Environ Sci Pollut Res DOI 10.1007/s11356-015-4254-8
RESEARCH ARTICLE
Managing produced water from coal seam gas projects: implications for an emerging industry in Australia Peter J. Davies & Damian B. Gore & Stuart J. Khan
Received: 2 December 2014 / Accepted: 17 February 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract This paper reviews the environmental problems, impacts and risks associated with the generation and disposal of produced water by the emerging coal seam gas (CSG) industry and how it may be relevant to Australia and similar physical settings. With only limited independent research on the potential environmental impacts of produced water, is it necessary for industry and government policy makers and regulators to draw upon the experiences of related endeavours such as mining and groundwater extraction accepting that the conclusions may not always be directly transferrable. CSG is widely touted in Australia as having the potential to provide significant economic and energy security benefits, yet the environmental and health policies and the planning and regulatory setting are yet to mature and are continuing to evolve amidst ongoing social and environmental concerns and political indecision. In this review, produced water has been defined as water that is brought to the land surface during the process of recovering methane gas from coal seams and includes water sourced from CSG wells as well as flowback water associated with drilling, hydraulic fracturing and gas extraction. A brief overview of produced water generation, its characteristics and environmental issues is provided. A review of past lessons and identification of potential risks, including disposal options, is included to assist in planning and management of this industry. Keywords Produced water . Coal seam gas . Risk management . Hydraulic fracturing . Treatment and disposal Responsible editor: Philippe Garrigues P. J. Davies (*) : D. B. Gore Faculty of Science and Engineering, Macquarie University, Sydney, NSW, Australia e-mail: [email protected] S. J. Khan School of Civil & Environmental Engineering, University of New South Wales, Sydney, NSW 2052, Australia
Introduction Coal seam gas (CSG)-produced water is water that is brought to the land surface during the recovery of methane gas. This can take the form of flowback water, often associated with hydraulic fracturing, as well as formation water that is present naturally within the coal seam. Flowback water is a mixture of hydraulic fracturing fluid and formation water, making it physically and chemically different to produced water. After the flowback water is removed, the formation water that continues to be co-produced with the gas is termed produced water. The amount of produced water taken from a well depends on the natural water content of the coal seam formation (Jamshidi and Jessen 2012); permeability of the formation (Zuber et al. 1997); and the time since the initiation of pumping, well spacing and density (Klohn Crippen Berger 2012). If the formation is sufficiently permeable, produced water may be generated over the entire gas-producing life of the well. However, produced water volumes generally decrease over time (Moore 2012; Freij-Ayoub 2012). Methane and coal Methane is held in coal seams along naturally occurring fractures, pores and other macro- and micro-inhomogeneities (collectively termed voids in this paper). The voids exhibit a bimodal size distribution (the dual porosity of Jamshidi and Jessen 2012), with fractures and macro-voids defining the coal fabric and micropores characterising the matrix. The ability of the gas to move through the coal depends on the type, number, size, orientation and connectivity of these voids and, particularly, on the dimensions of the connections between the voids. Most of the gas in coal usually occurs adsorbed to the walls of the smaller voids. While only a small proportion of gas is typically adsorbed to the walls of the larger voids, these larger
Environ Sci Pollut Res
