Unconventional Gas Extraction Research Articles

“We have the right to be arrested and processed according to law”: The Power of Effective Police Liaison at the Bentley Blockade

ABSTRACT For social movements engaged in protests, effective engagement with police can be particularly important in ensuring political success and overall safety. However, the way in which police are often determined to maintain control of public order in protest situations raises significant questions for protest movements about the limits and value of negotiation. Inherent contradictions remain between the aims of protestors engaged in disruptive campaigns and the police officers sent to contain them. I examine these contradictions here in relation to the Bentley blockade, a successful mass social movement campaign against the unconventional gas extraction industry in northeast New South Wales. Using a participant-observer approach and drawing on a range of primary source material including government briefing papers, media reports and interviews with police and protestors, this article examines the nature and effectiveness of the liaison process in what was a very large-scale and significant public order challenge for police.

Quantifying source contributions of volatile organic compounds under hydraulic fracking moratorium

Volatile organic compounds (VOCs) are precursors for ozone (O3) and secondary particulate matter, which contribute to asthma and cardiovascular diseases. With the technology development of hydraulic fracking, the United States experienced a shale gas boom in the last decade while the public raised concerns about the potential health impacts of co-emitted VOCs and other airborne pollutants. National Energy Technology Laboratory conducted stationary trailer-based ambient monitoring to study the sources of VOCs in Maryland, where the state enacted a moratorium on unconventional natural gas extraction. The campaign had two periods, May to August 2014 (summer) and November 2014 to February 2015 (winter). Ethane was the most abundant VOC, averaging 12.3 ppb (SD = 15.7 ppb) in summer and 21.7 ppb (SD = 21.6 ppb) in winter. The seasonal variation of VOCs indicated different source strengths. The sampling region was in the nitrogen oxides (NOx) limited regime for O3 production, and the O3 concentrations were sensitive to VOC/NOx ratios in the early mornings. We derived a six-factor profile using positive matrix factorization: motor vehicles, industrial, biogenics, coal burning, fugitive and evaporative, and ozone secondary. The fugitive and evaporative factor explained 44.5% of total VOCs, and the motor vehicles factor followed second with 15.5%. Oil and gas activities had a considerable impact on the abundance of VOCs in this region.

Sulfate precipitation in produced water from Marcellus Shale for the control of naturally occurring radioactive material

Produced water (PW) generated during unconventional oil and gas extraction is characterized by very high total dissolved solids (TDS) that mainly consist of alkali and alkaline earth metals. Dominant PW management strategy (i.e., injection in Class II disposal wells) is scrutinized by regulatory agencies, and the public and PW treatment that enables high water and salt recovery (i.e., evaporation/crystallization) is being considered as an alternative. Produced water generated in the Marcellus Shale play also contains very high levels of Naturally Occurring Radioactive Material (NORM) in the form of Ra-226 and Ra-228, which is one of the key impediments for the recovery of high-quality salts. This study was designed to evaluate the efficiency of Ra-226 removal using co- and post-precipitation with barium sulfate to enable advanced PW treatment processes. High Sr/Ba molar ratios in PW lead to relatively low Ba2+ and Ra2+ removal, and Ba2+ concentration adjustment is necessary to achieve required treatment standards (i.e., [Ba2+] < 10 mg/L and [Ra2+] < 50 pCi/L). Seeding the reactor with barium sulfate enhanced Ba2+ and Ra2+ removal through induced heterogeneous precipitation of barite. However, it was necessary to simultaneously adjust the Sr/Ba ratio and barite level to achieve treatment requirements while maintaining reasonable detention time in the reactor (i.e., <30 min) and minimizing sludge production. Experimental and modeling results revealed that low Ba2+ and Ra2+ effluent concentrations, with minimized sludge production, can be achieved only when the barium sulfate saturation index was above 4.7, Sr/Ba molar ratio was below 2 and there was at least 25 g/L of barite “seed” in the system. This study provides useful guidelines for centralized wastewater treatment facilities in shale plays and serves to optimize pretreatment of produced water to enable recovery of valuable resources (i.e., clean water and usable salts).

Optimization of thin film solid phase microextraction and data deconvolution methods for accurate characterization of organic compounds in produced water.

