Thesis (Ph. D.)--University of Texas at Austin, 2009. / Title from PDF title page (University of Texas Digital Repository, viewed on Sept. 10, 2009). Vita. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2010. / Title from document title page. Document formatted into pages; contains ix, 38 p. : col. ill., maps (some col.). Includes abstract. Includes bibliographical references (p. 36-37).

Thesis (M. Sc.)--University of Hong Kong, 2005.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

In conjunction with horizontal drilling, hydraulic fracturing or fracking has enabled the recovery of natural gas from low permeable shale formations. In addition to water, these fracking fluids employ proppants and up to 38 different chemical additives to improve the efficiency of the process. One important class of additives used in hydraulic fracturing is biocides. When applied appropriately, they limit the growth of harmful microorganisms within the well, saving energy producers 4.5 billion dollars each year. However, biocides or their harmful daughter products may return to the surface in produced water, which must then be appropriately stored, treated and disposed of. Little is known about the effect of mineral-fluid interactions on the fate of the biocides employed in hydraulic fracturing. In this study, we employed laboratory experiments to determine changes in the persistence and products of these biocides under controlled environments. While many minerals are present in shale formations, pyrite, FeS2(s) is particularly interesting because of its prevalence and reactivity. The FeII groups on the face of pyrite may be oxidized to form FeIII phases. Both of these surfaces have been shown to be reactive with organic compounds. Chlorinated compounds undergo redox reactions at the pyrite-fluid interface, and sulfur-containing compounds undergo exceptionally strong sorption to both pristine and oxidized pyrite. This mineral may significantly influence the degradation of biocides in the Marcellus Shale. Thus, the overall goal of this study was to understand the effect of pyrite on biocide reactivity in hydraulic fracturing, focusing on the influence of pyrite on specific functional groups. The first specific objective was to demonstrate the effect of pyrite and pyrite reaction products on the degradation of the bromine-containing biocide, DBNPA. On the addition of pyrite to DBNPA, degradation rates of the doubly brominated compound were found to increase significantly. DBNPA is proposed to undergo redox reactions with the pyrite surface, accepting two-electrons from pyrite, and thus becoming reduced. The primary product is the monobrominated analogue of DBNPA, 2-monobromo-3-nitrilopropionamide (or MBNPA). The surface area-normalized first-order initial degradation rate constant was found to be 5.1 L.m-2day-1. It was also determined that the dissolution and oxidation products of pyrite, FeII, S2O32- and SO42- are unlikely to contribute to the reduction of the biocide. Taken together, the results illustrate that a surface reaction with pyrite has the ability to reduce the persistence of DBNPA, and as a consequence change the distribution of its reaction products. The second objective was to quantify the influence of water chemistry and interactions with pyrite on the degradation of the sulfur-containing biocide. Dazomet readily hydrolyzes in water due to the nucleophilic attack of hydroxide (OH-) anions. Thus the half-life of dazomet during the shut-in phase of hydraulic fracturing will decrease with increasing pH: 8.5 hours at pH 4.1 to 3.4 hours at pH 8.2.Dazomet degradation was rapidly accelerated upon exposure to the oxidized pyrite surface, reacting five times faster than hydrolysis in the absence of pyrite at a similar pH. The products measured were identical to those identified on hydrolysis (methyl isothiocyanate and formaldehyde) and no dissolved iron was detected in solutions. This suggests that the dithiocarbamate group in dazomet was able to chemisorb onto the oxidized pyrite surface, shifting the electron density of the molecule which resulted in accelerated hydrolysis of the biocide. The third objective explored the reactivity of various biocide functional groups due to the addition of pyrite. Several elimination mechanisms were identified, and tied to the reactivity of the specific functional group involved. The addition of pyrite led to accelerated degradation of dibromodicyanobutane. This is because the bromine (-Br) group is easily reduced. For methylene bis(thiocyanate), hydrolysis was a noteworthy elimination mechanism since the thiocyanate (-SCN) functionality is a good leaving group. Benzisothiazolinone and methyl isothiazolinone were stable at low pH due to the stabilizing donor-acceptor interactions between the organic biocides’ carbonyl (–C=O) groups and salts in the solution. This body of work has illustrated that pristine pyrite can undergo redox reactions with brominated biocides used in hydraulic fracturing, reducing their persistence and altering the product distribution. This will change the efficacy and the risks associated with the use of these biocides in shales containing pyrite, particularly at lower pH where organic compounds are more stable to hydrolysis. However, at higher pH hydrolysis becomes more important, and additional studies will need to be conducted to investigate the pyrite contribution under these conditions. Conversely, the FeIII surface groups on oxidized pyrite can catalyze the hydrolysis of dazomet and may do so for other labile, sulfur-containing biocides as well. Overall, this research has shown that the physicochemical properties (such as the acid dissociation constant and the standard reduction potential) that govern the environmental reactivity of a molecule can be used to anticipate its reactivity in hydraulic fracturing.

