Efficiencies are Realized When Development Strategies Include Centralized Locations and Automated Systems
For perspective, 1,212 sq. mi. is one-quarter more land area than Dallas County, Texas. And, the volume of water it represents is 252.8 billion gallons —enough to fill 382,715 Olympic-size swimming pools. Water is the most common and most heavily used fluid in the petroleum industry. It is also the most heavily produced at an average of four barrels of water for every barrel of oil. And, it poses numerous well development challenges for operators, particularly those developing unconventional shale resources. Effectively managing water is rapidly becoming the leading challenge in both conventional and unconventional drilling and completion operations. Project economics and stringent regulations are incentivizing operators who require large volumes of water for hydraulic fracturing operations to look increasingly at reusing produced water.
Companies like TETRA Technologies are enabling and advancing frac water reuse through mechanical and chemical treatment techniques, automation, and the performance of new fracturing-chemical systems that accept high levels of chloride and other chemical concentrations. These technological improvements, combined with careful planning and best practices, have opened the way for economically viable techniques for reusing frac water at a time when the cost of fresh water is increasing and its availability is declining.
TAKING A CLOSER LOOK
Increasing the lateral length of wellbores brings added efficiency to production and development of shale plays. However, the volume of water required for fracturing a well significantly increases as a result. Operators face substantial challenges and costs in sourcing, transporting and storing water prior to the frac job. Water challenges continue once a well is brought online and production begins.
As oil is produced so is water, including salt-laden water from underground reservoirs, creating a toxic mix that could devastate farmland if released on the surface. Historically, drillers generally pump excess water into subsurface wells for disposal and often must transport it by truck. Now, with the development boom hitting historic levels, some injection zones are becoming over pressured due to increased volumes of produced water.
Operators often need to transport water further to dispose of it or drill into deeper injection zones. Deeper disposal wells are more difficult to drill, carry additional risk and cost more. Trucking produced-water to disposal wells also adds more risk. Addressing these challenges in an environmentally responsible manner frequently requires adding more oilfield services and personnel at each site. With four or more barrels of water produced for every barrel of oil, water disposal could add as much as $6 bbl. to company break-evens by 2025, according to a recent Wood Mackenzie study.
REUSE SUCCESS FACTORS
Recycling frac water flowback in a way that allows its reuse used makes both economic and environmental sense, as it reduces both the need for fresh water and the subsequent cost of trucking and disposal.
Economics and stringent regulations incentivize operators to look at reusing produced water.
At an average cost of $0.75 bbl. for fresh water and disposal costs ranging from $0.50 to $2.50 bbl., reusing produced water for completions makes economic sense. Environmental benefits include less freshwater use and less produced water disposal. Reducing truck traffic also reduces health, safety and environment (HSE) exposure as well as impact on the environment from dust, noise and emissions.
There are three critical success factors for reusing produced water:
1. A carefully considered, comprehensive water management plan that supports area operations;
2. Proper positioning and layout of field-wide water management infrastructure aligned with the water management plan;
3. Applying best practices and equipping infrastructure with the best available technology, including automation
Planning is crucial in ensuring water gathering and treatment operations reduce transportation, acquisition and disposal costs while maintaining the water operator’s need to successfully complete projects.
Centralized water gathering, storage and treatment should be an integral part of field development strategy. Project economics dictate that water sources be placed as close together as possible within a given operating area. An example of water infrastructure proximity for a Permian Basin reuse project is shown below.
Industry best practices call for use of non-freshwater sources when possible. This includes produced water, lowquality water from brackish reservoirs, and wastewater from industrial, power and municipal plants. A key challenge for operators is the wide variability in water quality and consistency.
Addressing quality and consistency challenges requires planning to determine how the water will be treated and to what level before it is used in fracing operations. For example, systems produced by TETRA Technologies are developed to handle the high variability inherent in nonpotable water supplies. With the acquisition of SwiftWater Energy Services, of Midland, Texas, TETRA expanded its ability to economically process alternative types of water, including subsurface saline water, produced water and effluent water.
Automated treatment systems chemically treat produced water through a four-step clarification process:
1. Chemical oxidation raises the oxidation reduction potential (ORP) level to eliminate bacteria and oxidize heavy metals present in the water;
2. Coagulation then agglomerates the dispersed colloidal particles. Suspended particles are usually very small and may have electrical charges either on or between them. Typically, these are negative charges, which cause them to repel one another. Coagulants neutralize the repulsive electrical charges by surrounding the particles and allowing them to come together to form larger clumps.
3. Flocculants (polymers) are added to facilitate settling of suspended particles in a solution. Flocculants facilitate agglomeration to create larger floccules, which then settle by gravity as clumps and can be removed from the water.
4. Filtration removes any remaining total suspended solids (TSS). TETRA’s process includes an automated backwashable disc filtration in combination with stringwound cartridge filters to provide filtration to 5 micron.
This system enables produced water recycling of up to 50,000 BWPD.
