PRISM :: Browsing by Author "Eaton, David"

Browsing by Author "Eaton, David"

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Open Access
Analysis of the Relationship between Hydraulic Fracture Pressure Trends and Facies of the Montney Formation
(2024-04-24) Virginillo, Nicole Antonette; Pedersen, Per; Eaton, David; Clarkson, Christopher
This study involves the integration of multiple disciplines and utilizes a novel approach to understand how geological properties influence the behaviour of hydraulic fractures in the Lower Triassic Montney Formation in the Pouce Coupe area in Alberta. Hydraulic fracturing data presents many uncertainties, and the utilization of different datasets is important to understand the different parameters impacting hydraulic fractures. The Montney Formation is often thought to be a homogeneous siltstone unit but there are significant heterogeneities present throughout the formation which have an impact on the efficacy of hydraulic fractures. This study utilizes the patterns portrayed by pressure curves reported in each stage of a horizontal well to determine how different geological properties influence hydraulic fractures. These pressure curves prove to be a useful dataset that brings insight into how geological properties influence the behaviour of hydraulic fractures. This study investigates the pressure curves in multi-stage horizontal wells completed using different technologies and landed in the Upper, Middle, and Lower Montney members. These pressure curves portray different patterns depending on completion technology and which member the wells are landed in. There is significant variation in geological properties within the Upper, Middle, and Lower Montney thus to further analyze how geological properties influence hydraulic fractures, this study investigates pressure curves of wells landed in different facies throughout the Montney. These facies have different sedimentological heterogeneities, changing bedding plane frequency, and natural fractures and faults which form geological barriers that hinder the productivity of hydraulic fractures. Results indicate that these geological properties impact fracture initiation and propagation of hydraulic fractures based on the patterns portrayed by the different segments along the pressure curves. This research implies that pressure curves are a useful dataset that can be utilized to further understand the influence that different geological properties have on hydraulic fractures. Rather than focusing on numerical point values to provide insight into hydraulic fracture behaviour, these pressure curves analyze how pressure changes with time to visualize the evolution of induced fractures and how they transform due to variations in the reservoir geology.
Embargo
Application of machine learning, ambient noise and 2-D seismic interpretation to investigate induced seismicity in western Canada
(2024-04-30) Rojas-Parra, Jesus; Eaton, David; Dettmer, Jan; Karchewski, Brandon Anthony James
In western Canada, the development of unconventional oil and gas resources in low-permeability reservoirs has increased dramatically in the last two decades. Production of these resources typically requires hydraulicfracturing stimulation to increase permeability, as well as disposal of excess brines into permeable rock units. Both of these industrial processes can lead to induced seismicity (human-caused earthquakes). This thesis applies several approaches in two study areas in western Canada where induced earthquakes have occurred, mainly using existing open-source software. Machine learning (ML), a rapidly growing artificial intelligence approach, is combined with a probabilistic non-linear global search algorithm to construct a new seismicity catalog for the northern Montney play in eastern BC using data from both public and private seismograph stations. PhaseNet, a popular ML method that has been pre-trained using historical earthquake catalogs from around the world, is used for detection of P- and S-wave arrivals (phases). A Gaussian mixture model associator, GaMMA, is used to associate phases into events. Hypocentre locations are determined from the phase picks using the NonLinLoc algorithm. Geological context for the seismicity event distribution is supplied by existing published faults as well as new fault interpretations using 2-D seismic profiles. A growing cloud of seismicity, consistent with the Kaiser effect, is observed along a mapped fault near a disposal zone. This phenomenon is modelled using pore-pressure diffusion, numerically simulated here using code that I developed. In the Musreau Lake region ofwestern Alberta, a different type of analysis is applied, in part because a comprehensive seismicity catalog has been published using a similar ML approach to that described above. Ambient-noise interferometry, which uses cross-correlation of background noise between pairs of seismograph stations, was used to investigate temporal changes in subsurface velocity associated with pore-pressure diffusion and induced seismicity. The results using the NoisePy software show a good recovery of relative velocity changes between pair stations. Further, statistical analysis is required to construct robust observations containing all retrieved signals. Finally, areas for possible future work are proposed, including the use of satellite interferometric synthetic aperture radar (InSAR) as a complementary method for seismological studies of induced earthquakes and slow-slip events, as well as fully coupled physics-based simulation and inversion of induced seismicity processes.
