Unconventional Gas Production Research Articles

A Fast Numerical Method for the Galvanic Measurement in Hydraulic Fracture Detection

Hydraulic fracturing is critical for unconventional oil and gas production. Recently, galvanic methods, including borehole-to-surface and surface-to-borehole electromagnetic methods, have been applied in hydraulic fracture evaluation. However, conventional computational electromagnetic methods require huge computational cost to simulate the common galvanic fracture model, which consists of a long cased borehole, 3-D thin fractures, and an underground stratified medium. More seriously, modeling both vertical and horizontal energized cased boreholes in layered media is exceptionally difficult. In this article, we present a hybrid numerical mode matching method with stabilized bi-conjugate gradient fast Fourier transform method (NMM-BCGS-FFT) as the forward solver to efficiently model 3-D fractures in the galvanic survey. Both vertical and horizontal energized cased boreholes are modeled in the forward solver. The numerical results show the accuracy and efficiency of the hybrid forward solver. The realistic field galvanic detection model analysis will show the practicability of the forward solver.

Experimental study of fracturing behaviour in ultralow permeability formations: A comparison between CO2 and water fracturing

As an alternative to water-based fracturing (WBF), CO2-based fracturing (CBF) with many unique advantages has been successfully used to enhance unconventional gas production. However, the study on the great difference of fracturing behaviours between WBF and CBF for different gas reservoirs is still scarce. The intention of this study is to investigate the fracturing mechanism and to compare the fracture geometry characters between WBF and CBF. A series of fracturing tests on sedimentary rocks, including siltstone and shale samples, was therefore conducted. According to experimental results, the breakdown pressure of CBF is lower than that of WBF for siltstone samples with permeability of 2.5 µD, and the difference of breakdown pressure between WBF and CBF for shale samples with permeability of 0.05 µD is much greater. In addition to the effect of higher tensile strength of shale rock, the much higher breakdown pressure for shale samples than siltstone samples indicates that the flow behaviour of injected fluid significantly influences the initiation of fractures and that high pore pressure within rock matrix can greatly decrease the breakdown pressure. The presence of macro pores in several hundred microns is responsible for the very rough fracture surfaces of siltstone samples, while much more smooth fracture surfaces are observed for shale samples with much tiny pore structures. CBF creates more loose particles and discrete blocks acting like proppants, and fracture aperture of CBF is 2–5 times of that of WBF. Multi-parallel fractures and bigger discrete blocks contribute to the low fracture compressibility, and the secondary shear fractures along the weak bedding planes in shale samples greatly increase the complexity of the fracture network.

Conventional Oil-The Forgotten Part of the Water-Energy Nexus.

The impacts of unconventional oil and gas production via high-volume hydraulic fracturing (HVHF) on water resources, such as water use, groundwater and surface water contamination, and disposal of produced waters, have received a great deal of attention over the past decade. Conventional oil and gas production (e.g., enhanced oil recovery [EOR]), which has been occurring for more than a century in some areas of North America, shares the same environmental concerns, but has received comparatively little attention. Here, we compare the amount of produced water versus saltwater disposal (SWD) and injection for EOR in several prolific hydrocarbon producing regions in the United States and Canada. The total volume of saline and fresh to brackish water injected into depleted oil fields and nonproductive formations is greater than the total volume of produced waters in most regions. The addition of fresh to brackish "makeup" water for EOR may account for the net gain of subsurface water. The total amount of water injected and produced for conventional oil and gas production is greater than that associated with HVHF and unconventional oil and gas production by well over a factor of 10. Reservoir pressure increases from EOR and SWD wells are low compared to injection of fluids for HVHF, however, the longer duration of injections could allow for greater solute transport distances and potential for contamination. Attention should be refocused from the subsurface environmental impacts of HVHF to the oil and gas industry as a whole.

Adsorption and Capillary Condensation-Induced Imbibition in Nanoporous Media.

