Repository for Oil and Gas Energy Research (ROGER)

Abstract:
In 1980, solid waste from oil and gas fields was exempt from US federal hazardous waste regulations (according to the US Environmental Protection Agency's Resources Conservation and Recovery Act, RCRA). However, recent developments in oil and gas extraction from deep shale formations warrant a closer look at this exemption. We obtained lab reports submitted to state regulators to characterize the solid waste generated from 231 shale gas wells in Pennsylvania. Of the 40 chemicals listed as toxic in RCRA, eight were present in our samples and two exceeded RCRA toxicity limits for classification as a hazardous waste (Ba and Cr). We also found overlap with chemicals listed in international lists of toxicity, suggesting that these wastes could pose health problems that would not be regulated by RCRA. Radiation in solid waste is regulated at the state-level; the maximum detected concentrations of radium-226 and radium-228 (51 picocuries/g and 8.87 picocuries/g, respectively) exceed the regulatory limits for landfills in Ohio and New York, however it is common practice to ship waste across state lines. Removing the RCRA oil and gas exemption would increase testing and reporting burdens but would leave most shale waste management practices unchanged while protecting against some hazardous outliers.

Abstract:
Shale gas exploitation is booming in China. Unlike the traditional oil extraction industry, shale gas extraction will generate more solid waste. Water-based drill cuttings (WBDC) as one of them is currently under regulatory vacuum. This article studied the status of heavy metal pollution and evaluated the ecological risk of WBDC. Cd, Cr, Cu, Hg, Mn, Ni, Pb and Zn were selected for the study. The results showed that except for Ni, other heavy metals showed different degrees of pollution, but the leaching toxicity was rather limited. Meanwhile, the ecological risks of all samples were significant, which posed a huge threat to environment. Though its limitation, this article can provide theoretical foundation for regulatory decisions of WBDC.

Abstract:
Public concern is heightened around flowback and produced water (FPW) generated by the hydraulic fracturing process. FPW is a complex mix of organic and inorganic solutes derived from both the injected hydraulic fracturing fluid and interactions with the subsurface lithology. Few studies to date have systematically investigated the composition of FPW or its individual components. Here, we provide the first systematic characterization of the composition of the solids associated with FPW by analyzing samples from three wells drilled into the Duvernay Formation in Alberta, Canada. The FPW initially returned to the surface with high total dissolved solids (greater than 170 000 mg L−1) and enriched with Fe(II), silica, sulfate, barium, and strontium. The solids form two distinct phases once the FPW reached the surface: (1) silica-enriched Fe(III) oxyhydroxides, and (2) a barite–celestine solid solution. We hypothesize that the precipitation of the amorphous silica-enriched Fe(III) oxyhydroxide is a two-step process, where first the silica precipitates as a function of the cooling of the FPW from elevated subsurface temperatures to ambient surface temperatures. Next, the silica acts as a template for the precipitation of Fe(III) oxyhydroxide as the diffusion of oxygen into the subsurface causes oxidation of aqueous Fe(II). The barite–celestine solid solution precipitates solely as a function of cooling. Elevated dissolved Fe concentrations in FPW and modeled saturation indices from five North American shale plays (Marcellus, Fayetteville, Barnett, Bakken, and Denver-Julesburg) indicate that solids similar to those found in Duvernay FPW, specifically Fe(III) oxyhydroxides, barite and quartz, are likely to occur. With the solids known to carry a significant portion of FPW's toxicity and organic contaminant load, the development of new treatment technologies, such as the oxidation of the Fe(II) in FPW, may increase FPW reuse and reduce the environmental risk posed by FPW.