Open Access
Cenozoic exhumation history of the northern Richardson Mountains: Results from apatite and zircon (U-Th-Sm)/He analysis
(2020-08-17) McKay, Ryan D.; Enkelmann, Eva; Hadlari, Thomas; Enkelmann, Eva; Hadlari, Thomas; Hubbard, Stephen; Eaton, David
New low-temperature thermochronology data from clastic sedimentary rocks in the northern Richardson Mountains, Canada, indicate significant exhumational cooling during late Eocene–early Oligocene time. Apatite (U-Th-Sm)/He (AHe) data were collected from 19 Proterozoic–Paleocene rocks across a 115 km transect. Eighty-eight single-grain AHe dates range from 300 ± 5 Ma to 16 ± 4 Ma but most dates (65%) range 56–24 Ma. AHe dates are generally younger than the stratigraphic ages, indicative of thermal resetting by burial. Additionally, zircon (U-Th)/He (ZHe) data were collected from two Jurassic sandstones. The ten ZHe dates range from 831 ± 12 Ma to 291 ± 4 Ma and are older than the stratigraphic age, which limits maximum burial to <160°C. Our results from thermal history modeling indicate three phases of cooling, during the Paleocene–early Eocene (>65–50 Ma), late Eocene–early Oligocene (40–30 Ma), and late Oligocene–early Miocene (30–15 Ma). Most samples were sensitive to cooling during the first and second phases, whereas the third phase is not as well constrained. The rocks were close to surface temperatures and below the sensitivity of AHe analysis since the early–middle Miocene. The results suggest a previously unrecognized phase of cooling and inferred deformation in the northern Richardson Mountains during late Eocene–early Oligocene time. Our findings contribute to previous work that recognizes Late Cenozoic deformation along the eastern margin of the Northern Cordillera, in the northeastern Brooks Range (e.g. O’Sullivan et al., 1993; 1998b) and in the Mackenzie Mountains (Enkelmann et al., 2019). We investigated the potential mechanisms of this widespread deformation and found that the exhumation may relate to kinematic changes of the North American plate relative to structural trends along the margin of the Northern Cordillera.
Open Access
Characterization of damage processes in Montney siltstone under triaxial compression using acoustic emission and diagnostic imaging
(Oxford University Press, 2021-11-04) Jia, Suzie; Wong, Ron; Eaton, David
Crack nucleation and rock failure processes in a fine-grained siltstone (Montney Formation) under triaxial compression are investigated using combined diagnostic techniques, including ultrasonic-wave measurement, acoustic-emission (AE) monitoring, computed tomography (CT) scanning, and thin-section imaging. The sample displays a weak-to-moderate inherent seismic anisotropy and noticeable stress-induced anisotropy prior to failure. No AE event was detected until the applied axial stress reached 95% of the peak value. The signal-to-noise ratio is relatively low, however, and detectable AE events are more diffuse than those observed in highly brittle rocks. The AE locations correlate with a shear fracture zone imaged by CT scanning. AE moment-tensor analysis reveals that events with larger relative magnitudes are characterized by high volumetric (tensile or compressive) components, and the initiation of the failure zone is dominated by combined shear-tensile failure. Stress inversion of the AE events with high tensile components is in good agreement with the known applied stress. Microscopic imaging of thin sections from the failed sample shows that the failure zone is an en echelon structure consisting of a major fracture with branching micro and minor cracks. This failure mechanism is consistent with a shear-tensile source mechanism and is interpreted to be associated with the fine granular structure and mineral composition of Montney siltstone.