voids control the permeability of the coals and the extraction of water and gas from them (Freij-Ayoub 2012; Jamshidi and Jessen 2012). The permeability of Australian coals typically ranges from 1 to 10 milliDarcies, although these estimates are based on few publically accessible data sets. By comparison, coals in the United States of America (USA) reach a permeability of 35 milliDarcies (Jamshidi and Jessen 2012). The release of gas from coal can be stimulated by the removal of water that occurs naturally in the rock formation. When water is removed and released from hydrostatic pressure, degassing of the formation and water occurs. Gas and water can then be removed by pumping from an extraction well. Recovery of methane can be enhanced by the injection of water and additives, referred to as hydraulic fracturing, or through gases such as nitrogen and carbon dioxide, which can reduce the amount of produced water generated (Jamshidi and Jessen 2012). A conceptual illustration of the co-production of produced water during CSG production is in Fig. 1. Cleats, the natural fractures in the coal seam, contain a mixture of water (blue matrix) and methane gas (white dots) that can also be dissolved in the water stream. Water is pumped from the coal seam via a well, reducing the pressure in the coal seam and enabling methane to desorb from the coal surfaces and flow up the well bore. Water and methane may flow through separate Fig. 1 Co-production of produced water during CSG extraction
pipes to the surface, or methane may be separated from the water via a gas/water separator at the wellhead. There are substantial differences in the moisture contents of coal formations that can impact on the volume of produced water generated during gas extraction (Burra et al. 2014; Jakubowski et al. 2014). For example, the southern coalfields of the Sydney Basin are widely regarded as dry (although this is a relative term and underground mines in those areas require dewatering operations, just as elsewhere). Northward, formation waters increase in volume, and the volume of produced water per unit volume of gas also increases (Queensland Water Commission 2012). The amount of produced water will not only vary regionally from coalfield to coalfield (National Water Commission 2011), it will also vary locally in response to variability in mineral content, grain size, pore size and connectivity and permeability. As an indication of potential differences in produced water yield, CSG extraction from the southern coalfields operation at Camden, to the south of Sydney, produces a maximum of 30 ML of water per year and in 2012 produced only 4.8 ML from 89 operational wells (NSW Department of Primary Industries 2013; AGL 2013). Further north, the estimates of produced water from the Gloucester Basin in NSW was 730 ML per year across 110 well (AECOM 2009). The coalfields in the Surat Basin in Queensland produce around 7 to 300 ML per year per well (NSW
Environ Sci Pollut Res
Department of Primary Industries 2013). Queensland is by far the greatest producer of CSG in Australia, and in terms of produced water, the industry extracted around 126–281 GL/ year in 2012 (Queensland Water Commission 2012), and this is expected to increase significantly by 2030 as part of the planned expansion of the industry (Klohn Crippen Berger 2012). Chemical composition The composition of produced water varies according to the depositional environment of the coal, the rank (thermal maturity) of the coal, the flux of fresh water into the coal formation from surrounding formations and the time of residence of the water (Nghiem et al. 2011; Alley et al. 2011; Hamawand et al. 2013). The geological depositional environment for coalbearing formations typically have either saltwater or fresh/ brackish water characteristics that are rich in cations such as Na+, K+, Ca2+, Mg2+, Ba2+, Sr2+ and Fe2+ and anions such as Cl−, SO42−, CO32− and HCO3−. Sodium bicarbonate and sodium chloride are the dominant cations and anions with total dissolved solids (TDS) being highly variable (150 to 39, 000 mg/L) (Dahm et al. 2011; Alley et al. 2011). The pH of produced water is typically strongly alkaline, with ranges of 8–9 being common (Nghiem et al. 2011). The elements that may create the greatest environmental concern are magnesium, aluminium, iron, strontium and barium (Alley et al. 2011). The rank of the coal affects some of its physical characteristics, including voids and water content (Dahm et al. 2011). The depositional environment and the rank of the coal also determine whether the methane generation pathway is dominated by thermogenic or biotic (sulphate-reducing) processes (Moore 2012). The permeability of the formation, and the availability and nature of water in surrounding formations, may dilute or concentrate various constituents in the produced water. The chemistry of the surrounding lithology also affects the formation water (Alley et al. 2011). Formations draining volcanic rocks rich in magnesium- and iron-bearing minerals, or granites rich in quartz, for example, will have very different chemistries of trace metals or naturally occurring radioactive materials (NORM). Finally, the length of time that the coal, bedrock and aquifer water have to react will also affect the chemistry of the water (Nghiem et al. 2011). Organic compounds, including aromatics, have been reported in produced water in the USA (Dahm et al. 2011). However, literature pertaining to the organic components of Australian produced water is scarce, with a few reports noting the association of elevated benzene, toluene, ethylbenzene and xylene (BTEX) chemicals with CSG and coal gasification in Queensland (Volk et al. 2011). Stearman et al. (2014) reported that polycyclic aromatic hydrocarbons (PAH) were present in around a quarter of samples of produced water from the