Abstract:
Naturally occurring radioactive materials (NORM) in solid waste or “drill cuttings” produced from unconventional drilling for natural gas extraction wells potentially pose environmental contamination risks; however, the composition and mobility of NORM in these solid wastes are poorly understood. In this study, the composition of NORM, including uranium, thorium, radium, lead, and polonium isotopes, was evaluated in three samples of drill cuttings extracted from a well drilled into the Marcellus Shale formation. Leachability of NORM in drill cuttings was characterized by leaching the solid waste with dilute acetic acid at four different pH values. The uranium-series radionuclides in cuttings and leachate samples displayed isotopic disequilibrium, suggesting some environmental mobility of radionuclides in these shale formations. Our results indicate that isotopic analysis of uranium-series radionuclides is needed for a more complete understanding of the potential environmental contamination risks associated with these solid wastes.

Abstract:
The effect of pH changes on leachability of light and heavy metals from shale drill cuttings generated from unconventional shale gas production was investigated. Cuttings, being the primary byproduct generated from drilling operations, belong to the potentially hazardous type of wastes due to presence of heavy and radioactive elements and remains of drilling fluid. In this regard, assessment of potentially dangerous components (PDCs) from rock waste materials was performed by application of batch leaching tests, which has provided information on the sensitivity of leaching under externally imposed changes in pH (natural or caused by treatment) in specific scenarios. The description of shale rocks mineralogical and chemical properties was performed by means of X-ray fluorescence spectroscopy, diffractometry as well as scintillation spectrometry. The concentrations of released constituents due to the leaching tests were measured by atomic absorption spectrophotometry. Results were compared and discussed accordingly with the waste acceptable criteria of elution limits. Analysis of the substrate revealed that the elemental composition was dominated by light elements, whereas heavy metals were present in trace amounts. However, noticeable release of barium (2.0–4.6%) was also recorded, which has originated from not only rock material but also drill mud. Minor mobility was observed for transition elements such as Cr, Co, Fe, Mn, Ni, Zn, Cu and Pb. Results revealed that drill cuttings follow the requirements for other than hazardous and municipal type of deposition, with exception for barium. Moreover, content of radioactive isotopes fulfill the requirements range of acceptable concentrations.

Abstract:
Formation of barite (BaSO4) scale is a potential problem for unconventional (shale) gas extraction, as the excessive scale can reduce well productivity by plugging the proppant pack. This study was designed to evaluate the impact of antiscalants on the formation and transport of barite particles through proppant sand under well-controlled laboratory conditions using batch and column experiments. Extensive attachment of BaSO4 particles to proppant sand was observed at typical background salinity and in the absence of antiscalants due to relatively large barite particle size and screened electrostatic interaction. Presence of polymeric antiscalants can enhance the mobility of BaSO4 particles by decreasing their size and providing electrosteric repulsion. Ethylene glycol that may be added to hydraulic fracturing fluid to prevent scale deposition can reduce the size of BaSO4 precipitates but has no impact on the deposition of BaSO4 particles during transport through proppant sand. Polymaleic acid and sulfonated poly-phosphino-carboxylic acid that are generally considered when the goal is to inhibit formation of mineral scales are unlikely to prevent barite formation at high supersaturation conditions that are typical for unconventional gas industry. However, they can reduce the size and alter the morphology of barite particles as well as inhibit the deposition of bulk precipitates onto proppant sand surface by inducing stronger repulsive interactions.

Abstract:
Shale gas exploitation by hydraulic fracturing involves a number of environmental hazards, among which the neutralization and management of fracturing flowback waters is of particular importance. Chemical compounds present in the flowback water mainly constitute a threat to surface waters. The aim of our research was to determine the effects of these compounds on the state of activated sludge in a wastewater treatment plant employing biological treatment processes. Based on the obtained results, it was concluded that prior to the transfer of flowback water to a biological wastewater treatment system, it should be diluted with fresh water to lower the chloride ion concentration to the level of 1,000 mg Cl-/dm3. Although such a procedure would ensure the proper performance of a biological wastewater treatment system, it would not limit the migration of phthalates and thihalomethanes to surface waters.

