Continental Disc Corporation was recently called on to solve a problem for an E&P (Exploration and Production) company in the Green River Basin of Sublette County, in western Wyoming.
The area is known as a vital source of natural gas, but also serves as the source of a lightweight form of sweet oil. Companies who wish to drill and operate in this specific area must first receive permits from the State of Wyoming. The permits are in place to control VOC emissions and are most commonly broken due to open thief hatches (venting vapors from the thief hatches without routing the vapors to a flare).
The E&P company that CDC assisted in had several drill sites, each typically occupied by five to six actively productive wellheads that fed into multiple three-phase separator stations. These stations house 2, three-phase separators: A high-pressure separator and a low-pressure separator. The well first feeds the high-pressure separator, which separates the water, oil, and natural gas. Next, the low-pressure separator further separates the hydrocarbons. Both the high and low pressure separators are protected using LaMOT Standard Rupture Disc and Union Holders.
After the natural gas, oil, and water is separated, the natural gas is scrubbed before being sent through the pipeline to the gas-processing plant. The oil and water are sent to on-site storage tanks that will later be removed by truck; the oil will be hauled to a refinery, and the water is sent to a treatment station. Each drill site has a different number of tanks, but typically have between three to six tanks staged in two lines. One line holds the oil, and the other line holds the water. Each line of tanks has an overhead header line without any pressure relief or any other devices that go to the flare to burn any emissions that were created from flashing during the filling of the tanks.
The tanks are always in positive pressure and vacuum protection is not a concern. The thief hatches were designed to vent into the atmosphere, then gradually seat back into sealed position as the pressure released from vents decreases, without leaking any emissions.
CDC was brought in to help solve a problem involving leakage of a particular make of vent. The leakage caused the E&P company running the oil field to seek a higher-performing alternative. The Viton seal in the valve in use did not reset properly and worked poorly in the low temperature weather—problems which ultimately led to excess leakage.
To solve the problem, 4” LOTRX Rupture Discs from CDC were installed. Prior to making the switch, approximately ten leaks a week would occur. The vent causing the leakage used a “sponge Viton”. The gasket seal would have to be replaced six to ten times a week to provide a proper seal. Replacing the vent valves with the LOTRX Rupture Discs led to the full elimination of emissions leakage.
The LOTRX Rupture Disc was either installed on a header system fed by three to four tanks, or on a single tank with a connecting header. The thief hatch in use, set at 16 oz (1 psig), served as the primary relief device on each tank while CDC’s rupture disc, set at 24 oz per inch (1.5psig), served as a secondary relief device. Both the thief hatch and rupture disc vented directly into atmosphere, and not to the flare system.
Ultimately, Continental Disc’s rupture disc provided a leak-tight seal, resulting in a 75% reduction in emissions from those released by the other brand’s vent- valve system. Moreover, these emissions were not fineable: The rupture disc serves as a vessel-protection device and thus remains exempt from EPA 40 CFR 60, Subpart OOOO (Quad O) regulations. The tanks did not have any other pressure relief devices or valve type products.
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