The continued rise in the extraction of unconventional oil and gas across the globe poses many questions about how to manage these relatively new waste-streams. Produced water, the primary waste by-product, contains a diverse number of anthropogenic additives together with the numerous hydrocarbons extracted from the well. Due to potential environmental hazards, it is critical to characterize the chemical composition of this type of waste before properdisposalor remediation/reuse. In this work, a thin film solid phase microextraction approach was developed and optimized to characterize produced water. The thin film device consisted of hydrophilic-lipophilic balance particles embedded in polydimethylsiloxane and immobilized on a carbon mesh surface. These devices were chosen to provide broad extraction coverage and high reusability. Various parameters were evaluated to ensure reproducible results while minimizing analyte loss. This optimized protocol, consisting of a 15min extraction followed by a short (3 s) rinsing step, enabled the reproducible analysis of produced water without any sample pretreatment. Extraction efficiency was suitable for both produced water additives and hydrocarbons. The developed approach was able to tentatively identify a total of 201 compounds from produced water samples, by using one-dimensional gas chromatography hyphenated to mass spectrometry and data deconvolution.

In Our Backyard: Perceptions About Fracking, Science, and Health by Community Members

Unconventional oil and gas (UOG) extraction (fracking) has increased in the United States, as well as interest in the associated risks and benefits. This study’s purpose was to qualitatively examine residents’ perceptions about UOG development in their community. Fifteen interviewees involving residents of Garfield County, Colorado, a drilling-dense region, were transcribed and analyzed. The study found six themes: (1) health concerns, both human and animal, (2) power struggles between government and industry/between industry and residents, and (3) perception and some acceptance of increased risk. Less common themes were (4) reliance on science to accurately determine risk, (5) frustration with potential threat and loss of power, and (6) traffic and safety concerns. Community perceptions of UOG development are complex, and understanding the position of community members can support the need for additional public health research and impact assessments regarding community exposures from UOG drilling operation exposures.

Application of isotopic and geochemical signals in unconventional oil and gas reservoir produced waters toward characterizing in situ geochemical fluid-shale reactions

Optimizing hydrocarbon production and waste management from unconventional oil and gas extraction requires an understanding of the fluid-rock chemical interactions. These reactions can affect flow pathways within fractured shale and produced water chemistry. Knowledge of these chemical reactions also provides valuable information for planning wastewater treatment strategies. This study focused on characterizing reservoir reactions through analysis of produced water chemistry from the Marcellus Shale Energy and Environmental Laboratory field site in Morgantown, WV, USA. Analysis of fracturing fluids, time-series produced waters (PW) over 16 months of operation of two hydraulically fractured gas wells, and shale rocks from the same well for metal concentrations and multiple isotope signatures (δ2H and δ18O of water, δ7Li, δ11B, 87Sr/86Sr) showed that the chemical and isotopic composition of early (<10 days) PW samples record water-rock interactions during the fracturing period. Acidic dissolution of carbonate minerals was evidenced by the increase in TOC, B/Na, Sr/Na, Ca/Na, and the decrease in 87Sr/86Sr in PW returning in the first few days toward the 87Sr/86Sr signature of carbonate cement. The enrichment of 6Li in these early (e.g., day 1) PW samples is most likely a result of desorption of Li from clays and organic matter due to the injection of fracturing fluid. Redox-active trace elements appear to be controlled by oxidation-reduction reactions and potentially reactions involving wellbore steel. Overall, PW chemistry is primarily controlled by mixing between early PW with local in-situ formation water however certain geochemical reactions (e.g., carbonate cement dissolution and desorption of 6Li from clays and organic matter) can be inferred from PW composition monitored immediately over the first ten days of water return.