Open Access
Crustal structure beneath Hudson Bay from ambient-noise tomography
(2012) Pawlak, Agnieszka; Eaton, David
Hudson Bay is a shallow inland sea located in north-central Canada. The underlying lithosphere preserves a complex deformational history that dates back to the Archean. The Hudson Bay Lithospheric Experiment, HuBLE, is a collaborative initiative aimed at understanding the lithospheric evolution beneath the Bay. The recent emergence of a methodology called ambient-noise tomography provides a tool to image the crust and upper mantle beneath the Bay with higher resolution than previously possible. Using ambient-noise generated by the Earth as a source, this technique requires continuous recordings of ground motion. The ambientnoise method is based on the cross-correlations of daily noise signals between station pairs to estimate empirical Green's Functions. This thesis is made up of there separate studies. The first is an isotropic application of the ambient-noise tomography method to image crustal structure beneath Hudson Bay. Results show crustal thinning beneath the Bay, allowing us to reject a hypothesis for eclogitization and crustal thickening, with support instead for an extensional hypothesis for the formation of the Hudson Bay basin. The next study focuses on anisotropic variations of velocity within the subsurface. Inversion results show a distinct outline of geologic boundaries in the upper to mid-crust that does not carry through into the lower crust. A significant change in anisotropic fabric is evident across the Trans-Hudson orogen (THO) suture zone, which allows us to establish that tectonic fabrics formed prior to collision. The third study employs joint inversion of ambient-noise data and teleseismic surface wave data for increasing resolution of the crust and upper mantle. Results show that the THO suture zone dips to the southeast within the crust and becomes vertical in the upper mantle. This feature is interpreted as a zone of weakness that extends through the lithosphere, providing a locus for initiation of localized lithospheric stretching.
Open Access
Delineating the Shallow Free-phase Gas Distribution at an Abandoned Exploration Well, Crystal Geyser
(2022-01-20) Lagasca, Patrick Arceo; Ryan, M. Cathryn; Bentley, Laurence; Eaton, David
Crystal Geyser is an abandoned exploration well and active cold-water geyser driven by the expulsion of CO2 gas. It is a case study of an unsealed well transporting stray CO2 gas to the surface. Previous studies in the Crystal Geyser area inferred the existence of free-phase gas (FPG) accumulations trapped beneath low permeability layers near the geyser, but did not specify their exact locations or depths. In our primary study, we used electrical resistivity tomography to image a siltstone-capped FPG plume within the sandstone aquifer beneath Crystal Geyser. The plume was identified from an anomalously high resistivity zone that was not caused by lithofacies changes or fault displacement, representing a portion of the aquifer with elevated FPG content in the pore space. FPG is transported via Crystal Geyser’s conduit and the nearby Little Grand Wash Fault into a plunging anticline trap. The poor well casing integrity allows FPG to migrate from the conduit into the surrounding aquifer and gas trap. The subsurface FPG plume delineation was compared to the “equivalent CO2 bubbling depth” – the shallowest depth at which the total CO2 mass (free-phase and dissolved-phase CO2) expelled from the geyser would occur in the dissolved phase. The bubbling depth was extrapolated from mass balance calculations based on field estimates of Crystal Geyser’s CO2 and water emissions. The estimated bubbling depth was much shallower than the imaged FPG plume. This underestimation can be caused by the leakage of ascending FPG into the surrounding subsurface, allowed by the poor casing integrity of the well.
Open Access
Discourses of life, machines, and control: How science organisations represent the Earth to the public on Instagram
(2024-04-17) Droboth, Jason Curtis; Dolphin, Glenn; Eaton, David; Dolphin, Glenn; Eaton, David; Dutchak, Alex; Blue, Gwendolyn
Scientific efforts have prompted significant changes in how the average person understands, and thus interacts with, the Earth. To ensure optimum Earth-human interactions, academic and policy leaders must have a clear accounting of exactly what scientific representatives are telling the public about the Earth. Yet, what little research exists tends to prioritise specific topics–climate change in particular–and media environments–like newspapers–at the expense of representations of the whole Earth or representations via new media environments like social media. Using a Multimodal Discourse Analysis, this study produced an inventory of the ways science organisations represent the Earth to the public through their official Instagram accounts. It found that the Earth is represented through, not just written language, but visual imagery, in a wide variety of ways, like ‘Earth is the water planet’, ‘Earth is beautiful’, and ‘humans are harming the Earth’. Nearly all the representations identified, however, contribute in some way to two dominant messages. That 1) the Earth is the blue water planet upon which life flourishes because of Earth’s many mechanistic life-support systems. Thus, 2) we must use science to wisely control earth to promote and protect, especially human, life. The list of identified discourses was then compared with what the National Science Foundation outlined in 2010 as the ‘9 big ideas about the Earth all citizens should know’. The study found that the current ideas science organisations advance align with the aspirational ‘9 big ideas’ in a few ways, especially in centring life as Earth’s most important and consequential attribute. However, they differ in many more, most notably in their evaluation of Earth’s dynamism. Though science organisations may intend to present Earth’s continually changing states–like Earthquakes and extinctions–as natural, they actually represent it as primarily negative and thus regrettable. Further contributing to the imperative for humans to use science to stabilise, and thus control the Earth.
