Coalbed methane produced water screening tool for ... - Inside Mines

Journal of Unconventional Oil and Gas Resources 5 (2014) 22–34

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Coalbed methane produced water screening tool for treatment technology and beneficial use Megan H. Plumlee a,⇑, Jean-François Debroux a, Dawn Taffler a, James W. Graydon a, Xanthe Mayer b, Katharine G. Dahm b,1, Nathan T. Hancock b, Katie L. Guerra b,1, Pei Xu b,2, Jörg E. Drewes b,3, Tzahi Y. Cath b,⇑ a b

Kennedy/Jenks Consultants, San Francisco, CA 94107, United States Colorado School of Mines, Golden, CO 80401, United States

a r t i c l e

i n f o

Article history: Received 8 June 2013 Revised 1 November 2013 Accepted 13 December 2013 Available online 28 December 2013 Keywords: Produced water Beneficial use Environment Treatment costs Coal bed methane

a b s t r a c t Produced water is a byproduct of oil and gas production and represents the largest volume waste stream in the oil and gas industry. Due to the high demand for water and the costs associated with current produced water disposal practices, energy companies and local water users are interested in cost-effective alternatives for beneficial use of produced water. The main objective of this study was to apply a previously developed and publicly available coalbed methane produced water screening tool to two simulated case studies to determine site-specific produced water treatment technologies and beneficial use options, as well as costs, using realistic conditions and assumptions. Case studies were located in the Powder River (Wyoming) and San Juan (New Mexico) Basins. Potential beneficial uses evaluated include crop irrigation, on-site use, potable use, and instream flow augmentation. The screening tool recommended treatment trains capable of generating the water quality required for beneficial use at overall project costs that were comparable to or less than existing produced water disposal costs, given site-specific conditions and source (raw produced) water quality. In this way, the tool may be used to perform a screening-level cost estimate for a particular site to determine whether the costs per barrel for beneficial use are more or less than site-specific disposal costs. The demonstrated technical and economic feasibility provide incentives to address the institutional and legal challenges associated with beneficial use of produced water. Ó 2013 Elsevier Ltd. All rights reserved.

Introduction Water is generated as a byproduct of oil and gas production and represents the largest volume waste stream in the industry (GWI, 2011). For coalbed methane (CBM) (coalbed natural gas), produced water is pumped to the surface during well development and production, dewatering the formation to enable release of gas from the coal seams. CBM production in the western United States (US) has grown significantly during the past two decades and will play a key role in the nation’s energy portfolio in the future. Water produced during gas extraction must be managed and disposed of according to state and federal regulatory and permit requirements, and ⇑ Corresponding authors. Address: Kennedy/Jenks Consultants, 303 Second St., Suite 300 South, San Francisco, CA 94107, United States. Tel.: +1 (415) 243 2471 (M.H. Plumlee). Address: Department of Civil and Environmental Engineering, Colorado School of Mines, 1500 Illinois St., Golden, CO 80401, United States. Tel.: +1 (303) 273 3402 (T.Y. Cath). E-mail addresses: [email protected] (M.H. Plumlee), tcath@ mines.edu (T.Y. Cath). 1 Present address: Bureau of Reclamation, Denver, CO 80225, United States. 2 Present address: New Mexico State University, Las Cruces, NM 88011, United States. 3 Present address: Technische Universität München, 85748 Garching, Germany. 2213-3976/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.juogr.2013.12.002

therefore produced water is a significant factor in the profitability of oil and gas production wells. Once the cost of managing and disposing of produced water reaches a critical threshold relative to the value of extracted gas, the CBM well is ‘‘shut in’’ (gas production is discontinued). Produced water disposal is typically via deep well injection or treatment and discharge, and therefore represents an operational challenge, an environmental risk, and a major cost for energy companies (NRC, 2010). Faced with increasing regulations, discharge water quality requirements, and costs associated with current disposal practices, energy companies are interested in cost-effective alternatives for disposal or beneficial use of their produced water. Produced water quantity, supply duration, and quality are key factors in evaluating potential beneficial uses. Beneficial use of produced water has the potential to minimize environmental impacts while providing a cost effective alternative to disposal, enhancing longevity and therefore gas recovery of CBM and gas shale fields. It also represents a new water source, potentially significant for the arid and semi-arid west of the United States and other regions around the globe. However, beneficial use of produced water faces many technical, economic, regulatory, and institutional challenges. More than 80% of current US CBM production takes place in the Rocky Mountain region, which includes the Powder River and San

