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Oil Removal at Wyoming Oil & Natural Gas

Removal of Oil and Hydrocarbons from Natural Gas Condensate

This oil and hydrocarbon removal project was located at a relatively new gas field in Natrona County, Wyoming. Planned and developed with sophisticated three-dimensional seismic techniques identified it as a large gas reservoir and determined the general limits of the field. Hydrocarbons are produced from three geologic intervals: shallow Tertiary coalbed methane, older Tertiary natural gas and condensate, and deeper Cretaceous-age natural gas and condensate. Water from wells producing from the Cretaceous formations is disposed by reinjecting it underground. Water from other formations is fresh enough to be discharged on the surface for use by livestock and wildlife. The owner holds a discharge permit from the Wyoming Department of Environmental Quality, Water Quality Division. The maximum oil content allowed by the permit is 10 mg/L (using EPA method 1664 for analysis). The permit requires bimonthly (six per year) effluent samples to be submitted for analysis.

Chronology

Aqua Technologies conducted a three-day field trial during May, 1997 in order to determine the ability of our product to remove oil and hydrocarbons associated with natural gas condensate. (Previous investigations had focused on the removal of crude oil.) Aqua Technologies used a trailer-mounted test unit to treat produced water at a rate of five gallons-per-minute (gpm). Two containers of ET-1 organoclay and one container of activated carbon were used to treat wastewater. Water samples were taken at three locations within the process:

• Before treatment (influent),
• After passing through the ET-1 organoclay, and
• After passing through ET-1 and activated carbon (effluent).

This trial was conducted early in the life of the field, and existing facilities were primitive. As the test results reveal, separation was not very efficient before the water entered the adsorption media.

As represented in Table IV, the field trial provided sufficient proof of success for the owner to submit and obtain the discharge permit by specifying ET-1 as the treatment method.

The produced water passes right to left through three vessels containing ET-1, an identical and redundant quantity of organoclay, and activated carbon, respectively. Effluent passes from the adsorption containers into an inspection tank, where water quality can be observed before passing to the outfall.

Prior to our involvement, the operator was replacing activated carbon every three weeks. According to various sources, materials cost (for activated carbon) was approximately 50¢ per barrel. Labor and downtime were also significant issues since gas production must be curtailed if the water cannot be disposed.

Operational Evaluation

Aqua Technologies now operates the facility for the owner. It currently treats approximately 700 barrels of produced water per day. To date, approximately 7 million gallons of water have been treated. During that time, the system has consistently operated in compliance with the facility’s discharge permit.

As table V indicates, additional sampling and analysis were conducted in August and September, 2000 due to increasing difficulty in achieving the desired water quality. First, we determined that the owner was using a foaming agent to remove water accumulating in wells. If the gas flow is not large enough to lift the associated water from the well, it will eventually quit flowing entirely. Foam assists in that effort, but it also interferes with separation. Second, these chemicals were being captured as part of the required Oil & Grease measurements. We discovered that the laboratory had to use an alternative method (EPA 1664 SGT-HEM) in order to measure only the produced hydrocarbons in the effluent water.

We have also conducted more comprehensive sampling and analyses than that required by the Department of Environmental Quality. The first of two comprehensive sampling programs was
performed after one week of operation.

Table VI shows that the ET-1 media brought the water from noncompliance to below detection limits for oil and grease. The BTEX components (benzene, toluene, ethylbenzene and xylene) were also reduced significantly.

The second comprehensive sampling program was performed in March, 2001. The sample in Table VII revealed a substantially higher oil and grease concentration because the sample was taken before the horizontal separator. Please note that the outlet concentration of 14.0 mg/L does not indicate a situation of permit noncompliance because the silica gel correction may not have entirely removed the non-oil organic material. The grab sample was also taken before an observation tank that allows further skimming or recycling through the system prior to discharge.

Current Operating Status

The project has exceeded our expectations regarding media life. Prior to our involvement, the owner was exchanging activated carbon at approximately three-week intervals. Based on our limited access to their water quality data, we originally expected a life of approximately 3-4 months. After 11 months of continuous operation, we upgraded our equipment. The original vessels and media were replaced and an inclined-plate separator replaced the existing coalescing knockout.

Commercial projects rarely have the luxury of unlimited laboratory analyses and absolute control over operating conditions. This project is no exception. The decision to upgrade the equipment was based on a conclusion that the media was nearly spent, based on three observations:

1. By estimating the mass of contaminant removed (subtracting the influent concentration from the effluent concentration), the media appears to be loaded with about 60% wt/wt hydrocarbons.
2. We note increasingly frequent episodes of poor observed water quality.
3. Media samples are observed to be highly saturated with hydrocarbons.

Summary

This project describes a successful response to a difficult problem:
• Petroleum dispersed into droplets too small to separate with existing equipment
• Production chemicals including foamers and methanol that affect interfacial tension
• Low water salinity, which interferes with the coalescing of droplets

Since enhanced separation equipment, such as hydrocyclones and centrifuges, have not been adopted in the Rocky Mountains, adsorption alone was used to remove free and dispersed hydrocarbons to below discharge limits (10 mg/L). ET-1 organoclay successfully removed these components, while activated carbon removed the bulk of the dissolved contaminants. The installation also handled the expected system upsets and even trapped an accidental truckload of invert-emulsion drilling fluid.