07123-05

Goal
This project seeks to demonstrate a cost-effective process for produced water purification at the wellhead using a low-temperature distillation unit. The researchers will construct a demonstration unit that can utilize solar energy and coproduced geothermal energy for wellhead produced water desalination and will conduct a pilot test at two wellhead locations for a period of one year. Technical feasibility and economic efficiency of the proposed process will be evaluated by testing the energy consumption, maintenance cost, and durability.

Performers
New Mexico Institute of Mining and Technology, Socorro, NM 87801
Harvard Petroleum Corpany, LLC, Roswell, NM 88202
Robert L. Bayless, Producer LLC, Farmington, NM 87499

Background
Produced water embodies the primary waste stream of oil, natural gas and coalbed methane production. It is very saline, sometimes nearly six times as salty as seawater, and contains dissolved hydrocarbons and organic matter as well. For many small oil/gas producers, purification of the produced water at the wellhead, and on-site disposal or use of the purified water for beneficial uses such as well drilling and stimulation, will be the primary options for cost-effective produced water management, due to the shortage of storage capacity and limitations of distribution technologies. Deployment of advanced technologies for removing salts and dissolvable organics is generally required for attaining surface water discharge standards or reuse criteria.

To purify produced water to substantial quality suitable for beneficial uses such as well drilling, stimulating or land revegetation, efforts have been focused on demineralization and organic removal. The demineralization technologies include reverse osmosis (RO), distillation, electrodialysis, freeze-thawing desalination, and ion exchange; air stripping, activated carbon adsorption, membrane filtration, biological treatment and wet air oxidation have been widely investigated for dissolved organic removal. Unfortunately, the applications of these technologies are highly limited due to environmental sensitivity (i.e., freeze-thawing) and energy intensity caused by floating oil and hydrocarbons (i.e., reverse osmosis and electrodialysis). Other factors such as feed water chemistry, water volume, and additives in produced water also show considerable influence on the process design and technology deployment. Even with the rapid advancement in water desalination technology and tremendous efforts in produced water purification, no process was reported to be cost-effective for produced water desalination. The desirable technology needs to be tolerant of the large variations in feed water quality and water volume for deployment at the wellhead.

In this project, a demonstration of low-temperature distillation unit with a built-in dehumidifier will be constructed for produced water purification. The use of solar energy for water heating is particularly designed for application in areas with abundant solar radiation, such as New Mexico. In addition, this water purification system can use co-produced energy sources to drive the desalination process, in which a considerable decline in electricity consumption is expected. The industry partners (Harvard Petroleum Company, and R.L. Bayless Producer) will review laboratory work and equipment design, providing feedback where necessary for meeting their site-specific requirements. In addition, the partners will also collect water samples for analysis, provide the primary researchers with other parametric data, and provide assistance with equipment installation and field evaluation.

Potential Impacts
The proposed desalination process could be shown to be cost-effective compared to conventional water management because the use of solar and coproduced energy sources will decrease the need for significant additional energy input. There is no sophisticated pretreatment required, and the process is less sensitive to water quality and quantity and thus can be fitted to both individual wells and local disposal sites. There are many marginal wells operating at the lower edge of profitability where a reduction in water management costs can potentially extend production.

Successful development from this project will result in a considerable decline in salt water disposal. The waters purified by the proposed process are very clean and could be a valuable clean water resource for land revegetation and oil production. In addition, any reduction in deep well injection will significantly reduce the risk of ground water contamination from injected produced water.

Finally, a supply of purified water is important to a variety of E&P activities. Various drilling and completion procedures currently require large amounts of fresh or brackish water. If water is routinely obtained from surface sources, activity may be curtailed in drought years or as population increases because water supplies have dried up or are completely appropriated for other higher-quality uses. A supply of purified water could significantly impact drilling activities through both cost reduction and reduced environmental impact.