Open Access
Downhole microseismic monitoring: processing, algorithms and error analysis
(2014-04-09) Akram, Jubran; Eaton, David
Basic microseismic data processing for hypocentre location estimates is a pre-requisite to extracting information about the stimulated reservoir volume as well as understanding the geomechanics of the fracturing process. The primary objective of this thesis is to investigate the basic processing of microseismic data acquired with receivers in a single observation well, with emphasis on the evaluation and parameter selection of processing algorithms and the associated hypocentre location error analysis. This thesis is made up of five independent studies. The first study discusses the development of a MATLAB based microseismic data processing package (Calgary microseismic processing system; CaMPS). This software is used to process the microseismic data from a hydraulic fracture treatment in western Canada. For reference, the results are compared with those obtained independently by a microseismic services company. The second study examines several single-trace event-detection and arrival-time picking algorithms for microseismic data. A dynamic threshold criterion for event detection and a hybrid, arrival-time picking approach are proposed. The performance of these algorithms is evaluated using synthetic and real microseismic data. The third study describes an iterative cross-correlation based workflow to refine the initial arrival-time picks. This workflow is compared with other single-trace and multi-trace techniques. The proposed workflow provides an arrival-time accuracy of ±0.5 − 1ms for both synthetic and real microseismic data examples considered in this study. The fourth study examines hypocentre location uncertainty and errors due to inaccurate velocity model. The Monte Carlo uncertainty analysis suggests that the velocity errors have a greater impact on hypocentre locations than arrival-time pick errors. The hypocentre location errors resulting from the model calibration process are also discussed, in particular the use of single vs. multiple calibration shots, a priori information, and first vs. direct arrival times. The fifth study discusses the remaining hypocentre location errors after anisotropic model calibration. The behaviour of hypocentre location is discussed when a 1-D layered, isotropic and homogeneous model is used to locate hypocentres from anisotropic and heterogeneous subsurface. The results emphasize the use of a detailed model with anisotropy and lithological or structural variations for improving hypocentre location accuracy.
Open Access
Experimental Simulation and Life Cycle Assessment Study of the Dense Hot Fluid Injection Process
(2016-02-03) Hovsepian, Christian Nubar; Pereira-Almao, Pedro; Bergerson, Joule; Eaton, David; Hejazi, Hossein; Nassar, Nashaat
The rapid decline in international oil prices forced oil and gas industries to reduce costs, improve productivity and layoff thousands of employees. Specifically, the majority of resources located in Alberta require thermal recovery methods due to their heavy characteristics. Innovation is required to displace current extraction methods that are becoming economically challenging. The present work studies the dense hot fluid injection (DHFI) process, which targets the in situ catalytic upgrading and extraction of Athabasca bitumen. A bench-scale set up was designed and built. The experimental results were integrated using process simulation and life cycle assessments (LCA) techniques to estimate GHG emissions of the new technology. Results confirmed quality improvement of the feedstock while maintaining a stable product. The experimental setup proved differences in the heat distribution profiles between SAGD and the DHFI. LCA demonstrated that the DHFI could produce less GHG emissions than SAGD under a set of assumed scenarios.
Open Access
Extended-FEM analysis of injection-induced slip on a fault with rate-and-state friction: Insights into parameters that control induced seismicity
(Springer, 2023-03-09) Hosseini, Navid; Priest, Jeffrey; Eaton, David
The extended finite element method (X-FEM) is utilised to simulate the behavior of a heterogeneous fault characterized by rate-state frictional rheology, embedded within a poroelastic medium. The displacement and pore-pressure fields that are discontinuous across the fault are computed using X-FEM, by enriching the standard finite element approximation with additional degrees of freedom for elements intersected by the fault. We investigate a Mw 4.1 injection-induced earthquake in western Canada; this model incorporates depth-varying rate-slip behavior wherein a high-pressure zone due to hydraulic fracturing stimulation intersects the fault within a stable layer, producing aseismic slip that progressively loads an unstable fault region, thereby triggering dynamic rupture. Parametric studies using our numerical approach provide insights into the influence of rate-state parameters on fault activation, as well as hydraulic properties of a damage zone that surrounds the fault. Results confirm that aseismic slip near the injection zone propagates outwards to seismogenic unstable regions of the fault. The coseismic slip profile, seismic moment, and slip latency are determined by the difference a − b for rate-state parameters of the unstable fault regions. Hydraulic diffusivity in the damage zone controls the rate of pore-pressure diffusion along the fault, which affects timing of the initial seismic event and aftershock productivity.
