Managing Water Quality and Fluid Compatibility Allows Use of Brackish and Produced Water in Fracturing
Many oilfields in the Middle East lack freshwater but feature a surprising abundance of brackish water. As oil and natural gas companies deploy modern hydraulic fracturing techniques in the region, demand for greater volumes of frac water will increase and new sources of water must be developed.
Water used for enhanced oil recovery and hydraulic fracturing in the Middle East is commonly sourced from freshwater generated by desalination, primarily reverse osmosis. As a result, water management costs are significantly higher in the Middle East than in the U.S.
Recently, hydraulic fracturing activity has gained ground in the Middle East, largely in gas well completions. Experience shows that flowback and produced water from these wells contain high amounts of inorganic minerals and other impurities not conducive to consumption or other applications without treatment. As a result, these fluids are usually pumped back underground via salt water disposal wells.
The desalination process, while producing freshwater volumes adequate for the needs of industry, is not only expensive, it also generates a significant amount of reject which needs to be handled separately. This reject may be concentrated to use as a heavy brine, but most often it is discarded in deep SWD wells.
Reusing flowback and produced water is not widely practiced in the region and by sourcing freshwater for completions, the industry is creating great volumes of unusable water for future generations and spending fortunes while doing so.
This linear chain of events uses freshwater and produces contaminated water that is disposed in deep SWD injection wells and it means the Middle East water economy is a linear economy.
Water is a closed-loop cycle and we believe this cycle of water supply-and-demand will soon become imbalanced if we don’t address overall water management practices. As an alternative, we propose a circular economy concept for oilfield water management.
Recent news reports suggest a growing interest by business leaders around the world in the concept of a circular economy.
The aim of the circular economy is to keep goods and materials in use for as long as possible. This will reduce resource extraction, pollution and waste. Benefits of a circular economy extend beyond sustainability, according to a February report by Newsweek Vantage, by providing access to new markets, enhanced competitiveness and increased revenues.
Strategies for adapting to a circular economy include new products that use less materials and energy to produce, products offered as services that are shared and reused, increased waste recovery and use of renewable materials in place of finite ones.
Rather than using freshwater for oilfield applications, there are alternative sources of water - provided we meet water quality criteria at an acceptable price. The circular economy concept is not only environmentally friendly but will also be economical. Limiting the use of fresh water will reduce water management costs and decrease overall lifting prices for the oil and gas operator.
As the table suggests, there are a variety of water management practices currently in use for oil and gas applications. Although different water management systems have been used, the dominant source for oilfield water in the Middle East is still the use of fresh water.
As we can see, brackish water after treatment is used for Middle East oilfield applications. However, produced water is primarily disposed of in deep SWD wells, which adds to the cost of the water management cycle.
To reduce costs, produced water can be treated and then blended with fresh water as a diluted mixture and is appropriate for waterflood EOR and for fracturing use.
To a lesser extent, 100 percent produced water is used by some operators after treatment for EOR injection and fracturing. Many in the industry see 100 percent reuse of produced water without the need for treatment as a holy grail of water flooding and fracturing jobs.
The circular economy concept is not only environmentally friendly but also economical.
The bottleneck comes from logistics and fluid compatibility.
To balance the need for high volumes of frac water with an existing shortage of fresh water, alternative sources must be explored to provide a base fluid for fracturing. The challenge of using alternative source water as a base fluid for fracturing is not due to a lack of the water treatment technologies or the cost associated with it.
The bottleneck to alternative sources comes from logistic hurdles of water management systems, a lack of compatible fracturing fluids and a lack of historical datasets on well performance using alternative sources as a base frac fluid.
In 2015, RecyClean began development of a technology for treating brackish and produced water for use as a base fluid for fracturing.
The availability of brackish wells in the oilfields of the Middle East field helped determine a suitable location for a pilot program. The program was designed to test a new process using a combination of ozination and electrocoagulation to deliver water that meets frac-water criteria. Frac-quality water criteria were based on data for formation, and asset and fluid compatibility in order to minimize risks such as scaling, corrosion, microbial induced corrosion, hydration of linear gel, premature and overcrosslinking and blockage of the formation. Instead of treating water quality and fluid compatibility as separate entities, it was decided to focus on the fluid compatibility issues in conjunction with our treatment technology and to evaluate brackish water TDS levels suitable for hydraulic fracturing.
A full-scale pilot was conducted at the brackish wellsite to treat highly-contaminated water. The treated water was tested for rheological stability and breaker test. The quality of influent brackish water and treated water are shown in table below.
A full-scale pilot project of our brackish water treatment technology was developed to realize a series of goals for production of frac-quality base fluid.
