Earth and Environmental Sciences

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Browsing Earth and Environmental Sciences by Author "Dusseault, Maurice"

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    Factors influencing the occurrence of energy wellbore leakage in Alberta
    (University of Waterloo, 2016-03-22) MacDonald, Daniel; Dusseault, Maurice
    Wellbore leakage refers to the unwanted leakage of subsurface fluids along the annuli of oil and gas wellbores. Wellbore leakage is of concern because it may cause natural gas - and exceptionally other fluids such as brine, hydraulic fracturing fluids, or other gases - to enter a shallow aquifer, thereby deteriorating the water quality, or be emitted directly to the atmosphere as a greenhouse gas. Wellbore leakage is also considered to be a first-order risk issue for CO2 sequestration projects and hydraulic fracture stimulation (particularly interaction with offset wells during stimulation). Watson and Bachu (2009) identified major impact factors on the occurrence of wellbore leakage for wellbores spud up until 2004 and established the basis for our current understanding of wellbore leakage development. However, there is uncertainty as to whether their findings are applicable to more recently completed wellbores because drilling practices and wellbore orientation are changing rapidly. The purpose of this research has been to evaluate the influence of well design (i.e., orientation), well type (i.e., produced hydrocarbon), drilling contractor and reported drilling issues on the development of wellbore leakage among wellbores drilled over the past decade (2004-2013) in Alberta. Consistent with past research, well design was found to have an influence on the development of wellbore leakage regardless of other factors (i.e., well type, drilling contractor or reported drilling issues). Specifically, non-vertical wellbores were generally more prone to leakage problems than vertical wellbores. The development of leakage problems within a particular well design was variable, depending on well type, drilling contractor and reported drilling issues. Construction challenges, e.g., cementing, might explain why non-vertical wellbores were more prone to leakage problems than vertical wellbores, but cannot explain why some non-vertical wellbores were more prone to leakage problems than other non-vertical wellbores. In contrast to previous research, a difference in the occurrence of leakage problems was found among wellbores producing different hydrocarbons. This finding was reasonably anticipated because some wellbores may be exposed to higher levels of operational stresses depending on the required production activities, e.g., steam-assisted gravity drainage. Furthermore, the occurrence of leakage problems among each well type appeared to be closely related to well design. This indicates that well design might also have an influence on the development of leakage problems among different well types. A statistically significant difference in the development of leakage problems was found between wellbores drilled by particular contractors. This finding might be attributed to best practice principles implemented by the various companies. Alternatively, the observed differences might be an artifact of varying standards for monitoring and reporting leakage problems between companies. Wellbores with, rather than without, reported drilling issues were found to have the lowest average occurrence rate of leakage problems. This finding was not expected, because it was hypothesized that wellbores with reported drilling issues would encounter challenges that would subsequently jeopardize the integrity of the wellbore. We speculate that this finding is the result of successful risk management of drilling issues by industry as to prevent further issues from being encountered (i.e., problems triggered more attention, leading to more care and better outcomes). Overall, this study indicated that there are occurrences of leakage problems that prove to be statistically significant in relation to well design, well type, drilling contractor and reported drilling issues. This study raises questions regarding our understanding of the mechanisms responsible for the development of leakage problems. Industry and regulators might focus future research and quality assurance on problematic wellbores identified in this research.
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    Modelling of Multistage Hydraulic Fracture Operations in Unconventional Resources – The Application of Geomechanics and Field Data to the Optimization of Fracture Spacing and Production
    (University of Waterloo, 2016-06-08) Skomorowski, Natalia; Dusseault, Maurice; Gracie, Robert
    Massive multistage hydraulic fracturing using horizontal wells has been an integral part of the natural resource industry in Canada. The process uses long horizontal wells divided into many stages to access large volumes of oil and gas bearing formations. Each well is divided into fracture stages. Fluids are pumped down into each stage of the well to generate a fracture which increases the porosity and permeability of the formation to allow economic resource extraction. The in situ geomechanical stresses of the formation do not remain static during the fracturing of the rock. Each fracture creates a volume change within the formation which in turn leads to alteration of the stress and strain conditions within the rock mass. There is the possibility that the alteration of stress conditions will have an effect on the initiation and propagation of subsequent stages of the multi-stage hydraulic fracture operation. This phenomenon is known as ‘stress shadowing’. Stress shadowing occurs when the minimum compressive stress in the formation is increased due to the fracturing of the rock. Increasing the minimum compressive horizontal stress can have several effects, including the rotation or diversion of fracture propagation, stages that do not initiate, thinner fractures, and reduced porosity and permeability within the fracture stage. Currently, many hydraulic fracture operations do not invest in advanced mathematical models of geomechanics. Some pressure monitoring is carried out during operations, but the data are inadequate to warrant advanced numerical methods to predict stress change and its effects. This thesis presents a semi-analytical solution for the stresses around an ellipsoid (the Eshelby Solution) for use in predicting fracture geometry and stress shadow effects. The program is quick to use and can be linked to field data. A study of field data from the Montney Formation is presented. The algorithm developed in this thesis is used to evaluate stress changes within the Montney Formation and the outputs are compared to the stress changes seen in the hydraulic fracture pressure data.
