Unconventional Gas Extraction Research Articles

Impact of natural fractures on hydraulic fracture propagation in Denver-Julesburg Basin: Insights from a decade of research

The Denver-Julesburg (DJ) Basin is a key region for unconventional oil and gas extraction, particularly from the Niobrara and Codell formations. This study synthesizes findings from a decade of research conducted in three different geographic areas of the basin as part of the industry consortium Reservoir Characterization Project at Colorado School of Mines. The research explores how natural fractures affect hydraulic fracture propagation, leveraging geophysical data sets including 3D seismic imaging, image logs, microseismic monitoring, and crosswell distributed strain sensing. Key observations reveal significant variations in hydraulic fracture orientations and propagation speeds between the Niobrara and Codell formations, which are the main targets for horizontal drilling and stimulation. High natural fracture densities and orientations notably influence the propagation of hydraulic fractures in the Niobrara Formation, deviating them from the regional maximum horizontal stress (SHmax) directions, while hydraulic fractures in Codell consistently align with SHmax where lower natural fracture densities are observed. The study also highlights the critical role of stress anisotropy and zipper fracturing sequences in dictating hydraulic fracture behavior. Additionally, a marked negative correlation between natural fracture density and hydraulic fracture propagation speed underlines the fracture network complexity added by natural fractures. These findings advocate for a comprehensive natural fracture characterization and tailored fracturing strategies to optimize well placement and completions. The implications for DJ Basin development from this study are profound, suggesting that understanding local geomechanics and fracture networks can significantly enhance hydrocarbon recovery. Future work should focus on more precise assessments of hydraulic fracture interactions with natural fracture systems to refine operational strategies further.

A decadal-scale qualitative comparison of lotic Odonata nymph surveys in northwestern Pennsylvania, USA, reveals possible assemblage restructuring

Detecting long-term changes to Odonata assemblages requires repeated sampling at fixed locations over decadal periods. However, few such biomonitoring efforts exist for Odonata, especially at low taxonomic resolution and immature life stages. We repeated a survey of Odonata nymphs conducted nearly thirty years ago in ten streams from a northern Pennsylvania forest reserve to qualitatively explore assemblage-scale changes and identify streams supporting species of conservation concern. Our survey collected five more species among all sites than the original survey, reflecting a 15% increase in richness despite a reduced sampling effort. Rank abundances of many species changed substantially between surveys. Some, such as Calopteryx maculata, fell in rank while other species like Boyeria vinosa and Phanogomphus lividus that were rare in 1994 became the most numerically dominant. We did not detect patterns in species richness or changes in richness between surveys along gradients of unconventional natural gas extraction or timber harvest among streams. The fraction of species deemed vulnerable or imperiled within Pennsylvania grew from 22 to 38% between surveys, highlighting the regional conservation value of protected area we sampled. Our sampling methodology precludes population estimates or quantitative community comparisons due to the sampling design and inconsistencies in the literature used for identification between surveys. However, the substantial differences in rank-abundance among species between surveys suggests potential long-term changes in these lotic Odonata assemblages. The collective findings presented here emphasize the high value of data from repeated surveys with species-level taxonomic resolution.

Systematic Review of Solubility, Thickening Properties and Mechanisms of Thickener for Supercritical Carbon Dioxide.

Supercritical carbon dioxide (CO2) has extremely important applications in the extraction of unconventional oil and gas, especially in fracturing and enhanced oil recovery (EOR) technologies. It can not only relieve water resource wastage and environmental pollution caused by traditional mining methods, but also effectively store CO2 and mitigate the greenhouse effect. However, the low viscosity nature of supercritical CO2 gives rise to challenges such as viscosity fingering, limited sand-carrying capacity, high filtration loss, low oil and gas recovery efficiency, and potential rock adsorption. To overcome these challenges, low-rock-adsorption thickeners are required to enhance the viscosity of supercritical CO2. Through research into the literature, this article reviews the solubility and thickening characteristics of four types of polymer thickeners, namely surfactants, hydrocarbons, fluorinated polymers, and silicone polymers in supercritical CO2. The thickening mechanisms of polymer thickeners were also analyzed, including intermolecular interactions, LA-LB interactions, hydrogen bonding, and functionalized polymers, and so on.