M.H. Plumlee et al. / Journal of Unconventional Oil and Gas Resources 5 (2014) 22–34

Juan Basins (Fig. 1). These two basins capture and contrast the known range of produced water quantity, quality, and management in western CBM basins (NRC, 2010) and were therefore selected as the locations for the case studies evaluated. The Powder River Basin extends between Wyoming and Montana, encompassing more than 25,000 square miles. The number of wells, gas production, and associated water production in the basin have increased dramatically since 1997. CBM and co-produced water are extracted from coal layers in the Paleocene Fort Union Formation and the overlying Eocene Wasatch Formation. The coal beds in the Fort Union Formation are on average 25 feet thick (NRC, 2010; Rice et al., 2002). The San Juan Basin covers approximately 7500 square miles in northwestern New Mexico and southwestern Colorado, with the majority located in the New Mexico portion of the basin (Fig. 1). Much of the CBM development in the San Juan Basin began in the 1980s, and by 2009, over 7000 CBM wells were active in the basin (NRC, 2010). The main methane-bearing unit is the Fruitland Formation, with CBM production at depths ranging from 550 to 4000 feet (NRC, 2010). The average thickness of coal seams is 6–9 feet with a maximum of 40 feet (ALL, 2003). The main objective of the present study was to apply a previously developed and publicly available spreadsheet-based screening tool for CBM produced water to two simulated case studies to determine site-specific produced water treatment technologies and beneficial use options, using realistic conditions and assumptions. Potential beneficial uses that were evaluated include crop

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irrigation, on-site use, potable use, and instream flow augmentation, among others. Methodology Case studies development Two simulated case studies were evaluated using the Produced Water Treatment and Beneficial Use Screening Tool (Screening Tool). The Screening Tool was previously developed by the Colorado School of Mines, Kennedy/Jenks Consultants, Stratus Consulting, and Argonne National Laboratory as a decision framework to aid in the evaluation of CBM produced water treatment and use given particular site conditions and user preferences (CSM/AQWATEC, 2013a). The Screening Tool was developed as part of an effort to address a lack of public information on selecting and applying technologies to treat produced water for beneficial use, increasingly important as interest in beneficial use of produced water grows (Stewart and Takaichi, 2007). The Screening Tool and related information are available on the project website (CSM/AQWATEC, 2013b), including a case study report that provides screenshots of the tool. Potential users include energy companies and water practitioners that are interested in reducing the disposal costs associated with, and the beneficial use of, produced water. Given CBM produced water volume, quality, anticipated supply duration, and other conditions, the Screening Tool was used to determine treatment technology alternatives and costs, potential beneficial uses, and overall project costs for these uses. The Screening Tool also predicts treated water quality for the recommended treatment train. The simulated case studies use data and information that are representative of the selected site locations. This information was developed using interviews with representatives of two energy companies, literature review, and data analysis. Sufficient information was collected or assumed to utilize all aspects of the Screening Tool. Because local regulations control the allowed produced water disposal methods or beneficial uses to an energy company, an evaluation of relevant Wyoming and New Mexico regulations (where the case studies take place) was conducted and a summary is available in the Supporting information (SI). Screening Tool inputs

Fig. 1. Selected coalbed methane basins in the Rocky Mountain region of the western US.

The Screening Tool evaluates potential beneficial use projects using four modules: Water Quality Module (WQM), Treatment Selection Module (TSM), Beneficial Use Selection Module (BSM), and Beneficial Use Economic Module (BEM). A description of the modules is available in the Screening Tool User’s Manual (CSM/AQWATEC, 2013c), and the flow of data is illustrated in Fig. 2. Inputs to the WQM include the project location, produced water quality, and average and peak flow rates from the well field available for beneficial use. For produced water quality, the user may input known water quality or use default water quality based on the location from an extensive produced water quality database that was developed to support the Screening Tool (CSM/AQWATEC, 2013a; Dahm et al., 2011). Peak flow rate is used by the Screening Tool to size the treatment influent storage facility, and for the present case studies, was estimated as a 50% increase of the average flow rate to account for operation of additional wells or wells at peak (initial) flow. For the Powder River Basin case study, water quality data available for wells in the region were input to the WQM (see screenshot of Screening Tool step in Fig. 3), whereas for the San Juan Basin case study, default water quality available in the Screening Tool was selected based on project location (see screenshot in Fig. 4).

