Energy Policy Act of 2005 (Ultra-deepwater and Unconventional Resources Program)
Pretreatment and Water Management for Frac Water Reuse and Salt Production
The goal of this project is to overcome this barrier by evaluating the applicability of three pretreatment processes to pretreat high-total dissolved solids (TDS), high hardness frac water, such as is found in the Marcellus shale, for thermal recovery of water and a salable salt product. This work will identify cost, performance, and adaptability to mobile operation for each of three pretreatment technologies to be investigated.
This project will develop a methodology of evaluating frac water pretreatment options. Based on field frac water data (flow and composition profiles) the team will establish feed composition and flow rate design bases for both mobile and stationary pretreatment processes. The team will conduct technical and economic assessments of three candidate pretreatment options and select a process for further development. Based on lab and modeling studies, the team will identify process issues (and resolutions as applicable) and develop process design and cost estimates for both stationary and mobile pretreatment facilities.
GE Global Research, Niskayuna, NY 12309
The contribution to the U.S. energy supply from unconventional natural gas sources such as shale is increasing dramatically. Shale gas production in the U.S. increased from 0.3 TCF in 1996 to 1.1 TCF in 2006, accounting for 6% of the nation's natural gas supply. To release natural gas from a shale deposit, 1 to 5 million gallons of water plus hydrofracturing chemicals and proppants (sand) are pumped under high pressure down a shale gas well. Often, this water is trucked in from remote locations. About 20-80% of this water returns to the surface as "frac flowback water". Much of the frac water has a high TDS level (>50,000 ppm). Currently, most frac water is trucked off-site for disposal by deep-well injection in salt formations; this has also been the primary disposal option for oil- and gas-produced water. A significant problem with many shale gas plays, particularly the Marcellus Shale, is that the capacity of nearby injection sites is severely limited. For example, frac water from Pennsylvania is currently trucked into Ohio for disposal by deep-well injection. Gaudlip et al. have quantified the frac water disposal problem for the Marcellus Shale. In other shale gas plays, such as the Barnett Shale, water availability for frac operations is limited. To avoid these water limitations and to further develop shale gas resources will require an economical process to recover and reuse water from hydrofracturing operations.
Frac water recovery by thermal evaporation is commercially practiced in a small number of shale gas applications. To avoid scaling on heat exchange surfaces and to enable reliable evaporator operation, incoming frac water must be pretreated to remove scale-causing ions (as well as suspended solids and dissolved organics). Current pretreatment methods typically utilize flocculation, mechanical separation (e.g. inclined plate clarifier), and filtration (e.g. filter press).
This project is focused on pretreatment techniques to remove hardness and other multivalent cations from high-TDS brines. Three pretreatment approaches are considered. These include chemical treatment, ion exchange, and nanofiltration. Chemical treatment in the form of lime softening and optional sulfate precipitation for barium removal is effective for softening chlor-alkali brine. Calcium hydroxide (lime) and/or caustic soda are added to precipitate scale-forming species. Lime softening may be conducted in a clarifier and generates a precipitate (lime sludge), which is filter pressed and may be either landfilled or calcined to recover the lime. ProChemTech International, Inc. describes a chemical treatment process that pretreats frac water using three sequential precipitation steps. The first step removes barium by precipitation as barium sulfate, which is non-leaching by Toxicity Characteristic Leaching Procedure (TCLP). The remaining scale formers are precipitated in subsequent precipitation steps.
The large volumes of water associated with hydrofracturing, combined with either limited deep well injection capacity in states such as Pennsylvania or limited availability of freshwater in states such as Texas, have led to a significant increase in truck traffic for hauling water. This has led to citizen concerns such as traffic congestion, damage to roads, dust, and noise. Thus, technology that enables cost-effective frac water reuse in shale gas production is essential for sustained development of this resource. Further, because gas wells are dispersed geographically and because most frac flowback occurs over a relatively short time period (e.g. <30 days after hydrofracturing), it is necessary to develop methods of frac water recovery that can be adapted to mobile operation.
Evaluation of the relative merits of the proposed pretreatment technologies for frac water reuse first requires a clear definition of the range of frac water feed composition to be treated. Second, target purity specifications for pretreatment will be established for frac water that is to be thermally concentrated and crystallized in order to ensure robust operation of the thermal equipment. Third, purity specifications will be established for both recovered water that is to be reused as frac water and for precipitated salt that is to be used as road salt. For reuse as frac water, the levels of hardness and multivalent species in recovered water must be reduced to levels that will not cause plugging in subsequent hydrofracturing operations. Further, the TDS level in the recovered water must be consistent with effective frac operations. Studies are underway to determine the minimum quality of water usable for hydrofracturing.