Multiphase flow phenomena in nanoporous media are encountered in many science and engineering applications. Shales, for example, possessing complex nanopore networks, have considerable importance as source rocks for unconventional oil and gas production and as low-permeability seals for geologic carbon sequestration or nuclear waste disposal. This study presents a theoretical investigation of the processes controlling adsorption, capillary condensation, and imbibition in such nanoporous media, with a particular focus on understanding the effects of fluid-fluid and fluid-pore wall interaction forces in the interconnected nanopore space. Building on a new theoretical framework, we developed a numerical model for the multiphase nanoporous flow and tested it against water vapor uptake measurements conducted on a shale core sample. The model, which is based on the density functional approach, explicitly includes the relevant interaction forces among fluids and solids while allowing for a continuum representation of the porous medium. The experimental data include gravimetrically measured mass changes in an initially dry core sample exposed to varying levels of relative humidity, starting with a low relative humidity (rh = 0.31) followed by a period of a higher relative humidity (rh = 0.81). During this process, water vapor uptake in the dry core is recorded as a function of time. Our model suggests that, under low rh conditions, the flow within the shale sample is controlled by adsorption- and diffusion-type processes. After increasing the rh to 0.81, the uptake of water vapor becomes more significant, and according to our model, this can be explained by capillary condensation followed by immiscible displacement in the core sample. It appears that strong fluid-pore wall attractive forces cause condensation near the inlet, which then induces water imbibition further into sample.

Environmental Justice in Unconventional Oil and Natural Gas Drilling and Production: A Critical Review and Research Agenda.

The drilling phase of oil and natural gas development is a growing area of environmental justice (EJ) research, particularly in the United States. Its emergence complements the longstanding EJ scholarship on later phases of the oil and gas commodity chain, such as pipeline transport, refining, and consumption. The growing scholarly attention to the EJ implications of drilling has been prompted by the surge in development of unconventional oil and gas resources in recent decades. More specifically, the oil and gas industry's adoption of horizontal drilling and hydraulic fracturing (a.k.a., "fracking" or "fracing") as methods for extracting oil and gas from a wider range of geologic formations has simultaneously heightened oil and gas production, brought extractive activities closer to more people, intensified them, and made well pad siting more flexible. Here, we provide a critical review of the novel EJ research questions that are being prompted by these on-the-ground changes in extractive techniques and patterns, propose an interdisciplinary conceptual framework for guiding EJ inquiry in this context, discuss key methodological considerations, and propose a research agenda to motivate future inquiry.

Experimental study on gas desorption characteristics for different coal particle sizes and adsorption pressures under the action of pressured water and superheated steam

Gas (i.e. methane and CO2) ad-/desorption characteristics are essential for unconventional gas production, and they are related to many factors such as coal particle size, adsorption pressure, external moisture and heat. In order to investigate the effect of these factors, as well as those arising from pressured water and superheated steam on gas desorption, a series of experiments were conducted. The experimental equipment designed by our research group could be used to supply pressured water and superheated steam during the gas ad-/desorption process. Our results were: 1) High-pressure water injection after adsorption resulted in a reduced gas desorption capacity. With an increase in the equilibrium adsorption pressure and water injection pressure, the desorption capacity of coal increased and decreased, respectively. 2) The desorption capacity of the residual adsorbed gas in coal increased with steam action, and it eliminated the influence of low gas adsorption pressure and high-pressure water injection on gas desorption. 3) The gas desorption velocity increased with steam action, which was reflected by a decrease in the critical value of time effect. The coal particle size had a certain influence on the desorption of the adsorbed gas. Finally, with an increase in the water injection pressure, the influence of coal particle size became larger. However, the desorption under steam was less affected by the coal particle size. These results may have significant implications for energy exploitation and utilization.

Estimating Methane Emissions From Underground Coal and Natural Gas Production in Southwestern Pennsylvania

AbstractProduction of coal and natural gas is responsible for one third of anthropogenic methane (CH4) emissions in the United States. Here we examine CH4 emissions from coal and natural gas production in southwestern Pennsylvania. Using a top‐down methodology combining measurements of CH4 and ethane, we conclude that while Environmental Protection Agency inventories appear to report emissions from coal accurately, emissions from unconventional natural gas are underreported in the region by a factor of 5 (±3). However, production‐scaled CH4 emissions from unconventional gas production in the Marcellus remain small compared to other basins due to its large production per well. After normalizing emissions by energy produced, total greenhouse gas emissions from Pennsylvania unconventional natural gas production produce half the carbon footprint compared to regionally produced coal, with carbon dioxide emissions from combustion being the dominant source of greenhouse gas emissions for both sources.

Does fracking drive you to drink? Unconventional oil and gas production and alcohol consumption in U.S. counties

Unconventional drilling technologies like hydraulic fracturing and directional drilling have markedly increased oil and gas production in the United States while also bringing production in proximity with many communities. Foundational research in rural sociology predicts the rise of local “boomtown” problems like excessive alcohol consumption as a result of sudden energy booms. In this paper, we use data from U.S. counties to understand the relationship between energy production and alcohol consumption. Results suggest that oil and gas production has very modest effects on binge drinking and heavy drinking, and that these effects may vary by gender and across U.S. states.