Investigation of the impact of heating and liquid nitrogen (LN2) cooling on the mechanical and acoustic emission (AE) properties of coal

Liquid nitrogen has emerged as a promising fracturing medium for unconventional natural gas extraction, particularly in the context of coalbed methane extraction, generating significant interest in recent times. In this paper, we analyze the acoustic emission (AE) characteristics of coal samples treated with liquid nitrogen under three-point bending load conditions using indoor experiments and field investigations. We investigate the impact of liquid nitrogen on coal samples by analyzing AE data. The mechanical properties of coal samples with varying initial temperatures were tested under three-point bending load conditions after treatment with liquid nitrogen. The load-displacement curve was analyzed to study the mechanical properties of the coal samples after treatment with liquid nitrogen. Through indoor three-point bending experiments, data analysis, and knowledge of mechanics, we systematically investigated the changes in mechanical properties caused by liquid nitrogen treatment under different conditions. The results demonstrate that the application of liquid nitrogen has significant impacts on the mechanical and AE characteristics of coal samples. The load-displacement curve indicated that the mechanical properties of the coal samples changed after treatment with liquid nitrogen. The AE experiment revealed regular changes in vibration and energy parameters of coal samples after liquid nitrogen treatment under different conditions. We further investigated the changes in mechanical properties and deformation characteristics of coal samples after undergoing liquid nitrogen freezing and thawing in differing environments. Graphs such as load-displacement curves, load-time curves, cumulative vibration count-energy count graphs, and RA-AF density distribution diagrams visually demonstrated the changes in mechanical properties and deformation characteristics. Through an integrated approach of indoor experiments, data analysis, and knowledge of mechanics, our study provides a better understanding of the behavior of coal samples under different conditions. This understanding can contribute to the development of safer and more efficient methods for extracting coalbed methane.

Optimizing unconventional gas extraction: The role of fracture roughness

In unconventional reservoir engineering, such as coalbed methane and shale gas extraction, fracture behavior is pivotal in gas accumulation, migration, and extraction, acting as a primary channel for gas flow. Current research inadequately addresses the quantitative impact of fracture roughness on gas extraction. In this study, we introduce a novel interdisciplinary model that quantitatively characterizes shale fracture roughness and correlates it with shale permeability. This model comprehensively considers factors affecting shale extraction, including fracture roughness, in situ stress, reservoir deformation, and adsorption-desorption dynamics. It provides a thorough analysis of how fracture roughness influences gas seepage, extraction efficiency, and reservoir stability under various physical conditions. Our validated findings reveal that fracture roughness significantly affects shale permeability, stress responses, and displacement. As the fracture roughness coefficient χ increases from 0.2 to 1.0, the maximum reduction in gas pressure within the hydraulically fractured region is 4.7%, while the maximum increase in reservoir stress is 2.8%. In shale reservoirs near extraction well, particularly in hydraulically fractured zones, the maximum decrease in shale gas pressure is 11.1%, and the maximum increase in stress is 3.2%, which offer a groundbreaking approach for optimizing extraction rates and ensuring project safety in the industry.

Whose future, whose security?: Unconventional oil and gas extraction and the economic vulnerability and forced participation of small-scale property owners

