Geometry-based finite volume methods for modelling transport on micro-CT images

Digital rock analysis has become increasingly popular for studying the microscopic structure of reservoir rocks. Direct numerical flow simulations are a common approach to compute petrophysical properties of rocks by modelling fluid flow on rock micro-Computed Tomography (CT) images. However, they are computationally demanding and complicated to include additional flow mechanisms. In this Thesis, a Pore-scale Finite Volume Solver (PFVS) is proposed that solves an elliptic diffusion equation to obtain the spatial pressure distribution on the entire micro-CT image. The flow results have 11% error compared to other solvers such as Stokes solver and Lattice-Boltzmann method. However, the computation times of PFVS are typically 5 times less compared to other solvers. PFVS is also capable of resolving the flow within the microporosity of rocks that cannot be captured by the previous solvers. PFVS is equipped with voxel agglomeration to merge pore voxels locally reducing the number of voxels in the system and the computation time by at least 59%. Furthermore, a Convolutional Neural Network (CNN) model is integrated into PFVS to predict the local conductivity of each voxel based on the training data, bypassing the iterative local largest inscribed radius algorithm. The method has a minor impact on flow results, while the computation time decreases significantly. Rock images commonly contain multiscale pores that are not fully resolved by the micro-CT scanners. A novel analytical formulation is introduced to include the effect of sub-resolution features in low resolution images on flow simulation. The results are validated against the flow directly simulated on corresponding high-resolution images where available. An extension of the PFVS is developed to approximate two-phase flow in porous media with the assumption that the viscous coupling can be ignored. Two fluids are simulated independently, and the results are compared against lattice Boltzmann simulations and determination of relative permeability curves are discussed. The results of this Thesis demonstrate the advantages of integrating innovative numerical methods for reliable simulation of fluid flow directly on rock images while minimising the computational requirements. This will contribute to improving capabilities of digital rock analysis to effectively and efficiently predict petrophysical properties of rocks

Tracing back the source of contamination

From the time a contaminant is detected in an observation well, the question of where and when the contaminant was introduced in the aquifer needs an answer. Many techniques have been proposed to answer this question, but virtually all of them assume that the aquifer and its dynamics are perfectly known. This work discusses a new approach for the simultaneous identification of the contaminant source location and the spatial variability of hydraulic conductivity in an aquifer which has been validated on synthetic and laboratory experiments and which is in the process of being validated on a real aquifer

Modeling and Analysis of Thermal Effects on A Fractured Wellbore During Lost Circulation and Wellbore Strengthening Processes

To successfully prevent fracture propagation and combat lost circulation, a thorough understanding of the stress state in the near-wellbore region with fractures is imperative. One important factor that is not yet fully understood is how temperature variation during lost circulation affects pre-existing or newly initiated fractures. To address this problem, a 3D finite element analysis was conducted in this study to simulate the transport processes and state of stresses in the near-wellbore region during mud invasion into fractures. To take the thermal effects into account, a thermo-poro-elasticity model was coupled with flow and heat transfer processes. This study included a series of sensitivity analyses based on different formation properties and mud loss conditions to delineate the relative importance of different parameters on induced thermal stresses. The results demonstrate how the stresses redistribute as non-isothermal mud invasion takes place in fractures. They show that a temperature difference between the formation rock and the circulating muds can facilitate fracture propagation during mud invasion. The thermal effect can also diminish the enhanced hoop stress, which is the tangential stress acts to close the fracture, provided by Wellbore Strengthening and other lost circulation prevention methods. Such information is important to successful management of lost circulation by taking into account thermal effects from different lost circulation prevention approaches. The conclusions of this study are particularly relevant when a large temperature difference exists between circulating fluids and surrounding rock as commonly seen in high-pressure high temperature (HPHT) and deepwater wells

Performance of the Horizontal Wells in a Naturally Fractured Carbonate Reservoir

About 60 percent of the world\u27s proven oil reserves and 40 percent of gas reserves are trapped in carbonate reservoirs. Recovery rates are relatively low in carbonate reservoirs, and it is extremely challenging to predict due to the heterogeneous nature of these reservoirs. The majority of carbonate reservoirs contain fractures which may vary in size from millimeters to kilometers. A typical example of this type of reservoirs is oil and gas fields in the northern Iraq. These fields are almost all developed by vertical wells. This study will investigate the use of horizontal wells to enhance the productivity in one of these reservoirs.;CMG software is used to simulate the Upper Qamchuqa reservoir of the Khabbaz oil field northeastern of Iraq. The Upper Qamchuqa reservoir is a subsurface anticline with a major normal fault on the eastern flank. Moreover, it mainly consists of dolomite, dolomitic limestone, limestone and marly limestone. The simulation model was validated by the history matching the production rates. Subsequently, horizontal wells were added to the model, and the optimum placement and lateral length investigated. Furthermore, the reservoir parameters that have a significant influence on the history matching and the predicted horizontal wells\u27 performance were identified for future development of the field. The results of this study can provide a guideline for reducing the operating costs and increasing the productivity of similar naturally fractured reservoirs in the area