Abstract:
Naturally occurring radioactive material (NORM) is a common feature in North Sea oil and gas production offshore but, to date, has been reported from only one production site onshore in the United Kingdom. The latter, Wytch Farm on the Dorset coast, revealed high activity concentrations of 210Pb in metallic form but little evidence of radium accumulation. NORM has now been discovered at two further onshore sites in the East Midlands region of the UK. The material has been characterized in terms of its mineralogy, bulk composition and disequilibrium in the natural uranium and thorium series decay chains. In contrast to Wytch Farm, scale and sludge samples from the East Midlands were found to contain elevated levels of radium and radioactive progeny associated with crystalline strontiobarite. The highest 226Ra and 228Ra activity concentrations found in scale samples were 132 and 60 Bq/g, with mean values of 86 and 40 Bq/g respectively; somewhat higher than the mean for the North Sea and well above national exemption levels for landfill disposal. The two East Midlands sites exhibited similar levels of radioactivity. Scanning electron microscope imaging shows the presence of tabular, idiomorphic and acicular strontiobarite crystals with elemental mapping confirming that barium and strontium are co-located throughout the scale. Bulk compositional data show a corresponding correlation between barium-strontium concentrations and radium activity. Scales and sludge were dated using the 226Ra/210Pb method giving mean ages of 2.2 and 3.7 years, respectively. The results demonstrate clearly that these NORM deposits, with significant radium activity, can form over a very short period of time. Although the production sites studied here are involved in conventional oil recovery, the findings have direct relevance should hydraulic fracturing for shale gas be pursued in the East Midlands oilfield.

Abstract:
Drill cuttings generated during unconventional natural gas extraction from the Marcellus Shale, Appalachian Basin, U.S.A., generally contain a very large component of organic-rich black shale because of extensive lateral drilling into this target unit. In this study, element concentrations and Pb isotope ratios obtained from leached drill cuttings spanning 600 m of stratigraphic section were used to assess the potential for short and long term environmental impacts from Marcellus Shale waste materials, in comparison with material from surrounding formations. Leachates of the units above, below and within the Marcellus Shale yielded Cl/Br ratios of 100–150, similar to produced water values. Leachates from oxidized and unoxidized drill cuttings from the Marcellus Shale contain distinct suites of elevated trace metal concentrations, including Cd, Cu, Mo, Ni, Sb, U, V and Zn. The most elevated Mo, Ni, Sb, U, and V concentrations are found in leachates from the lower portion of the Marcellus Shale, the section typically exploited for natural gas production. In addition, lower 207Pb/206Pb ratios within the lower Marcellus Shale (0.661–0.733) provide a distinctive fingerprint from formations above (0.822–0.846) and below (0.796–0.810), reflecting 206Pb produced as a result of in situ 238U decay within this organic rich black shale. Trace metal concentrations from the Marcellus Shale leachates are similar to total metal concentrations from other black shales. These metal concentrations can exceed screening levels recommended by the EPA, and thus have the potential to impact soil and water quality depending on cuttings disposal methods.

Abstract:
Development of unconventional shale gas wells can generate significant quantities of drilling waste, including trace metal-rich black shale from the lateral portion of the drillhole. We carried out sequential extractions on 15 samples of dry-drilled cuttings and core material from the gas-producing Middle Devonian Marcellus Shale and surrounding units to identify the host phases and evaluate the mobility of selected trace elements during cuttings disposal. Maximum whole rock concentrations of uranium (U), arsenic (As), and barium (Ba) were 47, 90, and 3333 mg kg−1, respectively. Sequential chemical extractions suggest that although silicate minerals are the primary host for U, as much as 20% can be present in carbonate minerals. Up to 74% of the Ba in shale was extracted from exchangeable sites in the shale, while As is primarily associated with organic matter and sulfide minerals that could be mobilized by oxidation. For comparison, U and As concentrations were also measured in 43 produced water samples returned from Marcellus Shale gas wells. Low U concentrations in produced water (<0.084–3.26 μg L−1) are consistent with low-oxygen conditions in the wellbore, in which U would be in its reduced, immobile form. Arsenic was below detection in all produced water samples, which is also consistent with reducing conditions in the wellbore minimizing oxidation of As-bearing sulfide minerals. Geochemical modeling to determine mobility under surface storage and disposal conditions indicates that oxidation and/or dissolution of U-bearing minerals in drill cuttings would likely be followed by immobilization of U in secondary minerals such as schoepite, uranophane, and soddyite, or uraninite as conditions become more reducing. Oxidative dissolution of arsenic containing sulfides could release soluble As in arsenate form under oxic acidic conditions. The degree to which the As is subsequently immobilized depends on the redox conditions along the landfill flow path. The results suggest that proper management of drill cuttings can minimize mobilization of these metals by monitoring and controlling Eh, pH and dissolved constituents in landfill leachates.