Open Access
Fault-Sketch: A Framework for Modeling Geological Faults and Displacements
(2024-02-15) Banaeizadeh, Arya; Costa Sousa, Mario; Samavati, Faramarz; Costa Sousa, Mario; Samavati, Faramarz; Eaton, David; Yanushkevich, Svetlana
Geological faults, which result from rock fracturing and displacement in the subsurface, play an important role in shaping the Earth's crust. Modeling fault surfaces and their impact on rock formations is, thus, useful for various geological applications. However, due to the complex configurations of faults, the modeling process can become difficult, requiring a framework with a specialized modeling toolkit. The primary challenge in fault modeling lies in properly correlating the geometry of faults with their effects on rock layers and other fault surfaces during displacement. The final models also have to satisfy certain properties to be reusable for further geological analysis. A factor that even if users who have both modeling and geology expertise cannot guarantee to have. To address this, we have developed a series of operators designed for fault modeling. In this manner, we present Fault-Sketch, a Sketch-Based Interface and Modeling (SBIM) framework that tackles the task of fault modeling and captures their influence on various geological structures. This framework enables the creation of surfaces as a result of rock configurations that have previously been largely overlooked in the existing literature. The collection of operators presented in Fault-Sketch are built upon a data structure fit for the purpose of consistently representing fault surfaces and their boundaries together with the influence they cause both on other surfaces and on the volumes they bound. Moreover, the operators are designed to mimic the geologic processes relevant to fault creation and displacement to facilitate their use by domain experts.
Open Access
Finite-difference Simulation of Synthetic Microseismograms in the Presence of Anisotropy and Attenuation
(2015-09-25) Rashedi, Hoda; Eaton, David
This study presents a suite of 2D synthetic microseismic events computed using three velocity models, incorporating varying degrees of anisotropy and attenuation. An explicit second-order finite-difference method is used, capable of handling general anisotropy, up to triclinic symmetry. The microseismic source is specified as an arbitrary moment tensor, subject to be located in an isotropic layer. The anisotropy in our models is confined to VTI (Vertically Transverse Isotropic) media. Attenuation can be simulated for both isotropic and VTI medium, so the method is suited to modeling wave propagation in shale. All of the examples shown in this thesis are for a downhole acquisition geometry using a vertical monitor well. Care is required to avoid contamination of the synthetic data by edge reflections due to the ineffectiveness of currently known FD absorbing boundary for general anisotropy. Synthetic data (SEGY) are available for benchmarking purposes including hypocentre location, moment tensor inversion, etc.
Open Access
Four Phenomena Observed on Microseismic Data
(2013-09-13) St-Onge, Andre Maurice; Eaton, David
Passive seismic data recorded in observation wellbores for hydraulic fracture monitoring are usually used to detect P- and S-wave arrivals from induced microseismic events. The time arrivals for these events are used to compute source locations to build a fracture location map. Along with these arrivals are a number of other coherent signal and noise events. The primary objective of this thesis is to examine various other types of coherent signal and noise on four microseismic datasets. This thesis is made up of four separate studies. The first study examines numerous coherent low-frequency (<100 Hz) arrivals characterized by conspicuous dispersion and quasi-linear moveout. Their apparent velocities and dispersion characteristics are consistent with Lamb waves, an elastic guided wave that propagates within finite media such as plates or cylindrical casing. Lamb waves may be used for monitoring degradation of casing cement over time. The second study examines two datasets to characterize frequency shifts in discrete narrow passbands caused by wellbore acoustic transmissivity due to geophone clamping. The passbands changed throughout two fracture stimulations in proportion to the hydraulic fracture pressure. Analytical and finite-element models suggest that these temporal variations may be caused by a relative change in geophone clamping force as the pressure external to the wellbore varies. This sensitivity suggests that passive seismic monitoring can be used for downhole detection of relative stress changes. The third study focuses on frequency content variations of 20 high S/N P- and S-wave events. The 20 events were grouped into four clusters based upon a geolocation algorithm and event cross-correlations. Spectral analysis shows variation in the signal within event sets. A 2-D elastic finite-difference simulation using a layered model shows that this variation could be ascribed to path effects associated with propagation of the signal from the source to the receivers. The fourth study examines a potential long-period long-duration (LPLD) seismic event and analyzes the phenomena in detail. LPLD events observed on microseismic data have been likened to deep low-frequency tremor attributed to slow-slip processes along pre-existing fractures or strike-slip regimes at subduction zones. The event may be the result of hydraulic fracture fluid leak-off out of the intended zone into a pre-existing fracture.