Fabrications and Applications of Micro/nanofluidics in Oil and Gas Recovery: A Comprehensive Review

Understanding fluid flow characteristics in porous medium, which determines the development of oil and gas oilfields, has been a significant research subject for decades. Although using core samples is still essential, micro/nanofluidics have been attracting increasing attention in oil recovery fields since it offers direct visualization and quantification of fluid flow at the pore level. This work provides the latest techniques and development history of micro/nanofluidics in oil and gas recovery by summarizing and discussing the fabrication methods, materials and corresponding applications. Compared with other reviews of micro/nanofluidics, this comprehensive review is in the perspective of solving specific issues in oil and gas industry, including fluid characterization, multiphase fluid flow, enhanced oil recovery mechanisms, and fluid flow in nano-scale porous media of unconventional reservoirs, by covering most of the representative visible studies using micro/nanomodels. Finally, we present the challenges of applying micro/nanomodels and future research directions based on the work

Extent of Hydraulic Fractures in a Multilayered Geologic Media

In this report, the vertical extent of hydraulic fractures in a layered geological formation was investigated. In reality, the geology of the earth is heterogeneous, and therefore fracture growth will be significantly different. Fracture growth was simulated by using numerical models with relevant geomechanical, fluid flow and proppant transport properties. Results show the horizontal stress gradient plays an important role in fracture propagation. Lower horizontal stress contrasts between layers allow for greater fracture propagation in the vertical direction. Higher fluid viscosities tend to increase the fracture height and width, while decreasing the fracture length. Several other geomechanical properties such as the elastic modulus, fracture toughness, and leakoff coefficient have some influence on the vertical fracture growth. To account for the variability of properties, 300 realizations were considered by using a statistical sampling method. Most of the simulated fractures (about 50%) extended into the immediate overburden layers. Results from these cases show that the clearance depth was in the range from about 4300 feet to 7500 feet

Computational fluid dynamics modelling of fluid flow inside fractured reservoirs.

Fractured media exist in most layers of the earth's crust, often dominating bulk properties of subsurface geological formations. Therefore, fractured media are involved in many key engineering sectors that impact humans living on Earth. Fractured formations consist of two distinct media sharing the same location: matrix and fracture, which affect each other's flow. Both have heterogeneous properties, such as anisotropic matrix permeability and rough fracture surfaces; also, fractures have varied orientation angles and exist in fractured formations in either discrete fracture form, or in connected networks with varied angles/patterns. Due to this heterogeneity, most fractured media modelling and studies in the literature have considered assumptions that don't represent flow in realistic conditions. This thesis therefore presents systematic investigations conducted on fractured media by using Computational Fluid Dynamic ANSYS CFD Fluent FVM to investigate fluid flow in many kinds of fractured media. These investigations ranged from simple and widely used fractured geometries to more complex ones. The research began with parallel plates fractures and rough fractures with horizontal orientation inside fractured domains. Both fractures were investigated with different fracture surface conditions in these fractured domain models to create most mimicked realistic fractured formation conditions; for example, through inclusion and exclusion of the matrix effect on flow, and matrix isotropic/anisotropic permeability's effects on flow. The results of these models were validated and compared with current understandings of fractured media model flow in the literature. The outcomes of these models have reflected that parallel plates fractures with a single aperture are unsuitable for representing flow in fractured media. These investigations have also shown that exclusion of matrix in fractured media flow will highly mislead flow calculations in fractured media. The second part of the research involved using the results of ANSYS CFD Fluent FVM rough fracture models to develop two fracture friction-factor models in realistic fractured media conditions (analytical and numerical friction-factor models). These accounted for the effect on entire fracture domain flow of both rough fracture geometry effects and also matrix permeability. Specifically, isotropic and anisotropic matrix permeability along layers of formations, along fracture length and in two directions of flow, X and Y, considering Kx and Ky anisotropic effect on lateral and perpendicular flow of each layer. Friction-factor is important for predicting pressure drop (Delta P / L) along fractures and accordingly on fluid migration in fractured formations. In the third part of the research, ANSYS CFD Fluent FVM rough fracture network models were created, which included many heterogeneous properties of fracture media, such as many patterns of network orientations (where each model has different inlets and outlets of flow) and matrix effect (including isotropic and anisotropic matrix permeability). The outcomes of these models have resulted in a new and interesting understanding of modelling fractured media. The research has proven that matrix functionality in fractured media is not only as fluid provider, but also has major effects on providing and transporting fluids in fractured media. As well, the research has provided new evidence that modelling a single fracture of fractured media will highly mislead flow calculation