Title: COMPOSITION AND ISOTOPE FRACTIONATIONS OF ACCUMULATED NATURAL GAS AND THEIR SIGNIFICANCE
Abstract: Hydrocarbon composition and stable carbon isotope composition of natural gas are fractionated by diffusion, dissolution, microbial degradation and cracking in gas reservoirs. The diffusive fractionation is determined by radius and density grads of the hydrocarbon molecules, the dissolving fractionation is controlled by bulk volume and hydration capability of the dissolved molecules. The two kinds of fractionations result in enrichment of heavy molecules in the gases (C~ 2 + ) and heavy carbon isotopic composition. Hydrocarbon gases could be biodegraded selectively by microbes in gas reservoirs when the reservoir temperatures less than 80℃. The biodegradating fractionation leads to decrease of C~ 2 + components and δ 13 C value. When gas reservoir buried to enough depth and its temperature over 200℃, the C~ 2 + molecules would be cracked, which increases δ 13 C value also. Application of chemical dynamics to rebuilding the fractionation history, the primary hydrocarbon composition and carbon isotope composition at beginning of the gas accumulation will be characterized, which is useful in quantitative identification of a gas-pool formation and estimation of the source ratio for the gases derived from different sources.
Publication Year: 2005
Publication Date: 2005-01-01
Language: en
Type: article
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Cited By Count: 4
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