Walloon Coal Measures (from the Bowen and Surat Basins, Queensland). Concentrations were very low (0.5 g/L and more severe impacts at TDS >2 g/L. High sodium concentrations in soil can cause deterioration of the physical condition of the soil, such as by waterlogging, the formation of crusts and reduced soil permeability. In
Environ Sci Pollut Res
severe cases, the infiltration rate can be greatly reduced, preventing plants or crops from accessing enough water for good growth. The sodium adsorption ratio (SAR), a simplified index of the relative sodium status of soil solutions, is used to indicate the degree of sodicity of the soil exchange complex. SARW is used to characterise irrigation water to predict the potential sodicity hazard to soils. SARW is calculated as a function of the concentrations of sodium [Na+], calcium [Ca2+] and magnesium [Mg2+] given in moles per cubic meter. ½Naþ SARW ¼ rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 2þ 2þ Ca þ Mg 2 SAR has often been used to predict potential infiltration problems. When the SARW is >3, the water is sodic and can increase the exchangeable sodium percentage of the soil (NSW Department of Primary Industries 2004). Summary guidelines for interpreting SARW values are provided as follows (NSW Department of Primary Industries 2004): & & & &
6: has increasing effect on all soils at low to moderate salinity and starts to reduce growth of most crop and pasture plants; >9: severe risk of increasing soil sodicity on most soils.
In addition to high sodium concentrations, the anionic components of produced waters are commonly dominated by bicarbonate (HCO3–) and carbonate (CO32–) ions. These ions contribute to what is known as high alkalinity in water, commonly measured as milligrams per liter of CaCO3 equivalent. Levels of alkalinity which may cause problems in irrigated soils are (NSW Department of Primary Industries 2004): & &
& &
RESEARCH ARTICLE
Managing produced water from coal seam gas projects: implications for an emerging industry in Australia Peter J. Davies & Damian B. Gore & Stuart J. Khan
Received: 2 December 2014 / Accepted: 17 February 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract This paper reviews the environmental problems, impacts and risks associated with the generation and disposal of produced water by the emerging coal seam gas (CSG) industry and how it may be relevant to Australia and similar physical settings. With only limited independent research on the potential environmental impacts of produced water, is it necessary for industry and government policy makers and regulators to draw upon the experiences of related endeavours such as mining and groundwater extraction accepting that the conclusions may not always be directly transferrable. CSG is widely touted in Australia as having the potential to provide significant economic and energy security benefits, yet the environmental and health policies and the planning and regulatory setting are yet to mature and are continuing to evolve amidst ongoing social and environmental concerns and political indecision. In this review, produced water has been defined as water that is brought to the land surface during the process of recovering methane gas from coal seams and includes water sourced from CSG wells as well as flowback water associated with drilling, hydraulic fracturing and gas extraction. A brief overview of produced water generation, its characteristics and environmental issues is provided. A review of past lessons and identification of potential risks, including disposal options, is included to assist in planning and management of this industry. Keywords Produced water . Coal seam gas . Risk management . Hydraulic fracturing . Treatment and disposal Responsible editor: Philippe Garrigues P. J. Davies (*) : D. B. Gore Faculty of Science and Engineering, Macquarie University, Sydney, NSW, Australia e-mail: [email protected] S. J. Khan School of Civil & Environmental Engineering, University of New South Wales, Sydney, NSW 2052, Australia