Process material and energy balances will be conducted for each process option in order to generate preliminary cost estimates. Each process option will be evaluated with respect to performance, cost, and the adaptability to mobile operation. The most promising candidate process will be evaluated in the lab using both synthetic and field sampled frac water.
Cost-effective frac water recovery and reuse is essential to continued development of shale gas production. As frac water reuse becomes widely practiced, a key benefit to the environment will be a greatly reduced net consumption of fresh water. Second, truck traffic, noise, and dust pollution will be significantly reduced. Third, by not reinjecting frac water into disposal wells, the risk associated with long-term contamination of the water supply will be avoided.
Work on this project began in August 2009. A Project Management Plan, consisting of a work breakdown structure and supporting narrative with a summary of the objectives and approach, and a Technology Status Assessment summary report, describing the state-of-the-art of the proposed technology, have been completed.
GE-GRC has already made a number of major accomplishments. They defined frac water composition and flow rate specifications for fixed and mobile treatment systems; ruled out ion exchange as a softening technique for high-hardness (10,000 ppm) frac water based on calculated volumes of regeneration chemicals and rinse water; summarized naturally occurring radioactive material (NORM) levels in New York Marcellus gas wells (from NYSDEC SDGEIS report); and defined lab experiments to test processes for NORM removal from frac flowback/produced water.
The project performer developed Aspen/OLI model for chemical treatment of frac water. They calculated material balances for lime softening and sulfate precipitation; defined feed composition range for stationary frac water treatment plant operating in northeast Pennsylvania; identified NORM and technologically enhanced NORM (TENORM) disposal options and costs (ongoing); assembled lab apparatus to simulate thermal brine concentrator and crystallizer (for thermal water and NaCl recovery); and demonstrated foaming issue on Marcellus frac water evaporation.
Three samples of produced water were obtained from shale gas wells in North Central PA. The samples were analyzed for NORM via scintillation counting, alpha/beta counting (in house) and gross alpha, gross beta, Ra226, and Ra228 (external lab). GE-GRC developed a scintillation counting method to measure NORM reduction in frac water by pretreatment methods (adsorption and precipitation). They also demonstrated effectiveness of sulfate precipitation for NORM removal from frac water and noted that initial NORM levels in brines obtained thus far is about 3-5X background. Later, a problem was discovered with the scintillation counting technique for measuring NORM in frac water samples (sample+cocktail yielded precipitate). Alternate scintillation cocktails were tested, and a new technique was developed.
Additional high-NORM frac water samples from North-Central PA were arranged for, and a frac water sample from North-Central PA was analyzed using outside lab: ca. 1000 pCi/L gross alpha; 5000 pCi/L gross beta. The lab could not measure Ra226 or Ra228 because of high matrix interference. Additional samples were sent to outside lab for gross alpha and beta analysis.
In other accomplishments, experiments were initiated using DOW RSC resin to remove radium from frac water. Ra226 standard solution was ordered, and a GE Radiation Safety Training course (20 hours) was completed.
This project has been completed. The final project report is listed below under "Additional Information".
Major tasks to complete this project and are summarized below.
Task 3- Technology Transfer - GE GRC will designate 2.5% of the amount of the award for funding technology transfer activities. Throughout the project, GE GRC will work with RPSEA to develop and implement an effective Technology Transfer Program at both the project and program level. In addition, GE GRC will provide information requested by RPSEA to support the quantitative estimation of program benefits.
Task 4- Define Feed Water and Well Attributes and Product Specifications - It is necessary to define the feed water and well attributes (both composition and water flow) to successfully evaluate the various pretreatment strategies and to define an effective inter-well water management strategy. It is also necessary to determine the product specifications in order to evaluate the ability of the various pretreatment strategies to produce a salable salt product.
Task 4.1- Determine Feed Composition - The team will determine a general composition profile of the frac flowback water from shale gas wells by mining extant data. It is important to determine a profile of the composition over the life of the well, and also the variability that may be seen from well to well, as this will have a significant impact on the pretreatment technology chosen and the overall water management strategy.
Task 4.2- Determine Feed Flowrate Profile - The team will determine a flowrate profile of the frac flowback water from shale gas wells by mining extant data and through discussions with STW Resources and producers of natural gas from gas shales. It is important to determine a profile of the flowback over the life of the well, as this will have a significant impact on the pretreatment technology chosen and the overall water management strategy.