Quantifying atmospheric reactive nitrogen concentrations, dry deposition, and isotope dynamics surrounding a Marcellus Shale well pad

Unconventional natural gas (UNG) extraction activities have become important contributors to regional NOx emissions inventories. Currently, there is a knowledge gap in the amount of total N deposition surrounding well pads undergoing UNG extraction despite the fact that some areas with extensive natural gas extraction activity are already in exceedance of nitrogen critical loads. In this study, we measured the magnitude of total dry N deposition from NO2, HNO3, and NH3 attributable to the development of two UNG wells at a Marcellus Shale well pad study site. This study documents concentrations, deposition fluxes, and isotope values of NO2, HNO3, O3, and NH3 up- and down-wind along a 750-m well pad passive sampling transect across a 16-acre well pad containing two unconventional wells during all phases of development and extraction comprising fifteen distinct sampling periods. An access road transect was also utilized to explore reactive N dynamics in a near-road environment on the well pad where NO2 concentration and isotope dynamics were highly correlated with daily traffic count (r2 = 0.78–0.88, p < 0.01). An onsite chemiluminescent NO2 source apportionment model was compared against δ15N–NO2 and δ18O–NO2 source apportionment models (r2 = 0.57 and 0.82 respectively), demonstrating the possible utility of δ18O–NO2 as a source apportionment tool in near-source environments. In addition, the δ15N–NO2 source apportionment method compared well against a background-subtraction method (slope = 0.82, r2 = 0.88, p < 0.001) during non-wintertime conditions and was used to find N loadings directly attributable to well pad activities. In total, the total N deposition across the transect, attributable to well pad activities, utilizing industry's best management practices, ranged from 0.16 to 0.55 kg N ha−1 yr−1. This magnitude of well pad attributable N deposition is high enough to result in exceedances of nitrogen critical loads in areas with high well count densities and high baseline N deposition.

Quantification of the water-use reduction associated with the transition from coal to natural gas in the US electricity sector

The transition from coal to natural gas and renewables in the electricity sector and the rise of unconventional shale gas extraction are likely to affect water usage throughout the US. While new natural-gas power plants use less water than coal-fired power plants, shale gas extraction through hydraulic fracturing has increased water utilization and intensity. We integrated water and energy use data to quantify the intensity of water use in the US throughout the electricity’s lifecycle. We show that in spite of the rise of water use for hydraulic fracturing, during 2013–2016 the overall annual water withdrawal (8.74 × 1010 m3) and consumption (1.75 × 109 m3) for coal were larger than those of natural gas (4.55 × 1010 m3, and 1.07 × 109 m3, respectively). We find that during this period, for every MWh of electricity that has been generated with natural gas instead of coal, there has been a reduction of ∼1 m3 in water consumption and ∼40 m3 in water withdrawal. Examining plant locations spatially, we find that only a small proportion of net electricity generation takes place in water stressed areas, while a large proportion of both coal (37%) and natural gas (50%) are extracted in water stressed areas. We also show that the growing contribution of renewable energy technologies such as wind and solar will reduce water consumption at an even greater magnitude than the transition from coal to natural gas, eliminating much of water withdrawals and consumption for electricity generation in the US.

Environmental baseline monitoring for shale gas development in the UK: Identification and geochemical characterisation of local source emissions of methane to atmosphere

Baseline mobile surveys of methane sources using vehicle-mounted instruments have been performed in the Fylde and Ryedale regions of Northern England over the 2016–19 period around proposed unconventional (shale) gas extraction sites. The aim was to identify and characterise methane sources ahead of hydraulically fractured shale gas extraction in the area around drilling sites. This allows a potential additional source of emissions to atmosphere to be readily distinguished from adjacent sources, should gas production take place.The surveys have used ethane:methane (C2:C1) ratios to separate combustion, thermogenic gas and biogenic sources. Sample collection of source plumes followed by high precision δ13C analysis of methane, to separate and isotopically characterise sources, adds additional biogenic source distinction between active and closed landfills, and ruminant eructations from manure.The surveys show that both drill sites and adjacent fixed monitoring sites have cow barns and gas network pipeline leaks as sources of methane within a 1 km range. These two sources are readily separated by isotopes (δ13C of −67 to −58‰ for barns, compared to −43 to −39‰ for gas leaks), and ethane:methane ratios (<0.001 for barns, compared to >0.05 for gas leaks). Under a well-mixed daytime atmospheric boundary layer these sources are generally detectable as above baseline elevations up to 100 m downwind for gas leaks and up to 500 m downwind for populated cow barns. It is considered that careful analysis of these proxies for unconventional production gas, if and when available, will allow any fugitive emissions from operations to be distinguished from surrounding sources.

