wave data revealed slow S-wave velocities between 600-800 m/s, while the post-injection data revealed velocities between 500-700 m/s (-6%). These velocity estimates produced high Poisson ratios between 0.36 and 0.46 for this highly porous (~ 50%) material. Differencing post-and pre-injection data revealed an increase in Poisson ratio of up to 5%. Both, velocity and Poisson estimates indicate the dissolution of CO 2 in the liquid phase of the reservoir accompanied by a pore-pressure increase. The results of the cross well experiments were corroborated by single well data and laboratory measurements on core data.

Geophysics, Jun 13, 2023

We analyze results of high-resolution seismic imaging at The Geysers geothermal reservoir in nort... more We analyze results of high-resolution seismic imaging at The Geysers geothermal reservoir in northern California, USA, using a dense seismic network to image the spatial heterogeneity of the reservoir structure and flow paths. The project uses 92 seismic stations spaced at approximately 500 m over a 5 km × 5 km study area. Microseismic data for more than 17,000 earthquakes have been acquired over a period of 13 months and automatically processed for P- and S-wave phase arrival times. The data are subsequently inverted using a joint inversion approach to image the spatial heterogeneity of the reservoir including the 3D P- and S-wave velocity structure and [Formula: see text]/[Formula: see text] ratio, and to locate earthquake hypocenters. The resulting tomographic images are appraised by integration into The Geysers’ 3D reservoir model and by a spatial correlation to the injection and production wells. Spatial correlation of P-wave velocity images to water injection and steam production wells reveal higher velocities below injection wells, due to higher water saturation, and lower velocities in the vicinity of steam-producing wells, due to the presence of steam in the surrounding reservoir rocks. The spatial correlation of [Formula: see text]/[Formula: see text] to steam in the reservoir indicates decreased estimates in the vicinity of steam production wells. In contrast, the [Formula: see text]/[Formula: see text] ratio reveals high values in the reservoir for regions near water injection wells and along the potential flow path of water through the reservoir. The estimates of shear modulus indicate high values in a region of competent graywacke, which is known for a lack of fractures and steam production, and low values in a region that is dominated by water flow, suggesting that fractured rock created a pathway for the water through the reservoir. The heterogeneity observed in the S-wave velocities indicates a compartmentalized reservoir, which correlates spatially with fault projections in the 3D reservoir model.

Borehole logs from the German Continental Deep Drilling Project (KTB) are analyzed to study the s... more Borehole logs from the German Continental Deep Drilling Project (KTB) are analyzed to study the small scale structure of the upper crust. An exponential function is found to best fit the autocorrelation function of the high frequency log data, with a correlation length of about 2 m. We separate the low frequency trend in the P wave velocity log, representing distinct geological lithology, emplaced by either original deposition processes or later tectonic activity, and investigate its power spectrum to determine a possible power law. A consL:wt slope of approximately-2, indicating fractal dimensions over a scale length nmging from 3.5 km to 100 m, best fits the spectrum. The power spectrum of the high frequency residual of the log revealed st.'ltionar

Rayleigh Scattering and Nonlinear Inversion of Elastic Waves

Seismological Research Letters, Aug 4, 2021

The recovery of seismic source parameters requires the use of calibrated velocity models. Althoug... more The recovery of seismic source parameters requires the use of calibrated velocity models. Although at long periods it is possible to use relatively simple plane-layered models, calibration is still needed to better constrain source parameters. For the Democratic People’s Republic of Korea (DPRK) nuclear tests, this is particularly true when considering the use of seismic stations in Japan where paths cross the Sea of Japan. In this study, we perform forward waveform modeling to calibrate velocity structures. We show that we can arrive at a set of models that minimizes Rayleigh group-velocity anomaly at stations located in China, South Korea, and Japan. Overall moment tensor capability with the new models is improved such that cross-correlation analysis of the 20–50 s period waveforms recovers the true time alignment of the data, enabling better automated source analysis. We performed source-type inversions for the moment tensor jointly for long-period regional waveforms and regional and teleseismic P-waves polarity data for the latest and largest DPRK nuclear test and examine event discrimination/screening capability, scalar moment, and yield estimates with uncertainty. We present the models for improved seismic source modeling of the region.