Since the ‘shale revolution’ of the late 2000s, unconventional oil and gas extraction (UOGE) has been hailed by many as a boon for local and regional economies, workers, and property owners. While energy social science has documented many realities that counter this narrative – natural resource dependent economies, ‘boom and bust’ cycles of the energy industry, and ‘resource curse’– there is less research examining economic impacts of UOGE for small-scale property owners. While some large-scale property owners lease their land, minerals, or water rights to oil and gas companies in exchange for royalties, other property owners are not able or do not wish to do so. Yet, nearby UOGE may negatively impact property values and thus threaten people's sense of economic stability. Several legal mechanisms – forced pooling, split estate, and rule of capture – significantly restrict the rights of many property owners while privileging other property rights. While property ownership represents a privileged status, it is the largest investment many Americans will make and is relied upon for retirement planning, financial stability, and transfer of generational wealth. Yet, despite the importance of property ownership, particularly home ownership, little is known about how proximity to oil and gas development impacts small-scale property owners. This paper analyzes how UOGE impacts property owners' sense of economic precarity. We conducted surveys of hundreds of affected households and interviews with 66 property owners in two Colorado towns that have experienced heavy UOGE. We find that the current regulatory regimes disempower small-scale property owners, create economic vulnerability, and ultimately privilege property rights of mineral owners and operators over others - creating uncompensated losses for small-scale property owners. We explore important implications, including the need for more responsive and community-based governance processes.

Elucidation of the corrosion rate enhancement mechanism in Mg–Er–Gd–Ni alloys with high volume fraction of LPSO phase and different Gd contents after extrusion

The microstructure evolution and corrosion mechanism of Mg–9Er–xGd–2Ni alloys, subjected to Gd addition and extrusion, were investigated in this study. Results shows that with the increase in Gd content from 1.0 wt.% to 5.0 wt.%, the second phase change from continuous network LPSO phase with intragranular γʹ phase to a monolithic continuous network LPSO phase, while the corresponding volume fraction of the second phase remains essentially unchanged. Moreover, it is noted that increasing Gd content contributed to a reduction in the corrosion rate of alloy by reducing galvanic corrosion couples and facilitating the formation of double Gd2O3 and Er2O3 corrosion-resistant films. Ultimately, what's most noteworthy is that compared with as-cast alloys, the corrosion rate of as-extruded alloys increased by 49.2%–125.3% with increasing Gd content, which is due to the streamlined LPSO phase distribution weakening the corrosion barrier effect of high-volume fraction network distribution LPSO phase alloy and grain refinement providing more corrosion interfaces that inhibited the formation of corrosion-resistant product films. This study provides new provides new insights for the development of highly degradable Mg–Er–Gd–Ni alloys that have high strength potential for applications in unconventional oil and gas extraction.

A Historical Timeline of Unconventional Oil and Gas Extraction and Fracking Studies in South Africa: Pointers for Policy Development

A Historical Timeline of Unconventional Oil and Gas Extraction and Fracking Studies in South Africa: Pointers for Policy Development

Employment and Income Effects of Investments Made Using the Act 13 Unconventional Natural Gas Impact Fee in Pennsylvania

Unconventional natural gas extraction presents numerous opportunities and risks for communities across the United States. To capture a portion of the revenue generated by the resource states tax unconventional natural gas development. While most states collect revenue via severance taxes, Pennsylvania took a novel approach and established an impact fee on the industry instead. Unlike severance taxes in other states, the fee is collected annually and distributed directly to municipalities. While reports show that municipalities use the funds to pay for critical infrastructure, no best practices on how to allocate the funds exist. Citing the literature on mineral resource extraction and infrastructure-led development in American communities, this study examined impact fee payments made to counties with unconventional natural gas wells. The study evaluated whether counties that used the funds to invest in infrastructure were better off in terms of employment and income than other shale-producing counties that did not. Panel fixed- and random-effects regressions suggested that no statistically significant employment or income effects existed. The results suggest that local infrastructural investments are not a successful way to overcome the resource curse issues identified in the literature.

Laboratory study of fracture initiation and propagation in Barre granite under fluid pressure at stress state close to failure

Hydraulic fracturing is frequently used to increase the permeability of rock formations in energy extraction scenarios such as unconventional oil and gas extraction and enhanced geothermal systems (EGSs). The present study addresses uncertainties in the hydraulic fracturing process pertaining to EGSs in crystalline rock such as granite. Specifically, there is debate in the literature on the mechanisms (i.e. tensile and/or shear) by which these fractures initiate, propagate, and coalesce. We present experiments on Barre granite with pre-cut flaws where the material is loaded to high far-field stresses close to shear failure, and then the fluid pressure in the flaws is increased to move the Mohr's circle to the left and observe the initiation and propagation of fractures using high-speed imaging and acoustic emissions (AEs). We find that the hydraulic fractures initiate as tensile microcracks at the flaw tips, and then propagate as a combination of tensile and shear microcracks. AE focal mechanisms also show elevated levels of tensional microfracturing near the flaw tips during pressurization and final failure. We then consider a numerical model of the experimental setup, where we find that fractures are indeed likely to initiate at flaw tips in tension even at relatively high far-field stresses of 40 MPa where shear failure is generally expected.