Task 4.3- Define Specifications for Frac Water and Salable Salt Product - The products from the proposed water treatment process are distilled water, which can be re-used in the drilling process, a salable salt product, and an impurity stream that depends on the pretreatment process. The team will work with STW Resources and well operators to define the purity specifications for water used to make hydrofracturing fluid. The team will also define specifications for the salt produced by the proposed process. One potential application for the produced salt is road salt.
Task 4.4- Identify Frac Flowback Water Source and Obtain Frac Flowback Water Samples Through STW Resources, GE GRC will work cooperatively with a producer of natural gas from gas shales to obtain frac flowback water samples and information on well characteristics (flow, composition histories). Deliverables will include the following: 1) a characteristic composition profile over the course of a well lifetime; 2) a characteristic flow profile over the course of a well lifetime; 3) a specification for the water to be used in the drilling and hydrofracturing processes; 4) a specification for the salable salt product; 5) identification of a natural gas producer willing to share information and water samples; and 6) frac flowback water samples obtained and analyzed.
Task 5- Evaluate Pretreatment Techniques - The frac flowback water composition varies significantly both from well-to-well, and for a specific well over the course of time. The performance and cost-effectiveness of each pretreatment technique depends on the frac water feed composition. Lab experiments with each pretreatment technique will need to be conducted, because performance of these pretreatment techniques at high salt concentrations is not well-characterized in the literature.
Task 5.1 - Develop a System Cost Model Based on Material and Energy Balances for Each Pretreatment Option - The models will capture the key aspects of each process. For example, the energy balance will include both thermal and electrical energy requirements; the material balance will account for the ionic equilibria of major components.
Task 5.2 - Conduct Bench-scale (0.5-1 liter) Laboratory Experiments for Each Pretreatment Option - The experiments will be conducted with synthetic feeds that mimic frac flowback water from typical shale gas wells. The team will measure the performance degradation that occurs with key foulants and/or poisons. For example, strong base anion exchange resins are known to be fouled by various metal complexes such as titanates, molybdates, and silicates. Each fouling and/or failure mode will be characterized. The team will also establish the feed flow rate turn-down capability as well as other process operating boundaries for each process option.
Task 5.3 - Test Treated Water for Downstream Processing Suitability - The treated water from each candidate pretreatment process will be tested for its suitability for downstream processing in a brine concentrator and a thermal crystallizer. Lab tests based on the experience of GE Water & Process Technology's Thermal Products Division (RCC) will be utilized. The deliverables will be a downselected pretreatment technique for further development and a go/no-go decision made based on system performance parameters evaluated.
Task 6 - Develop Process Model of Selected Pretreatment Process - A more extensive set of process models than those developed in Task 5 is required for estimating the selected system size and cost. A set of detailed process models for the pretreatment technique selected in Task 5 will be developed. These models will have the ability to predict both steady-state and transient behavior of the process. It is anticipated that the steady-state behavior, which will be based on rigorous ionic equilibria, will be modeled using Aspen Plus«. Key transient behavior, such as ion exchange breakthrough profiles, will be modeled using MATLAB« based on lab data from both the experiments of Task 5 and the literature. The deliverables will be steady-state and transient process models that capture the key process characteristics and define the basis for equipment design, sizing, and costing
Task 7- Determine Inter-well Water Management Strategy - Because of the transient nature of the frac flowback composition and flowrate, it will be essential to design the water treatment system accordingly. This task will determine the best strategy to achieve a cost-effective solution that yields the maximum environmental benefits.
Task 7.1ŚWork with Gas Producer to Define Specifications for Full-scale System Design - GE will work with STW Resources to collect information from gas producers in the Marcellus Shale play, regarding the number and schedule of planned wells at a specific site. The locations of the wells and proximity to roads will be documented. An estimate will be made for a schedule of water needs for well development and the frac flowback water collection. Based on this data, several scenarios will be considered for collection, storage, and redistribution of frac flowback water.
Task 7.2- Test Alternate Inter-well Water Management Strategies - The goals for an optimized inter-well water management strategy follow: 1) Minimize system cost with respect to natural gas production; 2) Minimize water transportation; 3) Minimize water storage; 4) Maximize equipment utilization; and 5) Minimize equipment footprint. Scenarios involving mobile water recycling systems that are transported from well to well will be compared with larger, less mobile systems in which water is delivered to a central processing facility by a temporary pipe network or by trucks. The different conceptual designs for the integrated water recycling system will be compared and analyzed using MS« Excel-based models that will estimate required tankage, truck transports, equipment throughput, and lifecycle cost.