On-the-fly water treatment systems generate chlorine dioxide (ClO2), an EPA-approved biocide, to prevent or eliminate bacteria in fresh, flowback and produced water. An environmentally sensitive oxidizer removes bacteria, hydrogen sulfide (H2S), iron sulfide (FeS) and other sulfides on the fly prior to fracturing, providing continuous, accurate chemical dosage volume. The system uses a twoprecursor method to produce ClO2, which can be injected into the target water system for continuous treatment.
Other fast-acting, water treatment additives degrade quickly after killing bacteria as frac water moves through the tanks. A benefit of continuous versus batch treatment is that 100 percent of the water is treated, not just the portion of the water column in the frac tanks. Because the system generates ClO2 through water flow in the transfer line, the unit stops when flow stops to ensure a safe working environment.
TETRA has developed an oil recovery after production technology called ORAPT™ oil separation system that provides additional treatment. Standalone ORAPT mobile units are designed to remove native oil, undesired light constituents, and oil slugs from unplanned bypasses at production facilities to deliver water with only trace amounts of oil at 50-100 ppm. Removed oil can be stored for sale or disposal to provide environmental and economic benefits. Nominal throughput of this system is 25,000 BWPD.
In many instances, well completion companies blend produced water with fresh or alternative waters to balance high salt content in the reservoir and achieve uniform total dissolved solids (TDS) and chloride levels. This helps sophisticated frac fluid systems perform optimally. Large spikes over or under the nominally required levels can hinder cross-linking performance. This can lead to over usage of chemicals, reducing cost efficiency and negating any savings realized through recycling produced water.
Optimal reuse requires blended water of consistent quality and stability in terms of TDS and chloride concentrations.
The goal of blending is to use all the available produced water. Achieving optimal reuse requires blended water of consistent quality and that it remain stable in terms of TDS and chloride concentrations.
A unique blending technology has been engineered by TETRA to enhance produced water economics beyond normal blending techniques. The company’s frac water blending system includes an automated blending controller coupled with a patented, on-the-fly blending manifold. The company reports this combination provides accurate parameter-based blending and consistent blend quality, whether directly filling frac tanks or for transfer to another location. A direct parameter control scheme for blending produced and fresh water results in a tighter, more accurate frac water makeup, which promotes greater produced water reuse.
Chloride variation peaks and valleys are smaller in magnitude so effective nominal blending ratios can be increased to include a higher volume of produced water. Conductivity is a practical parameter that can be correlated to chloride level. Well-selected conductivity probes that are robust and suitably adapted to industrial environments can provide reliable, repeatable measurements.
Accurate and consistent blending of different water sources in real time eliminates the need for intermediate storage. Additionally, injection ports can be installed upstream of the blending chamber for adding chemicals.
Finally, a distribution manifold minimizes environmental and personnel risks and ensures that frac tanks receive optimal water supply regardless of the source.
Integration and automation allows systems to work in unison to their fullest advantage. The most significant current developments in fluid transfer are the economies realized through automation. The same is true for fluid processing. Automated pump systems offer cellular-based communication, pressure limit controls, remote monitoring, real-time data access, and data logging to verify results. Lower fuel and labor costs, and demonstrably higher overall efficiency, have positioned automated systems as a new standard.
A closed-loop automation developed by TETRA operates across an integrated produced water recycling service and delivers unmatched efficiency in treating, recycling and optimizing water for fracing operations. The company’s treatment system provides continuous and accurate chemical dosage volume to ensure produced water is optimized to exact specification.
The company’s oil recovery-after-production automated system accumulates and removes residual oil from produced water in real time to ensure treatment performance and compliance with regulatory storage requirements. Accumulated oil can then be put back into the operator’s sale pipeline. Users report the volume of reclaimed oil has almost paid for the use of the system.
Automated blending controllers effectively measure the prescribed blending parameter post-blend and automatically adjust affluent flow rates locally to achieve the blended water setpoint. This measurement significantly reduces variability of frac-water quality. This is because any water variations in either influent stream, whether caused by actual water quality or flow-rate variations, are mitigated by the controller changing the blend ratio automatically in real time. Resulting frac-water blend is kept within the acceptable parameter range with a maximized producedwater portion to optimize reuse.
Automating tasks that previously required significant labor time helps maximize efficiency through integrated services, job planning and crew optimization. This allows team leaders the time to perform site assessments and hydraulic calculations before designing a plan for efficient positioning of hose, manifolds, pumps and road crossings to meet the operator’s needs while avoiding negative environmental impacts.
An operator in the Delaware Basin reports that an automated pumping system provided by TETRA returned savings on water transfer operations. In this case, TETRA used four pumps to reduce cost and increase productivity while maintaining constant system visibility and pressure protection. The system’s optimization and event mitigation yielded 50 percent in labor savings and up to 60 percent savings in fuel cost.
New industry paradigms born of economic, environmental and regulatory shifts are forcing operators and service companies to discover new ways to recycle water already in the system or to develop new means of disposing of it. Automation, integration, and best technologies and practices are enabling shale play operators to adapt to the new paradigms with methods and technologies not previously considered economically feasible but that are now practical and possibly preferred in the future.
Authored by Timothy Gabel and Dean Fanguy