Be careful what you wish for: Resource boomtowns and disillusionment in the Surat Basin

Communities near resource extraction projects are notoriously prone to boomtown dynamics, and in the Australian context, the boom and bust cycles have shaped the nation's economic history. Australia is the seventh largest gas producer in the world, with production escalating after the establishment of onshore unconventional gas extraction in the early 2000′s. This paper examines the rapid development of onshore unconventional gas extraction, specifically coal seam gas, in the Surat Basin of Queensland, which is also the location of long-established and highly valued agricultural industries. The impact of neoliberal economic principles and public policies, broadly imposed from the early 1980s, caused many services to be rationalised across the region and smaller communities. A new industry, promising industry diversification, alternative employment and royalties, was promoted by the Queensland government and the gas companies in 2005. Very quickly however, tensions between the gas companies and the agricultural industry regarding secretive agreements, land use conflict and lack of consultation developed into blockades, protests and antagonism. Towns were also impacted with an escalation in land prices and competition for labour. Many residents of the Surat believed the government had been greedy in its haste to provide approvals with an eye to lucrative royalties, with little consideration for their welfare or their livelihoods. Resource economies throughout the world are replete with examples of this scenario. This paper documents the conflicts and the subsequent measures undertaken by government and the gas companies to appease the residents of the Surat, all of which took considerable time and expense. If more considered consultation and understanding had been developed prior to the first approvals being granted, this could have been avoided. This paper is timely, given that the Queensland has once again granted exploration licenses in the highly sensitive western Channel country without consultation or consideration, causing angst and uncertainty.

A dissolvable Mg-Gd-Y-Zn-Cu alloy possessing the highest yield strength for the fabrication of fracturing plugging tools

Developing high-strength dissolvable magnesium alloys is always a pursuing goal for the fracturing plugging tools working in extremely unconventional oil and gas extraction. Herein, we reported a dissolvable Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu (wt.%) alloy with the highest yield strength reported so far, i.e. a tensile yield strength (TYS) of 434.9 MPa, compressive yield strength (CYS) of 478.1 MPa. High yield strength was derived from the composite effect of fine dynamic recrystallized (DRXed) grains caused by block long-period stacking ordered (LPSO) phase, LPSO phase with different morphologies, dense β’ precipitates. Moreover, this alloy attains a decent corrosion rate of 786.2 mm/y at 93 °C in 3 wt% KCl solutions, which mainly is attributed to the galvanic corrosion between the LPSO phase and the Mg matrix. This work provides an approving material selection for the fabrication of dissolvable fracturing tools used in the deep oil and gas well.

MULTIFRACTAL MODELING OF GAS–WATER RELATIVE PERMEABILITY CONSIDERING MULTISCALE AND MULTIEFFECTS: INVESTIGATION OF UNCONVENTIONAL GAS DEVELOPMENT

Unconventional gas is a momentous energy source due to its considerable reserves and eco-friendly properties, where relative permeability is a key evaluative parameter of unconventional gas extraction. However, the geo-complexity, multiscale and multieffect of the unconventional gas reservoir challenge the relative permeability evaluation and production enhancement. Here, we establish a gas–water flow model by integrating multifractal theory, covering from nanoscale to macroscale and regarding the effects of slip, gas desorption–diffusion and water film separation, to reliably evaluate the relative permeability evolution during unconventional gas development. Based on our model, we describe the permeability of the unconventional reservoir with an 88% less evaluation error compared to the single fractal Darcy with the literature benchmark. Moreover, we characterize the gas–water relative permeability with a no more than 10% evaluation error based on the experimental data. The slip effect plays the most crucial role in the evaluation precision of relative permeability. We reveal that the permeability of the unconventional gas reservoir is decreased by the increase of generalized fractal dimension which enhances the heterogeneity and tortuosity of pores. We uncover that the slip effect facilitates the relative permeability of gas and water. Besides, the gas desorption–diffusion boosts gas relative permeability while limiting water relative permeability, whereas water film separation enhances water relative permeability but hinders gas relative permeability. This work brings insights into the precise description of multiscale and multieffect gas–water porous flow in unconventional gas development.

