Aeration technology uses microscopic bubbles several orders of magnitude smaller than conventional technology to remove hydrocarbons from produced water.

Enhanced recovery methods, which include water flood in conventional oil reservoirs, steam assisted gravity drainage, and cyclic steam stimulation in oil sands, all require that massive amounts of fresh water be injected into reservoirs. The result is that injected water produced with the oil is contaminated and must undergo remediation.

The goal of most producers is to remove waste water from the site and process it to make it potable and usable for agriculture irrigation. Existing water remediation and cleansing technologies include initial treaters — holding tanks that let gravity do the work of separating out contaminants, followed by electrostatic systems and the use of chemicals or heat — all of which use a lot of energy. These methods also leave approximately 0.5% to 3% of residual oil in the separated water. That water must be disposed of, an objective that is frequently accomplished by injecting the water back into the reservoir or leaving it on the surface in toxic tailing ponds.

An alternative solution

A producer in Alberta, Canada, is in the process of deploying a solution that will reduce the amount of oil in the residual water waste to 0.005%. This safe and effective process for remediating oil and gas field contaminants at the well site is suitable for conventional oil production, enhanced oil recovery, steam-assisted gravity drainage, and cyclic steam stimulation.

The technology uses aeration inside a tank configuration where micron-sized gas bubbles are created using either natural gas or nitrogen, depending on the application. These bubbles, which are several degrees of magnitude smaller than those used in conventional aeration technology, supersaturate the produced water.

As the water is cleaned of hydrocarbons, heavy solids fall out. Meanwhile, lighter suspended solids rise and are encapsulated in the recovered oil. The oil and a slight amount of water are then separated as they flow through the remainder of the system, achieving total separation.

At this stage, the recovered oil flows into an oil collection tank, and the water, now free of oil and solids, is pumped down a disposal well back into the reservoir or sent on to undergo desalinization to become safe for drinking or for agriculture use. Through this process, the hydrocarbon content in the injected water is reduced from the conventional 5,000-30,000 parts per million (ppm) to less than 50 ppm. The hydrocarbon-free water can be re-injected either into a water flood injection well or a disposal well.

Virtually every desalinization technology that is currently available requires that saltwater be free of oil. Even slightly contaminated water requires significant downtime in the processing facilities and results in expensive maintenance. This aeration technology solution provides such a low concentration of oil that it avoids downtime for desalinization facilities and eliminates cost problems.

The aeration process can save companies up to 25% on certain operating costs. The economic benefits are many and include reducing the frequency of expensive remedial activities on injection wells, trucking, and disposal costs, as well as reducing the expense of maintaining surface treating facilities in some cases.

The process also recovers more oil. Using this solution, an operation injecting 1,000 b/d of water can recover an additional 5 to 30 b/d of oil.

System versatility

One Alberta producer currently has a prototype portable process unit that handles about 2,000 b/d of water-oil mixture. At 40 ft (12.2 m) long and 12 ft (3.7 m) wide, the unit can fit on the back of a semi-trailer truck. The majority of future units are expected to handle 200 to 500 bbl of produced fluids per day.

The prototype unit is entirely enclosed so operations can continue during the most extreme weather conditions in Canada, which often reach -86° to -104°F (-30° to -40°C).

Future units will be designed to be suitable for the particular weather conditions where they will be used. Units that will be used in the Texas panhandle, for example, will be open and will have a shade screen.

Potential

This new technology has the ability to help significantly with water shortages in a number of oil- and gas-producing areas, including the Barnett Shale area near Dallas and Fort Worth. Large volumes of groundwater are used for reservoir stimulation to produce the abundant natural gas. Water is a necessity. The problem is that much of Texas depends on groundwater for potable consumption. Today, the dirty water produced in conjunction with the gas is often injected down disposal wells and needs to be cleaned to minimize damage to injected sands. This new technology has the potential to address the groundwater issue and to minimize the need to dispose of contaminated water.

In Alberta, Canada, large quantities of water are being taken from natural sources for use in the tar sands upgrading facilities and oil sand extraction. Production is expected to nearly quadruple over the next two decades to 4 million b/d of oil in 2030. This level of production will require increased volumes of water. Using current oil sand extraction practices, it takes between 2 and 4 bbl of fresh water to produce 1 bbl of synthetic crude. Today, existing and approved oil sand operations are licensed to remove and use 2.5 billion bbl of water.

Application of the new water remediation technology will help cut down the massive amount of water used in oil sands production by allowing producers to recycle more of the water instead of dumping it into tailings ponds.

The need is great. According to Alberta Environment, a government organization dedicated to protecting and enhancing the province’s natural environment, oil sands mining operations in 2006 contaminated 540 million bbl of natural water from the Athabasca River — a 950-mile (1,129-km) river that is the largest freshwater source for oil sands production in the province. In addition to the depletion of water from the river for oil production, 264,172 gallons (1 million liters) of waste water, including grease and oil, leaked into the river last September.

Another perspective

Many erroneously believe that the needs of the planet are diametrically opposed to hydrocarbon extraction processes. In actuality, the petroleum industry has a documented, excellent track record of protecting the planet and preventing damage. And when the odd occurrence does take place, the industry has consistently shown a commitment to making things right again, whatever the cost. The industry has also invested heavily to develop technologies that make operations safer for the environment. So it is with water remediation today.

Fit-for-purpose water remediation solutions that effectively remediate produced water for other purposes exist and are in use today. Aggressive financial and social investment in water remediation will go a long way toward showing real progress by the petroleum industry in what is most likely the most important issue of this century — assuring affordable energy in an environmentally responsible way.