The development of hydrocarbon energy resources from shale, a fine-grained, low-permeability geological formation, has altered the global energy landscape. Constricting pressure exerted on a shale formation has a significant effect on the rock's apparent permeability. Gas flow in low-permeability shales is significantly different from liquid flow due to the Klinkenberg effect caused by gas molecule slip at the nanopore wall surfaces. This has the effect of increasing apparent permeability (i.e., the measured permeability). Optimizing the conductivity of the proppant assembly is another critical component of designing subsurface hydrocarbon production using hydraulic fracturing. Significant fracture conductivity can be achieved at a much lower cost than conventional material costs, according to the optimal partial-monolayer proppant concentration (OPPC) theory. However, hydraulic fracturing performance in unconventional reservoirs is problematic due of the complex geomechanical environment, and the experimental confirmation and investigation of the OPPC theory have been rare in previous studies. In this dissertation, a novel multiphysics shale transport (MPST) model was developed to account for the coupled multiphysics processes of geomechanics, fluid dynamics, and the Klinkenberg effect in shales. Furthermore, A novel multi-physics multi-scale multi-porosity shale gas transport (M3ST) model was developed based on the MPST model research to investigate shale gas transport in both transient and steady states, and a double-exponential empirical model was also developed as a powerful substitute for the M3ST model for fitting laboratory-measured apparent permeability. Additionally, throughout the laboratory experiment of fracture conductivity with proppant, the four visible stages documented the evolution of non-monotonic conductivity and proppant concentration. The laboratory methods and empirical model were then applied to the shale plugs from Central Appalachia to investigate the formation properties there. The benefits of developing these regions wisely include a smaller surface footprint, reduced infrastructure requirements, and lower development costs. The developed MPST, M3ST, double-exponential empirical models and research findings shed light on the role of multiphysics mechanisms, such as geomechanics, fluid dynamics and transport, and the Klinkenberg effect, in shale gas transport across multiple spatial scales in both steady and transient states. The fracture conductivity experiments successfully validate the theory of OPPC and illustrate that proppant embedment is the primary mechanism that causes the competing process between fracture width and fracture permeability and consequently the non-monotonic fracture conductivity evolution as a function of increasing proppant concentration. The laboratory experimental facts and the numerical fittings in this study provided critical insights into the reservoir characterization in Central Appalachia and will benefit the reservoir development using non-aqueous fracturing techniques such as CO2 and advanced proppant technologies in the future. / Doctor of Philosophy / Production of oil and gas from the extremely tight rock has changed the global energy industry, including job growth, energy security, and environment protection. However, the oil and gas production from the tight rock is difficult because of the complex rock properties. Hydraulic fracking can resolve the issue and contribute to the high production. The higher and safer production needs us to have a better understanding of oil and gas flow under the ground. A series of laboratory experiment were conducted, and a new shale gas transport model is introduced in this dissertation to explain the oil and gas flow under the complicated scenarios. The experimental results show that many factors can impact the oil and gas flow, and the model can match the experimental results very well. A few statistical methods are also used in the data analysis. The optimization of proppant pack is another important component of hydraulic fracking. Proppant particles are usually man-made ceramic tiny balls, which will be injected into the underground to keep the fractures from closing during the production. From the previous papers, it is possible to achieve high fracture conductivity at a much lower cost than traditional proppant costs. Many groups of laboratory experiment were conducted to demonstrate this guess. Many rock samples in the experiment are from Central Appalachian area, which can help the resource development in this area. The developed model and experimental research findings in this study provided critical insights into the role of the many physics mechanisms on shale gas transport, proppant optimization, and hydraulic fracking.

