Successful creations of multiple hydraulic fractures in horizontal wells are critical for economic development of unconventional reservoirs. The recent advances in diagnostic techniques suggest that multi-fracturing stimulation in unconventional reservoirs has often caused complex fracture geometry. The most important factors that might be responsible for the fracture complexity are fracture interaction and the intersection of the hydraulic and natural fracture. The complexity of fracture geometry results in significant uncertainty in fracturing treatment designs and production optimization. Modeling complex fracture propagation can provide a vital link between fracture geometry and stimulation treatments and play a significant role in economically developing unconventional reservoirs. In this research, a novel fracture propagation model was developed to simulate complex hydraulic fracture propagation in unconventional reservoirs. The model coupled rock deformation with fluid flow in the fractures and the horizontal wellbore. A Simplified Three Dimensional Displacement Discontinuity Method (S3D DDM) was proposed to describe rock deformation, calculating fracture opening and shearing as well as fracture interaction. This simplified 3D method is much more accurate than faster pseudo-3D methods for describing multiple fracture propagation but requires significantly less computational effort than fully three-dimensional methods. The mechanical interaction can enhance opening or induce closing of certain crack elements or non-planar propagation. Fluid flow in the fracture and the associated pressure drop were based on the lubrication theory. Fluid flow in the horizontal wellbore was treated as an electrical circuit network to compute the partition of flow rate between multiple fractures and maintain pressure compatibility between the horizontal wellbore and multiple fractures. Iteratively and fully coupled procedures were employed to couple rock deformation and fluid flow by the Newton-Raphson method and the Picard iteration method. The numerical model was applied to understand physical mechanisms of complex fracture geometry and offer insights for operators to design fracturing treatments and optimize the production. Modeling results suggested that non-planar fracture geometry could be generated by an initial fracture with an angle deviating from the direction of the maximum horizontal stress, or by multiple fracture propagation in closed spacing. Stress shadow effects are induced by opening fractures and affect multiple fracture propagation. For closely spaced multiple fractures growing simultaneously, width of the interior fractures are usually significantly restricted, and length of the exterior fractures are much longer than that of the interior fractures. The exterior fractures receive most of fluid and dominate propagation, resulting in immature development of the interior fractures. Natural fractures could further complicate fracture geometry. When a hydraulic fracture encounters a natural fracture and propagates along the pre-existing path of the natural fracture, fracture width on the natural fracture segment will be restricted and injection pressure will increase, as a result of stress shadow effects from hydraulic fracture segments and additional closing stresses from in-situ stress field. When multiple fractures propagate in naturally fracture reservoirs, complex fracture networks could be induced, which are affected by perforation cluster spacing, differential stress and natural fracture patterns. Combination of our numerical model and diagnostic methods (e.g. Microseismicity, DTS and DAS) is an effective approach to accurately characterize the complex fracture geometry. Furthermore, the physics-based complex fracture geometry provided by our model can be imported into reservoir simulation models for production analysis. / text

To analyse the influence of fractures on hydraulic andmechanical behaviour of fractured rock masses, it is essentialto characterise fracture geometry at exposed rock faces. Thisthesis describes three semi-automatic methods for measuring andquantifying geometrical parameters of fractures, and aims tooffer a novel approach to the traditional mapping methods. Three techniques, i.e. geodetic total station, close-rangephotogrammetry and 3-D laser scanner, are used in this studyfor measurement of fracture geometry. The advantages of thesetechniques compared with the traditional method are: i)fracture geometry is quantified semi-automatically in threedimensions; ii) fracture measurements are obtained withoutphysically touching the rock face; iii) the accuracy offracture measurements is improved comparing with thetraditional method; iv) both quantitative and spatial analysisof fracture geometry is possible; v) it offers a way todigitally record the rock surface in three dimensions and invisual format as a database for other applications. The common approach for fracture mapping by using the noveltechniques comprises three main steps: i) capturing 3-Dco-ordinates of target points; ii) quantifying geometricalparameters of fractures from the recorded co-ordinates; iii)documenting the results of fracture mapping. The details ofcapturing 3-D co-ordinates of target points are introduced. Anew algorithm is developed for computing orientation offracture planes. A multiple approach for documenting thefracture mapping results is presented. Application of thesetechniques for measuring and quantifying the geometricalparameters of fractures, such as orientation, trace length andsurface roughness, are demonstrated. The presented methods can greatly improve the quality offracture measurements and avoid the drawbacks inherent intraditional methods. However, it can not replace the humancapacity to filter out and interpret the large amount ofgeometrical information displayed on the rock faces. Themethods may offer an assistance to engineers or geologists inobtaining as much information as possible about the geometryand orientation of rock fractures for rock engineeringapplications. <b>Keywords:</b>3-D laser scanner, close-range photogrammetry,engineering geology, fracture geometry, fracture mapping, rockengineering, rock faces, rock mechanics, three-dimension, totalstation.