Surface Water Microbial Community Response to the Biocide 2,2-Dibromo-3-Nitrilopropionamide, Used in Unconventional Oil and Gas Extraction

Production of unconventional oil and gas continues to rise, but the effects of high-density hydraulic fracturing (HF) activity near aquatic ecosystems are not fully understood. A commonly used biocide in HF, 2,2-dibromo-3-nitrilopropionamide (DBNPA), was studied in microcosms of HF-impacted (HF+) versus HF-unimpacted (HF-) surface water streams to (i) compare the microbial community response, (ii) investigate DBNPA degradation products based on past HF exposure, and (iii) compare the microbial community response differences and similarities between the HF biocides DBNPA and glutaraldehyde. The microbial community responded to DBNPA differently in HF-impacted versus HF-unimpacted microcosms in terms of the number of 16S rRNA gene copies quantified, alpha and beta diversity, and differential abundance analyses of microbial community composition through time. The differences in microbial community changes affected degradation dynamics. HF-impacted microbial communities were more sensitive to DBNPA, causing the biocide and by-products of the degradation to persist for longer than in HF-unimpacted microcosms. A total of 17 DBNPA by-products were detected, many of them not widely known as DBNPA by-products. Many of the brominated by-products detected that are believed to be uncharacterized may pose environmental and health impacts. Similar taxa were able to tolerate glutaraldehyde and DBNPA; however, DBNPA was not as effective for microbial control, as indicated by a smaller overall decrease of 16S rRNA gene copies/ml after exposure to the biocide, and a more diverse set of taxa was able to tolerate it. These findings suggest that past HF activity in streams can affect the microbial community response to environmental perturbation such as that caused by the biocide DBNPA.IMPORTANCE Unconventional oil and gas activity can affect pH, total organic carbon, and microbial communities in surface water, altering their ability to respond to new environmental and/or anthropogenic perturbations. These findings demonstrate that 2,2-dibromo-3-nitrilopropionamide (DBNPA), a common hydraulic fracturing (HF) biocide, affects microbial communities differently as a consequence of past HF exposure, persisting longer in HF-impacted (HF+) waters. These findings also demonstrate that DBNPA has low efficacy in environmental microbial communities regardless of HF impact. These findings are of interest, as understanding microbial responses is key for formulating remediation strategies in unconventional oil and gas (UOG)-impacted environments. Moreover, some DBNPA degradation by-products are even more toxic and recalcitrant than DBNPA itself, and this work identifies novel brominated degradation by-products formed.

Determining conventional and unconventional oil and gas well brines in natural samples I: Anion analysis with ion chromatography

Unconventional natural gas extraction by hydraulic fracturing requires millions of gallons of water and generates flowback water, produced water and recycled fluids of varying chemical composition. Ion chromatography (IC) is a relatively low cost and efficient means to determine the anionic composition, however, the wide range in anionic content of these fluids poses a challenge to analytical methods developed for “natural” waters. We report here that the combination of UV and conductivity detectors increased detection sensitivity (e.g., 10–50 ppb) and expanded the number of anions detectable in a single sample run. Samples from four unconventional shale gas wells, two impoundments, nine conventional oil wells, two freshwater streams and mine drainage samples were analyzed in this study. All produced water samples and impoundment samples had high chloride (17,500–103,000 mg L−1, 93,900 to 134,000 mg L−1, 27,700 and 30,700 mg L−1), bromide (178–996 mg L−1, 183–439 mg L−1, 230 and 260 mg L−1) and conductivity (38,500–160,000 μS/cm3, 95,300 to 183,000 μS/cm3, 61,500 and 103,000 μS/cm3), respectively, relative to mine drainage and freshwater stream samples. Molar ratio analysis using Cl−/Br− to Cl− and SO42−/Cl− to Br− revealed significant differences between the samples, providing a simple means for distinguishing water impacted by different sources of contamination.

