Browsing by Author "Eaton, David W."
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Item Open Access Analysis of Production Data from Communicating Multi-Fractured Horizontal Wells(2022-08-08) Ahmadi, Hossein; Clarkson, Christopher R.; Hassanzadeh, Hassan; Mattar, Louis; Chen, Zhangxing; Eaton, David W.; Miskimins, JenniferThe most common technology used for the development of low-permeability (unconventional) oil and gas reservoirs is multi-fractured horizontal wells (MFHWs), which are designed to maximize fracture surface area in contact with the reservoir. In current development practice, multiple MFHWs are typically drilled from the same pad; over time, fracture and well (lateral) spacing have decreased, resulting in greater interference between wells (vertically and laterally). This interference, which commonly occurs through hydraulic fractures, can affect well performance, and complicate reservoir and fracture characterization efforts. Rate-transient analysis (RTA) is a reservoir engineering approach that is commonly used to derive reservoir/fracture properties for MFHWs producing from unconventional reservoirs. However, RTA methods/models are generally applicable to single wells and do not specifically account for inter-well communication through hydraulic fractures. It is the purpose of this dissertation to develop RTA methods/models that account for inter-well communication. In order to account for inter-well communication through fractures, both semi-analytical and machine learning approaches are developed for RTA of MFHWs. The semi-analytical approach developed herein utilizes the dynamic drainage area (DDA) concept. Two and three reservoir/fracture region semi-analytical DDA models are first developed to history match and forecast two MFHWs communicating through hydraulic fractures. These models, which account for two-phase flow (dry gas, water), and pressure-dependent porosity and permeability, are successfully verified with fully-numerical simulation results. Their practical applicability is also demonstrated using a field dataset consisting of six wells (drilled from two neighboring pads) exhibiting different degrees of communication. The final semi-analytical model developed is in the form of a new straight-line analysis (RTA) method, referred to as the “DDA-corrected” RTA model. When this method is applied to two wells that are communicating through hydraulic fractures, and are put on production at different times, two straight lines can be obtained for the first well that comes on production. Because the method assumes that the wells are fully connected, the slope of the first straight line (i.e., before the second well is put on production) corresponds to an equivalent fracture whose half-length is a portion of the total summation of individual fracture half-lengths depending on the permeabilities of individual fractures. This method, which also accounts for two-phase flow (gas, water), and pressure-dependent porosity and permeability, is successfully verified against fully-numerical simulation results, and its practical applicability is demonstrated with the same field case as the history match/forecasting models. Finally, machine learning (ML) algorithms, along with an optimization method, are employed to develop a history matching tool for three-phase flow of oil, gas and water associated with two communicating wells (staggered production). The basic concept used in ML algorithm training is that a change in the slope of the square-root of time plot for the first (parent) well occurs due to the second well coming on production. A dataset consisting of synthetic simulation cases is generated by varying some of the reservoir and fracture parameters to produce all the possible production scenarios for a two-well base model. After preprocessing the outliers, ML models are trained and tested. These models can generalize the relationship between the reservoir and fracture parameters and the square-root of time plot slope values for the parent well. The goal of developing a history matching tool is then attained by using the best performing ML model and an optimization algorithm which can estimate the reservoir and fracture parameters for a set of slopes obtained from the square-root of time plot of the parent well. Fundamentally, this dissertation advances RTA methods that can be applied to two wells that are in communication through hydraulic fractures.Item Open Access Anatomy of a buried thrust belt activated during hydraulic fracturing(2020-10-18) Riazi, Naimeh; Eaton, David W.Tectonically active fault networks are often inter-connected, but in the case of injection-induced seismicity, prior knowledge of fault architecture tends to be severely limited. In most cases, reactivated faults due to fluid injection are inferred, after-the-fact, by the spatial distribution of induced-seismicity hypocenters; such reliance on post-injection