Proper disposal of produced water in mature oil fields is crucial because the water-to-oil ratio increases significantly as the reservoir ages. Subsurface disposal using existing wells saves companies time and money while better ensuring the safety of surrounding ecosystems.
One of the biggest challenges for companies operating a mature oil field is properly disposing of produced water. This water, typically generated in greater amounts in mature or older fields and often the output from concurrent waterflood operations, is laden with salts, hydrocarbons, heavy metals, and sometimes naturally occurring radioactive materials. If not managed correctly, it can pose serious environmental and public health risks that often result in regulatory infractions and significant operational and cost issues that compromise efficiency and limit profitability.
Today’s most proactive, forward-looking companies make it a primary goal to handle produced water more effectively. These companies use a combination of improved processes and advanced technologies to modernize infrastructure. They also adopt the most efficient disposal methods to reduce freshwater use, cut operating costs, extend the productive life of their fields, and avoid costly interruptions. While the best solution for produced water frequently involves a combination of methods tailored to the local geology, water chemistry, and regulatory landscape, subsurface disposal of produced water is fundamental to a cost and operationally efficient approach.
Water Injections Are Vital to the Mature Field Oil Production Process
A common issue in mature oil fields is a natural decline in reservoir pressure as oil is extracted. Water injection helps replace the produced fluid and drive reservoir pressure higher, which, in turn, sweeps oil toward the production wells and helps prevent production or field decline. As oil and water are extracted from a well, the water needs to be separated and disposed of without negatively affecting the surrounding environment, including groundwater sources as well as lakes and rivers. There are several potential drawbacks associated with surface disposal of this produced water, including:
- Environmental contamination risks—If not disposed of properly, contaminants can sterilize soil, kill vegetation and fish, harm aquatic systems, and pollute drinking water sources.
- Regulatory and legal liabilities—Surface disposal is heavily regulated and often restricted or banned because of environmental risks. Failure to meet standards can lead to fines, lawsuits, and revoked permits.
- Public health concerns—If not properly managed, surface disposal can expose local communities to toxic chemicals, pathogens, and radioactive materials.
- Reputation and environmental, social, and governance (ESG) risk—Companies using surface disposal may be perceived as ignoring sustainable water management practices, which then damages investor confidence and public trust.
In order to mitigate these negative consequences, many companies invest in subsurface disposal as a more efficient solution in terms of operations and cost. In fact, subsurface disposal of produced water, typically through deep well injection into porous underground formations, is one of the most common methods used in the oil and gas industry.
The US Environmental Protection Agency (EPA) reports that the industry has used underground disposal for water or brine since the 1930s. The practice has increased dramatically in recent years, with produced water volume in the Permian Basin expected to increase by more than 30% by 2028, according to B3 Insight in late 2024. The Groundwater Protection Council, in its most recent report (2022) on produced water, said that eight states produced more than 1 billion bbl of produced water the previous year and that more than 95% of that water was disposed of underground.
There are several benefits associated with subsurface disposal of produced water, including:
- Environmental containment—Subsurface disposal helps prevent contamination of surface water, soil, and crops. It also limits the release of volatile organic compounds into the air.
- Regulatory acceptance—Subsurface disposal is a well-established and regulated method accepted by the EPA and state agencies that allows companies to more easily comply with environmental regulations.
- Operational simplicity and scalability—Disposal wells can handle large volumes of produced water continuously, reducing the need for extensive surface storage or trucking. Modern disposal systems also can be automated and monitored remotely to further improve efficiency.
- Cost efficiency—Disposal wells minimize water hauling, surface disposal costs, and associated emissions.
- Public and aesthetic benefits—Subsurface disposal has a smaller physical and visual footprint than evaporation ponds or surface spreading, which communities often oppose. In addition, disposals do not generate odors, produce dust, or attract wildlife.
To achieve these benefits, it’s critical for organizations to overcome challenges that can arise during the subsurface disposal process.
Challenges Associated With Produced Water Disposal
There are numerous issues associated with surface disposal of produced water, such as increased regulatory scrutiny that can slow operations and increase costs, difficulty finding safe and cost-efficient disposal locations, and increased environmental risks. Meanwhile, subsurface disposal of produced water has unique challenges. They include induced seismicity (human-made earthquakes), limited formation capacity because of pressure limitations and reservoir suitability, risk of leaks, high initial setup costs, and the need to continuously monitor disposal volumes, pressure, and chemical composition to avoid violations.