[pt] Um dos principais objetivos da engenharia de petróleo é desenvolver e aplicar técnicas capazes de aumentar a produtividade de poços de petróleo, incluindo a estimulação da formação através de operações que aumentem a permeabilidade da rocha-reservatório e facilitem o escoamento do fluido. Dentre as técnicas de estimulação, a mais utilizada é o fraturamento hidráulico, a qual tem viabilizado a exploração em cerca de 40 por cento dos poços produtores de petróleo em todo o mundo. Durante o fraturamento hidráulico, um material granular conhecido como material de sustentação ou propante, é injetado nas fraturas recém-criadas com o objetivo de mantê-las abertas e garantir-lhes condições de alta permeabilidade. A produção de material de sustentação (proppant flowback) é termo usado para descrever o refluxo do propante para o interior do poço, juntamente com o hidrocarboneto produzido. O controle do fluxo de propante representa um grave desafio para a indústria de petróleo, pois pode causar graves problemas operacionais e de segurança, relacionados com o desgaste dos equipamentos de produção, problemas econômicos associados ao custo de limpeza, paralisação das operações e intervenção no tratamento da fratura, problemas ambientais relacionados com a disposição de sólidos impregnados por hidrocarbonetos, etc. Neste contexto, a presente dissertação apresenta um estudo detalhado dos principais tipos de propante e de suas propriedades, bem como descreve os mecanismos que influem no refluxo do material de sustentação da fratura e analisa os principais modelos apresentados na literatura para previsão deste fenômeno. Uma retroanálise considerando os dados de campo em 22 poços da Petrobrás, localizados em Sergipe, permite uma comparação da eficiência entre quatro dos modelos, desenvolvidos com base em resultados de ensaios de laboratório, indicando suas vantagens e desvantagens para aplicação na prática da engenharia. / [en] One of the main objectives of petroleum engineering is to develop and to apply techniques aiming the productivity increase of oil fields, including the stimulation of the rock through operations that increase the permeability of the oil reservoir and makes the flow of the fluid toward the well more efficient. Among the stimulation techniques, the most used is the hydraulic fracturing, carried out in about 40 percent of the producing oil wells around the world. During hydraulic fracturing, a granular material known as proppant, is injected into the just created fractures with the objective to keep them open and in order to guarantee the designed conditions of high permeability. Proppant flowback is the technical terminology employed to describe the flow of proppant from the fracture to the interior of the oil well, together with the produced hydrocarbon. An efficient and reliable control of this problem is still a major challenge to the oil industry, given the serious operational and security problems that it may cause, including costs of interrupted operations, cleaning measures, environmental contamination risks associated with the disposal of residues impregnated by oil, etc. In this context, the present thesis presents a detailed description on the main proppant materials and their engineering properties and available treatments, as well as on the physical mechanisms that control the flowback phenomenon. Several simple models published in the literature, that permit the forecast of proppant flowback in a fast and easy way, are also presented and discussed. Finally, a back-analysis considering the actual conditions in 22 Petrobras oil wells located in Sergipe was also carried out, what permitted a comparison among the results calculated according 4 prediction models, putting in evidence their advantages, shortcomings and adequacy as a design or control tool in the design and exploration of oil fields stimulated by hydraulic fracturing.

Each hydraulic fracturing well uses up to 5,000 tons of silica-containing sand, or proppant, during its operational lifetime. Over one million wells are currently in operation across the continental United States. The resulting increase in demand resulted in the production of 54 million metric tons of sand for use as hydraulic fracturing proppant in 2015. The goal of this study was to determine the relative risk of occupational exposure to respirable crystalline silica to workers performing tasks associated with mining, processing, and transport of proppant. Sand samples were aerosolized in an enclosed chamber. Bulk and respirable samples were submitted to a commercial lab for silica analysis. A risk ratio was calculated by comparing respirable dust concentrations to the current occupational safety regulations. Raw sand produced higher concentrations of respirable dust and a higher risk ratio (3.2), while processed dust contained higher percentages of respirable crystalline silica but a lower risk ratio (0.5). When vibration was introduced prior to aerosolization, concentrations tended to increase as vibration times increased, resulting in an increase of the associated risk ratio (2.3). Results of the study indicate that workers in sand mines and workers exposed to proppant that has undergone low-frequency vibration are at increased risk of exposure to respirable crystalline silica compared to workers who are exposed to proppant that has not undergone vibration.

This investigation carried out the analysis of fracture conductivity in a tight reservoir using laboratory experiments, by applying the procedure known as the dynamic fracture conductivity test. Considering the large number of experiments necessary to evaluate the effect of each parameter and the possible interaction of their combinations, the schedules of experiments were planned using a fractional factorial design. This design is used during the initial stage of studies to identify and discharge those factors that have little or no effect. Finally, the most important factors can then be studied in more detail during subsequent experiments. The objectives of this investigation were focused on identifying the effect of formation parameters such as closure stress, and temperature and fracture fluid parameters such as proppant loading over the final conductivity of a hydraulic fracture treatment. With the purpose of estimating the relation between fracture conductivity and the design parameters, two series of experiments were performed. The first set of experiments estimated the effects of the aliases parameters. The isolated effect of each independent parameter was obtained after the culmination of the second set of experiments. The preliminary test results indicated that the parameters with major negative effect over the final conductivity were closure stress and temperature. Some additional results show that proppant distribution had a considerable role over the final fracture conductivity when a low proppant concentration was used. Channels and void spaces in the proppant pack were detected on these cases improving the conductivity of the fracture, by creating paths of high permeability. It was observed that with experiments at temperatures around 250 degrees F, the unbroken gel dried up creating permeable scales that resulted in a significant loss in conductivity. The results of this investigation demonstrated that dynamic fracture conductivity test procedure is an excellent tool to more accurately represent the effects of design parameters over the fracture conductivity. These results are also the first step in the development of a statistical model that can be used to predict dynamic fracture conductivity.