Open Access
Hydraulic-fracturing induced seismicity in Alberta, Canada: Analysis and interpretation using dense local arrays
(2021-04-28) Igonin, Nadine; Eaton, David; Lauer, Rachel; Lawton, Donald
Unconventional oil and gas development is associated with anthropogenic earthquake activity worldwide. In particular, hydraulic fracturing, which involves the injection of high-pressure fluids into the subsurface, has been observed to trigger induced seismicity in some areas. The Duvernay Formation in Alberta is a target of hydraulic fracturing and has experienced induced earthquakes up to magnitude 4.2. To study hydraulic fracturing-induced seismicity in greater detail, a local dense array of sensors was used to collect four weeks of passive seismic data over a 4-well pad. In this thesis, this dataset is processed and interpreted using a variety of techniques. Supplementary information, such as waveform data from broadband seismometers and an accelerometer that were co-located with the dense geophone array, is also used to aid the interpretation. In some cases, it is found that the magnitude-frequency distribution obtained from the monitored seismicity deviates from the expected power-law form associated with the Gutenberg-Richter relationship. In particular, the largest earthquakes, greater than Mw 3.0, are larger than statistically expected given the observed seismicity. Spectral analysis of a subset of events reveals complex source spectra. For example, some of the events show evidence of a double corner frequency and a source time function with multiple peaks. A detailed analysis of the timing of events relative to the hydraulic fracturing stages reveals that natural fracture networks within the Ireton Shale, overlying the target Duvernay Formation, provided permeable conduits for an expanding region of elevated pore pressure. Using simple diffusive modelling, it is shown that these fracture networks allowed pore pressure to perturb fault systems at distances of over 1 km, consistent with observations of fault activation during treatment. In two datasets that are used in this thesis, shear-wave splitting analysis of microseismic waveforms provides evidence for stress rotation near the largest faults. Integration of these investigations provides a basis for a new working model for induced seismicity in the Fox Creek, Alberta, area.
Open Access
Integrated approach for fracture characterization of hydraulically stimulated volume in tight gas reservoir
(2019-04-17) Maulianda, Belladonna; Prakasan, Aruvin; Wong, Ron C; Eaton, David; Gates, Ian D
Abstract Hydraulic fracturing is conducted on unconventional reservoir which has very low permeability. It increases the production from unconventional oil and gas reservoirs through the creation of a connected stimulated rock volume (SRV) with higher conductivity. The permeability and the SRVs dimension are important parameters which increase the performance of hydraulically fractured wells. Microseismic monitoring is used to estimate the seismically stimulated volume within the reservoir, which can provide a proxy for the SRV. Finite element analysis was used in this study in the determination of SRV characteristics by utilizing field data from a horizontal well hydraulic-fracturing program in the Hoadley Field, Alberta, Canada. Coupled fluid-flow geomechanics finite element (FE) model was used. The permeability of the SRV is altered to match the field bottom-hole pressure. The pressure drop and in situ stress changes within the SRV are determined through the matching of the FE model. Fracture aperture, number and spacing in the SRV are then inferred from the estimated reservoir parameters by using a semi-analytical approach.
