Proppant flowback in fractures under confining pressures is not well understood and difficult to reproduce in a laboratory setting. Improper management of proppant flowback leads to flow restrictions near the well bore, poor fracture conductivity and costly production equipment damage. A simple, scalable model is developed using a discrete element method (DEM) particle simulator, to simulate representative cubic volumes consisting of fracture openings, fracture walls and the confining formation. The effects of fracture width, confining stress, fluid flow velocity and proppant cohesion are studied for a variety of conditions. Fracture width is found to be dependent on confining stress and fluid flow velocity while proppant production is also dependent on cohesion. Three regimes are observed, with complete fracture evacuation occurring at high flow rates and low confining stresses, fully packed fractures occurring at high confining stresses and open but mostly evacuated fractures occurring in-between. From these observations, a recommended flowback rate can be estimated for a given set of conditions. A slow and controlled well flowback is recommended to improve proppant pack stability. The rate ramp-up time is dependent on the leak-off coefficient. / text

Matrix acidizing is a well stimulation technique used to remove formation damage in the near wellbore region. But it comes with an associated set of challenges such as corrosion of the tubulars and iron precipitation in the formation. To counter these challenges, different chemicals, or additives, are added to the acid solution such as corrosion inhibitors and iron control agents. These additives may change the relative permeability of the spent acid, and formation wettability, and may either hinder or improve spent acid clean-up. Such effects of additives on the spent acid clean-up have not been documented. The aim of this research effort was to document the aforementioned change in the spent acid concentration (by using one additive at a time) before and after gas flowback. This was achieved by acidizing cores and creating wormholes halfway through them, then CT scanning them to observe the spent acid region. Later on, gas was flown through the core opposite to the direction of acid injection for 2 hours, and another CT scan was taken. The difference between the two CT scans was documented. Using a different additive each time, a series of such CT scans was obtained to develop an idea about whether the said additive was beneficial or detrimental to spent acid clean-up. It was found that the corrosion inhibitor FA-CI performed the best in terms of spent acid recovery after gas flowback for both Indiana Limestone and Texas Cream Chalk cores. Moreover, the corrosion inhibitor MI-CI was the worst for Indiana Limestone and the non-emulsifying agent M-NEA the worst for Texas Cream Chalk for spent acid recovery after gas flowback.

Hydraulic fracturing has unlocked a tremendous resource across the United States and around the world—shale. However, these processes have also come with a myriad of potential environmental effects, including a substantial demand for water. Hydraulic fracturing can require anywhere between two and four million gallons per well. The need for such large quantities of water can produce severe stresses on local water resources. In response to this issue, operators have developed several ways to alleviate some of the stresses brought on by the extensive water use such as alternative sourcing and reuse technologies. Companies are driven to exercise these options and decrease their fresh water usage for hydraulic fracturing processes for multiple reasons, including changes in regulation, to gain support of local communities, and to increase efficiencies of operations. Whatever the motivation may be, there are a variety of options companies have at their disposal to reduce fresh water demands—dependent on specific formation characteristics, the qualities and quantities of available water, among others. The Eagle Ford shale is one of the most rapidly growing shale plays in the country. However, this formation is located in a fairly arid part of the country. Because of meager average rainfall totals, water availability to meet demand is an issue of great concern. Due to nearly exponential increases in shale production, stresses on local water supplies have dramatically increased as well. The objectives of this thesis are as follows: 1) to establish the enormous resource that has become available; while still recognizing the environmental impacts associated with development processes, focusing primarily on water requirements and associated wastewater production; 2) to break down current water demand for shale development, as well as wastewater management practices in the Eagle Ford, with a brief comparison to other shale plays across the country; 3) to obtain an understanding of operator motivation—what factors affect wastewater management strategies; and 4) to analyze techniques operators presently have at their disposal to reduce fresh water demands, specifically through the use of brackish waters and recycling/reuse efforts, and finally to quantify these efforts to evaluate potential fresh water savings. / text

No description available.

Proppants are a specific application of granular materials used in oil/gas well stimulation. Employment of hard and soft particle mixtures is one of the many approaches availed by the industry to improve fracture resistance and the stability of the granular pack in the hydraulic fracture. Current industrial practices of proppant characterization involve long term and expensive conductivity tests. However, the mechanics governing the proppant pack response, in particular the effects due to material, shape and size of particles on the pack porosity, stiffness and particle fragmentation are not understood clearly. The present research embodies analytical and experimental approach to model hard (ceramic) and soft (walnut shell and/or pure aluminum) proppant mixtures by taking into account polydispersity in size, shape and material type of individual particles. The hydraulic fracture condition is represented through confined compression and flowback loads. The particle interactions clearly illustrate changes in pore space as a function of pressure, mixture composition and friction. Single particle compression tests on individual particles are carried out to obtain mechanical properties which are incorporated into the finite element models and are further correlated with the compression/crush response of the mixture. The proppant pack stiffness and particle fragmentation depends strongly on the mixture composition as illustrated in the models and experiments. The flowback models demonstrated that the formation of a stable arch is essential to pack stability. Additional variables that enhance flowback resistance are identified as: addition of softer particles to a pack, softer rock surfaces and higher inter-particle friction. The computational studies also led to the discovery of better, and more efficient pack compositions such as - short and thin pure Al needles/ceramic and the pistachio shells/ceramic mixtures. These analytical results have generated great interest and are engaged in the design of experiments to formulate future proppant pack mixtures at Baker Hughes Pressure Pumping, Tomball, TX.