Hydraulic fracture conductivity in ultra-low permeability shale reservoirs is directly related to well productivity. The main goal of hydraulic fracturing in shale formations is to create a network of conductive pathways in the rock which increase the surface area of the formation that is connected to the wellbore. These highly conductive fractures significantly increase the production rates of petroleum fluids. During the process of hydraulic fracturing proppant is pumped and distributed in the fractures to keep them open after closure. Economic considerations have driven the industry to find ways to determine the optimal type, size and concentration of proppant that would enhance fracture conductivity and improve well performance. Therefore, direct laboratory conductivity measurements using real shale samples under realistic experimental conditions are needed for reliable hydraulic fracturing design optimization. A series of laboratory experiments was conducted to measure the conductivity of propped and unpropped fractures of Barnett shale using a modified API conductivity cell at room temperature for both natural fractures and induced fractures. The induced fractures were artificially created along the bedding plane to account for the effect of fracture face roughness on conductivity. The cementing material present on the surface of the natural fractures was preserved only for the initial unpropped conductivity tests. Natural proppants of difference sizes were manually placed and evenly distributed along the fracture face. The effect of proppant monolayer was also studied.

Workers involved in hydraulic fracking processes are exposed to various types of chemicals and dusts in their workplaces, such as proppants, which hold open the fissures created in the fracking process. Recently, ceramic proppants have been developed that may be less hazardous to workers than traditional proppants. Pulmonary function testing of workers producing ceramic proppant was used to assess the potential inhalation hazards of ceramic proppant. Male workers (n = 100) from a producer of ceramic proppant were evaluated with pulmonary function test data collected and evaluated using The American Thoracic Society (ATS) acceptability criteria. A comparison group was selected from the Third National Health and Nutrition Examination Survey (NHANES III) spirometry laboratory subset. No pulmonary function deficits were found in the worker group in comparison to the NHANES III population. Multiple linear regression analysis showed that the mean FEV1 and FVC values in workers were 0.11 and 0.08 liters respectively, and were greater as compared to the NHANES III population. Curiously, an FEV1/FVC ratio of less than 0.8, when compared to the NHANES III group, produced an odds ratio of 0.44 in worker group, indicating less risk of preclinical pulmonary dysfunction. Overall, exposure to ceramic proppant was not found to produce an adverse impact on pulmonary function in workers engaged in the manufacture of ceramic proppant.

No description available.

[pt] A técnica para estimulação de um campo de petróleo através de fraturamento hidráulico inclui a injeção, com o fluido de fraturamento, de um material para sustentação da abertura da fratura, denominado propante. Uma das dificuldades deste processo é o refluxo do material de sustentação para o interior do poço durante a fase de produção de óleo, ocasionando diversos problemas que podem chegar, em situações extremas, à interrupção definitiva da produção. O controle do fluxo de propante representa, portanto, um grande desafio para a indústria do petróleo. Alguns modelos empíricos - correlação Stimlab, modelo de cunha livre, modelo da velocidade mínima de fluidificação, modelo semi- mecânico - foram desenvolvidos para a previsão desse fenômeno, mas não contemplam todas as variáveis que influenciam no refluxo do material de sustentação da fratura. Uma alternativa aos modelos empíricos é utilizar o método dos elementos discretos para simular computacionalmente a instabilidade do pacote granular. Nesta dissertação busca-se modelar o comportamento do refluxo do propante utilizando uma modelagem 3D da fratura, partículas e fluxo de óleo com auxílio do programa computacional PFC3D baseado no método dos elementos discretos. Os dados das análises (tipos de propante, temperatura, características do fluido e do propante, etc) se referem a 4 cenários principais considerando fraturas sob diversos níveis de tensão e forças de arraste. Foram feitas discussões considerando os resultados numéricos obtidos por análises computacionais bi e tridimensionais, bem como comparações com modelos empíricos de previsão do refluxo do material de sustentação. / [en] The technique for stimulating an oil field through hydraulic fracturing consists of pumping into the oil bore the fracturing fluid mixed with a material to hold the fracture open, called proppant. One of the difficulties in this process is the occurrence of proppant flowback into the well bore during oil production, causing several problems that can result, in critical situations, in a definitive interruption of the oil production. Control of proppant flowback represents a great challenge for the petroleum industry. Some empirical models - Stimlab correlation, propped- free wedge model, minimum fluidization velocity, semi-mechanistic model - were developed for prediction of proppant flowback, yet they do not encompass all variable that play a role in this complex phenomenon. An alternative is to employ the discrete element method in order to computationally simulate the instability of the granular package. The main goal of this thesis is to investigate the proppant flowback phenomenon, through a 3D model of the fracture, particles and flow conditions using the computational program PFC3D, a code based on the discrete element method. The input data (type of proppant, temperature, characteristics of the fluid and proppant, etc.) relate to 4 main scenarios that consider fractures under several levels of stress closure and drag forces. The numerical results computed from 2D and 3D analyses were discussed, as well as comparisons were done with the predictions obtained with empirical methods.

