TECHNOLOGY Organoclay cost effectively removes oil from produced water

April 14, 1997
George Alther Biomin Inc. Ferndale, Mich. The trailer for on site produced water treatment includes bag filters, and organoclay and carbon vessels (fig. 2) An organoclay-based method can economically treat produced water that is reinjected into formations. Oraganoclay refers to bentonitic clay platelets modified with quaternary amine. Operators can dispose of the spent organoclay in landfills, as long as it is nonhazardous, or ship it to asphalt producers or fuel blenders. Activated carbon is
George Alther
Biomin Inc.
Ferndale, Mich.

The trailer for on site produced water treatment includes bag filters, and organoclay and carbon vessels (fig. 2)

An organoclay-based method can economically treat produced water that is reinjected into formations. Oraganoclay refers to bentonitic clay platelets modified with quaternary amine.

Operators can dispose of the spent organoclay in landfills, as long as it is nonhazardous, or ship it to asphalt producers or fuel blenders.

Activated carbon is regenerated or incinerated if it is hazardous.

Operators reinject produced water into formations either for water disposal or waterflooding to recover additional oil. In either case to minimize formation plugging, it is important to remove oil and other materials from the water.

If removing metals, the media must be designed carefully for each situation.

Disposal regulations

In the U.S., discharge permits are becoming more stringent for disposing of water that contains oil, grease, and certain heavy metals. Hauling waste water off site is also expensive, $0.10-1.00/gal, and has its own liabilities such as accidents during transport.

The U.S. Environmental Protection Agency (EPA) divides oil production by offshore and coastal regions. BAT (Best Available Technology) effluent limitations specify a maximum of 29 mg/l. oil in the water, averaged over 30 days. Offshore BCT (Best Conventional Technology) regulations specify 48 mg/l., averaged over 30 days.1

These federal limits are not difficult to achieve with chemical treatment, but state regulations tend to be tougher. For example, Chapter 4 of Wyoming Water Quality Rules and Regulations deals not only with oil from produced water, but also with water contaminated by fuel oil, gasoline, aviation fuel, etc. Section 4a says, oil releases shall not be present in, or threaten state waters in amounts that would cause conditions such as oil and grease content over 10 mg/l.

Apparently the ultimate goal is, based on BAT, to establish potable water standards for ground water and surface water.

EPA Region 10 permits require numerical limits of heavy metals in produced water for copper, arsenic, zinc, total aromatic hydrocarbons, and whole effluent toxicity. This means that cleanup methods that include granular activated carbon and ion exchange resins are required for successful on site treatment. A combination of state and EPA measures are leading toward zero discharge of produced water in coastal areas.1

When produced water is used in polymer and waterflood programs, the limits for oil in the water are 50 ppm upon leaving the retention pond. Furthermore, freshwater aquifers used as a potable water source are often found above the producing zone and are endangered by oil contamination in the injected water. Kuwait is an extreme case where potable ground water, which is rare and precious there, has been contaminated by oil over wide areas as a result of the Gulf War.

On site train

An on site treatment train for cleaning up produced water consists of an oil/water separator, possibly with a liquid emulsion breaker injection system (acid or demulsifier), a bag filter, a filter vessel filled with granular organoclay and, in some cases, followed by a vessel with granular activated carbon for removing volatile aromatic hydrocarbons and ion exchange resins for removing heavy metals (Fig. 1) [37710 bytes].

All this equipment can be placed on a trailer to conduct the treatment on site in the same manner as landfill leachate or storm water runoff is cleaned up on site (Fig. 2).

This treatment train is familiar to the remediation industry, except for the addition of organoclay. The organoclay is in a granular form, usually 8 x 30 U.S. Mesh size, blended with anthracite of the same size. The anthracite, which has the same bulk density as organoclay (56 lb/cu ft), is to keep the interstitial pore space open to obtain a longer life from the media.

The organoclay blend is used at oil concentrations of 70 ppm or less, as a post-polisher for oil/water separators, and/or prepolisher for activated carbon.

The organoclay removes about 50% of its weight in oil, or seven times as much as activated carbon. Because of this, it has been accepted as a polisher for carbon, primarily by the end users who pay for the cleanup.

For a long time, the drilling industry has used powdered organoclay as a viscosifier/

suspension additive for oil-based mud systems. This organoclay is effective up to 175° F., based on boiler feed water clean up in a refinery.

Partitioning is the chemical process that takes place between the organoclay and oil droplets. Quaternary amines render the bentonite organophilic and hydrophobic to partition or dissolve into the oil droplets and fixate them by means of Coulombic forces (Fig. 3) [34659 bytes].

When organoclay powder is mixed into hydrocarbons it swells, causing the fluid to thicken and provide lubrication to drill bits and a coating to the well bore.

Water disposal economics

An application in Central Michigan shows the economic benefits of an organoclay treatment. In this case, the operator disposed of an oil field's produced water, about 3,500 bw/d containing 500 ppm of residual oil, in a water injection well.

Because the remaining oil in the water reduced water injection rates by plugging the reservoir, the well had to be worked over every 2-3 months. This work required a workover rig along with the injection of hydrochloric acid and xylene-based solvents to partially restore the permeability.

A workover rig for 3 days, along with the acid/solvent injection job, costs an estimated $7,500 every 2-3 months. Because of this cost, the alternate of removing the residual oil from the water was initiated.

A small oil/water separator was set up near the well head. The effluent water from the separator was pumped to a 3-ft diameter filter vessel filled with 1,200 lb of Biomin's EC-100 organoclay.

Oil content in the treated water was lowered to about 5 ppm, a 100 fold reduction. Water injection rates have remained constant.

The new system eliminated the need for well workovers. The separation/filtration equipment, as installed, is easy to maintain and requires little cost and attention to operate.

Installation cost is estimated at $5,900 (separator $2,000, skimmer $500, pump $400, and filter $3,000).

The Biomin EC-100 organoclay is recharged once every 3 months at a cost of $1,200/charge. Equipment for the Biomin residual oil removal system costs about the same as working the well over one time and, therefore, a $6,000 savings is realized every 2-3 months because workovers have been eliminated.

Reference

  1. Veil, J.A., "Npdes permits have increased emphasis on control of toxic pollutants," OGJ, Jan. 6, 1997, pp 46-52.

The Author

George Alther is president and owner of Biomin Inc. in Ferndale, Mich. He has been involved in the environmental market for over 20 years. Alther has an MS from the University of Toledo.