Abstract:
This paper presents a compilation of published mineralogic and trace element data from nine gas shales in the United States. Formations analyzed include the Antrim, Bakken, Barnett, Eagle Ford, Haynesville, Marcellus, New Albany, Utica and Woodford. These mineralogic and trace element data can be used to assess the potential for environmental impacts during hydraulic fracturing. Impacts addressed in this study include: 1) the potential for acid rock drainage generation during gas shale weathering, 2) the distribution of trace elements in gas shales and comparison with regulatory guidelines, and 3) the implications for environmental management of well cuttings. The use of the mineralogic data to assess the fracability of the gas shales is also considered. Compilations of the mineralogy and geochemistry of gas shales can be a valuable resource for managing real and perceived environmental problems associated with their exploitation. Comprehensive environmental assessment to fully address these issues, in addition to other potential environmental impacts, will require collection and collation of additional data on the mineralogy and trace element geochemistry of gas and other hydrocarbon producing shales.

Abstract:
Drilling operations in preparation for natural gas extraction from the Marcellus Shale formation generate large amounts of rock cuttings, which return to the surface coated in drilling mud. Solids control is commonly implemented so that the mud can be recycled, but total removal of the cuttings is uneconomical, so any non-reclaimed cuttings are processed to reduce moisture and then deposited in landfills. Laboratory analyses were conducted to characterize two samples of drill cuttings and to present characterization methods that may be relevant in assessing the beneficial reuse potential of drill cuttings. A key aspect of this study was to evaluate several approaches for providing consistent size distribution data. In addition, degradation testing was performed by submitting cuttings to moderate forms of attrition and sonication. Analyses provided particle size distributions, ash values, moisture content, and total organic carbon content of the samples. Materials analyzed included cuttings from the vertical portion of a wellbore mixed with water-based mud as well as Marcellus Shale cuttings from the horizontal portion of the same wellbore, mixed with oil-based mud. It was found that the size distribution of the water-based cuttings was much broader and finer than that of the oil-based cuttings for the samples analyzed in this study. Size degradation by attrition was minimal. Attempts to disperse the material using sonication were successful but lead to significant particle degradation. On a dry basis, the ash values of the water-based cuttings ranged from 94% to 98% by weight compared to 85–89% by weight for the oil-based cuttings. Total organic carbon content of the oil-based cuttings was approximately 10.6%. Additional testing may be required to ensure compliance with applicable regulations for beneficial reuse of the cuttings.

Abstract:
To produce large volumes of newly discovered unconventional gas, hydraulic fracturing of wells is commonly practiced in basins where shale gas and coal bed methane are extracted. Hydraulic fracturing of wells during oil and gas (O&G) exploration consumes large volumes of fresh water and generates larger volumes of contaminated wastewater. In this study, a novel application of forward osmosis (FO) was tested for treatment and reclamation of water from drilling waste to facilitate beneficial water reuse. By using FO, two major benefits were achieved: both the volume of the waste stream and the need for a fresh water source were greatly reduced. Results indicate that FO can achieve high rejection of organic and inorganic contaminants, membrane fouling was reversible, and that the process was able to effectively recover more than 80% of the water from the drilling waste. Osmotic backwashing was demonstrated to be an effective membrane cleaning technique; successfully removing fouling and restoring water flux.

