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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 65 (1981)

Issue: 5. (May)

First Page: 1007

Last Page: 1007

Title: Methane Concentration and Distribution in Pressurized Core Samples from Mississippian Delta Sediments: ABSTRACT

Author(s): Thomas Whelan III, W. R. Bryant, W. A. Dunlap

Article Type: Meeting abstract

Abstract:

Elevated concentrations of shallow biogenic methane are common in regions of rapid sediment deposition. A pressure core barrel was designed and implemented by Texas A&M University, in conjunction with the U.S. Geological Survey Mississippi Delta Project, to study these gas-charged shallow sediments of the continental shelf. Methane measurements were made on 10 pressurized cores taken in the South Pass region of the Mississippi delta. The results of these measurements indicated methane was present in concentrations ranging from 3,450 to 137,140 ppm (┬Ál CH4(STP)/l wet sediment). Methane values were generally higher than found in comparative samples taken with conventional wire-line equipment. However, these values were lower than predicted by theoretical calculations and also lower than pressure corrected saturation values for methane solubility in seawater. Stepwise decompression experiments were performed on selected samples to study the rate of methane release into the surrounding inert atmosphere of the pressurized sampling container. Results showed that at least 98% of the methane was released from the sediment matrix within 3 to 5 hours after opening the pressurized core. Samples containing higher total methane concentrations demonstrated no change in concentration with pressure during stepwise decompression while those containing lower total methane concentration demonstrated a marked change in concentration with pressure. These experimental results, successfully obtained with pressurized core barrel techniques, provide further in ight into the physical and chemical properties of gas in sediments.

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