Accomplishments
Work on this project began on August 9, 2008 and the accomplishments are summarized as:

• Produced water desalination by low-temperature distillation was tested by bench scale experiments. Water productivity and latent heat recovery of the two air-water contactors were investigated. Bench tests indicated that the total organic carbon (TOC) was removed from 470.2 mg/l to 17.8 mg/l with a removal efficiency of >98% and the total dissolved solids (TDS) were reduced from 1.98×104 to 76.3 mg/l with a removal efficiency of >95%.
• Two air-water contactors including column with shell and tubes and built-in capillary tubing bundle were established for enhancing latent heat recovery. The water productivity was increased from 48 to 311 ml/(m2.h) as the built-in capillary tubing bundle was used for latent heat recovery. The influence factors, such as feed water temperature and feed water/air ratio, on the water productivity were also investigated. Increasing feed water temperature or feed flow rate increases the heat loss, but the water productivity and recovery increase as a result of more efficient heat use.
• A demonstration unit was constructed and tested to evaluate the efficiency of high-salinity (TDS>70,000 mg/L) produced water desalination and to optimize the operating parameters for enhanced performance. The water productivity ranges from 5 to 10 gallon/hr at feed water flow rate of 30 gallon/hr.
• Laboratory tests have been accomplished, the process design has been finished, and a solar water heating system for produced water heating has been designed and is ready for field installation.
• Modification of the water condensation unit was carried out and the feed water flow rate will be increased to 60 to 100 gallon/hr.
• New steam heating system was installed and new water pump was purchased for increasing the feed water from 1.0 L/min to 3 L/min. Testing on the prototype with actual produced water is under investigation and results suggest that purified water has a total dissolved solid (TDS) less than 300 ppm.
• The water treatment prototype was installed for testing. At feed water flow rate of 1.0 L/min, about 52.7% water will evaporate with an air flow rate of 3516 L/min. Due to the limitation of feed water flow rate during experimental conditions, about 4.7% of water could be recovered as clean water. All the tests show >92% ion removal by the prototype.
• A new dehumidification chamber was installed for testing. The feed water temperature was varied from 60C to 85C and the feed water flow rate was varied from 0.3 L/min to 2.0 L/min. Due to circulation pump air lock limitation, the feed water flow rate was limited at 2.0 L/min. A new circuation pump was installed.
• The prototype was tested at feed water flow rate of 3.0 to 4.5 liter/min and 11 liter/hr purified water was collected.
• Two papers have been published or accepted for publication:
  • X. Li, S. Muraleedaaran, L. Li, and R. Lee, “A Humidification Dehumidification Process for Produced Water Purification,” Desalination, in press, 2010.
  • S. Muraleedaaran, X. Li, L. Li, and R. Lee, “Is Reverse Osmosis Effective for Produced Water Purification: Viability and Economic Analysis,” SPE 115952, Presented at the 2009 SPE Western Regional Meeting Held in San Jose, USA, 24-26, March 2009.
• Other technology transfer efforts:
  • L. Li, et al., "Cost-Effective Treatment of Produced Water by Using Co-Produced Energy Sources for Small Producer," RPSEA Small Producer Technology Transfer Meeting, Midland, Feb. 3, 2010.
  • Xinhua Li, Master thesis, “Experimental Analysis of Produced Water Desalination by a Humidification-Dehumidification Process,” December, 2009.
  • A presentation is scheduled for the 2011 Produced Water Society meeting on Jan. 18 2011.

