川东北地区长兴组酸性气藏中硫化氢来源及成因

Translated title of the contribution: Origin of H2S in sour gas reservoirs in the Upper Permian Changxing Formation in northeastern Sichuan Basin

Kaikai Li, Chunfang Cai, Lei Jiang, Xunyun He, Zheng Huang

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

High H2S concentrations found in gas reservoirs within the Upper Permian Changxing Fm(P3ch)and Lower Triassic Feixianguan Fm (T1f) are generally thought to be formed via a process known as thermochemical sulfate reduction (TSR). However, unlike the T1f Fm, rare gypsum/anhydrite beds or anhydrite nodular were found in the P3ch Fm. This cast doubts over the accepted model for the souring process of the P3ch reservoirs. This study provides an analysis of palaegeopressure and carrier system within this system using carbonate-associated sulfate (CAS), isotopes, trace and rare earth element data. Results shows that, the H2S of high concentrations within the P3ch reservoirs were not derived from downward migration of sour gas from the T1f Fm, but were generated in situ through TSR; reactive sulfates were mainly derived from cross-formational brines migration from the T1f Fm, but with insignificant contributions from the Late Permian P3ch seawater and sulfate-rich brines within the Lower Triassic Jialingjiang Fm and Middle Carboniferous Honglong Fm formations, and the down-migration of T1f brines may have resulted in the P3ch TSR calcites having positive Eu anomaly, high Sr contents (up to 7767 ppm) and Ba contents (up to 1279 ppm) close to the T1f TSR calcite, and 87Sr/86Sr ratios (0.70724~0.70755) more radiogenic than those of the late Permian seawater; the cross-formational brine flow mainly occurred during sedimentary stage or the early stages of diagenesis, and seepage reflux during contemporaneous-penecontemporaneous stage and differential compaction flux during early-mid burial stage might serve as the main migration mechanisms; (4) CAS released during dolomization was another possible sulfate source, which brought the δ34S values of H2S and bitumen a little lower than those of the T1f Fm.

Original languageChinese
Pages (from-to)183-192
Number of pages10
JournalOil and Gas Geology
Volume36
Issue number2
DOIs
Publication statusPublished - 8 Apr 2015
Externally publishedYes

Keywords

  • CAS
  • differential compaction
  • TSR
  • H₂S
  • sour gas reservoir
  • Changxing Formation
  • northeastern Sichuan Basin

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