seismicity impedes any pre-operational risk analysis, as well as development of a more holistic understanding of fault-system models. By combining high-resolution, depth-migrated 3-D seismic data with a new focal-depth estimation method that reduces spatial uncertainty of hypocenters, this study pinpoints microearthquake fault activation within a buried thrust belt in the Montney Formation in western Canada (British Columbia). During hydraulic-fracturing operations, rupture nucleation occurred on seismically imaged thrust ramps that cut through the Debolt Formation, a massive carbonate layer that underlies the stimulated zone. High-resolution seismic images reveal transverse structures, interpreted as basement-controlled fold hinges or tear faults that transferred displacement between thrust faults during Late Cretaceous - Paleogene compressional shortening. The spatio-temporal pattern of induced seismicity suggests that these transverse structures provide permeable pathways for aseismic pore-pressure diffusion, thus connecting distinct thrust faults and enabling earthquake triggering on a timescale of days and at distances of up to 2 km from the injection wells. Inferred relationships highlight how the fault system is connected, including apparent stress concentrations at the intersections of transverse structures and orogen-parallel thrust ramps.Item Open Access Application of Focal-Time Analysis for Improved Induced Seismicity Depth Control: A Case Study from the Montney Formation, British Columbia, Canada(2020-08-10) Riazi, Naimeh; Eaton, David W.; Aklilu, Alemayehu; Poulin, AndrewCharacterization of induced seismicity and associated microseismicity is an important challenge for enhanced oil recovery and development of tight hydrocarbon reservoirs. In particular, accurately correlating hypocenters of induced events to stratigraphic layers plays an important role in understanding the mechanisms of fault activation. Existing methods for estimating focal depth, however, are prone to a high degree of uncertainty. A comprehensive analysis of inferred focal depths is applied to induced events that occurred during completions of horizontal wells targeting the Montney Formation in British Columbia, Canada. Our workflow includes a probabilistic, nonlinear global-search algorithm (NonLinLoc), a hierarchical clustering algorithm for relative relocation (GrowClust) and depth refinement using the recently developed focal-time method. The focal-time method leverages stratigraphic correlations between P-P and P-S reflections to eliminate the need for an explicit velocity model developed specifically for hypocenter depth estimation. We show that this approach is robust in the presence of noisy picks and location errors from epicenters obtained using a global-search algorithm, but it is limited to areas where multicomponent 3-D seismic data are available. A novel method to determine statics corrections is developed here, to ensure that both passive seismic observations and 3-D seismic data share a common datum in areas of moderate to high topography. Our results highlight the importance of transverse faults, which appear to provide permeable pathways for activation of other faults at distances of up to 2 km from hydraulic fracturing operations.Item Open Access Finite Element Modelling of Induced Rupture on Faults with Non-negligible Cohesion(2018-09-05) Sattari, Arsalan; Eaton, David W.; Garagash, Dmitry I.; Krebes, Edward Stephen; Davidsen, Jörn; Lauer, Rachel M.A finite-element (FE) simulation approach is used to investigate earthquake rupture processes on faults with cohesion. This study is motivated by evidence that, unlike tectonically active systems, faults that have been inactive on a timescale of centuries or longer (well-healed faults) have non-negligible cohesion. Inclusion of cohesion, along with friction, into the basic physical model for fault activation may be important for calculating hazards associated with injection-induced seismicity, where earthquakes are typically concentrated in formerly quiescent regions. The problems addressed in this thesis are framed by a series of hypotheses: 1) cohesion loss plays a key role in stress drop and seismic efficiency of well-healed faults; 2) co-seismic stress drop affects only the shear stress acting on a fault in proximity to a free surface; 3) inclusion of dynamic processes in the numerical simulation, such as slip overshoot, has an important effect on the magnitude of surface deformation; 4) fault slip is modified by coupling between dynamic rupture and body waves in the surrounding medium. Chapter 2 tests hypotheses 1 and 2 using an adapted and improved version of a 2-D plane-strain, static FE modelling method for a dip-slip fault. The result of the model is in good agreement with analytical models and shows that both cohesion and friction loss can contribute to stress drop. Chapter 3 uses a similar FE model setup to