Den technologischen Hintergrund für diese Arbeit liefert die bei der Erschließung tiefer Lagerstätten (Erdgas, Erdöl, Erdwärme) eingesetzte Stimulationstechnik des Hydraulic Fracturing. Bei dieser Technik werden mittels hydraulischem Druck Risse im Lagerstättengestein erzeugt, die durch Einspülen von Feststoffkörnern (Proppants) offengehalten werden sollen. Der inhaltliche Schwerpunkt liegt auf der theoretischen und experimentellen Untersuchung der Einbettung von Proppants in das Lagerstättengestein unter besonderer Berücksichtigung des Einflusses auf die hydraulische Leitfähigkeit eines durch Proppants gestützten Risses. Thematisch teilt sich die Arbeit in die beiden Schwerpunkte: (1) Berechnung der Proppant-Einbettung auf der Grundlage kontaktmechanischer Ansätze und (2) experimentelle Untersuchungen an realen Proppant-Schüttungen. Zur mathematischen Formulierung der Proppant-Einbettung wurde die in der Werkstofftechnik entwickelte Theorie des mechanischen Verhaltens rauer Oberflächen unter Lasteintrag (Kontaktmechanik) mit der ebenfalls aus der Werkstofftechnik bekannten Messung und Interpretation der Oberflächenhärte nach Meyer gekoppelt. Diese neuartige Formulierung ermöglicht es, die Einbettung von Proppants in Abhängigkeit der Materialeigenschaften der Formation, des Spannungszustandes, der Korngrößenverteilung und der Proppants-Konzentration zu berechnen. Zur Prognose des Erfolges einer Stimulation wurde ein 2D-numerischer Algorithmus (MATLAB®) entwickelt, der den Gesamtprozess der Einbettung, der Durchlässigkeitsentwicklung und deren Folgen für die Produktivität der Sonden widerspiegelt. Zur Verifizierung des Berechnungsalgorithmus wurde die Einbettung realer Proppant-Schüttungen in Lagerstättengesteinen (Tonschiefer, Shale) untersucht. Hierfür wurde in einer dafür konzipierten Flutzelle ein durch Proppants gestützter Riss nachgebildet, belastet und durchströmt. Ziel der Versuche war dabei zu messen, welchen Einfluss ein Spannungsanstieg auf die Einbettung und damit auf die hydraulische Leitfähigkeit hat. Diese Versuche wurden an zwei verschiedenen Shale-Gesteinen mit zwei verschiedenen Proppant-Konzentrationen durchgeführt. Zusätzlich zu den hydraulischen Experimenten wurden mechanische Untersuchungen (Härtemessungen) ausgeführt und nach der Meyer-Analyse der Werkstofftechnik interpretiert. Ein besonderer Vorteil dieser Auswertungsmethode liegt in ihrer durch Dimensionsanalyse erzielten Übertragbarkeit der Ergebnisse von Werkstoffen auf Gesteine. Der Vergleich von gemessenen und berechneten Einbettungen und hydraulischen Leitfähigkeiten ergab eine zufriedenstellende Übereinstimmung und erlaubt es festzustellen, dass mit der neuen Formulierung die planerische Voraussage von Frac-Stimulation möglich ist, wobei alleine die relativ einfachen laborativen Messverfahren zur Härtemessung (Gestein) und zur Korngrößenanalyse (Proppant) erforderlich sind.

No description available.