Thomas Daley - Independent Researcher (original) (raw)

Papers by Thomas Daley

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Environmental Science & Technology, Jul 2, 2012

The risk of CO 2 leakage from a properly permitted deep geologic storage facility is expected to ... more The risk of CO 2 leakage from a properly permitted deep geologic storage facility is expected to be very low. However, if leakage occurs it could potentially impact potable groundwater quality. Dissolved CO 2 in groundwater decreases pH, which can mobilize naturally occurring trace metals commonly contained in aquifer sediments. Observing such processes requires adequate monitoring strategies. Here, we use laboratory and field experiments to explore the sensitivity of time-lapse complex resistivity responses for remotely monitoring dissolved CO 2 distribution and geochemical transformations that may impact groundwater quality. Results show that electrical resistivity and phase responses correlate well with dissolved CO 2 injection processes. Specifically, resistivity initially decreases due to increase of bicarbonate and dissolved species. As pH continues to decrease, the resistivity rebounds toward initial conditions due to the transition of bicarbonate into non-dissociated carbonic acid, which reduces the total concentration of dissociated species and thus the water conductivity. An electrical phase decrease is also observed, which is interpreted to be driven by the decrease of surface charge density as well as potential mineral dissolution and ion exchange. Both laboratory and field experiments demonstrate the potential of field complex resistivity method for remotely monitoring changes in groundwater quality due to CO 2 leakage.

Interpretation, Feb 1, 2019

Distributed Acoustic Sensing (DAS) can revolutionize the seismic industry by using fiber-optic ca... more Distributed Acoustic Sensing (DAS) can revolutionize the seismic industry by using fiber-optic cables installed permanently to acquire on-demand VSP data at fine spatial sampling. With this, DAS can solve some of the issues associated with conventional seismic sensors. Studies have successfully demonstrated the use of DAS on cemented fibers for monitoring applications, however, such applications on tubing deployed fibers are relatively uncommon. Application of tubing deployed fibers is especially useful for preexisting wells, where there is no opportunity to install a fiber behind the casing. In the CO2CRC Otway Project, we acquired a 3D DAS VSP using a standard fiber-optic cable installed on the production tubing of the injector well. We aim to analyze the quality of the 3D DAS VSP on-tubing, as well as discuss lessons learnt from the current DAS deployment. We show the limitations associated with the DAS on-tubing, as well as ways to improve the quality of the datasets for future surveys at Otway. Due to the reduced coupling and the long fiber length (~20 km), the raw DAS records show a high level of noise relative to the signal. Despite the limitations, the migrated 3D DAS VSP data recorded by cable installed on tubing is able to image interfaces beyond the injection

Recent CO 2 sequestration pilot projects have implemented novel approaches to well-based subsurfa... more Recent CO 2 sequestration pilot projects have implemented novel approaches to well-based subsurface monitoring aimed at increasing the amount and quality of information available from boreholes. Some of the drivers for the establishment of new well-based technologies and methodologies arise from: (1) the need for data to assess physical and geochemical subsurface processes associated with CO 2 emplacement; (2) the high cost of deep boreholes and need to maximize data yield from each; (3) need for increased temporal resolution to observe plume evolution; (4) a lack of established processes and technologies for integrated permanent sensors in the oil and gas industry; and (5) a lack of regulatory guidance concerning the amount, type, and duration of monitoring required for long-term performance confirmation of a CO 2 storage site. In this paper we will examine some of the latest innovations in well-based monitoring and present examples of integrated monitoring programs.