Regulations to protect groundwater resources during unconventional oil and gas extraction using fracking

AbstractUnconventional oil and gas (UOG) extraction using fracking can damage groundwater resources, a crucial resource in many countries. Protecting groundwater will become more urgent as climate change and population growth increase pressure on water demand, especially in water‐scarce countries. But despite the strategic importance of groundwater, it is often poorly managed during UOG extraction. This review considers three types of regulation (command‐and‐control, market‐based and voluntary) in countries where UOG extraction is allowed, to identify the best suite of regulations to protect groundwater resources during this process. We propose a regulatory framework that includes both “hard” command‐and‐control regulations and “soft” market‐based and voluntary regulations. If regulations are to protect groundwater resources effectively, public disclosure of UOG operations must be required and the information must be stored in publicly accessible databases. This would allow for independent scientific review of data by academia and the private sector, in addition to government scrutiny of the data. These parties can then make recommendations to government, allowing timeous and appropriate adaptive management and the amendment of regulations as necessary. And, most importantly, these regulations must be properly enforced to avoid (in some cases irreversible) damage to groundwater resources.This article is characterized under: Engineering Water &gt; Sustainable Engineering of Water Human Water &gt; Water Governance Science of Water &gt; Water Quality

Zwitterion-Modified Ultrafiltration Membranes for Permian Basin Produced Water Pretreatment

Unconventional oil and gas extraction generates large quantities of produced water (PW). Due to strict environmental regulations, it is important to recover and reuse PW. In this study, commercial polyethersulfone (PES) ultrafiltration (UF) membranes were surface-modified with zwitterionic polymer 3-(3,4-Dihydroxyphenyl)-l-alanine (l-DOPA) solution to alleviate membrane fouling during the ultrafiltration of shale oil PW of the Permian Basin. UF membranes were coated in l-DOPA solution by using a dip coating technique. Membrane characterization tests confirmed successful l-DOPA coating on UF membranes. While performing the experiments, permeate flux behaviors of the uncoated and coated membranes and antifouling resistance of the zwitterionic coating were evaluated. Among the coated UF membranes with varying coating times from one day to three days, the three-day coated UF membrane showed a good flux performance and the highest fouling resistance. The flux reduced by 38.4% for the uncoated membrane, while the reduction was 16% for the three-day coated membrane after the 5 h ultrafiltration of PW. Both improvements of the flux performance and recovery ratio are attributed to a negatively-charged surface developed on the membranes after the zwitterionic coating. The UF pretreatment also improved the flux behavior of the later forward osmosis (FO) process for PW treatment.

Alkali earth ratios differentiate conventional and unconventional hydrocarbon brine contamination

The large increase in unconventional shale gas extraction has raised concerns about potential water contamination from leaks and spills. Shale gas produced water is challenging to detect in areas impacted by legacy contamination, particularly from conventional sources. Previous studies have proposed combinations of Br, SO4, Ba, Cl, and other more specialized stable isotope systems to delineate shale gas produced water from 1) non-impacted waters and 2) other sources of water contamination. In general, the efforts that rely on relatively simple chemistry do not allow differentiation between conventional and unconventional brine chemistry. We examined variations in Ca/Mg and Ca/Sr ratios that seem to arise from variation in temperature with depth, to differentiate among conventional brines, unconventional brines, and non-impacted waters. This approach was applied to four sedimentary basins in the USGS produced water database: Williston, Michigan, Appalachian, and the Green River basin. In addition, the utility of the system was demonstrated with field samples taken during periods of known unconventional brine releases to surface waters. The Ca/Mg and Ca/Sr ratios allow distinction among these three water types in all basins, suggesting a relatively simple and direct way to evaluate water chemistries in landscapes dominated by unconventional shale gas extraction.

Effective CH4 enrichment from N2 by SIM-1 via a strong adsorption potential SOD cage