Another significant problem that companies using subsurface disposal often encounter is mud loss. Also known as lost circulation, mud loss is a costly problem in oil and gas drilling operations and can lead to shutting down wells. It occurs during drilling when drilling fluid, or mud, escapes into the surrounding rock formations instead of returning to the surface. The good news is that organizations can minimize risk and use abandoned wells in these mud-loss zones as effective, cost-efficient disposal wells, allowing companies to save on drilling costs without compromising formation integrity.
Solutions to Produced Water Disposal Challenges
Subsurface features and rock formation characteristics, which include faults, fractures, and thickness, are often responsible for the severity of mud losses. Cutting-edge technology, such as microseismic sensors, borehole imaging, and advanced algorithms, makes it easier to map mud-loss zones and identify subseismic fractures and other attributes that may induce losses that cannot be cured with loss circulation material. Companies use these tools to determine everything from rock type to formation attributes and reservoir properties.
This wealth of information, along with highly accurate injectivity tests, enables subsurface experts to determine which existing wells can be converted to disposal wells within the mud-loss area instead of simply being abandoned. The usual process involves reviewing existing openhole log data, conducting injectivity testing to determine how much the well can take, and, when results are sufficient, recompleting the well into a disposal well.
Sufficient results are typically like well injectivity tests that show low rates of 10 bbl/min at 1200-psi surface pressure. This is equivalent to 14,000 bbl of water per day (BWPD)—optimal for use as disposal wells. In instances of higher rates and excellent formation attributes, between 50,000 and 70,000 BWPD disposal or more is achievable. These wells can be very cost-effective for companies. At a time when produced water is generated at a rate higher than ever, using abandoned wells for produced water disposal helps companies achieve greater value from existing assets while saving money on drilling and transportation costs and reducing their environmental impact.
Today, it’s easier to address additional challenges with produced water disposal. For example, companies can use deeper, more geologically suitable zones in the subsurface within sedimentary and basement rocks with known faults to minimize seismicity. To reduce formation pressure, companies can rotate disposal across multiple well patterns to distribute the pressure load and reduce the risk of overpressurization. Organizations can commit to environmental responsibility by exploring water reuse and treatment options alongside disposal. Unfortunately, the high cost of treatment because of water volume, complexity of treatment, regulatory requirements, and required energy makes this option difficult to accomplish in the current marketplace.
While subsurface disposal of produced water is used widely, it’s critical for it to be engineered carefully to prevent induced mud losses and environmental contamination. Mud losses escalate drilling costs and compromise formation integrity and disposal performance. Proactive formation evaluation and pressure management are essential to minimize this risk.
When executed correctly and monitored closely, subsurface disposal of produced water provides a secure, scalable, and relatively low-impact method to manage the vast quantities of water generated during oil and gas operations. It balances operational needs and environmental protection, making it a highly effective option, especially in areas without water reuse infrastructure.
Proper Management of Produced Water Is Critical in Mature Oil Fields
Efficient and responsible produced water management shows an obligation to minimize harm and maximize resource recovery. By adopting best practices and innovative technologies, operators of mature oil fields can continue to produce energy and align with ESG expectations. That means finding a subsurface formation suitable for produced water disposal and ensuring the compatibility of produced water before disposal. It is imperative for companies to avoid surface disposal on land or in rivers. Doing so lowers disposal costs, increases the efficiency of their operations, and demonstrates good stewardship at a time when companies are under increasing pressure to reduce their environmental footprint.
As part of their efforts to be more environmentally responsible, it is paramount for companies to foster a culture where geologists and petroleum engineers work together closely on the subsurface disposal of produced water. It is essential for geologists to accurately predict the nature and characteristics of the rock and for petroleum engineers to process the produced water in compliance with regulations and compatibility requirements. When these two teams collaborate, accidents and risks are minimized and positive results are maximized, helping companies improve their bottom line and public image.
For Further Reading
Challenges & Opportunities of Reusing Produced Water by A. Hardberger
Underground Injection Wells For Produced Water Disposal by R. McCurdy, Chesapeake Energy
U.S. Produced Water Volumes and Management Practices, Groundwater Protection Council
Produced Water Volumes Are Soaring, B3 Insight
Wastewater Treatment Comes at High Cost by D. Baddour, Houston Chronicle