A Volumetric Model for Evaluating Tight Sandstone Gas Reserves in the Permian Sulige Gas Field, Ordos Basin, Central China

To accurately measure and evaluate reserves is critical for ensuring successful production of unconventional oil and gas. This work proposes a volumetric model to evaluate the tight sandstone gas reserves of the Permian Sulige gas field in the Ordos Basin. The reserves can be determined by four major parameters of reservoir cutoffs, net pay, gas‐bearing area and compression factor Z, which are controlled by reservoir characteristics and sedimentation. Well logging, seismic analysis, core analysis and gas testing, as well as thin section identification and SEM analysis were used to analyze the pore evolution and pore‐throat structure. The porosity and permeability cutoffs are determined by distribution function curve, empirical statistics and intersection plot. Net pay and gas‐bearing area are determined based on the cutoffs, gas testing and sand body distribution, and the compression factor Z is obtained by gas component. The results demonstrate that the reservoir in the Sulige gas field is characterized by ultralow porosity and permeability, and the cutoffs of porosity and permeability are 5% and 0.15×10–3 μm2, respectively. The net pay and gas‐bearing area are mainly affected by the sedimentary facies, sand body types and distribution. The gas component is dominated by methane which accounts for more than 90%, and the compression factor Z of H8 (P2h8) and S1 (P1s1) are 0.98 and 0.985, respectively. The distributary channels stacked and overlapped, forming a wide and thick sand body with good developed intergranular pores and intercrystalline pores. The upper part of channel sand with good porosity and permeability can be sweet spot for gas exploration. The complete set of calculation systems proposed for tight gas reserve calculation has proved to be effective based on application and feedback. This model provides a new concept and consideration for reserve prediction and calculation in other areas.

Importance of Superemitter Natural Gas Well Pads in the Marcellus Shale.

A large-scale study of methane emissions from well pads was conducted in the Marcellus shale (Pennsylvania), the largest producing natural gas shale play in the United States, to better identify the prevalence and characteristics of superemitters. Roughly 2100 measurements were taken from 673 unique unconventional well pads corresponding to ∼18% of the total population of active sites and ∼32% of the total statewide unconventional natural gas production. A log-normal distribution with a geometric mean of 2.0 kg h-1 and arithmetic mean of 5.5 kg h-1 was observed, which agrees with other independent observations in this region. The geometric standard deviation (4.4 kg h-1) compared well to other studies in the region, but the top 10% of emitters observed in this study contributed 77% of the total emissions, indicating an extremely skewed distribution. The integrated proportional loss of this representative sample was equal to 0.53% with a 95% confidence interval of 0.45-0.64% of the total production of the sites, which is greater than the U.S. Environmental Protection Agency inventory estimate (0.29%), but in the lower range of other mobile observations (0.09-3.3%). These results emphasize the need for a sufficiently large sample size when characterizing emissions distributions that contain superemitters.

Putting on partisan glasses: Political identity, quality of life, and oil and gas production in Colorado

Unconventional oil and gas technologies—such as hydraulic fracturing—have drastically increased the volume of oil and gas produced in the U.S., while simultaneously bringing drilling closer to residential areas. We examine quality of life impacts of unconventional oil and gas production, arguing that how people perceive its local effects is rooted in their political identities. Using survey data from three northern Colorado communities, we employ counterfactual mediation methods to understand relationships between political identity, perceived socio-environmental and community changes from oil and gas development, and self-reported quality of life. We find significant differences in how people perceive local development based upon political identity, whereby Tea Party supporters see little negative impact, and in turn are likely to believe that local development improves their quality of life. At the other extreme, Democrats perceive more negative community changes from oil and gas development and are more apt to believe that it reduces their quality of life. Republicans who do not support the Tea Party and political independents hold more mixed views. Overall, our analysis suggests that people's perceptions of local energy development and how it matters for their quality of life is, to some degree, a function of their political identities.

Methane emissions from conventional and unconventional oil and gas production sites in southeastern Saskatchewan, Canada

Energy development in southeastern Saskatchewan, Canada, is unique because conventional and unconventional oil and gas production is co-located. Mobile surveys are ideal for understanding emissions in this area because the overlap of production makes it difficult for airborne or satellite-based methods to differentiate emissions from each type of infrastructure. In this study, we conducted truck-based mobile surveys in the unconventional Canadian Bakken and conventional Weyburn-Midale fields to enumerate and attribute individual methane plumes, estimate methane (CH4) emission rates, and compare emission vectors. We sampled downwind of 645 conventional and 289 unconventional sites, covering over 4500 km of public roads. We found that 28% of surveyed conventional sites were emitting, compared to 32% of surveyed unconventional sites. Mean emissions intensities in each development were 20 m3CH4/day per conventional site and 59 m3CH4/day per unconventional site. Emissions intensities in southeastern Saskatchewan fall on the lower range of other emissions estimates from developments in the US and Canada.