address hypotheses 1, 2 and 3. In this case, a dynamic FE method is used in which d'Alembert forces (inertial components) are considered, leading to slip overshoot. The results indicate that seismic efficiency increases with the ratio of cohesion to normal stress. A previous theoretical model that places an upper bound on seismic efficiency (0.06) is therefore valid only if cohesion is neglected. Chapter 4 tests hypothesis 4 using a suite of 3-D dynamic FE models of strike-slip faulting, a more common mechanism for induced earthquakes. Rupture is initiated by abrupt loss of cohesion within a discrete fault patch (asperity), thereupon propagating outwards into a marginally stable region of the fault. The results indicate that cohesion loss is sufficient to sustain dynamic rupture. Modelled oscillatory behavior of stress drop is interpreted to be a footprint of dynamic interaction between the rupture front and body waves propagating in the surrounding rockmass.Item Open Access Geophysical constraints on basement faulting in west-central Alberta: Implications for induced seismicity and post-collisional modification of western Laurentia(2020-06-29) Johnson, Eneanwan Ekpo; Eaton, David W.; Gilbert, Hersh; Nair, Rajeev; Lawton, Don Caleb; Unsworth, Martyn J.Tectonic elements that make up the core of the Canadian Shield were formed during collisional assembly of the craton, Laurentia, between 2.0 Ga to 1.75 Ga. In west-central Alberta, the Precambrian crystalline crust that underlies the Western Canada Sedimentary Basin (WCSB) is dominated by curvilinear arcuate domains that were welded onto the edge of the Archean Rae Province ca. 2.0 -1.9 Ga. Evidence from various sources, including geophysical data acquired as part of Canada’s LITHOPROBE program, indicates that faults in the Precambrian crystalline basement exerted a profound influence on the Phanerozoic development of the sedimentary cover. In the upper crust, however, these faults may be (near) vertical, rendering them difficult to image using conventional seismic methods. The importance of identifying and delineating basement faults has recently come into sharper focus due to the localized onset, about one decade ago, of induced seismicity from unconventional resource development. This long-standing problem is revisited in this thesis using a multidisciplinary approach that incorporates modelling of potential-field data, investigation of duplex waves in LITHOPROBE seismic shot records, and petrographic analysis of drillcores. In one area that is prone to induced seismicity near Fox Creek, Alberta, aeromagnetic anomaly patterns reveal conspicuously rectilinear boundaries along the northern and southern margins of the southern Chinchaga domain (SCD). These margins have near-perfect (jigsaw-like) conjugate geometry and appear to bound a regionally extensive mid-crustal sill complex known as the Winagami Reflection Sequence (WRS) on seismic reflection profiles. To explain these features, I propose that the SCD may have formed as a pull-apart basin in a back-arc setting. Modern back-arc extension analogs include the Omineca belt in the Canadian Cordillera, the Basin and Range in southwest US and the Japan Sea. Restoration of putative extension implied by this model aligns two otherwise dismembered continental arcs, suggesting a simpler model for tectonic evolution for northern Alberta basement than previously hypothesized models that focus primarily on collisional assembly. Examination of sparse drillcore from the SCD indicates that basement composition contains undeformed mafic igneous rocks, consistent with a back-arc extensional setting. A north-south linear magnetic high that underlies the region of recent occurrence of induced seismicity, herein named the Simonette Anomaly (SA), is interpreted as the expression of a strike-slip fault that was active as a transform fault during back-arc extension. This feature is inferred to be the basement root to shallower fault segments that have been reactivated by hydraulic fracturing. A regional framework for this interpretation has been developed through modelling and analysis of regional gravity and magnetic data. In addition, I assess the feasibility to delineate near-vertical basement faults using duplex waves, which are waves that reflect from a vertical boundary as well as a deeper horizontal reflector. Probable duplex waves observed in a LITHOPROBE seismic shot record, where the WRS reflections furnish the deeper horizontal reflection, provide the first documented case where a near-vertical fault in the crystalline basement has been seismically imaged. Taken together with the proposed back-arc rifting model, this thesis thus provides new evidence that is significant for understanding post-collisional modification of western Laurentia.Item Open Access Integrated Interpretation of Microseismic with Surface Seismic Data in a Tight Gas Reservoir, Central