Overall project goals:
• Evaluate a cost-effective and an environmentally-friendly system for treating produced and brackish water for oilfield applications.
• Evaluate a water quality and fluid compatibility approach to treating brackish water for fracturing in a Middle East oilfield.
• Evaluate for efficiency and consistency a new technology that uses a combination of ozination and electrocoagulation with eventual implementation of a full-scale brackish water treatment and produced water reuse project.
• Develop a process to reduce to greater than 98 percent of hardness and deliver treated water on a consistent basis.
A full-scale treatment facility was designed to handle raw water quality of greater than 145000 mg/L of TDS, greater than 40,000 mg/L of hardness, greater than 7,500 mg/L of calcium, and greater than 2,700 mg/L of magnesium.
The results were expected to deliver water quality of less than 450 mg/L of hardness, less than 100 mg/L of calcium, less than 50 mg/L of magnesium, less than 2 mg/L of iron and less than 100 mg/L of sulfate.
In addition to water quality, the program was intended to provide data on expected throughput and a cost-benefit analysis. As engineered, the system was to produce between 100 and 1,500 cubic meters per day.
The project’s water quality goal for minerals reduction is shown in the chart below.
Development and field testing of this water treatment technology was intended to demonstrate its differentiation from other treatment techniques. The results indicated the following:
• A highly efficient mechanical treatment design that results in a lower cost per barrel, decreased maintenance, increased automation, lower chemical costs and reduced environmental impact.
• Reduced overall treatment time to less than 10 minutes.
• Included spill containment, safety sensors, real-time water monitoring sensors, and modular design.
• Small footprint with 20 ft. units.
• Capable of handling all types of waste water, including oilfield, power plants, industrial, municipal, and agriculture waste waters.
• Scalable to fit any volume per day requirement
• Complements and can be used in conjunction with other water treatment technologies for increased treatment efficiency and reduced downtime.
As shown in the diagram above, the oxidation tank, which is the first frac tank in the system, is filled with the brackish well water. An influent water sample is collected for analysis before the treatment starts.
Influent water from the oxidation tank enters the treatment system via an ozone pump and is oxidized. Inline sensors test for pH, oxidation reduction potential and temperature to give a real-time analysis of influent and treated water. Based on this, an on-site operator determines if the level of oxidation is sufficient. If needed, oxidized water from the treatment unit is returned to the oxidation tank for continuous oxidation of the influent water.
Once the ORP of treated water reaches +300.0 mV, an electro-coagulation process starts at the HP #1 unit via an EC pump. Real-time sensors monitor pH and once the optimal pH is achieved, the EC treatment process starts.
Treatment time in the Hydro-Pod unit is less than 5 minutes. After the electro-coagulation process, further monitoring of pH, ORP and temperature takes place in real time. Efficiency of the EC process can be evaluated by the ORP level and a visual inspection of the flock formation by taking a sample at the sample port.
Following the EC process, treated water moves to a settling tank. Further sampling compares influent quality to effluent. After an analysis, buffer reagents can be added and mixed in the dry chemical mixer depending on the reduction level for hardness, barium and sulfate.
Treated water remains in the settling tank from 30 – 60 minutes to allow solids to settle. After the solids have settled, water is sampled for analysis from the settling tank to ensure that treated water meets all criteria. If it does not, additional buffer adjustments can be made and continuously tested until it meets the criteria. Having an on-site lab enables immediate adjustment of key water criteria if required.
Once water at the settling tank shows a sufficient level of quality, clear water is transferred for filtration and adjusted to neutral pH in a single step. After filtration, an operator monitors and adjusts pH on the fly if needed, through an inline chemical feed system during transfer to a clean tank.
Finished treated water in the clean tank can then be transported to the frac location to use as a base fluid for fracturing. The pilot program included a 3-inch diesel pump for transferring treated water from the clean tank to water trucks for delivery to the frac site.
The initial run at the pilot facility resulted in six frac tanks, or 2,400 bbl, of treated water that met all required water quality criteria and was ready to be used as a base fluid for fracturing. During the process, it was learned that the volume of reagents used varied with the quality of the influent water. Further operation included updates on status and safety along with volumes of water treated, power consumed, reagent consumed, and before and after water quality analysis.
This brackish water treatment project demonstrated that treated water is compatible with fracturing fluids and can be used as an alternative source water for hydraulic fracturing. Using treated water eliminates the need for freshwater in hydraulic fracturing and can reduce the cost of handling produced water, resulting in an increase to the overall bottom line.
Authored by Mark Stanley and Rajendra Ghimire