Quantitative characterization of the pore volume fractal dimensions for three kinds of liquid nitrogen frozen coal and its enlightenment to coalbed methane exploitation

Liquid nitrogen fracturing technology is an important means to improve the permeability of coal seams and realize unconventional natural gas extraction. In order to study the fractal characteristics of pore structure of coal frozen by liquid nitrogen, the pores of both nonfrozen and frozen samples of lignite, bituminous coal, and anthracite were measured with a high-pressure adsorption meter, a mercury porosimeter, and a low-field nuclear magnetic resonance (NMR). The test results showed that after freezing in liquid nitrogen, the pores of coal were effectively expanded. Among them, Nitrogen adsorption of lignite, bituminous coal and anthracite increased by 20.82%, 6.54% and 20.39%. The conversion rates from adsorption pore to seepage pore were 2.16%, 0.78% and 3.57%. The research results of pore fractal dimension showed that the multifractal characteristics of macropores were higher than that of mesopores and micropores. After liquid nitrogen freezing, the pore fractal dimension of lignite, bituminous coal and anthracite decreased by 0.031, 0.009 and 0.003, and the pore structure tends to be smooth. It showed the liquid nitrogen freezing coal enhances the migration and drainage of coalbed methane, which has reference significance for the further research of liquid nitrogen fracturing technology.

A mobile application to protect groundwater during unconventional oil and gas extraction.

Unconventional oil and gas (UOG) is an important energy source for many countries, but requires large quantities of water for its development, and may pollute water resources. Regulations are one of the main tools to achieve government policy on natural resource protection. South Africa, which is energy-constrained, but also water-scarce, is currently considering UOG extraction as an additional energy resource. UOG development could commence as soon as regulations to protect natural resources such as water have been published. Such regulations are, however, often not effectively enforced, which negatively affects the protection of water resources during UOG extraction. This study addresses these enforcement challenges in South Africa. It focuses on the science–society–policy interface by proposing a civic informatics platform to assist with on-the-ground enforcement of regulations via a mobile application. This mobile application aims to address both groundwater monitoring and management as well as UOG extraction operations in a single platform, to enable regulators to protect groundwater resources more effectively during UOG extraction, while simultaneously enhancing transparency in the UOG industry.

Modelling the impact of coal seam methane on the Mongolian economy

Energy independence is one of the most important issues for almost every country and the world. Mongolia strives to have various types of energy sources and reduce energy dependence. Energy dependence always influences economic dependence of any country. Utilising its own country’s resources is optimal to reduce energy dependence. In recent years, the Mongolian Government has been encouraging unconventional oil and gas exploration and foreign investment and implementing supporting policies, such as coal bed (seam) methane. As a result of these activities, unconventional oil and gas investment and exploration have been intensified in the last few years in Mongolia, especially during pandemics. There are 32 oil and gas blocks in Mongolia and coal bed methane exploration and foreign investments have been invested in eight blocks. In 2022, some foreign investment companies are going to introduce proven reserves of coal bed methane to the Mongolian Government and Parliament. Therefore, we have to model the positive and negative impacts of coal bed methane on the Mongolian economy and find methods to increase the positive sides. Unfortunately, there is no experience in any situation for unconventional oil and gas exploration, extraction, and field development. Because of it, we have cooperated with Australian scientists and experts and completed some studies for making a model of the impact of coal seam methane on the Mongolian economy. For today’s condition, the Mongolian Government or Mongolian private companies can’t process coal bed methane activities because of lack of capital expenses and experience. To raise the positive impacts of coal bed methane, foreign investment is of course very important. There are some main purposes to model the impact of coal seam methane on the Mongolian economy.