Abstract:
Soil and water (sludge) obtained from reserve pits used in unconventional natural gas mining was analyzed for the presence of technologically enhanced naturally occurring radioactive material (TENORM). Samples were analyzed for total gamma, alpha, and beta radiation, and specific radionuclides: beryllium, potassium, scandium, cobalt, cesium, thallium, lead-210 and -214, bismuth-212 and -214, radium-226 and -228, thorium, uranium, and strontium-89 and -90. Laboratory analysis confirmed elevated beta readings recorded at 1329 ± 311 pCi/g. Specific radionuclides present in an active reserve pit and the soil of a leveled, vacated reserve pit included 232Thorium decay series (228Ra, 228Th, 208Tl), and 226Radium decay series (214Pb, 214Bi, 210Pb) radionuclides. The potential for impact of TENORM to the environment, occupational workers, and the general public is presented with potential health effects of individual radionuclides. Current oversight, exemption of TENORM in federal and state regulations, and complexity in reporting are discussed.

Abstract:
Dramatic increases in the development of oil and natural gas from shale formations will result in large quantities of drill cuttings, flowback water, and produced water. These organic-rich shale gas formations often contain elevated concentrations of naturally occurring radioactive materials (NORM), such as uranium, thorium, and radium. Production of oil and gas from these formations will also lead to the development of technologically enhanced NORM (TENORM) in production equipment. Disposal of these potentially radium-bearing materials in municipal solid waste (MSW) landfills could release radon to the atmosphere. Risk analyses of disposal of radium-bearing TENORM in MSW landfills sponsored by the Department of Energy did not consider the effect of landfill gas (LFG) generation or LFG control systems on radon emissions. Simulation of radon emissions from landfills with LFG generation indicates that LFG generation can significantly increase radon emissions relative to emissions without LFG generation, where the radon emissions are largely controlled by vapor-phase diffusion. Although the operation of LFG control systems at landfills with radon source materials can result in point-source atmospheric radon plumes, the LFG control systems tend to reduce overall radon emissions by reducing advective gas flow through the landfill surface, and increasing the radon residence time in the subsurface, thus allowing more time for radon to decay. In some of the disposal scenarios considered, the radon flux from the landfill and off-site atmospheric activities exceed levels that would be allowed for radon emissions from uranium mill tailings. Implications: Increased development of hydrocarbons from organic-rich shale formations has raised public concern that wastes from these activities containing naturally occurring radioactive materials, particularly radium, may be disposed in municipal solid waste landfills and endanger public health by releasing radon to the atmosphere. This paper analyses the processes by which radon may be emitted from a landfill to the atmosphere. The analyses indicate that landfill gas generation can significantly increase radon emissions, but that the actual level of radon emissions depend on the place of the waste, construction of the landfill cover, and nature of the landfill gas control system.

Abstract:
The Barnett Shale in north central Texas contains natural gas generated by high temperatures (120 to 150 degrees C) during the Mississippian Period (300 to 350 million years ago). In spite of the thermogenic origin of this gas, biogenic sulfide production and microbiologically induced corrosion have been observed at several natural gas wells in this formation. It was hypothesized that microorganisms in drilling muds were responsible for these deleterious effects. Here we collected drilling water and drilling mud samples from seven wells in the Barnett Shale during the drilling process. Using quantitative real-time PCR and microbial enumerations, we show that the addition of mud components to drilling water increased total bacterial numbers, as well as the numbers of culturable aerobic heterotrophs, acid producers, and sulfate reducers. The addition of sterile drilling muds to microcosms that contained drilling water stimulated sulfide production. Pyrosequencing-based phylogenetic surveys of the microbial communities in drilling waters and drilling muds showed a marked transition from typical freshwater communities to less diverse communities dominated by Firmicutes and Gammaproteobacteria. The community shifts observed reflected changes in temperature, pH, oxygen availability, and concentrations of sulfate, sulfonate, and carbon additives associated with the mud formulation process. Finally, several of the phylotypes observed in drilling muds belonged to lineages that were thought to be indigenous to marine and terrestrial fossil fuel formations. Our results suggest a possible alternative exogenous origin of such phylotypes via enrichment and introduction to oil and natural gas reservoirs during the drilling process.