Alberta, Canada(2015-05-05) Rafiq, Aamir; Eaton, David W.Integrated interpretation of microseismicity with surface seismic data can provide valuable information about reservoir characteristics, mechanical stratigraphy, induced and pre-existing fracture systems. Although there are numerous integrated studies that focus on unconventional plays, relatively little attention has been given to tight gas environments. Typical interpretation of microseismic data focuses on the spatial and temporal distribution of microseismic events to estimate stimulated reservoir volume and, in some cases, to infer the character and geometry of discrete fracture networks. This thesis describes a methodology for integrated interpretation of 3D seismic data with microseismicity recorded during the open hole stimulation of two horizontal treatment wells of a tight-sand unit deposited in the Hoadley field, a Cretaceous marine barrier-bar complex in Western Canada. I introduce a novel approach, Microseismic Facies Analysis (MFA), to extract additional information from microseismic clusters. The interpreted microseismic facies are then correlated with surface seismic attributes in order to delineate reservoir partitions that are interpreted to reflect lithofacies variations associated with depositional trends.Item Open Access Large variations in lithospheric thickness of western Laurentia:Tectonic inheritance or collisional reworking?(Elsevier, 2015-09) Bao, Xuewei; Eaton, David W.The ca. 2.0–1.8 Ga tectonic assembly of Laurentia provides a record of complex processes resulting in amalgamation of distinct lithospheric domains. In global and continental-scale teleseismic tomographic models, however, the subcontinental lithosphere beneath western Laurentia appears to have a deceptively simple structure that lacks a clear correlation with mapped crustal domains. Here we present a new shear-velocity model of the upper mantle beneath western Laurentia through Rayleigh-wave tomography, using data from several newly deployed broadband seismic arrays. Our models show prominent heterogeneities that appear to correlate well with crustal domains and other geophysical observations. The tomographic results delineate high-velocity keel-shaped anomalies beneath the Archean Hearne Province and the Paleoproterozoic Buffalo Head Terrane; these features are inferred to extend to depths of up to 260 km and likely represent ancient thick cratonic roots, whereas relatively thin lithosphere characterizes the adjacent Wabamun domain and Medicine Hat Block. A regional isostatic residual gravity anomaly in the foreland of the Cretaceous–Paleocene southern Canadian Rockies coincides with an area of inferred thick lithosphere in the Hearne Province, suggesting that along-strike variations in flexural rigidity correlate with lithospheric thickness. Taken together, our results suggest that high-amplitude basal topography of the lithosphere–asthenosphere boundary beneath cratons reflects a complex lithospheric evolution that combines effects of both tectonic inheritance and collisional reworking.Item Open Access Microseismic Monitoring of a Duvernay Hydraulic-Fracturing Stimulation, Alberta Canada: Processing and Interpretation assisted by Finite-Difference Synthetic Seismograms(2019-12) Rodríguez-Pradilla, Germán; Eaton, David W.; Lawton, Don C.; Gilbert, Hersh J.; Chen, Shengnan; Brudzinski, MikeThe increase in the development of unconventional oil and gas reservoirs in the past years has triggered anomalously high seismic activity in several sedimentary basins around the world, particularly in North American basins located in central and eastern United States and in western Canada. The Duvernay shale play, located in central Alberta, Canada, is an example of the seismicity-triggering effect by hydraulic fracturing stimulations required to produce hydrocarbons from low-permeability formations. To better understand the seismic mechanisms associated with hydraulic fracturing in this area, a local seismic monitoring array comprised by short-period and broadband sensors, was temporally installed to monitor a multi-stage hydraulic-fracturing (MSHF) stimulation on four horizontal wells drilled in the Duvernay Formation near the town of Fox Creek, Alberta, where multiple earthquakes associated with HF have been reported in recent years. This thesis presents a robust workflow for modelling and processing passive seismic data acquired with this local monitoring array, in order to automatically detect and characterize the microseismicity associated with the monitored MSHF stimulation. This characterization includes the epicentre location, depth, magnitude, fault size, and radiated energy of all the detected microseismic events, and the focal mechanisms of the seismic events with the largest magnitudes (up to ML 3.77 in this study). The obtained microseismicity is then integrated with other datasets from the monitored reservoir (well logs and