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Fig. 2. Flow of information through the four modules of the Screening Tool (CSM/AQWATEC, 2013c).

In addition to data imported from the WQM, the TSM requires scoring based on the importance determined by the user for 12 screening criteria (i.e., footprint, energy demand, modularity, capital cost, etc.; see screenshot in Fig. 5 for example), as well as information on the preferred percent water recovery for any desalination technologies. The preferable treatment approach for produced water depends on the beneficial use. Several potential beneficial uses may be considered (NRC, 2010; ALL, 2003, 2006). The Screening Tool groups beneficial uses into five categories listed in the first column of Table 1, and uses a set of water quality criteria for key parameters for each of the five categories. For example, the TDS criterion for Category 2 (crop irrigation) is 5000 mg/L, compared to 500 mg/L for Category 5 (potable use). In addition to the treated water quality criteria, the influent quality (produced water source) from the WQM, and the above user-input screening criteria, the TSM selects treatment technologies based on an analysis of over 40 produced water treatment technologies reported previously (CSM/AQWATEC, 2009).

Inputs to the BSM include data generated by the TSM, information on the anticipated produced water supply duration and reliability, and the estimated current cost of produced water disposal ($/barrel (bbl)) for comparison to the beneficial use costs. Based on these inputs, the BSM estimates treatment costs and scores project feasibility (more details are provided in Section ‘Beneficial uses’). The BEM requires information on the selected overall beneficial use project, such as land area and infrastructure required, in addition to the information generated in the WQM, TSM, and BSM. Based on these inputs, the BEM estimates the overall project costs. Additionally, the BEM provides a range of the estimated potential value of the produced water for the selected beneficial use ($mil/year), as well as estimated environmental and social benefits ($mil/year), to provide further context for the estimated costs. The value ranges are provided in the tool for each beneficial use and were based on input from one of the tool developers (Stratus Consulting) with expertise in water resources valuation (Stratus Consulting, 2006). An exhaustive presentation of the assumptions and analysis for determining the value of the water and associated benefits is outside the scope of this article. The estimated value of environmental and social benefits are intended to provide a broad assessment of potential opportunities that may be available to support the beneficial reuse of produced water. Many of the case study inputs are presented with the results below, and more detailed information on the inputs and screen shots of the module outputs are available online (CSM/AQWATEC, 2013b). Background on case study locations Produced water volume and quality The average water production rate during CBM extraction for the 1995–2005 period in the Powder River Basin was 2.2 bbl per thousand cubic feet (MCF) of gas, compared to 0.03 bbl per MCF

Fig. 3. Produced water quality data for Powder River Basin case study (screenshot of WQM output). Notes: Water quality data input from Dahm et al. (2011) or, if no data was available, from the Screening Tool WQM database.


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Fig. 4. Produced water quality data for San Juan Basin case study (screenshot of WQM output). Notes: Water quality data input from the Screening Tool WQM database.

Fig. 5. TSM selection criteria user scores for the Powder River Basin case study (screenshot).

Table 1 Potential beneficial uses and preferred treatment trains for the Powder River Basin, Wyoming case study from the Treatment Selection Module (TSM) of the Produced Water Treatment and Beneficial Use Screening Tool. Screening tool category beneficial use

Preferred treatment traina

1 2 3 4

No treatment required Anion IX Anion IX Chemical disinfection, media filter, tight NF (brine disposal: deep well injection)

– Livestock watering; impoundments; dust control – Crop irrigation; non-potable use – Constructed wetlands – Surface water discharge/instream flow augmentation; fisheries 5 – Potable use; aquifer storage and recovery (ASR)

Chemical disinfection, media filter, tight NF, chemical disinfection (brine disposal: deep well injection)

Anion IX = anion exchange; ASR = aquifer storage and recovery; NF = nanofiltration. a Descriptive information for each unit process is available in CSM/AQWATEC (CSM/AQWATEC, 2009).

in the San Juan Basin (Osborne and Adams, 2005), where one bbl is equal to 42 US gallons (159 L). Based on average data, water

production from San Juan Basin CBM wells is 25 bbl/day per well (USGS, 2000). The amount of water produced from an individual