Magister Scientiae - MSc / The prospect of unconventional shale-gas development in the Karoo Basin (South Africa) has created the need to obtain baseline data on natural radioactivity in Karoo groundwaters. The Karoo Basin groundwater radiological baseline developed through this study could serve as a reference to research potential future radiological contamination effects due to hydraulic fracturing. The major naturally occurring radioactive material (NORM) studied was radon (222Rn), in particular in-water activity concentrations; however, supplementary radium (226Ra and 228Ra) in-water activity concentrations and uranium (238U) in-water concentrations measurements were also made. A total of 53 aquifers across three provinces were sampled for groundwater and measured, with three measurement series from 2014 to 2016. The aquifers were categorized as shallow, mixed, or deep source. The radon-in-water baseline of the Karoo Basin can be characterised by a minimum of 0.6 ± 0.9 Bq/L, a maximum of 183 ± 18 Bq/L and mean of 41 ± 5 Bq/L. The radon-in-water levels from shallow sources (with water temperature < 20 °C) were systematically higher (40 Bq/L) than for deep sources (with water temperature > 20 °C). The natural fluctuations in radon-in-water levels were predominantly associated with shallow aquifers compared to almost none observed in the deep sources. The uranium in-water baseline can be characterised by a minimum of below detection level, a maximum of 41 μg/L, and the mean of 5.10 ± 0.80 μg/L. Similar to radon-in-water levels, uranium in-water levels for shallow sources were systematically higher than for deep sources. The limited (six aquifers) radium (228Ra and 226Ra) in-water activity-concentration measurement results were very low, with a maximum of 0.008 Bq/L (226Ra) and 0.015 Bq/L (228Ra). The 228Ra/226Ra ratio baseline were characterised by a minimum of 0.93, a mean of 3.3 ± 1.3, and a maximum of 6.5. The radium isotopes’ activity concentration ratio is an isotopic tracer for hydraulic fracturing wastewater. Pollution and contamination (radiological), due to unconventional shale gas development, in water resources has been noticed in the Marcellus Basin (United States). Consequently, developing and improving continuous baseline monitoring are of importance to study the environmental radiological effect of hydraulic fracturing.

North Dakota’s oil boom is aided by a new technology, fracking. But this technology implies large amounts of wastewater. The methods of dealing with this wastewater are now an issue. Currently, North Dakota locks it into deep injection wells in the Bakken formation. With the development of membrane technologies to treat wastewater, it may be feasible to treat the wastewater and reuse it. This study uses a mathematical programming model to minimize the total cost of dealing with wastewater using three methods - deep well injection, on-site treatment, and off-site treatment. The model results show it is cost-effective to use on-site and large capacity off-site treatment to treat the 20% of the wastewater that flows back within the first 30-60 days after a well is drilled.

No description available.

Hydraulic fracturing is a process for the extraction of hydrocarbons from underground formations. It involves pumping a specialized fluid into the wellbore under high pressures to form and support fractures in the rock. Fracturing stimulates the well to increase the production of oil and the natural gas which are the pillars of the energy economy. Key to this process is the use of proppants, which are solid materials used to keep the fractures open. Understanding the transport of proppant particles through a fluid is important to improve the efficiency and reduce environmental impact of fracturing. An increase of the settling velocity for instance, will impede the hydraulic fracturing process by reducing well productivity, or necessitate use of chemical additives. This thesis presents a theoretical investigation of the settling velocity of proppant particles. The effect of different parameters on the settling velocity were studied by manipulating the main factors that can influence particle transport. These include size of the particle (300 μm- 2000 μm), sphericity, density (1200 kg/m3-3500 kg/m3) and concentration. These typical values were obtained from commercially available proppants currently used in industry. Various correlations were investigated, assuming the carrier (fracturing) fluid to be an ideal Newtonian and as a power law (non-Newtonian) fluid. This will help predict the settling velocity for proppant particles in order to increase well productivity, and improve hydraulic fracturing efficiency. The models show that changing the carrier fluid viscosity and particle properties such as diameter, density, sphericity, and concentration leads to a significant change in the proppant settling velocity. For instance, reduction in particle size, density, and sphericity tend to reduce the settling velocity, while increasing the concentration of the particles and the fluid viscosity reduce the settling velocity.

This work addresses the poroelastic effect on the processes involved in hydraulic fracturing and post-fracture production using a finite element based fully coupled poroelastic model which includes a triple system of wellbore-fracture-reservoir. A novel numerical procedure for modeling hydraulic fracture propagation in a poroelastic medium is introduced. The model directly takes into account the interaction of wellbore, hydraulic fracture and reservoir in a fully coupled manner. This allows realistic simulation of near fracture phenomena such as back stress and leak-off. In addition, fluid leak-off is numerically modeled based on the concept of fluid flow in porous media using a new technique for evaluating local pressure gradient. Besides, the model is capable of accommodating the zone of reduced pressure (including intermediate and fluid lag zones) at the fracture front so as to capture the behavior of fracture tip region more realistically. A fully coupled poroelastic model for gas reservoirs has been also developed using an innovative numerical technique. From the results of this study it has been found that fracture propagation pressure is higher in poroelastic media compared to that of elastic media. Also high formation permeability (in the direction normal to the hydraulic fracture) and large difference between minimum horizontal stress (in case of it being the smallest principal stress) and reservoir pressure reduce the rate of fracture growth. Besides, high pumping rate is more beneficial in elongating a hydraulic fracture whereas high viscous fracturing fluid is advantageous in widening a hydraulic fracture. It has been also shown that rock deformation, permeability anisotropy and modulus of elasticity can have a significant effect on fluid flow in a hydraulically fractured reservoir. Furthermore, it has been shown that long stress reversal time window and large size of stress reversal region can be caused by high initial pressure differential (i.e. the difference between flowing bottomhole pressure and reservoir pressure), low initial differential stress (i.e. the difference between maximum and minimum horizontal stresses) and low formation permeability in tight gas reservoirs. By taking advantage of production induced change in stress state of a reservoir, this study has also shown that a refracture treatment, if carried out in an optimal time window, can lead to higher economic gain. Besides, analysis of stress reversal region has depicted that a small region with high stress concentration in the vicinity of the wellbore could impede refracture from initiating at the desired place. Moreover, re-pressurization of the wellbore can result in further propagation of the initial fracture before initiation or during propagation of the secondary fracture.