Introduction Coal seam gas (CSG)-produced water is water that is brought to the land surface during the recovery of methane gas. This can take the form of flowback water, often associated with hydraulic fracturing, as well as formation water that is present naturally within the coal seam. Flowback water is a mixture of hydraulic fracturing fluid and formation water, making it physically and chemically different to produced water. After the flowback water is removed, the formation water that continues to be co-produced with the gas is termed produced water. The amount of produced water taken from a well depends on the natural water content of the coal seam formation (Jamshidi and Jessen 2012); permeability of the formation (Zuber et al. 1997); and the time since the initiation of pumping, well spacing and density (Klohn Crippen Berger 2012). If the formation is sufficiently permeable, produced water may be generated over the entire gas-producing life of the well. However, produced water volumes generally decrease over time (Moore 2012; Freij-Ayoub 2012). Methane and coal Methane is held in coal seams along naturally occurring fractures, pores and other macro- and micro-inhomogeneities (collectively termed voids in this paper). The voids exhibit a bimodal size distribution (the dual porosity of Jamshidi and Jessen 2012), with fractures and macro-voids defining the coal fabric and micropores characterising the matrix. The ability of the gas to move through the coal depends on the type, number, size, orientation and connectivity of these voids and, particularly, on the dimensions of the connections between the voids. Most of the gas in coal usually occurs adsorbed to the walls of the smaller voids. While only a small proportion of gas is typically adsorbed to the walls of the larger voids, these larger
Environ Sci Pollut Res
voids control the permeability of the coals and the extraction of water and gas from them (Freij-Ayoub 2012; Jamshidi and Jessen 2012). The permeability of Australian coals typically ranges from 1 to 10 milliDarcies, although these estimates are based on few publically accessible data sets. By comparison, coals in the United States of America (USA) reach a permeability of 35 milliDarcies (Jamshidi and Jessen 2012). The release of gas from coal can be stimulated by the removal of water that occurs naturally in the rock formation. When water is removed and released from hydrostatic pressure, degassing of the formation and water occurs. Gas and water can then be removed by pumping from an extraction well. Recovery of methane can be enhanced by the injection of water and additives, referred to as hydraulic fracturing, or through gases such as nitrogen and carbon dioxide, which can reduce the amount of produced water generated (Jamshidi and Jessen 2012). A conceptual illustration of the co-production of produced water during CSG production is in Fig. 1. Cleats, the natural fractures in the coal seam, contain a mixture of water (blue matrix) and methane gas (white dots) that can also be dissolved in the water stream. Water is pumped from the coal seam via a well, reducing the pressure in the coal seam and enabling methane to desorb from the coal surfaces and flow up the well bore. Water and methane may flow through separate Fig. 1 Co-production of produced water during CSG extraction
pipes to the surface, or methane may be separated from the water via a gas/water separator at the wellhead. There are substantial differences in the moisture contents of coal formations that can impact on the volume of produced water generated during gas extraction (Burra et al. 2014; Jakubowski et al. 2014). For example, the southern coalfields of the Sydney Basin are widely regarded as dry (although this is a relative term and underground mines in those areas require dewatering operations, just as elsewhere). Northward, formation waters increase in volume, and the volume of produced water per unit volume of gas also increases (Queensland Water Commission 2012). The amount of produced water will not only vary regionally from coalfield to coalfield (National Water Commission 2011), it will also vary locally in response to variability in mineral content, grain size, pore size and connectivity and permeability. As an indication of potential differences in produced water yield, CSG extraction from the southern coalfields operation at Camden, to the south of Sydney, produces a maximum of 30 ML of water per year and in 2012 produced only 4.8 ML from 89 operational wells (NSW Department of Primary Industries 2013; AGL 2013). Further north, the estimates of produced water from the Gloucester Basin in NSW was 730 ML per year across 110 well (AECOM 2009). The coalfields in the Surat Basin in Queensland produce around 7 to 300 ML per year per well (NSW
Environ Sci Pollut Res