ASEG extended abstracts, Dec 1, 2018

Distributed Acoustic Sensing (DAS) is an optical interferometric method for acquisition of acoust... more Distributed Acoustic Sensing (DAS) is an optical interferometric method for acquisition of acoustic and seismic signals. It uses laser pulses that travel along the length of a fibre-optic cable and backscatter as they encounter small inconsistencies in the fibre. Impinging seismic waves cause strain on the cable, resulting in differences in phase of the backscattered light. Interest in DAS has increased significantly in the past decade as it is particularly suited for VSP acquisitions, including for permanent reservoir monitoring. Fibreoptic cables can be installed permanently in the well, cemented behind the casing or attached to tubing; they offer a relatively cheaper and efficient solution when compared to conventional borehole sensors. This study is part of the CO2CRC Otway Project. The Otway Project site is located approximately 240 km south-west of Melbourne, Australia. The Stage 2C of the project aims to monitor a small injection (15 kt) of CO2/CH4 gas mixture at a depth of approximately 1500 m. Here, we show the results of a 3D VSP survey acquired using DAS cable deployed on production tubing in the injector well. The DAS up-going wavefield shows a high level of noise. However, DAS is able to record the main reflections, including at the injection depth. After 3D migration of the data, noise levels reduce significantly. Events on DAS inline match with events on a corridor stack produced from a geophone check-shot data. Due to the directionality pattern, DAS was only able to image up to approximately 300 m radius from the well.

Lawrence Berkeley National Laboratory, May 29, 2008

Triplication of a wavefront, also classically known as birefringence, can and does occur in trans... more Triplication of a wavefront, also classically known as birefringence, can and does occur in transversely isotropic (TI) media. With the growing interest in shear waves, and in particular, converted shear waves, it becomes necessary to study this phenomenon, and the bright spots that accompany it. In a plane that includes the medium's rotational symmetry axis, there may exist a range of angles within which the qSV wave, whose polarization lies in that plane, may propagate at three distinct velocities. The region of the qSV wave curve where this can occur always corresponds to the region of the qSV slowness curve where the closed qSV curve about the origin is concave. When the range of angles is small and the three arrivals are close together, the usual situation, the qSV wave within that small range will be significantly brighter than in other directions. When the range of angles is large, the two cusps of the wave surface, on the borders of the region of triplication will both be bright spots.

A nine-component VSP was acquired in a 3000 ft. well at the Conoco test site in Newkirk, OK with ... more A nine-component VSP was acquired in a 3000 ft. well at the Conoco test site in Newkirk, OK with the intent of measuring subsurface fracture properties. This site has been the subject of previous geologic and geophysical studies which have interpreted fracture properties and fracture-induced seismic anisotropy for a vertical fracture set. We use the zero-offset shear-wave VSP data, modified by a 4-component Alford rotation, to approximate a data set polarized normal and tangential to the dominant fracture orientation. This rotated data set has shear-wave polarizations aligned with the subsurface anisotropy axis of symmetry. The Alford .rotation angles, determined from the shear-wave first arrivals, indicate a N67°E azimuth for the axis of symmetry .. This azimuth is consistent with previous studies. After rotation, we observe that these two shear:. wave data sets have a maximum 3.3% velocity anisotropy. The observed shear-wave splitting does appear to vary with depth, implying variation in fracture properties with depth. We use the spectral ratio method to measure attenuation (Q), as a function of depth, for both polarizations. We use adaptive multi-spectral tapering to improve the spectral estimates used for the spectral ratio. We observe anisotropy in shear-wave attenuation. The tangential polarization (tangential to . the fracture orientation) has a larger Q than the normal polarization (normal to fracture orientation). The average Q anisotropy is 55%. We attempt to interpret depth-dependent changes in velocity anisotropy and Q anisotropy, however scatter in the Q values does not allow detailed interpretation. The velocity anisotropy data does allow interpreted in terms of isotropic and anisotropic regions.