Methane enrichment from nitrogen is a necessary means for low-quality unconventional natural gas (coal mine methane) extraction, where adsorption-separation technology has become a research hotspot due to its low energy consumption and cost-effectiveness. In this work, three SOD-type ZIFs (ZIF-8, ZIF-90 and SIM-1, the latter also known as ZIF-94) are taken as methane sorbents for CH4/N2 separation. The experimental results show that SIM-1 (ZIF-94) has the highest CH4 adsorption capacity (1.5 mmol/g, 298 K and 1 bar) and adsorption heat (23.9 kJ/mol), although its surface area is the lowest (597 m2/g). No other known ZIF material has a higher CH4 adsorption capacity than SIM-1(ZIF-94), although some rare MOF and other porous materials can achieve such a high value. By comparing its CH4 adsorption capacity and BET surface with ZIF-93 (RHO type), which has the same units as Zn-almeIm, SIM-1(ZIF-94) has a high adsorption capacity of CH4 due to its suitable SOD cage size (0.84 nm) acting as a strong adsorption potential. Indeed, excellent enrichment–separation of the CH4/N2 mixture (30:70 and 50:50, v/v) with a high adsorption selectivity of 7.0 (IAST) rarely occurs for sorbents at room temperature and ambient pressure. Both the experimental and simulated data of the gas mixtures indicate that SIM-1 (ZIF-94) has excellent capability for enriching and removing nitrogen from methane, and it shows extraordinary industrial value.

Comparison of the degree of fouling at various flux rates and modes of operation using forward osmosis for remediation of produced water from unconventional oil and gas development

Driven by increased energy demands and technological advancements, the energy landscape of the United States has been changed by the expansion of unconventional oil and gas extraction. Unconventional development requires well stimulation, which uses millions of gallons of water per well and generates billions of gallons of wastewater annually. The waste matrix, referred to as produced water, has proven to be challenging to treat due to the complex physical, chemical, and biological composition, which can change over the lifetime of a production well. Here, forward osmosis was used as a remediation technique to extract fresh water from produced water procured from the Permian Basin region of west Texas. These data examine the durability of thin-film hollow-fiber membranes by determining how quickly the membranes irreversibly fouled at various flux rates during two modes of operation: a) active layer in contact with the draw solution (AL-DS); and b) active layer in contact with the feed solution (AL-FS). Membranes used in AL-DS mode fouled faster than their counterparts used in AL-FS mode. Additionally, membranes used with higher flux rates fouled more quickly than those used under low flux conditions. Ultimately, it was determined that produced water will require pretreatment prior to being concentrated using forward osmosis.

Developmental exposure to chemicals associated with unconventional oil and gas extraction alters immune homeostasis and viral immunity of the amphibian Xenopus

Although aquatic vertebrates and humans are increasingly exposed to water pollutants associated with unconventional oil and gas extraction (UOG), the long-term effects of these pollutants on immunity remains unclear. We have established the amphibian Xenopus laevis and the ranavirus Frog Virus 3 (FV3) as a reliable and sensitive model for evaluating the effects of waterborne pollutants. X. laevis tadpoles were exposed to a mixture of equimass amount of UOG chemicals with endocrine disrupting activity (0.1 and 1.0 μg/L) for 3 weeks, and then long-term effects on immune function at steady state and following viral (FV3) infection was assessed after metamorphosis. Notably, developmental exposure to the mixture of UOG chemicals at the tadpole stage affected metamorphic development and fitness by significantly decreasing body mass after metamorphosis completion. Furthermore, developmental exposure to UOGs resulted in perturbation of immune homeostasis in adult frogs, as indicated by significantly decreased number of splenic innate leukocytes, B and T lymphocytes; and a weakened antiviral immune response leading to increased viral load during infection by the ranavirus FV3. These findings suggest that mixture of UOG-associated waterborne endocrine disruptors at low but environmentally–relevant levels have the potential to induce long-lasting alterations of immune function and antiviral immunity in aquatic vertebrates and ultimately human populations.

Numerical analysis of the effects of bedded interfaces on hydraulic fracture propagation in tight multilayered reservoirs considering hydro-mechanical coupling