The Effect of Bedding Plane Angle on Hydraulic Fracture Propagation in Mineral Heterogeneity Model

The bedding planes of unconventional oil and gas reservoirs are relatively well developed. Bedding planes directly interfere with hydraulic fracture expansion. Determining how bedding planes influence hydraulic fractures is key for understanding the formation and evolution of hydraulic fracturing networks. After conducting X-ray diffraction analysis of shale, we used Python programming to establish a numerical model of mineral heterogeneity with a 0-thickness cohesive element and a bedding plane that was globally embedded. The influence of the bedding-plane angle on hydraulic fracture propagation was studied. Acoustic emission (AE) data were simulated using MATLAB programming to study fracture propagation in detail. The numerical simulation and AE data showed that the propagation paths of hydraulic fractures were determined by the maximum principal stress and bedding plane. Clearer bedding effects were observed with smaller angles between the bedding surface and the maximum principal stress. However, the bedding effect led to continuous bedding slip fractures, which is not conducive to forming a complex fracture network. At moderate bedding plane angles, cross-layer and bedding fractures alternately appeared, characteristic of intermittent dislocation fracture and a complex fracture network. During hydraulic fracturing, tensile fractures represented the dominant fracture type and manifested in cross-layer fractures. We observed large fracture widths, which are conducive to proppant migration and filling. However, the shear fractures mostly manifested as bedding slip fractures with small fracture widths. Combining the fracture-network, AE, and fractal dimension data showed that a complex fracture network was most readily generated when the angle between the bedding plane and the maximum principal stress was 30°. The numerical simulation results provide important technical information for fracturing construction, which should support the efficient extraction of unconventional tight oil and gas.

Geochemistry and Multiomics Data Differentiate Streams in Pennsylvania Based on Unconventional Oil and Gas Activity.

ABSTRACTUnconventional oil and gas (UOG) extraction is increasing exponentially around the world, as new technological advances have provided cost-effective methods to extract hard-to-reach hydrocarbons. While UOG has increased the energy output of some countries, past research indicates potential impacts in nearby stream ecosystems as measured by geochemical and microbial markers. Here, we utilized a robust data set that combines 16S rRNA gene amplicon sequencing (DNA), metatranscriptomics (RNA), geochemistry, and trace element analyses to establish the impact of UOG activity in 21 sites in northern Pennsylvania. These data were also used to design predictive machine learning models to determine the UOG impact on streams. We identified multiple biomarkers of UOG activity and contributors of antimicrobial resistance within the order Burkholderiales. Furthermore, we identified expressed antimicrobial resistance genes, land coverage, geochemistry, and specific microbes as strong predictors of UOG status. Of the predictive models constructed (n = 30), 15 had accuracies higher than expected by chance and area under the curve values above 0.70. The supervised random forest models with the highest accuracy were constructed with 16S rRNA gene profiles, metatranscriptomics active microbial composition, metatranscriptomics active antimicrobial resistance genes, land coverage, and geochemistry (n = 23). The models identified the most important features within those data sets for classifying UOG status. These findings identified specific shifts in gene presence and expression, as well as geochemical measures, that can be used to build robust models to identify impacts of UOG development.IMPORTANCE The environmental implications of unconventional oil and gas extraction are only recently starting to be systematically recorded. Our research shows the utility of microbial communities paired with geochemical markers to build strong predictive random forest models of unconventional oil and gas activity and the identification of key biomarkers. Microbial communities, their transcribed genes, and key biomarkers can be used as sentinels of environmental changes. Slight changes in microbial function and composition can be detected before chemical markers of contamination. Potential contamination, specifically from biocides, is especially concerning due to its potential to promote antibiotic resistance in the environment. Additionally, as microbial communities facilitate the bulk of nutrient cycling in the environment, small changes may have long-term repercussions. Supervised random forest models can be used to identify changes in those communities, greatly enhance our understanding of what such impacts entail, and inform environmental management decisions.