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.

No description available.

Microalga-based technologies are introduced to provide a new generation of biofuels. The cultivation of microalgae in wastewater as the growth medium may offer the dual benefit of wastewater treatment and sustainable biofuel production. The potential of microalgal biomass to be converted into biodiesel depends on the accumulation of lipids, mainly triacylglycerols. However, the presence of toxic contaminants in municipal or industrial wastewater could negatively affect the biomass growth and modify the pattern of lipid accumulation in algae cells. This research aims to evaluate the potential of cultivating microalgae in wastewater for the removal of selected contaminants and the production of biodiesel. The hypothesis underlying this work was that growing microalgae in the presence of contaminants, typically found in wastewater, may induce a stress response that potentially increases the lipid productivity and enhances the biofuel yield. This research explored the potential of microalgae to be used for the removal of wastewater pollutants while accumulating high concentrations of neutral lipid that can be converted into biodiesel. Physiological and transcriptional responses of two genera of green algae were observed in the presence of stresses induced by toxic metals in raw hydraulic fracturing flowback water and pharmaceuticals found in municipal wastewater. Two green algae, Dunaliella salina and Chlorella vulgaris, were selected based on the availability of genetic information, current trends in the alga industry, and specific growth requirement in hypersaline flowback water and municipal wastewater. The first part of this research focuses on the possibility of using the salt-tolerant green microalga, D. salina, for the removal of toxic metals from hydraulic fracturing flowback water. In the second part of this research, the freshwater green microalga, C. vulgaris, was exposed to a suite of pharmaceuticals, commonly found in municipal wastewater, and the effects on the biomass growth and lipid accumulation were evaluated. In Chapter 3, aqueous geochemical characteristics of hydraulic fracturing flowback water were determined. Metagenomic analysis was also used to characterize the microbial community structure of the water samples. This technique included DNA extraction, PCR amplification of genes for 16S and 18S ribosomal RNA, and pyrosequencing. Although the two flowback water samples were shown to have water property measures in the range of reported values in literature, they were significantly different from each other regarding water properties such as total dissolved solids and total organic carbon. They also had distinct microbial community structures. It was shown the flowback water samples contained mainly halophilic, anaerobic, and thermophilic species with a pattern that was expected to be seen in natural gas shale reservoirs. Chapter 4 covers the characterization of the effects of contaminants (toxic metals) in hydraulic fracturing flowback water on the biomass growth and cellular lipid accumulation in Dunaliella salina. Metals were analyzed using ICP-MS. Biomass accumulation was determined by spectrophotometry and gravimetric methods. Lipid accumulation and composition were determined by GC-MS after conversion into fatty acid methyl esters. D. salina was successfully cultivated in saline hydraulic fracturing flowback water, and algal biomass growth was associated with a significant reduction of several toxic metals in the samples. D. salina, grown in flowback water, accumulated high levels of cellular lipids. Also, the estimated biodiesel properties were comparable with other algal biodiesel and complied with the US and EU biodiesel standards. The last chapter of part one presents the effects of a collection of metals commonly found in hydraulic fracturing flowback water and other industrial wastewaters on growth and lipid accumulation of D. salina. The impacts of the nitrogen concentration in the growth medium were also observed. The Nile red assay (fluorescence measurement after Nile red staining) was used to assess lipid accumulation. A range of toxic effects on the algal growth was observed. However, the effects were lower at higher nitrogen level that may indicate to an improved toxicity resistance when nutrient stress is minimal. Even with a high dose-dependent toxicity on growth, some toxic metals increased lipid accumulation. Chapter 6 describes the microplate-based toxicity test conducted to characterize the effect of a range of emerging contaminants (pharmaceuticals) commonly found in municipal wastewater on the biomass growth and cellular lipid accumulation measured by Nile red staining assay. Similar to what was observed for metals in Chapter 5, some pharmaceuticals increased lipid accumulation, even with a high dose-dependent toxicity on algal growth. Most tested pharmaceuticals at municipal wastewater levels (low) did not have a significant effect on the algal growth and lipid accumulation. Toxicity data (EC50 of growth) were well in agreement with what was reported in literature and antibiotics were the most toxic compounds among the different pharmaceutical classes. Chapter 7 presents a further characterization of the effects of a few selected compound from the previous chapter. Changes in the algal lipid composition upon exposure to the selected compounds were determined by qualitative and quantitative analysis of the extracted lipids using GC-MS. FT-IR spectroscopy was used to detect changes in the cellular constituents. The transcriptional responses of the key genes involved in the lipid metabolism of C. vulgaris were also investigated upon exposure to tetracycline using reverse-transcription real-time PCR and the results were interpreted based on the measured levels of cellular lipids and other metabolites. Lipid accumulation was changed upon exposure of algae to pharmaceuticals; however, the FAMEs profile did not show a significant variation. FT-IR spectroscopy highlighted the subtle changes in the cellular basis, and FT-IR peak associated with lipids was strongly correlated with total FAMEs quantified by GC-MS (Pearson correlation coefficient = 0.89). Gene expression analysis showed a general down-regulation of genes involved in the lipid biosynthesis. Results from this research are expecting to help develop and optimize innovative algal-based technologies combining the benefits of wastewater treatment, sustainable biofuel production, and mitigation of carbon dioxide emissions. / Civil Engineering

No description available.