Current Status (January 2011)
The key tasks to be undertaken following the submission of the Project Management Plan and Technology Status Assessment are outlined as:

Development Purification Technology for Wellhead Deployment – The researchers will develop a low temperature-of-distillation process that can be deployed at the wellhead for produced water purification. The desalination unit will be tailored to fit the water production requirements at individual wells. Built-in dehumidifiers with different configurations will be designed and tested for maximizing the energy efficiency and latent heat recovery. This task has three subtasks:

• Design and demonstration of a low-temperature distillation process for produced water desalination. Two types of built-in condensers will be evaluated for enhancement of heat transfer and latent heat recovery. The first configuration is a bundle of capillary tubing embedded in an evaporating casing. The second configuration is a separation unit with many evaporation and condensation chambers stacked in parallel.
• Design optimization to enhance the internal heat transfer and improve the latent heat recovery.
• Testing of the water purification process, focusing on optimizing operational parameters for maximum water production, and energy efficiency. Water chemistry, feed water temperature, water/air flow ratio, and airflow rate will be varied for evaluating their impacts on separation efficiency.

Process Design and Equipment Procurement for Solar and Coproduced Energy Sources - The researchers will construct a demonstration unit that will utilize solar energy and coproduced geothermal energy for produced water desalination at the wellhead. This task has three subtasks:

• Quantitative analyses of coproduced geothermal and solar radiation in the San Juan and Permian Basins to determine the adequacy of the renewable energy supply for driving low-temperature distillation in different seasons. Integration of the solar heat collector and coproduced geothermal energy will be investigated for a continuous operation.
• Procurement and modification of the equipment needed for the test units. A commercial solar collector will modified to meet site-specific needs. Equipment for wellhead fluid separation will be procured. Centrifuging or gravity sedimentation for oil/water separation will be evaluated. The influence of pretreatment on water temperature will be monitored and effective water temperatures after pretreatment will be determined. The researchers will evaluate the economic viability of the use of solar radiation and co-produced energy sources for heating produced water to the desired temperature for desalination.
• Construction of a CBM produced water purification prototype for the pilot test, based on the experimental results. The prototype will be constructed in a trailer and will have a capacity of ~30 bbl/d.

Pilot Tests – The researchers will conduct a pilot test at two wellhead locations for a period of one year. Technical feasibility and economic efficiency of the proposed process will be evaluated by recording and evaluating energy consumption, maintenance costs, and durability. This task has four subtasks:

• Produced water purification pilot tests at the selected wellhead locations for a period of one year, monitoring fluid temperature, produced water quality, solar radiation, and water purification efficiency for the duration of the test. It is anticipated that scale formation may be a problem. If so, the researchers will evaluate scale for composition, mechanisms of deposition, and any resulting influences on unit efficiency. Periodic acid cleaning of the equipment for scale removal will be implemented as necessary.
• Examination and evaluation of methods of managing concentrate from the water desalination process. The research team will examine the chemical composition of the concentrate under different water recovery rates (30%, 50%, and 70%). Conventional deep well injection and salt crystallization for recycling will be evaluated for concentrate management.
• Monitoring of the chemical composition of the purified produced water throughout the demonstration period. Potential end uses of the purified water will be evaluated including drilling fluid, stimulating fluid, water flooding and re-vegetation.
• Evaluation of the technical feasibility and economic efficiency of the product and process, including an economic evaluation based on the capital cost, lifetime of each operation, and maintenance and operation costs.

The primary goal of this project is to develop and demonstrate a thermal-based desalination process for produced water purification at wellhead. Work in this period of time focuses on bench scale testing and process design:

(1) A bench scale air-enhanced distillation process has been setup for laboratory test
Bench scale experiments have been carried out on an evaporator with built-in capillary tubing bundles for heat exchange. The feed water temperatures were varied from 60^o to 80^oC while the feed flow rate was increased from 10 to 30 ml/min. About 2,000 ml of purified water was obtained in this bench test. The ion and organic composition of both feed water and purified water were investigated by ion chromatograph (IC, Dionex I-20) and total organic carbon analyzer (TOC, Shimadzu). Figure 1 gives organic removal efficiency and TOC in purified water as a function of operating temperature. Figure 2 shows ion removal efficiency at different temperatures.

