Validation of salt water disposal well treatment plants with handheld oil in water sample analyzer

At a truck unloading facility, the water flow rate can vary wildly as trucks dump water at irregular intervals. In pipeline fed facilities, the flow rate can be more stable, but can still have quick changes.

A typical oil/water separation system is a relatively simple system with no, or minimal, moving parts and is designed for a set of conditions (flow rate, oil concentration, oil gravity, pH, solids content, etc.). When the process is operating within the design parameters, the water quality will be good, the injection well will operate with low maintenance costs, and most of the available oil will be collected. However, in processes that fluctuate greatly, it is common for the conditions to be outside the design parameters. Also, as these SWD facilities grow with increased water volumes, the treatment systems will be even more challenged by upset conditions.

Surveys and Pilot Demonstrations

Before approving a facility improvement project, the owners of a SWD well facility must have some data on current process conditions and performance. Usually a pilot, or demonstration, plant is tested before a full-scale facility is built. Before and after flow rate and oil concentration data should be collected from these systems to verify the design is correct and the capital expenditure can be approved.

Ideally, a continuous online monitor would be used for collecting data to determine upset frequencies, duration and normal conditions. Many of the SWD facilities and demonstration plants do not have a budget that allows for continuous monitoring. However, high frequency sample analysis can be performed on site, using a portable analyzer. Easy to use, low cost field analyzers, such as the TD-500D, are essential for optimizing the effectiveness of treatment systems during pilot studies and meeting a budget that includes frequent measurements.

Two Blackwall Process Studies

In a recent Blackwall Process demonstration, preliminary data reported that the SWD facility treated 4,600 barrels of water per, and that the gun barrel tanks skimmed an average of 380 barrels of oil per month. Oil in water measurements averaged 2,753 parts per million (ppm).

Backwall Process installed its water treatment system for a 2-week trial. During this trial the system treated 2,000 barrels of water per day and 570 barrels of oil were skimmed. To compare this to the original flow rate, approximately 2,622 barrels of oil would have been skimmed per month. This skim volume shows that the water averaged 20,357 ppm oil content. It also proves that the original treatment system was only removing about 10 percent of the oil, with the remainder being lost in the disposal well. This data also illustrates that the disposal well probably had significant maintenance costs due to the high oil concentration.

This demonstration facility showed significant oil removal, but was not able to collect frequent enough data during the trial to analyze upset frequencies or upset magnitude.

Blackwall Process conducted a second demonstration at a pipeline-fed facility. It used a fluorescent sample analyzer to analyze 30 samples per day for a high frequency, thorough survey of the process. The samples were collected in the water intake lines, after the unloading tanks and the gun barrel tanks.

The data collected before the demonstration showed that the inlet water oil concentration fluctuated between 2,777 ppm and 11,772 ppm, with a 6,421 ppm mean. The unloading tanks removed some oil, especially when the concentration was high. At low oil concentrations, the unloading tanks did not remove much oil. The gun barrel tanks were effective, with a discharge concentration between 1,292 ppm and 2,095 ppm. However, the plant operators did not report any oil skimmed during this period.
The Blackwall Process treatment system was then added to the process. For 2 weeks 30 samples per day were collected and analyzed on site, using the TD-500D to verify the demonstration plant`s performance.

The data collected during the demonstration showed that the water inlet concentration and oil removal by the unloading tanks was similar to the period before the demonstration. The Blackwall Process produced much cleaner water with a stable concentration during the demonstration. The plant operators were able to skim 68 barrels during this period proving the Blackwall Process was effective.

There is a market for the skimmed oil to be sold, which will offset the cost of treatment, and is not included in this study. Although there is no data to show the reduced maintenance cost of the disposal well, at 66-80 percent less oil injection, it is easy to determine that maintenance costs will be significantly lower.