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    Tectonic Stresses and Injection-Induced Fault Slip Assessment
    (University of Waterloo, 2022-09-14) Yaghoubi, Ali; Dusseault, Maurice; Leonenko, Yuri
    Understanding the Earth's stress state at depth is fundamental to a wide variety of subsurface projects, ranging from seismology projects to studies on underground energy storage or extraction. The primary objectives of this dissertation are first to constrain the state of stress by combining drilling-induced wellbore failures and earthquake focal mechanisms, and second to use a probabilistic approach for stresses, pore pressures and rock properties to assess injection-induced fault slip in unconventional and geothermal resources. Knowledge of the state of stress in an area helps us understand the seismic hazard and crustal-scale seismicity pattern issues (>10 km); the energy development (3-6 km) issues from hydrocarbon to geothermal resources; the reservoir scale issues (0.1-1 km) of induced seismicity arising from energy extraction; and borehole scale engineering issues (up to 100 m) related to casing shear and borehole stability. As part of this dissertation, I measure the orientation and constrain the magnitude of present-day stresses in the Dezful Embayment within Iran’s Zagros Fold and Thrust Belt (ZFTB), Alberta's Fox Creek area, the Montney Formation in Alberta and British Columbia, and Alberta's Grande Prairie area. The ZFTB in southwest Iran is one of the world's most seismically active areas. The Dezful Embayment (DE) within the ZFTB is also one of the richest hydrocarbon regions in the world, hosting many onshore hydrocarbon fields. Western Canada is also home to some of the largest oil and gas reserves in the world, including unconventional resources such as the Montney and Duvernay Formations. The injection-induced earthquakes in western Canada have some of the largest magnitudes reported worldwide, such as those near Fort St. John in British Columbia and Fox Creek in Alberta. Considering the economic importance of the region and the seismic activity in these areas, it is important that we gain a better understanding of the state of stress in ZFTB and Western Canada. It is noteworthy that tectonic stresses have not been studied on such a large scale in these regions. To understand the state of stress in each region, two datasets were used. The first included petrophysical data from drilled wells, and the second contained natural and injection-induced earthquake focal mechanisms. Formal stress inversion analysis of the tectonic earthquake focal mechanisms in ZFTB demonstrates that there is currently a compressional stress state in the basement below the sediments. The seismologically determined SHmax direction is NE-SW, nearly perpendicular to the strike of most faults in the region. However, borehole geomechanics analysis in the ZFTB region using rock strength and drilling evidence leads to the counterintuitive result that the shallow state of stress is a normal/strike-slip regime. Based on Coulomb faulting theory, these results indicate that a reverse fault regime with a maximum horizontal principal direction of SW-NE is unfavorable for slip along the N-S strike-slip basement Kazerun Fault System. In Alberta and British Columbia, a similar approach but using injection-induced earthquakes indicates that strike-slip faulting with NE-SW SHmax directions dominates the region. It has been observed that relative stress magnitudes are primarily related to pore pressure variation in Alberta and British Columbia. In the compartmentalized Montney Formation of western Alberta and northeastern British Columbia, these characteristics are evident. Stress measurements will always contain some level of uncertainty due to either inadequate data or inherent uncertainties. These uncertainties impact any project in which the stress plays a central role at different scales. Therefore, probabilistic methods are necessary to quantify the impact of these uncertainties on each project. The uncertainty invariably associated with the state of stress measurements affects the analysis of subsurface events such as seismicity induced by hydraulic fracture (HF) stimulation. HF for energy extraction from underground conventional, unconventional, and geothermal resources is typically accompanied by anthropogenic seismicity. Increasing pore pressure by injecting fluid into naturally fractured media leads to slip/shearing of faults and fractures, resulting in detectable earthquakes. The magnitude and rate of such human-made earthquakes are directly related to stress orientations and magnitudes. This uncertainty in the stress state, plus a variety of uncontrollable subsurface parameters including the original pore pressure, size, and density of pre-existing faults/fractures, fault/fracture orientation, and frictional strength make up the most important factors affecting the probabilistic assessment of fault/fracture slip. In HF treatments, accounting for parametric uncertainty by using appropriate statistical probability distributions leads to better decision-making/risk management for user-controlled parameters such as injection pressure. Historically quiet areas in Alberta and eastern British Columbia have experienced noticeably higher seismicity rates over the last decade. Shale gas and shale oil production from the unconventional plays in the Western Canada Sedimentary Basin has grown with the use of multi-stage HF (Hydraulic Fracture stimulation) technology. Supported by high oil prices and new HF technology availability, development started in 2005 and accelerated significantly in 2011; accordingly, the seismicity rate has increased. The anthropogenic seismicity for this area includes some of the largest MW values reported globally, including events near Fort St. John of MW 4.6 on August 17, 2015, and MW 4.2 on November 30, 2018. Most of these occur during HF treatments and are spatially and temporally restricted to the region around the wells at a scale of 1-2 km, rather than being regional at a scale of more than two kilometers. As part of this dissertation, the probability assessment of fault/fracture slip due to fluid injection has been used and implemented in three different case studies. These include Alberta’s Fox Creek area, the Montney Formation of western Alberta and northeastern British Columbia, and Alberta’s Grande Prairie area. In each case study, geomechanics parameters are expressed as probability distributions using different datasets from borehole petrophysical data to injection-induced focal mechanisms. Monte Carlo simulations are applied to assess the potential slip tendency of local faults. The cumulative distribution function of critical pore pressure to cause slip on each known fault is developed by using analyses of the Mohr-Coulomb shear parameters and local tectonic stress state. Injection-induced seismicity in the region is a formation-related phenomenon governed by the in-situ formation conditions and pre-existing fault patterns. A map is developed that can be used to predict which area of the Montney Formation is at greater risk of earthquakes caused by fracking. Probabilistic maps of fault stability can provide a basis for future fluid injection projects, such as wastewater disposal, hydraulic fracture stimulation, CO2 storage, and geothermal energy extraction.