Inverting temporal velocity changes at SAFOD from cross-well active source seismic data using a Markov Chain Monte Carlo approach

AGU Fall Meeting Abstracts, Dec 1, 2020

Tracking Subsurface Supercritical CO 2 Using Advanced Reflection Seismic and Well Log‐Based Workflows Incorporating Fluid Density and Pore Pressure Effects

Geophysical Monitoring for Geologic Carbon Storage, 2022

Subsurface Imaging Using Buried DAS and Geophone Arrays - Preliminary Results from CO2CRC Otway Project

78th EAGE Conference and Exhibition 2016, 2016

A permanent geophone array along with a fibre optic distributed acoustic sensing (DAS) array were... more A permanent geophone array along with a fibre optic distributed acoustic sensing (DAS) array were deployed at the CO2CRC Otway Project site in order to conduct seismic monitoring of a CO2 plume during a small-scale injection test. This study aims to assess the ability for a permanent geophone array to overcome issues related to different acquisition (receiver) designs, high ambient noise level and seasonal variations in the near surface, as well as to test the DAS system for performing cost-effective time lapse seismic measurements. The acquisition of 3D seismic data is performed for this purpose using ~3000 vibroseis source points. We show the preliminary results of seismic reflection imaging conducted using DAS data. We observe the differences in performance between a standard commercially available tactical fibre optic cable and a custom helically wound cable. The results of this study and the workflows established will be used for processing a complete 3D seismic dataset acquired with a DAS array before being compared to a conventional geophone array.

CO2 messes with rock physics

The Leading Edge, 2021

Seismic techniques are the main monitoring tools for CO2 storage projects, especially in saline a... more Seismic techniques are the main monitoring tools for CO2 storage projects, especially in saline aquifers with good porosity. The majority of existing commercial and pilot CO2 injections have resulted in clear time-lapse seismic anomalies that can be used for leakage detection as well as refinement of the reservoir models to conform with the monitoring observations. Both tasks are legal requirements imposed on site operators. This paper revisits the rock-physics effects that may play an important role in the quantitative interpretation of seismic data. First, we briefly describe a standard approach to the rock-physics modeling of CO2 injections: Gassmann-type fluid substitution accounts for the presence of compressible CO2 in the pore space, and dissolution/precipitation of the minerals changes the pore volume. For many geologic conditions and injection scenarios, this approach is inadequate. For example, dissolution of the carbonate cement may weaken the rock frame, wave-induced flu...

Crosswell CASSM (continuous active-source seismic monitoring) data was acquired as part of the Fr... more Crosswell CASSM (continuous active-source seismic monitoring) data was acquired as part of the Frio-II brine pilot CO 2 injection experiment. To gain insight into the CO 2 plume evolution, we have integrated the 3D multiphase flow modeling code TOUGH2 with seismic simulation codes via a petrophysical model that predicts seismic velocity for a given CO 2 saturation. Results of forward seismic modeling based on the CO 2 saturation distribution produced by an initial TOUGH2 model compare poorly with the CASSM data, indicating that the initial flow model did not capture the actual CO 2 plume dynamics. Updates to the TOUGH2 model required to better match the CASSM field data indicate vertical flow near the injection well, with increased horizontal plume growth occurring at the top of the reservoir sand. The CASSM continuous delay time data are ideal for constraining the modeled spatiotemporal evolution of the CO 2 plume and allow improvement in reservoir model and estimation of CO 2 plume properties.

Using an orbital vibrator source (2-components), and a 40 level 3-component geophone string, a 6-... more Using an orbital vibrator source (2-components), and a 40 level 3-component geophone string, a 6-component crosswell survey was acquired before and after a CO2 injection in a saline aquifer. Decomposition of the two source components and component rotation of both source and sensors created good separation of P-and S-wave energy allowing independent analysis of travel time and reflectivity. A time-lapse VSP was also acquired.

Cost-effective imaging of CO2 injection with borehole seismic methods

The leading edge, Oct 1, 2006

Currently there is a critical need to increase oil and gas recovery from existing and new reservo... more Currently there is a critical need to increase oil and gas recovery from existing and new reservoirs. In addition, the ever-increasing need to sequester CO 2 in the subsurface places further emphasis on accurate imaging methods to validate CO 2 injection strategies. Two ...