production from the monitored and nearby wells, and 3D seismic) to identify reactivated faults that triggered the largest-magnitude seismic events detected during this monitoring program, and to characterize the unconventional reservoir to forecast the hydrocarbon production after the stimulation. A magnitude scale based on the duration of coda waves was also calibrated for the study area in central Alberta, which can be implemented similar seismic monitoring programs for magnitude estimation as it does not require the installation of broadband sensors. Finally, the generated ground motions of the seismic events with the largest magnitudes detected in this dataset, were determined using the local and regional seismic monitoring arrays to assess the uncertainty of a set of Ground Motion Prediction Equations (GMPE) recently developed for the Fox Creek Area at close and distant hypocentral distances. These GMPEs are fundamental to quantify the seismic hazard of induced earthquakes to nearby communities and infrastructure.Item Open Access Stress Inversion and Damage Quantification in Tight Gas Shale with Application to Hydraulic Fracturing(2019-11) Jia, Suzie Qing; Wong, Ron; Eaton, David W.; Wan, Richard; Zhou, Qi; Wong, Teng-fong; Priest, Jeffrey A.This thesis aims to advance the quantitative analysis of stress and failure process in tight gas shale under hydraulic fracturing by integrating stress inversion, microseismic monitoring, acoustic emission and discrete element modeling techniques. With the introduction of a modified Bott hypothesis that allows for out-of-plane slip, a stress inversion algorithm is developed accounting for tensile components of the source mechanism. Synthetic test datasets are employed to quantify the error in stress determination that arises when the conventional stress inversion based on the original Bott hypothesis is applied in the presence of non-double-couple sources. The proposed method is evaluated using microseismic data collected from Barnett Shale in the Fort Worth Basin, Texas. Results show the modified method introduces a roughly 15 degree correction as compared with the inversion results from the conventional algorithm. With the same dataset, a case study is conducted to investigate the dynamic interactions between injected fluids and hydraulic fractures through the spatial-temporal analysis of microseismicity. Two types of triggering front expansion patterns are evident. With the presence of a dominant hydraulic fracture, the radius of the triggering front expands linearly with time, and the microseismic event cloud forms a planar shape with low tensile components. On the other hand, in the case of a complex fracture network with the absence of any major hydraulic fracture, the triggering front grows non-linearly with time, which can be treated as equivalent to a diffusion model. The microseismic events exhibit more tensile components and an equidimensional event cloud. Two stages of the microseismic dataset are analyzed and the derived fracture widths and fluid-loss coefficients fall into a realistic range of general observations. Two acoustic emission (AE) laboratory experiments are carried out to examine the failure behavior of Montney shale samples under conventional triaxial compression and fluid injection. Detailed analysis for the triaxial compression test includes deformation-induced velocity anisotropy, source hypocenter determinations, source mechanism analysis, and stress inversions. For the hydraulic fracturing test, the mechanical correlation with the AE activity is analyzed. The AE locations correlate reasonably well with the spatial distribution of shear fracture and hydraulic fracture imaged by X-ray computer tomography (CT) scanning. However, the signal-to-noise ratio of the AE waveform emitted from Montney shale sample is relatively low, especially for the hydraulic fracturing test, which makes the data processing quite challenging. Distinct characteristics of the AE activity in Montney shale are identified, which are different from those in granite, a type of rock that has been more extensively investigated in the past. These differences could arise from the different stress settings, the low brittleness and stiffness of shale. Additionally, the AE test under triaxial compression is simulated using dynamic micromechanical models based on the discrete element method, in which the transversely isotropic feature of Montney shale and moment tensor calculations are considered. Calibration and verification are conducted against the results of previous laboratory experiments in terms of the anisotropic behavior. The model results indicate some of the low energy AE signals might not be captured by the experimental recording system, and it further demonstrates that the shear fracture initiation contains high tensile failure components.Item Open Access Structure of the continental Moho and Lithosphere-Asthenosphere