Impact of anisotropy and fracture density on the approximation of the effective permeability of a fractured rock mass using 2D models

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Sensitivity of Fractured Reservoir Performance to Static and Dynamic Properties, and History Matching

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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

Forchheimer Model for Non-Darcy Flow in Porous Media and Fractures

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Improved simulation of naturally fractured reservoirs using unstructured grids and multi-rate dual-porosity models

Naturally Fractured Reservoirs (NFR) hold about half of the world’s remaining oil reserves and are typically very heterogeneous. NFR are also important for many other subsurface engineering applications including (nuclear) waste storage, CO2 sequestration, groundwater aquifers, and geothermal energy extraction. They contain faults, fracture corridors, large fractures but also many small-scale fractures as well as a heterogeneous rock matrix. Multi-phase flow in NFR is strongly influenced by this multi-scale heterogeneity. Therefore, accurate conceptual models that reliably quantify fluid flow in NFR are needed. In this thesis, three important contributions are made towards an improved simulation of multi-phase flow processes in NFR. First, the Implicit Pressure Implicit Saturation (IMPIS) method using unstructured grids was implemented to numerically simulate two-phase flow in a Discrete Fracture and Matrix (DFM) model. Second, a Multi-Rate Dual-Porosity (MRDP) model was developed including fracture-matrix transfer functions that are based on analytical solutions for spontaneous imbibition and gravity drainage. Finally, the two approaches were combined to a DFM-MRDP model. This model represents the multi-scale heterogeneity inherent to NFR more accurately by resolving fluid-flow processes in large-scale fractures directly using the DFM model while accounting for complex matrix heterogeneities when modelling fluid exchange between small-scale fractures and rock matrix using the MRDP model

Characterization and Simulation of Discrete Fracture Networks in Unconventional Shale Reservoirs

Fracture characterization and simulation of complex fracture networks are investigated with the emphasis on better and faster approaches to generate fractures by conforming to available data resources, and on accurate, robust, and efficient techniques to grid and discretize complex fracture networks. Three fracture characterization techniques such as fractal-based, microseismic-constrained, and outcrop-based are presented. Natural fractures are generated either stochastically from fractal-based theory, or constrained by microseismic information, or from outcrop maps. Hydraulic fractures are computed from a fast proxy model for fracture propagation that incooperates material balance and lab-measured conductivity data. Then, optimization-based unstructured gridding and discretization technique is developed to handle complex fracture networks with extensively fracture clustering, nonorthogonal and low-angle fracture intersections, and nonuniform fracture aperture distributions. Moreover, through fracture simulation, sensitivity analysis of natural fracture related parameters, nonuniform fracture aperture, and unstructured gridding related parameters on well production performance are investigated, which are followed by well testing behaviors and CO2 EOR of complex fracture networks. This work presents an integrated workflow to model discrete fractures in unconventional shale reservoirs, together with detailed illustrations of each critical component using both synthetic and field application examples

Equivalence between volume averaging and moments matching techniques for mass transport models in porous media.

This paper deals with local non-equilibrium models for mass transport in dual-phase and dual-region porous media. The first contribution of this study is to formally prove that the time-asymptotic moments matching method applied to two-equation models is equivalent to a fundamental deterministic perturbation decomposition proposed in Quintard et al. (2001) [1] for mass transport and in Moyne et al. (2000) [2] for heat transfer. Both theories lead to the same one-equation local non-equilibrium model. It has very broad practical and theoretical implications because (1) these models are widely employed in hydrology and chemical engineering and (2) it indicates that the concepts of volume averaging with closure and of matching spatial moments are equivalent in the one-equation non-equilibrium case. This work also aims to clarify the approximations that are made during the upscaling process by establishing the domains of validity of each model, for the mobile–immobile situation, using both a fundamental analysis and numerical simulations. In particular, it is demonstrated, once again, that the local mass equilibrium assumptions must be used very carefully

Application of upscaling methods for fluid flow and mass transport in multi-scale heterogeneous media : A critical review

Physical and biogeochemical heterogeneity dramatically impacts fluid flow and reactive solute transport behaviors in geological formations across scales. From micro pores to regional reservoirs, upscaling has been proven to be a valid approach to estimate large-scale parameters by using data measured at small scales. Upscaling has considerable practical importance in oil and gas production, energy storage, carbon geologic sequestration, contamination remediation, and nuclear waste disposal. This review covers, in a comprehensive manner, the upscaling approaches available in the literature and their applications on various processes, such as advection, dispersion, matrix diffusion, sorption, and chemical reactions. We enclose newly developed approaches and distinguish two main categories of upscaling methodologies, deterministic and stochastic. Volume averaging, one of the deterministic methods, has the advantage of upscaling different kinds of parameters and wide applications by requiring only a few assumptions with improved formulations. Stochastic analytical methods have been extensively developed but have limited impacts in practice due to their requirement for global statistical assumptions. With rapid improvements in computing power, numerical solutions have become more popular for upscaling. In order to tackle complex fluid flow and transport problems, the working principles and limitations of these methods are emphasized. Still, a large gap exists between the approach algorithms and real-world applications. To bridge the gap, an integrated upscaling framework is needed to incorporate in the current upscaling algorithms, uncertainty quantification techniques, data sciences, and artificial intelligence to acquire laboratory and field-scale measurements and validate the upscaled models and parameters with multi-scale observations in future geo-energy research.© 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)This work was jointly supported by the National Key Research and Development Program of China (No. 2018YFC1800900 ), National Natural Science Foundation of China (No: 41972249 , 41772253 , 51774136 ), the Program for Jilin University (JLU) Science and Technology Innovative Research Team (No. 2019TD-35 ), Graduate Innovation Fund of Jilin University (No: 101832020CX240 ), Natural Science Foundation of Hebei Province of China ( D2017508099 ), and the Program of Education Department of Hebei Province ( QN219320 ). Additional funding was provided by the Engineering Research Center of Geothermal Resources Development Technology and Equipment , Ministry of Education, China.fi=vertaisarvioitu|en=peerReviewed