Geomechanically coupled modelling of fluid flow partitioning in fractured porous media.

Naturally fractured reservoirs are characterised with complex hydro-mechanical dynamics. In these reservoirs, hydrocarbons can be stored and produced from the rock matrix, the fracture network, or both. Normally the fracture network is depleted much faster than the matrix blocks due to its increased hydraulic conductivity; consequently, the recovery factor is low for these reservoirs. Additionally, the in-situ stress profile changes with reservoir depletion and affects fluid flow dynamics of the fractured reservoir. Therefore, dynamic characterisation of fractured reservoirs is considered a challenging task, responsible for inefficient exploitation of their reserves. This dissertation focuses on characterising matrix-fracture fluid flow partitioning subjected to variable overburden stress loading. Understanding of the matrix-fracture hydro-mechanical interaction would assist in developing optimum production plans to maximize recovery from fractured reservoirs. Initially, three different fracture implementation techniques - (1) simulating fracture as an equivalent porous medium; (2) implementing it as a sub-dimensional feature within the porous matrix; and (3) considering fracture domain as an open channel - were evaluated using a set of published laboratory core flooding data. The best fracture simulation approach was identified to be fracture implementation as an open channel interacting with matrix block. This approach takes into consideration the coupling of Darcy flow equation in the matrix domain to Navier-Stokes flow formulation in the fracture. The efficiency of this fracture simulation approach was significantly enhanced when coupled further with poro-elasticity physics and stress dependent permeability. In the next step, the coupled open channel fracture simulation approach was applied to perform a sensitivity analysis on the effect of all parameters of the governing equations on fracture and matrix flow. The results of this analysis were statistically analysed, with specific attention to the analytical formulation of the governing equations, to develop coupled empirical flow models for fracture and matrix. These empirical models incorporate both flow physics of matrix and fracture, as well as mechanical loading impacts. An analysed multiphase flow scenario demonstrated the compatibility of the coupled simulation approach with multiphase flow investigations in fractured porous media. A novel core flooding set-up, capable of separated fracture and matrix flow measurement, was designed and built to enable laboratory evaluation of the developed empirical models. This set-up enabled monitoring of pressure front within matrix and fracture, taking the advantages of several differential pressure transducers along the core plug length. Variation of the matrix and fracture flow in response to different stress loading scenarios was investigated in the laboratory. Furthermore, laboratory validation indicated that the matrix flow model is capable of predicting laboratory measurements with an acceptable accuracy; however, the fracture flow model seemed to need more improvement. Probable factors that could have caused inaccuracy in the fracture flow model were discussed and actions for improving it were recommended as an extension to this research. Application of the empirical models in fractured porous medium characterisation simulations reduces the coupling-related numerical complexities. The coupled empirical models can predict flow dynamics of fractured reservoirs under various stress regimes. They demand much less computational effort and, as they incorporate geometrical factors, they can be up-scaled conveniently. In terms of production planning for fractured reservoirs, the empirical models can assist engineers to manage matrix and fracture production efficiently based on overburden stress variations

Medical education reform: a catalyst for strengthening the health system

Key points: Medical education reform of Canadian specialist doctors presents a unique opportunity for designing parallel health systems interventions. Applying a Health System Framework reveals wider implications of Competence by Design (CBD) and provides impetus for health system strengthening. CBD implications may include staffing shortages in academic hospitals, annual variation in medical education financing needs, new roles for clinician teachers, and greater demand for human health resource surveillance and patient outcome monitoring and analysis. Each implication provides an opportunity to strengthen Governance and Leadership processes, namely by increasing coordination, harmonization, and system responsiveness

Coupled reservoir geomechanics and multiphase flow in fractured porous media.

As a result of a rapid pressure reduction and lack of understanding of hydromechanical behaviour at the fracture matrix interface, a considerable amount of hydrocarbon reserves will remain in place in fractured reservoirs. Therefore, rigid numerical modelling of multiphase flow in geologically complex reservoirs is an essential issue for petroleum reservoir engineers

Multiphase flow modelling in fractured reservoirs using a novel computational fluid dynamics approach.

Numerical modelling of multiphase flow in naturally fractured reservoirs is a challenging issue for petroleum reservoir engineers. As a result of high degree heterogeneity in flow characteristics in fractured reservoirs, several mathematical, discretization, and numerical methods are introduced to forecast the hydrodynamic behaviour of naturally fractured reservoirs. This paper demonstrates two different numerical modelling approaches that have been developed using the discrete- fracture matrix model (DFM) for studying the behavior of multiphase flow in fractured porous media. The first model utilizes the viscous loss term as a source term in the momentum equation to capture the value of permeability in both free channel (fracture) and porous matrix. On the other hand, the second model is based on the coupled Navier-Stokes equation in the free channel of fracture and viscous loss term as a mass source term to measure the permeability in the porous matrix. Later, the Corey method is employed to observe saturation, relative permeability, and capillary pressure at the fracture matrix interface. Both models are validated against a Berea Sandstone imbibition core flooding experimental data. Furthermore, the first and second model numerical simulation results match with the Berea Sandstone experimental core flooding data within a 4.2% and 29% error margin, respectively. The simulation results prove that the first model which uses viscous loss term to capture permeability in the fracture and porous matrix is more accurate in comparison to the implementation of the Navier-Stokes equation in the fracture channel in the second model

Evaluation of caprock integrity for underground storage of CO2 in depleted oil and gas reservoirs using machine learning approaches.