Boundary: Insights from receiver-function analysis and numerical modelling(2018-10-19) Maiti, Tannistha; Eaton, David W.; Krebes, Edward Stephen; Lawton, Don C.The Moho and lithosphere-asthenosphere boundary (LAB) are fundamental discontinuities in the Earth’s outermost layers. The structure of these features can be discerned using seismic methods, providing important insights into the tectonic history of a region. This thesis is focused on the structure of these discontinuities in and around cratons, which are large, coherent domains of Earth’s continental lithosphere that have attained long-term stability with little internal deformation. The receiver-function method is an approach that uses locally scattered waves to image discontinuity structure beneath a seismograph station. P-wave receiver functions (PRFs) are often used to study Moho characteristics. Here, synthetic PRFs are used to understand the nature of the Moho in different scenarios. This approach is applied to observations from EarthScope Transportable Array (TA) stations in the western U.S. within a region that exhibits a complex transition from the craton and the Cordillera. Beneath the Cordillera, a flat Moho is interpreted to reflect lower crustal channel flow, whereas beneath the North American craton the Moho exhibits greater structural relief. By definition, the LAB forms the lower boundary of a tectonic plate. Using geophysical imaging methods, the LAB is not as easily mapped as the Moho, leading to the use of various proxies, such as a boundary between layers with differing seismic anisotropy. In the upper mantle, seismic anisotropy is generated by lattice-preferred orientation of constituent minerals, especially olivine. A numerical-simulation approach is employed based on a self-consistent model that extends from the Earth’s surface to the mantle transition zone. Mantle flow is investigated by 3-D numerical solution of the boundary-value problem using a finite-element method. The flow velocity is converted to anisotropic elastic stiffness tensors to create an anisotropic model with 21 independent c ijkl parameter plus density. Teleseismic P and S wavefields are simulated using a finite-difference method to characterize mantle discontinuities. P and S wave receiver functions are computed using the synthetic waveforms to understand the effectiveness and limitations of these approaches for imaging the LAB. Anisotropy has a strong influence, due to change in S wave velocity in radial and transverse directions.Item Open Access The influence of glacial isostatic adjustment on intraplate seismicity in northeastern Canada(2013-04-30) Steffen, Rebekka; Eaton, David W.; Wu, PatrickDue to changes in the Earth’s climate, the Earth has experienced colder periods, which generated the growth of continental ice sheets at higher latitudes. The build up of an ice sheet induces flexural stresses in the lithosphere and mantle affecting the stability of pre-existing faults. During and after the end of deglaciation, these faults are activated and the flexural stresses are released as earthquakes. The last ice sheet in North America started to melt 20ka ago, and was gone by 6ka. Here, (re-)activated faults were found, which show vertical fault scarps of up to 100m. As moderate seismicity is observed in North America now, it is of major societal and economic importance to investigate the relationship of this activity to the ongoing rebound. The extended seismological network in northeastern Canada gives us the possibility to analyze local seismicity in more detail than previously possible. Thrust-faulting mechanisms are estimated for five moderate earthquakes that occurred in northern Hudson Bay, and the related stress is NW-SE directed. Comparing this stress direction to results from rebound models and the general background stress field with NE-SW directions, a large difference is found, which might be due to a local fault zone disturbing the main stress field. This study presents an improved two-dimensional rebound model including a fault, which is able to move in a stress field consisting of rebound stress, and horizontal and vertical background stresses. The sensitivity of this fault is tested regarding lithospheric and crustal thickness, viscosity structure of upper and lower mantle, ice-sheet thickness and width, and fault parameters including coefficient of friction, depth, angle and location. Fault throws of up to 64m are obtained using a fault of 30° dipping below the ice-sheet centre. Thicknesses of the crust and lithosphere are two of the major parameters affecting the total fault throw. The ice-sheet width has an impact on the activation time. Even steep-angle faults can be activated. Most faults start to move close to the end of deglaciation, and movement stops after one thrusting/reverse earthquake. However, certain conditions may also lead to several fault movements after the end of glaciation.