A critical evaluation of unconventional gas recovery from the marcellus shale, northeastern United States
07 Apr 2011-Ksce Journal of Civil Engineering (Korean Society of Civil Engineers)-Vol. 15, Iss: 4, pp 679-687
TL;DR: In this paper, the authors discuss the challenges involved in the economic recovery of gas from tight gas shales in general and the Marcellus in particular, and discuss some of the most significant technological obstacles, including prospecting, access by drilling, stimulation, and recovery.
Abstract: The Marcellus tight gas shale represents a significant resource within the northeastern United States. It is both a large reserve, with an estimated 30 to 300 TCF of recoverable gas, and is close to some of the largest prospective markets in the country. However, production is fraught with technological obstacles, the most significant of which include prospecting, access by drilling, stimulation, and recovery. Prospecting is difficult because viability of the reservoir relies both on the original gas in place and in the ability to access that gas through pre-existing fractures that may be developed through stimulation. Drilling is a challenge since drilling costs typically comprise 50% of the cost of the wells and access to the reservoir is improved with horizontal drilling which may access a longer productive zone within the reservoir than cheaper vertical wells. Finally, stimulation methods are necessary to improve gas yields and to reduce the environmental impacts of both consumptive water use and the subsequent problems of safe disposal of fracwater waste. We discuss the challenges involved in the economic recovery of gas from tight gas shales in general and the Marcellus in particular.
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TL;DR: The areas of energy, water and food policy have numerous interwoven concerns ranging from ensuring access to services, to environmental impacts to price volatility as mentioned in this paper, and these issues manifest in very di...
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Cites background from "A critical evaluation of unconventi..."
...Disclaimer This document represents work in progress and is intended to generate comment and discussion....
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...This paper briefly describes some of the linkages at a high-level of aggregation – primarily from a developing country perspective – and via case studies, to arrive at some promising directions for addressing the nexus....
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TL;DR: In this article, the authors present new core and outcrop data from 18 shale plays that reveal common types of shale fractures and their mineralization, orientation, and size patterns, and identify a need for further work in this field and on the role of natural fractures generally.
Abstract: Natural fractures have long been suspected as a factor in production from shale reservoirs because gas and oil production commonly exceeds the rates expected from low-porosity and low-permeability shale host rock. Many shale outcrops, cores, and image logs contain fractures or fracture traces, and microseismic event patterns associated with hydraulic-fracture stimulation have been ascribed to natural fracture reactivation. Here we review previous work, and present new core and outcrop data from 18 shale plays that reveal common types of shale fractures and their mineralization, orientation, and size patterns. A wide range of shales have a common suite of types and configurations of fractures: those at high angle to bedding, faults, bed-parallel fractures, early compacted fractures, and fractures associated with concretions. These fractures differ markedly in their prevalence and arrangement within each shale play, however, constituting different fracture stratigraphies—differences that depend on interface and mechanical properties governed by depositional, diagenetic, and structural setting. Several mechanisms may act independently or in combination to cause fracture growth, including differential compaction, local and regional stress changes associated with tectonic events, strain accommodation around large structures, catagenesis, and uplift. Fracture systems in shales are heterogeneous; they can enhance or detract from producibility, augment or reduce rock strength and the propensity to interact with hydraulic-fracture stimulation. Burial history and fracture diagenesis influence fracture attributes and may provide more information for fracture prediction than is commonly appreciated. The role of microfractures in production from shale is currently poorly understood yet potentially critical; we identify a need for further work in this field and on the role of natural fractures generally.
709 citations
TL;DR: In this article, the authors quantify gas and wastewater production using data from 2189 Marcellus wells located throughout Pennsylvania and find that despite producing significantly less wastewater per unit gas recovered, developing the region has increased the total wastewater generated in the region by approximately 570% since 2004, overwhelming current wastewater disposal infrastructure capacity.