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CBM extraction well typically declines over the course of gas production (e.g., approximately 10 years, see Fig. 6). For a group of wells or a well field, the total water production available for beneficial use depends on management practices such as the timing of bringing new wells online while others are being shut in or their water production rate declines. Well spacing ranges approximately 40–80 acres per well in the Powder River Basin (ALL, 2003) and 160–320 acres per well in the San Juan Basin (Bryner, 2002). A produced water supply may be maintained by the operation of new wells within the well field or nearby. With respect to water quality, the major constituents of interest in produced water are the salt content (as total dissolved solids [TDS] and conductivity), oil and grease, total organic carbon, various inorganic and organic chemicals, and naturally occurring radioactive material (CSM/AQWATEC, 2013d). The salt content of produced water can range from as high as 170,000 mg/L TDS, which is approximately five times the concentration of seawater, to as low as 200 mg/L TDS, which is below the EPA secondary drinking water standard (500 mg/L TDS) (NRC, 2010; Rice et al., 2002; CSM/AQWATEC, 2013d). Compared to CBM produced water from the Powder River Basin in Wyoming and Montana, produced water from the San Juan Basin in Colorado and New Mexico is high in salinity, with TDS concentrations that can sometimes exceed 100,000 mg/L. Therefore, produced water from the San Juan Basin, without treatment, is expected to exceed water quality standards for drinking water, agricultural irrigation, and livestock watering applications (NRC, 2010). Existing disposal infrastructure Information on existing produced water disposal practices is not necessary to run the CBM produced water Screening Tool, but was reviewed for informational purposes based on case study interviews and literature review. In the Powder River Basin, multiple disposal options for produced water may be exercised by a single energy company in a given area (ALL, 2003, 2006). Disposal methods and uses that require treatment are generally avoided where possible given the cost of water treatment and the fact that no revenue is typically received for produced water delivery (e.g., for irrigation and livestock watering by local ranchers). The primary disposal options in the state of Wyoming are direct discharge to surface waters with or without treatment, depending on water quality, injection (such as into a deep well or using shallow, subsurface drip systems), or disposal into impoundments, referred to as pits or reservoirs in Wyoming regulations (NRC, 2010; Wyoming SEO, 2011; WOGCC,

2011; Wyoming DEQ, 2011). A description of the Wyoming CBM regulatory framework is provided in the SI. Even though stream discharge may be considered beneficial use (i.e., instream flow augmentation), operators view it as disposal. In a typical scenario, an operator will construct a pipeline network to transport water from wells to various disposal routes and uses, none of which usually produce revenue. The pipelines are located 6 feet underground and deliver water produced from a single well, if it is in a geographically remote location, or more often from a group of nearby wells (e.g., up to 100 wells), to a trunk line. The produced water discharges are comingled regardless of water quality, which can vary for different wells. Water is rarely delivered by gravity and must be pumped. Depending on the distance between clusters of wells and disposal routes, as well as limitations imposed by local land owners or other factors, water may be transported over distances ranging from less than a mile to more than 20 miles. Water may be delivered to multiple endpoints including on or offsite treatment plants if treatment is required for disposal compliance, to stream discharge, to a deep injection well, or most commonly, to impoundments. A typical Powder River Basin operator may manage hundreds of impoundments near wells and groups of wells ranging in capacity from less than 1 acre-foot (1233 m3) to up to 100 acrefeet (123,000 m3). Photographs of a produced water aeration structure (for treatment) and nearby impoundment are provided in Fig. 7. Impounded water evaporates and infiltrates into the ground as a means of disposal. Wyoming regulations require groundwater monitoring beneath the impoundments. From impoundments, some water may be diverted to beneficial uses such as irrigation by local ranchers, livestock watering, or on-site uses (e.g., road dust control, drilling, and enhancing wells). For untreated irrigation water where water quality is sometimes unsuitable for ranchers, the produced water may be treated by gypsum addition to reduce sodium adsorption ratio (SAR) and salting of the soils. In contrast to CBM producers in the Powder River and other basins who rely on a combination of multiple disposal options, the primary disposal option in the San Juan Basin is deep well injection with minimal treatment (NRC, 2010). A 2002 study indicated that 99.9% of produced water in the San Juan Basin is injected (Bryner, 2002). This is due to the relatively low volumes and high salinity of produced water in the San Juan Basin. However, deep well injection is a costly disposal method and provides no significant benefit. Most producers temporarily store the produced water in aboveground storage tanks prior to injection. Treatment by chlorination is required prior to injection to address bacterial contamination,

Barrels of Produced Water Per Day (bbl/d)

1400 Well 1 1200

Well 2 Well 3

1000

Well 4 Well 5

800

Well 6 600

Well 7 Well 8

400

Well 9 Well 10

200

Mean 0 0

2

4

6

8

10

12

Time (years) Fig. 6. Mean water production curves (bbl/d) over the life of CBM wells (Powder River Basin case study).