Open Access
Investigating Fault-Sealing Effects on Pore Pressure Distribution, Induced Seismicity and Hydraulic Fracture Propagation: Numerical Modelling and Case Study in Northeastern British Columbia
(2023-02-24) Esmaeilzadeh, Zahra; Eaton, David; Clarkson, Christopher; Gilbert, Hersh; Chen, Nancy; Lauer, Rachel; Fox, Amy
This thesis focuses on the effects of sealing faults and associated lateral pore-pressure gradients on induced seismicity and hydraulic fracturing (HF) operations. The studied formation is the Montney, a Triassic geological unit located in the Western Canada Sedimentary Basin that hosts one of the most productive unconventional plays in the world. The study area is located in northeastern British Columbia (BC), situated within the Kiskatinaw seismic monitoring and mitigation area (KSMMA), in the Septimus field where a significant induced earthquake sequence occurred in November 2018. Previously published reports show that pore pressure in the Montney Formation is compartmentalized, indicating that permeable and impermeable features such as fractures and sealing faults may control the reservoir fluid flow. Notably, the locations of pressure discontinuities are generally consistent with known faults, supporting a previous hypothesis that pressure compartments are fault-bounded. This thesis tests this hypothesis and models the effects of a horizontal pressure gradient (∆P) on fault activation and hydraulic fracture propagation. Novel methodologies have been developed for investigating complex interactions between pore-pressure gradient, seismicity and hydraulic fracturing mechanism, consisting of three workflows based, respectively, on statistical analysis of pore-pressure data, numerical simulation of hydraulic fracturing, and numerical modelling of fault activation. First, a comprehensive reservoir model is considered to characterize regional hydrodynamic, petrophysical and mechanical properties. The compiled data are used to construct a new pressure map of the Montney Formation, yielding insights into relationships between pressure boundaries and seismicity. The results confirm that pressure discontinuities are generally fault-bounded, but seal preservation depends on depth and fault properties. Earthquakes (both induced and natural) appear to cluster preferentially in areas of a high lateral pore-pressure difference. Next, using grid oriented hydraulic fracture extension replicator (GOHFER) software, HF growth is modelled in the presence of an impermeable fault and surrounding permeable damage zone. Different scenarios are considered based on ∆P and damage-zone properties. Results show that fault sealing behaviour depends on the pressure difference, stage shadowing effects, fault throw, injection rate and fault damage-zone permeability. The adverse effects of a damage zone on fluid loss of injected fluid are more pronounced when there is a lateral pressure gradient across the fault. The order of importance of these parameters implied by the modelling results is: stress shadowing > lateral pressure gradient > fault seal properties. Finally, the effect of lateral pressure gradient on fault activation is tested using 3D distinct element code (3DEC) software- 3D numerical modelling code that simulates the mechanical response of rock mass with discontinuities such as fractures and faults. Using this tool, sensitivity analysis of fault activation is performed based on the presence or absence of a significant pressure difference and a highly fractured and permeable damage zone on both sides of the fault. Strong ∆P may lead to asymmetric fracture geometry and considerable leakage of pore pressure into the lower pressure domain. A damage zone around the fault appears to channel pore pressure along the fault, leading to a more uniform distribution of fault aperture and pore pressure than in the absence of a damage zone, where the fault opening is concentrated near the HF intersection.
Open Access
Microseismic Data Processing, Modeling and Interpretation in the Presence of Coals: A Falher Member Case Study
(2014-09-29) Pike, Kimberly Anne; Eaton, David
Low-velocity, low-density coal units are prevalent throughout the Cretaceous section of the Western Canadian Sedimentary Basin. Their elastic properties differ considerably from the surrounding clastic units, resulting in complex seismic propagation paths and interference patterns. This thesis presents a case study evaluating the implications these coal units have on the processing, finite-difference modeling and interpretation of a borehole microseismic dataset recorded in the Falher Member of western Alberta's Deep Basin. Seismic energy generated during hydraulic fracturing of the Falher Member manifests as low-velocity, high-amplitude channel waves. A Matlab-based processing workflow is developed to analyze the data set, with emphasis on velocity model calibration, receiver orientation and hypocentre location in the presence of coals. Finite-difference modeling is used to evaluate the propagation of seismic energy through the monitoring interval, leading to the identification of complex P- and S-wave arrival patterns which significantly complicate microseimsic processing. Alternative acquisition geometries are evaluated via finite-difference modeling and offer improvements to the original acquisition design. The resulting hypocentre distribution suggests that the completion design effectively stimulated the reservoir along the wellbore. Systematic error introduced by the coal layers may contribute to distance-dependant uncertainty in the final hypocentre locations.