Tight multilayered hydrocarbon reservoirs are typical in unconventional oil and gas extraction, in which widespread bedded interfaces have crucial effects on hydraulic fracturing propagation behavior. However, because of the complex natural properties of bedded interfaces in natural layers, such as geometric structure, distribution, strength, and contact conditions, their effects on fracture propagation and governing mechanisms are not well understood. In particular, traditional theoretical models are not suitable for characterizing the propagation behavior of hydraulic fractures in multilayered reservoirs and conventional numerical methods cannot effectively simulate the interactions between hydraulic fractures and bedded interfaces. In this study, the adaptive finite element-discrete element method was introduced to probe the effects of bedded interfaces on hydraulic fracture propagation. Different numerical models of five deviation angles of representative bedded interfaces were established based on the geometric and physical parameters of natural multilayered reservoir rocks. Some novel techniques (local remeshing near the fracture tips to guarantee accurate fracture propagation path, mesh coarsening to improve the computation efficiency, characterization technology for bedded interfaces and contacts between layers, and hydro-mechanical coupling between fluid flow in fracture network and porous rock matrix in the fracturing process) were comprehensively utilized. Furthermore, the fracturing-induced microseismic damaged and contact slip events were identified based on the computed moment tensors to detect the interactions between the hydraulic fractures and bedded interfaces. The results of the cases with single and multiple perforations in horizontal wells show that the bedded interfaces disturb the stress continuity, reselect propagation direction of hydraulic fractures in multiple perforations, induce hydraulic fracture growth, and promote the occurrences of fracturing-induced damaged and contact slip events. The offset and deflection of hydraulic fractures increase with increasing deviation angles between hydraulic fractures and bedded interfaces and the offset vanishes when the deviation angle is 0°.

Financial return and energy return on investment analysis of oil sands, shale oil and shale gas operations

People's focus on either financial benefit or ecological benefit makes decisions on unconventional oil and gas extraction hard. This paper combines the energy return ratio with the financial return ratio through a comprehensive analysis model, which is more parsimonious and more objective than other comprehensive analysis models. The model was applied to analyze the comprehensive energy/financial efficiency of seven sample unconventional petroleum (oil and gas) companies in North America. Among them, four are oil sands operating companies with the largest oil sands production and three are shale oil and shale gas operating companies with the largest number of drilled but uncompleted shale wells, and complete available data. Results of our analysis indicate that during the most recent seven years the selected companies' energy return ratio and financial return ratio of unconventional oil and gas extraction operations show obviously different tendencies as a result of oil price fluctuations. However, their comprehensive energy/financial efficiency indicators show no significant trend, which was different from the cases for either one of the individual indicators. We demonstrated that a comprehensive indicator combining both energy and financial efficiency indicators could be more accurate than either one of them individually, to measure the sustainability and the true value of a company or business unit, recognizing both economic and biophysical value. We concluded by suggesting that the energy return on investment indicator and the comprehensive efficiency indicator both be disclosed and audited along with financial and commodity reserves metrics. Such a summary statistic will be more useful for investors and public policy analysts than the various energy efficiency statistics buried in the Global Reporting Initiative (GRI) reports voluntarily produced by various companies. We argue that this summary statistic would provide incentives for companies to innovate and to improve efficiency as well as meet public policy objectives in energy and environment even when the commodity price makes it easier to meet financial objectives.

Loading rate effect on the mechanical behavior of brittle longmaxi shale in nanoindentation

Understanding the properties of sedimentary rock shale is critical for wellbore stability and hydraulic fracturing design in unconventional shale gas extraction. The mechanical properties of shale are a function of various environmental factors, such as stress, temperature, saturation and loading rate. Thus, in this study, the loading rate effect on the mechanical behavior of shale using nanoindentation was investigated. Nanoindentation tests were performed at a peak load of 500 mN and loading rates of 5–30 mN/s. In addition, X-ray diffraction (XRD) analysis was performed to identify the composition of the selected shales, and reveal the target sample is brittle. Scanning electron microscopy (SEM) analyses were performed to determine the surface morphology and demonstrate the existence of pile up and sink-in events. The results of the nanoindentation study indicate that the material behavior of rock depends on the loading rate at the nanoscale: with the increase in the loading rate, the contact hardness, Young's modulus, yield stress and indentation shear stress gradually increase. However, final penetration depths, the contact penetration depths, the maximum penetration depths and the contact stiffness decrease with increasing loading rates. Pop-ins were imperceptible at both the low and high loading rates, reflecting that the shale is brittle. Comparison of the pressure hardening coefficient in the elastic–plastic yield criterion model and the strain hardening coefficient in the strain rate sensitivity model indicates that shale is more sensitive to pressure hardening than strain hardening. A discussion regarding the uncertainty of evaluating the mechanical properties via nanoindentation indicates that the contact surface determination and the loading rate control are both critical to obtain a meaningful value for the mechanical parameters.