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Fig. 7. Produced water aeration structures in the Powder River Basin used to remove iron and manganese prior to impoundment.

and filtration is commonly conducted to prevent plugging of the injection well (NRC, 2010). Deep injection wells in the San Juan Basin are either companyowned or commercially operated. To transport produced water from the storage tanks to the injection wells, operators use pipelines or commercial trucking services, depending upon the location of the well. Aquifer replenishment and enhanced gas recovery may be ancillary benefits of well injection (NRC, 2010). With respect to produced water disposal, a description of the New Mexico CBM regulatory framework is available in the SI. Hydraulic fracturing In the course of completing this study, hydraulic fracturing was identified as a key potential beneficial use of interest for the San Juan Basin produced water. Hydraulic fracturing is a well stimulation process that uses water to enhance natural gas recovery. Produced water is increasingly recognized as a source water and is being used for hydraulic fracturing, driven by high produced water disposal costs coupled with water scarcity (AWI, 2011). Fluids and sand are injected under pressure into the formation to form fractures and pathways for gas (or oil, in the case of oil production) to reach the well. Then the gas, fracturing fluids, and produced water are pumped to the surface (flowback) for recovery and disposal. Estimates of the fluids recovered range from 15% to 80% (i.e., a portion of the water used for hydraulic fracturing returns to the surface in the flowback, along with produced water [groundwater]) (AWI, 2011; EPA, 2004). Hydraulic fracturing is infrequently used in the Powder River Basin where the natural permeability of the methane-bearing formations is high, but it is commonly used in the San Juan Basin (NRC, 2010). Each well may require fracturing at multiple depths, and each fracturing event requires thousands of barrels of water, depending on the fracturing method used. Required volumes range from 50,000 to 350,000 gallons in a coalbed formation (EPA, 2004) to 2–6 million gallons per well in a shale formation (AWI, 2011; Stewart, 2011; EPA, 2010). Currently, water from the San Juan and Animas Rivers is used as the base fluid for hydraulic fracturing in the San Juan Basin (Huang et al., 2005). Alternatively, produced water from adjacent wells can be beneficially used for fracturing operations. Produced water volume from a given well will typically exceed the volume required for hydraulic fracturing of that well, and thus excess water is available for other beneficial uses or must

be disposed. These other beneficial uses may be considered using the Screening Tool. Results and discussion Powder River Basin, Wyoming Produced water volume and quality The Powder River Basin simulated case study focuses on produced water from an assumed group of 400 wells operating in an 80-square mile area in the Wyoming part of the basin. The assumed well spacing is relatively large at approximately 130 acres per well. The anticipated life of this well field and associated water production, in terms of the longevity of the gas resource, is 10–20 years, depending upon the continued development of additional wells within the well field area. The produced water volume, quality, and existing disposal approach utilized for the case study are representative of energy companies operating in the basin. A mean production curve (Fig. 6) was developed by averaging produced water quantity data for ten CBM wells having at least a ten-year history, available from the Montana Online Oil and Gas Information System for Big Horn County (DNRC, 2010) located in the Powder River Basin. The production curve is consistent with production behavior described by energy companies during case study interviews. Operators stagger the initiation of new wells in order to manage and minimize the total volume and variability of produced water from a well field, because water production is highest at the early stage of well production. Additional constraints, such as wildlife-related permitting restrictions, may limit new well construction to certain periods. The case study produced water volume available for beneficial use from the 400-well field was estimated assuming the mean well production curve (Fig. 6) and yearly initiation of new wells according to an assumed permitting schedule over a 20 year period, resulting in an average total water production of 45,000 bbl/d (1.9 MGD; 2120 acre feet per year; 7200 m3/d). This value was input to the WQM of the Screening Tool. Average produced water quality utilized for the case study is provided in Fig. 3 and was based on water quality data for approximately 90 wells in the Powder River Basin in Wyoming (Dahm et al., 2011). The average TDS concentration of the dataset is 912 mg/L, which is less than the limit for beneficial use for irrigation in Wyoming (2000 mg/L) and for livestock watering (5000 mg/

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L), and would generally be considered fresh water (