Bench tests indicated that both organic and salt in produced water can be removed efficiently through the low-temperature distillation process. The TOC of produced water declined from 470.2 mg/l to 17.8 mg/l with a removal efficiency of 96.2% at 80^oC. Feed water temperature shows minimum impact on organic removal efficiency: decreasing from 96.2% to 95.4% as temperature declines from 80^oC to 60^oC. The ion separation performance in bench test is summarized in Table 1. The produced water used in this study has a typical TDS of 1.98×104 mg/l and suspended particulates of 99.6 mg/l. After the treatment, the TDS is reduced to 76.3 mg/L and the suspended particulates are undetectable. The water quality of purified produced-water meets the most of requirements by beneficial uses, such as general irrigation, tower cooling and chemical processing.

Table 1. Chemical composition of purified produced-water

(2) Construction of separation unit for produced water desalination
According to the bench scale experimental results, efficiency of water evaporation at contacting of flowing air is relatively low at temperatures below 70^oC. Researchers have modified the design of demonstration unit by controlling the vacuum of the evaporation chamber for achieving high water production capacity and improved energy efficiency. Water desalination prototype is constructed in a moving container with built-in facilities including water separation unit, clean water tank, pump unit and process control and monitoring panel, as shown in Figure 3.

Figure 3. Demonstration unit for wellhead deployment of water desalination

(3) Site preparation and pilot test
Researchers are currently investigating the performance of the prototype at different feed water quality and operating conditions, i.e., feed water temperature and varied air flow rate. Such test is scheduled for the next few weeks. The next step is to install the separation unit at the wellhead and integrate with the solar system for water purification tests on site. Figure 4 schematically shows demonstration unit for wellhead application.

Figure 4. Schematic diagram of demonstration unit for wellhead application

Main components of the produced water desalination unit include: (1) water heating system by using co-produced energy or solar energy sources, (2) water evaporation unit with high latent heat recovery, and (3) water recovery system with heat pump system. Produced water from the wellhead has a temperature around 45-60^oC. The produced water will be further heated to the designed temperature (i.e., 60-80^oC) by using solar energy. Produced water at elevated temperature is introduced into the desalination unit by a water sprayer and forms thin water film at the surface of packing material for enhanced water vaporization. As water falls to the bottom of the vessel and contacts with air flowing in a counter direction, water vapor will be extracted by flow of air and from humidified air stream. The humidified air enters into the adjacent condensation chamber and water condenses on the surface with latent heat recovery: creating clean water for beneficial uses. Temperature and pressure sensors have been installed along the longitudinal of the separation unit to monitor the temperature and pressure changes at different temperatures and operating conditions. A water meter is installed to record total amount of clean water generated from the process. Both feed water and purified water will be collected at specified time intervals and analyzed by IC and TOC analyzer.

Project Start: August 9, 2008
Project End: August 5, 2010 (extended)

DOE Contribution: $420,543
Performer Contribution: $683,163

Contact Information:
RPSEA – Charlotte Schroeder (cschroeder@rpsea.org or 281-690-5506)
NETL – Chandra Nautiyal (Chandra.Nautiyal@netl.doe.gov or 281-494-2488)
Performer Company – Liangxiong Li (Li@prrc.nmt.edu or 575-835-6721)

Additional Information

Final Project Report [PDF-2.79MB]

Is Reverse Osmosis Effective for Produced Water Purification? Viability and Economic Analysis [PDF-1.42MB] - Shanker Muraleedaaran, Xinhua Li, Liangxiong Li, and Robert Lee - SPE 115952

Cost Effective Treatment of Produced Water Using Co-Produced Energy Sources for Small Producers [PDF-1.36MB] - Liangxiong Li - Program Review Presentation

A Humidification-Dehumidification Process for Produced Water Purification [PDF-105KB] - Xinghua, Li, Shanker Muraleedaaran, Liangxiong Li, and Robert Lee

Thesis Document [PDF] - Xinhua Li