Task 7.3- Define Inter-well Water Management System - Based on the analysis in Task 7.2, the best design for managing water on a specific Marcellus Shale play will be determined. A lifecycle cost analysis will be conducted to determine the impact on the cost of natural gas. In addition, an assessment will be made as to how transferable this inter-well water management system will be to other shale gas plays, and under what conditions different strategies will be warranted. Deliverables are to include a defined inter-well water management strategy for a specific Marcellus shale gas play; determination of applicability of strategy to other shale gas plays; and a determination of potential mobile water treatment system design.
Task 8- Validate Process to Define Process Lifecycle - Prior to the pilot-testing, which is planned after successful completion of this project, the pretreatment technology downselected in Task 5 must be scaled-up to identify potential process issues. In addition, the suitability of the pretreated water in the downstream processes of evaporation and crystallization must be confirmed on a larger scale.
Task 8.1- Demonstrate Selected Pretreatment Process at Pre-pilot Scale - The selected pretreatment process will be scaled-up approximately 10-fold from 0.5-1 L/min in Task 5 to a feed rate of 5-10 L/min. This scale is designed to enable process issues to be identified. For ion exchange pretreatment, the long-term regenerability, particle attrition rates, and the resin susceptibility to trace poisons (besides those found in Task 5) will be established. For nano-filtration, membrane fouling and cleaning processes will be determined. For lime softening, waste sludge will be characterized and cation leak-through to processed water will be measured.
Because synthetic wastewater made in the laboratory never behaves exactly like water obtained from the field, the test rig will be operated with field water. It is expected that at least 500 gallons of frac flowback water from the Marcellus Shale play will be transported to GE GRC for these tests.
The process performance will be characterized so that the process model developed in Task 6 may be validated. With a validated process model, the integrated system model in Task 6 may be used to accurately predict performance and estimate lifecycle costs.
Task 8.2- Screen Process Conditions for Thermal Evaporator Suitability and Verify Product Quality - The pretreated water resulting from the selected process will be evaluated for suitability with GE's Thermal Products (GE RCC) evaporation and crystallization technology, which is used extensively in zero liquid discharge (ZLD) applications. GE's ZLD technology is a two-step process of concentration followed by crystallization. In a ZLD application of pretreated brine, approximately 70% of the water is evaporated in a brine concentrator; the remaining 30% is recovered in the crystallizer. Small-scale laboratory tests to qualify purified water for evaporation will be conducted using GE's proven screening techniques. To confirm material selection for the concentrator and crystallizer, small-scale coupon corrosion tests will be conducted in accordance with GE's standard techniques. Finally, the crystallized salt product will be characterized to confirm that it meets the specifications required for sale. This characterization will include composition analysis as well as particle size, both of which are critical to the Department of Transportation in most states.
Task 8.3- Generate Pretreated Water Sample for Pilot Thermal Evaporator Test - Subsequent to the small-scale screening tests, it is common to run a large sample through GE RCC's pilot brine concentrator. This rig, located at GE's facility in Bellevue, WA, accurately represents the conditions in a full-scale brine concentrator. The brine concentrator is based on a multi-tube, falling film, mechanical vapor compression design. The pilot rig tests a single tube under the actual conditions in the brine concentrator. It is estimated that 500 gallons of pretreated water will be required for this task. This pretreated water will be shipped from GE GRC to GE RCC for the tests.
Task 8.4- Run Brine Concentrator Test at GE RCC - The pilot-scale brine concentrator test will be conducted with frac flowback water that has been pretreated with the selected technology. Based on this test, an accurate estimate of the size and cost for the full-scale evaporator will be made. Deliverables will include the following: 1) identification of process issues; 2) determination of suitability of pretreated frac flowback water for evaporation and crystallization; 3) generation of 500 gallons for pretreated water for concentrator pilot test; 4) results from pilot test; and 5) conceptual process design and cost estimate of concentrator and crystallizer for full-scale frac flowback water recycle system.
Project Start: August 17, 2009
Project End: August 16, 2011
DOE Contribution: $1,105,000
Performer Contribution: $326,000
RPSEA - Bob Siegfried (firstname.lastname@example.org or 281-690-5502)
NETL - Skip Pratt (email@example.com or 304-285-4396)
GE Global Research Center - James Silva (firstname.lastname@example.org or 518-387-6472)
Final Project Report [PDF-2.57MB]