Abstract: [1] Hydraulic fracturing has made vast quantities of natural gas from shale available, reshaping the energy landscape of the United States. Extracting shale gas, however, generates large, unavoidable volumes of wastewater, which to date lacks accurate quantification. For the Marcellus shale, by far the largest shale gas resource in the United States, we quantify gas and wastewater production using data from 2189 wells located throughout Pennsylvania. Contrary to current perceptions, Marcellus wells produce significantly less wastewater per unit gas recovered (approximately 35%) compared to conventional natural gas wells. Further, well operators classified only 32.3% of wastewater from Marcellus wells as flowback from hydraulic fracturing; most wastewater was classified as brine, generated over multiple years. Despite producing less wastewater per unit gas, developing the Marcellus shale has increased the total wastewater generated in the region by approximately 570% since 2004, overwhelming current wastewater disposal infrastructure capacity.
332 citations
Cites background from "A critical evaluation of unconventi..."
...5 tcm, gas in place) [Lee et al., 2011; U.S. DOE, 2009] and most spatially expansive [>246,000 km(2); U....
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...The Marcellus shale is the largest (8.3–76.5 tcm, gas in place) [Lee et al., 2011; U.S. DOE, 2009] and most spatially expansive [>246,000 km2; U.S. DOE, 2009] shale gas deposit in the United States....
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TL;DR: There was a reduction in microbial richness and diversity after fracturing, with the lowest diversity at 49 days, and Thirty-one taxa dominated injected, flowback, and produced water communities, which took on distinct signatures as injected carbon and electron acceptors were attenuated within the shale.
Abstract: Microorganisms play several important roles in unconventional gas recovery, from biodegradation of hydrocarbons to souring of wells and corrosion of equipment. During and after the hydraulic fracturing process, microorganisms are subjected to harsh physicochemical conditions within the kilometer-deep hydrocarbon-bearing shale, including high pressures, elevated temperatures, exposure to chemical additives and biocides, and brine-level salinities. A portion of the injected fluid returns to the surface and may be reused in other fracturing operations, a process that can enrich for certain taxa. This study tracked microbial community dynamics using pyrotag sequencing of 16S rRNA genes in water samples from three hydraulically fractured Marcellus shale wells in Pennsylvania, USA over a 328-day period. There was a reduction in microbial richness and diversity after fracturing, with the lowest diversity at 49 days. Thirty-one taxa dominated injected, flowback, and produced water communities, which took on disti...
233 citations
TL;DR: Preliminary evidence is provided that these and similar WWTPs may not be able to provide sufficient treatment for this wastewater stream, and more thorough monitoring is recommended.
Abstract: Unconventional natural gas development in Pennsylania has created a new wastewater stream. In an effort to stop the discharge of Marcellus Shale unconventional natural gas development wastewaters into surface waters, on May 19, 2011 the Pennsylvania Department of Environmental Protection (PADEP) requested drilling companies stop disposing their wastewater through wastewater treatment plants (WWTPs). This research includes a chemical analysis of effluents discharged from three WWTPs before and after the aforementioned request. The WWTPs sampled included two municipal, publicly owned treatment works and a commercially operated industrial wastewater treatment plant. Analyte concentrations were quanitified and then compared to water quality criteria, including U.S. Environmental Protection Agency MCLs and “human health criteria.” Certain analytes including barium, strontium, bromides, chlorides, total dissolved solids, and benzene were measured in the effluent at concentrations above criteria. Analyte concent...
218 citations
References
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TL;DR: In this paper, the authors described some of the technology-based solutions that have been used to successfully exploit these reservoirs, such as horizontal drilling, multi-stage completions, innovative fracturing, and fracture mapping.