For more than five decades, hydraulic fracturing has been widely used to enhance oil and gas production. Hydraulic fracturing in solid materials (e.g., rock) has been studied extensively. The main goal of this thesis is a comprehensive study of the physical mechanisms of hydraulic fracturing in cohesionless sediments. For this purpose, experimental techniques are developed to quantify the initiation and propagation of hydraulic fractures in dry particulate materials. We have conducted a comprehensive experimental series by varying such controlling parameters as the properties of particulate materials and fracturing fluids, boundary conditions, initial stress states, and injection volumes and rates. In this work, we suggest principle fundamental mechanisms of hydraulic fracturing in particulate materials and determine relevant scaling relationships (e.g., the interplay between elastic and plastic processes). The main conclusion of this work is that hydraulic fracturing in particulate materials is not only possible, but even probable if the fluid leak-off is minimized (e.g., high flow rate, high viscosity, low permeability). Another important conclusion of this work is that all parts of the particulate material are likely to be in compression. Also, the scale effect (within the range of the laboratory scales) appears to be relatively insignificant, that is, the observed features of fractures of different sizes are similar. Based on the observed fracture geometries, and injection pressures we suggested three models of hydraulic fracturing in particulate materials. In the cavity expansion or ??e driving model, the fracturing fluid is viewed as a sheet pile (blade) that disjoints the host material, and the cavity expansion occurs at the fracture (blade) front. The shear banding model is also consistent with a compressive stress state everywhere in the particulate material and explains the commonly observed beveled fracture front. The model of induced cohesion is based on the fluid leak-off ahead of the fracture front. The induced cohesion may be caused by the tensile strain near the fracture tip (where the stress state is also compressive), which, in turn, induces the cavitation of the leaked-off fluid and hence capillary forces.

<p>To analyse the influence of fractures on hydraulic andmechanical behaviour of fractured rock masses, it is essentialto characterise fracture geometry at exposed rock faces. Thisthesis describes three semi-automatic methods for measuring andquantifying geometrical parameters of fractures, and aims tooffer a novel approach to the traditional mapping methods.</p><p>Three techniques, i.e. geodetic total station, close-rangephotogrammetry and 3-D laser scanner, are used in this studyfor measurement of fracture geometry. The advantages of thesetechniques compared with the traditional method are: i)fracture geometry is quantified semi-automatically in threedimensions; ii) fracture measurements are obtained withoutphysically touching the rock face; iii) the accuracy offracture measurements is improved comparing with thetraditional method; iv) both quantitative and spatial analysisof fracture geometry is possible; v) it offers a way todigitally record the rock surface in three dimensions and invisual format as a database for other applications.</p><p>The common approach for fracture mapping by using the noveltechniques comprises three main steps: i) capturing 3-Dco-ordinates of target points; ii) quantifying geometricalparameters of fractures from the recorded co-ordinates; iii)documenting the results of fracture mapping. The details ofcapturing 3-D co-ordinates of target points are introduced. Anew algorithm is developed for computing orientation offracture planes. A multiple approach for documenting thefracture mapping results is presented. Application of thesetechniques for measuring and quantifying the geometricalparameters of fractures, such as orientation, trace length andsurface roughness, are demonstrated.</p><p>The presented methods can greatly improve the quality offracture measurements and avoid the drawbacks inherent intraditional methods. However, it can not replace the humancapacity to filter out and interpret the large amount ofgeometrical information displayed on the rock faces. Themethods may offer an assistance to engineers or geologists inobtaining as much information as possible about the geometryand orientation of rock fractures for rock engineeringapplications.</p><p><b>Keywords:</b>3-D laser scanner, close-range photogrammetry,engineering geology, fracture geometry, fracture mapping, rockengineering, rock faces, rock mechanics, three-dimension, totalstation.</p>

[pt] Valkó e Oligney propuseram um modelo que estima a evolução da fratura utilizando uma interpretação direta da curva de pressão de fundo medida durante uma operação de fracpack. Os únicos dados de entrada necessários para a aplicação do modelo são os registros geralmente disponíveis durante e após a operação. Considerando uma fratura de geometria radial e utilizando equações simples de fluxo e de geomecânica, o modelo obtém raios de empacotamento a partir da inclinação positiva da curva de pressão de fundo nos períodos de tip screenout. Nesta dissertação o modelo de Valkó e Oligney é aprimorado com a inclusão e o ajuste das equações de estado para o crescimento da fratura e para o processo de filtração, respectivamente. O modelo é também estendido para outras geometrias bidimensionais de fratura, PKN e KGD. A aplicação do modelo foi realizada utilizando os registros de pressão de oito operações de fracpack. Os resultados obtidos são a curva de propagação da fratura, o crescimento da abertura, a eficiência ao longo do tempo e a distribuição final do agente de sustentação na fratura. Para a validação desses resultados foram utilizados dois simuladores comerciais com modelos tridimensionais. Os estudos de caso indicaram que os ajustes realizados aproximaram os resultados do modelo aos obtidos nos simuladores comerciais. Além disso, a aplicação dos modelos desenvolvidos para cada geometria de fratura e a comparação com os resultados dos simuladores comerciais, permitiu confirmar a tendência esperada que, durante uma operação de fracpack, a geometria da fratura se aproxima da radial. / [en] Valkó and Oligney developed a model to estimate fracture evolution using a direct interpretation of the measured bottom hole pressure curve during a fracpack operation. The only input data needed to use the model are the usual records of the job, available during and after the operation. Considering radial fracture geometry and using simplified equations of flow and geomechanics, the model estimates a packing radius of the fracture using the slope of the increasing bottom hole pressure curve during the tip screenout period. In this work, Valkó and Oligney method is enhanced with the inclusion of state equations for the fracture growth and for the leakoff process in order to improve the model, but still maintaining minimum input data. The method is also extended to other two-dimensional fracture geometries, PKN and KGD. To apply the enhanced method, eight fracpack operation data were used. The results obtained are fracture propagation, width growth and fluid efficiency in time as well as the final proppant distribution in the fracture. To validate these results, this work used two commercial simulators with three-dimensional models. The case studies show that the modifications done to Valkó and Oligney method approximate the two-dimensional model results to the ones obtained using the commercial simulators with threedimensional models. Furthermore, the comparison between the application of the model for each fracture geometry and the commercial simulators results confirmed the expected tendency for the fracture geometry during a fracpack operation, which is a radial fracture.