Department of Primary Industries 2013). Queensland is by far the greatest producer of CSG in Australia, and in terms of produced water, the industry extracted around 126–281 GL/ year in 2012 (Queensland Water Commission 2012), and this is expected to increase significantly by 2030 as part of the planned expansion of the industry (Klohn Crippen Berger 2012). Chemical composition The composition of produced water varies according to the depositional environment of the coal, the rank (thermal maturity) of the coal, the flux of fresh water into the coal formation from surrounding formations and the time of residence of the water (Nghiem et al. 2011; Alley et al. 2011; Hamawand et al. 2013). The geological depositional environment for coalbearing formations typically have either saltwater or fresh/ brackish water characteristics that are rich in cations such as Na+, K+, Ca2+, Mg2+, Ba2+, Sr2+ and Fe2+ and anions such as Cl−, SO42−, CO32− and HCO3−. Sodium bicarbonate and sodium chloride are the dominant cations and anions with total dissolved solids (TDS) being highly variable (150 to 39, 000 mg/L) (Dahm et al. 2011; Alley et al. 2011). The pH of produced water is typically strongly alkaline, with ranges of 8–9 being common (Nghiem et al. 2011). The elements that may create the greatest environmental concern are magnesium, aluminium, iron, strontium and barium (Alley et al. 2011). The rank of the coal affects some of its physical characteristics, including voids and water content (Dahm et al. 2011). The depositional environment and the rank of the coal also determine whether the methane generation pathway is dominated by thermogenic or biotic (sulphate-reducing) processes (Moore 2012). The permeability of the formation, and the availability and nature of water in surrounding formations, may dilute or concentrate various constituents in the produced water. The chemistry of the surrounding lithology also affects the formation water (Alley et al. 2011). Formations draining volcanic rocks rich in magnesium- and iron-bearing minerals, or granites rich in quartz, for example, will have very different chemistries of trace metals or naturally occurring radioactive materials (NORM). Finally, the length of time that the coal, bedrock and aquifer water have to react will also affect the chemistry of the water (Nghiem et al. 2011). Organic compounds, including aromatics, have been reported in produced water in the USA (Dahm et al. 2011). However, literature pertaining to the organic components of Australian produced water is scarce, with a few reports noting the association of elevated benzene, toluene, ethylbenzene and xylene (BTEX) chemicals with CSG and coal gasification in Queensland (Volk et al. 2011). Stearman et al. (2014) reported that polycyclic aromatic hydrocarbons (PAH) were present in around a quarter of samples of produced water from the
Walloon Coal Measures (from the Bowen and Surat Basins, Queensland). Concentrations were very low (0.5 g/L and more severe impacts at TDS >2 g/L. High sodium concentrations in soil can cause deterioration of the physical condition of the soil, such as by waterlogging, the formation of crusts and reduced soil permeability. In
Environ Sci Pollut Res
severe cases, the infiltration rate can be greatly reduced, preventing plants or crops from accessing enough water for good growth. The sodium adsorption ratio (SAR), a simplified index of the relative sodium status of soil solutions, is used to indicate the degree of sodicity of the soil exchange complex. SARW is used to characterise irrigation water to predict the potential sodicity hazard to soils. SARW is calculated as a function of the concentrations of sodium [Na+], calcium [Ca2+] and magnesium [Mg2+] given in moles per cubic meter. ½Naþ SARW ¼ rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 2þ 2þ Ca þ Mg 2 SAR has often been used to predict potential infiltration problems. When the SARW is >3, the water is sodic and can increase the exchangeable sodium percentage of the soil (NSW Department of Primary Industries 2004). Summary guidelines for interpreting SARW values are provided as follows (NSW Department of Primary Industries 2004): & & & &
6: has increasing effect on all soils at low to moderate salinity and starts to reduce growth of most crop and pasture plants; >9: severe risk of increasing soil sodicity on most soils.
In addition to high sodium concentrations, the anionic components of produced waters are commonly dominated by bicarbonate (HCO3–) and carbonate (CO32–) ions. These ions contribute to what is known as high alkalinity in water, commonly measured as milligrams per liter of CaCO3 equivalent. Levels of alkalinity which may cause problems in irrigated soils are (NSW Department of Primary Industries 2004): & &
& &