Abstract: A significant portion of gas production in North America comes from unconventional reservoirs such as gas shales, coalbed methane (CBM) deposits and tight gas sands. Due to their limited permeability, stimulation processes are needed for economic recovery from wells drilled into these formations. This paper described some of the technology-based solutions that have been used to successfully exploit these reservoirs, such as horizontal drilling, multi-stage completions, innovative fracturing, and fracture mapping. Economic production depends on the matrix permeability of these reservoirs as well as the conductivity that can be generated in hydraulic fractures and network fracture systems. Simulations have shown that a fracture network of moderate conductivity is needed in ultra-low shale permeabilities. The spacing between fractures must be small to obtain reasonable recovery factors. Such networks are achievable according to results of microseismic mapping. In contrast, tight gas sands may be successfully depleted without inducing complex fracture networks because they have orders of magnitude greater permeability than gas shales. However, the recovery in tight gas sands is complicated by other issues of damage and zonal coverage in these reservoirs. It was concluded that fracture mapping can help improve the understanding of fractures and improve the ability to change the fracture complexity through operational changes to the well design and treatment implementation. 47 refs., 15 figs.
288 citations
01 Jan 2008
TL;DR: In this article, the authors described some of the technology-based solutions that have been used to successfully exploit these reservoirs, such as horizontal drilling, multi-stage completions, innovative fracturing, and fracture mapping.
Abstract: A significant portion of gas production in North America comes from unconventional reservoirs such as gas shales, coalbed methane (CBM) deposits and tight gas sands. Due to their limited permeability, stimulation processes are needed for economic recovery from wells drilled into these formations. This paper described some of the technology-based solutions that have been used to successfully exploit these reservoirs, such as horizontal drilling, multi-stage completions, innovative fracturing, and fracture mapping. Economic production depends on the matrix permeability of these reservoirs as well as the conductivity that can be generated in hydraulic fractures and network fracture systems. Simulations have shown that a fracture network of moderate conductivity is needed in ultra-low shale permeabilities. The spacing between fractures must be small to obtain reasonable recovery factors. Such networks are achievable according to results of microseismic mapping. In contrast, tight gas sands may be successfully depleted without inducing complex fracture networks because they have orders of magnitude greater permeability than gas shales. However, the recovery in tight gas sands is complicated by other issues of damage and zonal coverage in these reservoirs. It was concluded that fracture mapping can help improve the understanding of fractures and improve the ability to change the fracture complexity through operational changes to the well design and treatment implementation. 47 refs., 15 figs.
283 citations
"A critical evaluation of unconventi..." refers background in this paper
...…typically increases fracture conductivity to between 0.5 and 10 md-ft, which represents an overall increase in formation permeability between 1 and 7 orders of magnitude, depending on the width of the fractures; larger permeability values lead to greater gas recovery (Warpinski et al., 2008)....
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...5 and 10 md-ft, which represents an overall increase in formation permeability between 1 and 7 orders of magnitude, depending on the width of the fractures; larger permeability values lead to greater gas recovery (Warpinski et al., 2008)....
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TL;DR: Etude de huit carottes de schistes a gaz provenant du bassin des Appalaches (Etats-Unis). Determination de la permeabilite, de la porosite, and du potentiel productif des schistses
Abstract: Etude de huit carottes de schistes a gaz provenant du bassin des Appalaches (Etats-Unis). Determination de la permeabilite, de la porosite et du potentiel productif des schistes
280 citations
01 Jan 2009
206 citations
"A critical evaluation of unconventi..." refers background or methods in this paper
...This relationship has been expressed in the following model (Valko, 2009):...
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...This relationship has been expressed in the following model (Valko, 2009): (1) where q is the production rate (gas per time), t is time since construction, n is a model parameter, and τ is the characteristic time constant....
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...Estimated Ultimate Recovery (EUR) Per well in the Barnett Shale (Valko, 2009)...
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01 Jan 2009
189 citations
"A critical evaluation of unconventi..." refers background in this paper
...Generally, the gas is sufficiently pressurized to flow to the surface without any additional pumping (Ozkan et al., 2009)....
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...The objectives of hydraulic fracturing are to increase fracture density in the formation and decrease fracture spacing (Ozkan et al., 2009)....
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