AT THE RECENT GAS PROCESSORS Association convention in Denver, Carter Tannehill, Purvin & Gertz, Dallas, summed up nearly 4 years of GPA Technical Committee efforts to gauge the extent of contamination from mercury and other trace elements.
In September 1992, Technical Section A (plant design) was asked to investigate trace contaminants in natural gas that could cause problems with gas-processing facilities. In particular, the section members indicated arsenic and mercury should be studied.
Tannehill volunteered to develop information on these two contaminants. For the 1996 committee meeting, Tannehill conducted a literature search and a processing-company survey to determine the extent of the problem caused by contaminants, measurement techniques for trace incidences, and extent of the problems and possible solutions at the processing plant level.
Literature search
The literature search on arsenic indicated no occurrences of arsenic in natural gas in the U.S. other than the ABO field in New Mexico. Phillips Petroleum has completed research on arsenic removal methods.
There was some indication of a problem with arsenic in natural gas in Europe.
The literature search for mercury in natural gas indicated worldwide occurrences, but no specific locations within the U.S. Indications of mercury in natural gas and liquids were found in Thailand; Alberta, Canada; the Irish Sea; The Netherlands; Japan; and China.
It appears Mobil has done a significant amount of research, with Amoco and Phillips also completing some investigations.
In Chicago on Feb. 10-11, 1992, the Gas Research Institute (GRI) conducted a workshop on mercury contamination in natural gas with a topical report issued in April 1994.
Significant articles include the following:
"Natural Gas-Determination of Mercury," International Standard ISO 6978 (1992).
"Determination of Mercury Content in Venezuelan Natural Gas Streams," Intevep and Corpoven (1993).
"Quality Survey of Natural Gas in the United States," IGT (1993).
"Characterization and Measurement of Natural Gas Trace Constituents," IGT (1993).
"Methods to Combat Liquid Metal Enbrittlement in Cryogenic Aluminum Heat Exchangers," Central Environmental and Cortest Laboratories (1994).
Survey of operators
In February 1995, Tannehill sent a letter to each of 43 companies which represent more than 80% of the natural gas processed in the U.S. The letter requested information on any experience in detecting mercury at any of their processing plants.
Of these 43, only 15 failed to respond. Of the 28 companies which responded, 16 knew of no occurrences of mercury at their domestic plants. Of the 12 companies knowing of mercury occurrence, the locations were 4 in Wyoming, 3 in South Texas, 1 in Kansas, and 5 of undisclosed locations.
One of the primary locations of mercury occurrence is in South Texas and along the Texas Gulf Coast, up to the Sabine Pass, separating Texas from Louisiana. The prevalent formation containing mercury in this area of Texas appears to be the Lower Wilcox.
The other area of significant mercury discovery is in the southwest corner of Wyoming.
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