A sustainable solution for removal of glutaraldehyde in saline water with visible light photocatalysis

Glutaraldehyde (GA) is the most common biocide used in unconventional oil and gas production. Photocatalytic degradation of GA in brine simulating oil and gas produced water using Ag/AgCl/BiOCl composite as a photocatalyst with visible light was investigated. Removal of GA at 0.1 mM in 200 g/L NaCl solution at pH 7 was 90% after 75 min irradiation using 5 g/L of the photocatalyst. The GA removal followed pseudo-first order reaction with a rate constant of 0.0303 min−1. At pH 5 or at 300 g/L NaCl, the photocatalytic removal of GA was almost completely inhibited. Similar inhibitions were observed when adding dissolved organic carbon (from humic acid) at 10 and 200 mg/L, or Br− at 120 mg/L to the system. The removal rate of GA markedly increased with increasing pH (5–9), photocatalyst loading (2–8 g/L) and under 350 nm UV (compared to visible light). On the contrary, the removal rate of GA markedly decreased with increasing NaCl and initial GA concentrations (0–300 g/L for NaCl and 0.1–0.4 mM for GA). A quenching experiment was also conducted; electron holes (h+) and superoxide (▪) were found as the main reactive species responsible for the removal of GA while OH had a very limited effect.

Brittleness Logging Evaluation of Shihezi Formation in Yanchang Gas Field in Ordos Basin Based on Rock Mechanical Characteristics

Brittleness determines the effect of reservoir fracturing and is important for increasing the production of unconventional oil and gas. The reservoir of Yanchang gas field is characterized by low porosity, low permeability and strong heterogeneity, which make it difficult to produce industrial gas flow under natural conditions. Triaxial compression tests in sandstone samples of Shihezi formation in Yanchang gas field show that the main fracturing mode is multiple horizontal splitting, the main cracks are completely fractured, and the brittleness index ranges from 46.1% to 51.4%. After S-wave velocity model in the study area is established, the conversion relation of dynamic and static mechanical parameters could be obtained, that is,Es=0.4142Ed+10.769(R2=0.8387),and μs=1.1076 μd-0.068(R2=0.7366), according to which, the dynamic mechanics parameters calculated by well logging can be adjusted, and then the reservoir brittleness could be quantitatively evaluated. Combining with the brittleness index calculated by mineral component method, it can be concluded that the brittleness calculated by well logging is reliable and the brittleness of Shihezi formation in Yanchang gas field is high, which is beneficial for reservoir fracturing.

East coast gas: resource potential at different gas price scenarios (Part 2: commercialisation of unconventional gas resources)

Rising gas prices in the eastern Australian gas market, as well as forecast supply shortages in years to come, are driving speculation about LNG import requirements for the market. There are significant similarities with the gas market experience in the USA in the early 2000s which led to the construction of many LNG import terminals, the parallel rise of unconventional gas production and the subsequent mothballing of the LNG import facilities at huge economic cost. A comprehensive east coast gas market study has been carried out based on the 2P reserves positions for domestic gas producers. This data has been paired with a range of gas demand forecasts to identify the probable supply gap on the east coast over the next 10 years. A market response to the high gas pricing in the form of new developments is already underway. In a separate paper (Part 1) all potential domestic sources of unconventional gas to fill that gap were analysed to determine likely gas supply rates, development schedules and breakeven supply costs for each of the major demand centres. This paper (Part 2) illustrates the required gas prices to drive unconventional gas development in Australia, the subsequent scale of new unconventional gas supplies to the forecast gaps in the market and describes how those developments can reverse the trend of rising prices over time.

East coast gas: resource potential at different gas price scenarios (Part 1: quantification of unconventional gas resource potential)

A qualitative ranking of the remaining gas potential of Australian east coast basins was undertaken using a spatial analysis methodology of play fairway sweet-spot mapping. Play components considered important for the presence and recovery of unconventional gas were mapped across the plays of interest in Australian east coast basins. Modelled horizontal well type curves and development plans from North American analogues for unconventional gas production were used to quantify the sweet-spot mapping using a methodology we developed called common recovery segment mapping. A range of potential resource numbers were calculated for each play, leading to a quantification of the potential resource across the entire area of interest. Part 2 of this paper will show how these undeveloped unconventional gas resources may ultimately contribute to the east coast Australia energy mix.