Carbon Dioxide (CO2) geosequestration represents one of the most promising options for reducing atmospheric emissions of CO2. Caprock integrity - ascertained based on the petrophysical and geomechanical properties of caprock - is vital to ensure safe and sustainable storage of CO2 (Liu et al., 2020). Shale and carbonate rocks are typical caprock for CO2 geological storage, but their failure behaviours have not been fully understood due to their severe heterogeneity and anisotropy (Liu et al., 2020). It is therefore vital to apply machine learning techniques in order to understand caprock behaviour under several conditions. No other study so far has focused on caprock integrity using machine learning to select the best depleted petroleum reservoirs for CO2 storage, based on caprock mechanical and petrophysical properties. The aim of this research is to evaluate caprock integrity under cyclic stress loadings based on variation in pressure and CO2 injection temperature

Horizontal stress rotation due to reservoir depletion.

The principal stress rotations axes are observed due to fluid injection into reservoirs, hydrocarbon production, and around the fractures during wellbore stimulation operation and faults. Local stress fields around the fractures will change during reservoir depletion due to the fluid flow and deformation induced by fractures mechanical interference. The stress rotation is controlled by the magnitude of anisotropic stress, which is dependent on several reservoir and material properties. The angle of stress rotation itself manifests the physical response of a reservoir to fluid injection or depletion. The stress reorientation depends on the magnitude of the initial differential stress, the material properties of the formation, and the reservoir development, such as injection rate and fluid temperature. Thus, if stress rotations are observed and a sufficient amount of reservoir properties are known, the information can improve geological reservoirs geomechanical characterization. The factors that lead to horizontal stress reorientation include Formation permeability, injection rates, the opening of hydraulic fracture, and production of fluids in the reservoir. This study addressed depletion in an idealized finite reservoir, using Finite Element Method (FEM), where a reservoir is bounded by an impermeable fault that acts as a barrier to fluid flow. The authors believe that there are two reasons why changes in the reservoir pressure may be the cause of apparent stress rotations near faults. First is a case where the orientation of maximum horizontal stress in a reservoir appears to change with time, and second, the stress orientations followed the local strike of the reservoir bounding faults

Practical solutions for implementation of Transition to Practice curricula in a competency-based medical education model.

Background: Although transition from residency to practice represents a critical learning stage, there is a paucity of literature to inform local curriculum development and implementation.Objectives: To describe local curriculum development for Transition to Practice (TTP) for use within a competency-based medical education model, including important content and suitable teaching and assessment strategies. Design: We reviewed the literature to construct a definition and develop initial curriculum content for TTP. We then gathered local residency program directors’ views on TTP content, teaching, and assessment via online survey and an international educational conference workshop. Results: We identified 21 important TTP content areas in the literature and analyzed 35 survey responses, representing 33 residency programs. Survey participants viewed Further sophistication of clinical skills, How to set up a practice, and Time management skills as the three most important content areas. Views on content importance varied by program. For learning and teaching strategies, most respondents preferred: assessing what residents could do, providing real-life practice opportunities, and offering workplace-based assessments. Conclusions: TTP curricula implementation should reflect nationally set, specialty-specific curriculum elements; locally developed priority content; and learning and teaching strategies. Individual learner needs and imminent practice context should guide faculty approaches to curriculum delivery

A Study on Philosophical Intuition and Thought Experiment: Kripke's Critical encounter with Reductive Physicalism

In philosophy, many reflections and categories were the result of intuition and thought experiments. Intuition is defined as direct, immediate, and non-inferential knowledge accompanied by a sense of certainty. The thought experiment has always been a source of new insights by imagining possible situations to demarcate concepts and revise common philosophical theories. Metaphysicians usually have consensus on the informativity of intuition, but in the analytical tradition, there are severe challenges in dealing with this type of knowledge. On the other hand, some contemporary philosophers believe that the thought experiment induce the unjustified and unacceptable results in the mind of audience. In this article, by referring to some aspects of Kripke's thought, we show that his use of intuition and thought experiments in his critique of radical physicalism is defensible. By distinguishing between fixing the referent of the mental state and the physical phenomenon, Kripke has been committed to the theory of property dualism, which is a critical approach to physicalism in the realm of philosophy of mind