Open Access
Microseismic Interpretation of Hydraulic Fracture Processes in Unconventional Reservoirs: Geomechanics, Numerical Simulations and Data Integration
(2016) Boroumand, Neda; Eaton, David; Lawton, Don; Krebes, Edward; Aguilera, Roberto; Angus, Doug
New techniques are presented to advance microseismic interpretation of the hydraulic fracture process. Numerical simulations were developed to present the majority of the claims of novelty and a few previously developed ones were modi ed to present new insights. First, two processing techniques are used for analysis of a microseismic double couple source mechanism. A time shifted hyperbolic Radon transform scheme was applied to a synthetic and a real microseismic event to obtain its lag time and spatial location. Second, a new method is developed to deal statistically with missing microseismic events that are too far from the monitoring well to be detected. This new method, b value energy correction method (MbEC), begins by unbiasing the catalogue as a function of distance and magnitude, then characterizing the frequency magnitude distribution and nally correcting for missing radiated seismic energy. The corrected energy is compared to the fracture energy to calculate seismic e ciency and the fracture energy is compared to injection energy to compute fracture e ciency. The energy correction and comparisons are useful for evaluating changes in microseismic activity. Third, a numerical algorithm is developed to analyse the energy breakdown of the hydraulic fracture process. This energy breakdown based model technique is developed by incorporating microseismic events in space. This model is able to constrain and validate the model geometry through parameter adjustments. The novelty is in the integration of microseismic observations in the numerical simulation that was developed speci cally to characterize the reservoir. Fourth, a numerical algorithm is developed that couples the multi-physics interaction between formation elasticity, fracture uid ow and mechanics equations to initiate and propagate a fracture. The novelty in this algorithm lies in using the microseismic events as the fracture propagation criteria, in time and space, for reservoir property characterization. Case studies are presented in all chapters to illustrate the applicability of each new idea.
Open Access
Microseismic moment-tensor inversion
(2011) Forouhideh, Farshid; Eaton, David
It is common practice in the oil and gas industry to use a single vertical well with limited number of geophones to monitor the microseismicity induced by hydraulic fracture treatment. In this thesis, I have employed a synthetic and stochastic modeling approach to investigate the effects of monitoring geometry and noise on inverting recorded P- and S-wave amplitudes for the moment tensor and source parameters responsible for generating the observed seismograms. The results of the synthetic modeling have shown that microseismic moment-tensor inversion using data from a single vertical monitoring wellis ill-conditioned and incapable of resolving all six components of the moment tensor. Mitigating this problem requires introducing new constraints and a-priori assumptions on mversion.
Open Access
Multi-scale analysis of the influence of sedimentary fabric and composition on the geomechanical properties of organic-rich mudstones: a case study from the Duvernay Formation, Alberta, Canada
(2021-06-24) Venieri, Marco; Pedersen, Per; Eaton, David; Ghanizadeh, Amin; Priest, Jeffrey; Wust, Raphael; Hart, Bruce
In this research, the influence of sedimentary fabric and composition on the geomechanical properties of organic-rich mudstones has been investigated at the seismic, wireline log and core scale with resolution ranging from 50m- to the cm-scale. Our analysis reveals that a relationship is observable between composition, fabric, and elastic properties of the rock units at each scale of observation. Generally, carbonate-rich facies show the highest values of Young’s modulus (YM) and Poisson’s ratio (PR); clay-rich facies show the lowest YM and intermediate PR; biogenic silica-rich (“organic-rich”) facies show intermediate YM and the lowest PR. At the seismic scale, for which the resolution does not allow for assessment of intra-Duvernay mechanical heterogeneity characterization, significant difference in computed elastic moduli is observed between the organic-rich Duvernay Formation and its bounding strata which show different mineralogy. Analysis at the m- and cm-scale of compositional and geomechanical properties of the Duvernay Formation from outcrop samples reveals significant heterogeneity within the Duvernay Formation. Our research suggests that geological and geomechanical heterogeneity within the Duvernay Formation is facies-dependent. In fact, organic-rich mudstones show nearly twice as much variability in composition and mechanical hardness than carbonate-rich facies. This, in conjunction with our analysis of vertical and lateral geological heterogeneity within the Duvernay Formation from subsurface data, suggests that a cautionary approach should be adopted when using averaged or upscaled data for subsurface modeling which risk oversimplifying reservoir complexity. In this case, heterogeneity of rock properties should be included in reservoir models as a measure of uncertainty on the input data.