Sorption, degradation and microbial toxicity of chemicals associated with hydraulic fracturing fluid and produced water in soils

Spills of hydraulic fracturing (HF) fluids and of produced water during unconventional gas extraction operations may cause soil contamination. We studied the degradation and microbial toxicity of selected HF chemical components including two biocides (methylisothiozolinone- MIT, chloromethylisothiozolinone- CMIT), a gel-breaker aid (triethanolamine -TEA), and three geogenic chemicals (phenol, m-cresol and p-cresol) in ultrapure water, HF fluid and produced water in five different soil types (surface and subsurface soils). The degradation of the two biocides (in soils treated with HF fluid or ultrapure water) and of the three geogenic chemicals (in soils treated with produced water) was rapid (in all cases DT50 values < 2 days in surface soils). In contrast, the loss of TEA was much slower in soils, especially in those treated with HF fluid (DT50 > 30 days). Sorption coefficients (Koc in L/Kg) in these soils ranged from 71 to 733 for TEA, 64–408 for MIT and 11–72 for CMIT. In terms of soil microbial toxicity, exposure to HF fluid and produced water reduced microbial respiration, albeit temporarily. The overall microbial activities in surface soils contaminated with produced water had fully recovered in most soils. In contrast, the HF fluid addition to soils completely inhibited the nitrification in all soils, with little recovery over the 60 day experimental period. In the case of produced water exposure, three out of five surface soils showed complete recovery in nitrification during the study period. The functional genes for nitrogen fixation (nifH) and carbon cycling (GA1) and microbial community composition (16 S rRNA) were significantly affected by HF fluid in some soils. Overall, the study shows that the HF fluid can have significant detrimental impact on soil microbial functions, especially on nitrogen cycling. More work is needed to identify the exact cause of microbial toxicity in soils contaminated with HF fluid.

Analysis of Regulatory Framework for Produced Water Management and Reuse in Major Oil- and Gas-Producing Regions in the United States

The rapid development of unconventional oil and gas (O&amp;G) extraction around the world produces a significant amount of wastewater that requires appropriate management and disposal. Produced water (PW) is primarily disposed of through saltwater disposal wells, and other reuse/disposal methods include using PW for hydraulic fracturing, enhanced oil recovery, well drilling, evaporation ponds or seepage pits within the O&amp;G field, and transferring PW offsite for management or reuse. Currently, 1–2% of PW in the U.S. is used outside the O&amp;G field after treatment. With the considerable interest in PW reuse to reduce environmental implications and alleviate regional water scarcity, it is imperative to analyze the current regulatory framework for PW management and reuse. In the U.S., PW is subject to a complex set of federal, state, and sometimes local regulations to address the wide range of PW management, construction, and operation practices. Under the supervision of the U.S. Environment Protection Agency (U.S. EPA), different states have their own regulatory agencies and requirements based on state-specific practices and laws. This study analyzed the regulatory framework in major O&amp;G-producing regions surrounding the management of PW, including relevant laws and jurisdictional illustrations of water rules and responsibilities, water quality standards, and PW disposal and current/potential beneficial reuse up to early 2022. The selected eastern states (based on the 98th meridian designated by the U.S. EPA as a tool to separate discharge permitting) include the Appalachian Basin (Marcellus and Utica shale areas of Pennsylvania, Ohio, and West Virginia), Oklahoma, and Texas; and the western states include California, Colorado, New Mexico, and Wyoming. These regions represent different regulations; climates; water quantities; quality diversities; and geologic, geographic, and hydrologic conditions. This review is particularly focused on the water quality standards, reuse practices and scenarios, risks assessment, knowledge gaps, and research needs for the potential reuse of treated PW outside of O&amp;G fields. Given the complexity surrounding PW regulations and rules, this study is intended as preliminary guidance for PW management, and for identifying the knowledge gaps and research needs to reduce the potential impacts of treated PW reuse on the environment and public health. The regulations and experiences learned from these case studies would significantly benefit other states and countries with O&amp;G sources for the protection of their environment and public health.