One approach to the study of gas pricing based on gas supply systems modelling (the case of Northeast Asia)

The article deals with the approach to gas pricing analysis based on the use of optimization models of gas supply systems. The object of the study is the Northeast Asian gas market. The model of the excessive gas supply system in Northeast Asia is described. The primal problem of the model is to minimize the sum of gas production and transportation costs under the infrastructure constraints. The solutions to the primal problem are the volumes of gas produced in each production point and transported via each route. The solutions to the dual problem (dual variables or shadow prices) are node prices in the points of gas supply system, the producers’ rent and the transporters’ rent. It is highlighted that the dual analysis plays an important role. It allows evaluating price relations between the points of gas supply system, identifying export routs characterized by the highest rent, evaluating the competitiveness of suppliers in the different scenarios of technological development, energy policy and market environment. The analytical capacities of the dual analysis are illustrated by the study of the impact of “unconventional” gas development in the importing countries on the Northeast Asian gas market environment. When the costs of unconventional gas production rise, gas trade patterns change, more competitive players enter the market, and gas prices in all consumption points as well as producers’ rents increase. It is concluded that if importers seek to lower import dependency while keeping the same price level, they have to lower the costs of unconventional gas production by technological development and/or to subsidize the industry to make it more competitive.

Information booms and busts: Examining oil and gas disclosure policies across the states

Today's 'fracking debate' includes a familiar set of actors and arguments. Advocates of unconventional oil and gas production contend that it has contributed to an economic renaissance for many subnational governments and has improved American energy security. Opponents suggest that unconventional production is an environmental and public health hazard. One way that states are trying to balance the economic benefits of continued energy production with environmental protection is through the use of information disclosure requirements. Prior work notes that the rigor of state disclosure standards relative to unconventional oil and gas production vary. Through measures of association and exact logistic regression, this project expands the disclosure literature by focusing on three types of disclosure: pre-drilling notification, chemical disclosure during operations, and trade secret exemptions.

A Critical Review of State-of-the-Art and Emerging Approaches to Identify Fracking-Derived Gases and Associated Contaminants in Aquifers.

High-volume, hydraulic fracturing (HVHF) is widely applied for natural gas and oil production from shales, coals, or tight sandstone formations in the United States, Canada, and Australia, and is being widely considered by other countries with similar unconventional energy resources. Secure retention of fluids (natural gas, saline formation waters, oil, HVHF fluids) during and after well stimulation is important to prevent unintended environmental contamination, and release of greenhouse gases to the atmosphere. Here, we critically review state-of-the-art techniques and promising new approaches for identifying oil and gas production from unconventional reservoirs to resolve whether they are the source of fugitive methane and associated contaminants into shallow aquifers. We highlight future research needs and propose a phased program, from generic baseline to highly specific analyses, to inform HVHF and unconventional oil and gas production and impact assessment studies. These approaches may also be applied to broader subsurface exploration and development issues (e.g., groundwater resources), or new frontiers of low-carbon energy alternatives (e.g., subsurface H2 storage, nuclear waste isolation, geologic CO2 sequestration).

Simulating three dimensional hydraulic fracture propagation using displacement correlation method

The TOUGH-FEMM simulator is used to investigate the interaction of multiple simultaneous hydraulic fractures. In TOUGH-FEMM simulator, rock deformation is modeled using the hybrid Finite Element-Meshfree Method (FEMM) and fluid flow is simulated through the Transport Of Unsaturated Groundwater and Heat (TOUGH2) simulator. The stress intensity factors are calculated by using the Displacement Correlation Method (DCM). The equivalent mode I stress intensity factor is used for determining fracture propagation criterion and direction. Successfully creating multiple hydraulic fractures in horizontal wells is critical for unconventional gas production economically. These previous works focussed on the propagation of fractures which are parallel initially. However, because of inevitable error in practical engineering and natural flaws in rock, the initial fractures might be inclined. The overall objective of the current work is to study the influence of initial fracture orientation on the simultaneous hydraulic fracturing of a horizontal well. The results of the present work show that initial fracture orientation has significant effect on the fracture propagation direction and final fracture contour. Different fracture contours will result in distinct fracture network, which will greatly affect the reservoir permeability.