TY - JOUR
T1 - TSR origin of sulfur in Permian and Triassic reservoir bitumen, East Sichuan Basin, China
AU - Cai, Chunfang
AU - Li, Kaikai
AU - Zhu, Yangming
AU - Xiang, Lei
AU - Jiang, Lei
AU - Tenger,
AU - Cai, Xunyu
AU - Cai, Liu Lu
PY - 2010/9
Y1 - 2010/9
N2 - Solid bitumen, H2S, pyrite and anhydrite samples from the Lower Triassic Feixianguan Formation and Upper Permian Changxing Formation, and source rock kerogen samples from the Cambrian, Ordovician, Silurian and Permian in the East Sichuan Basin were analyzed for their sulfur content and δ34S values, to determine if the measurements were consistent with a thermochemical sulfate reduction (TSR) origin of the produced H2S and solid bitumen. The results show that the solid bitumen samples have sulfur contents from 2.6 to 12.5wt.% and δ34S values from+13.4‰ to+22.1‰. The δ34S values are significantly heavier than those of potential Upper Permian source rock kerogens that average+1.3‰ (n=3), suggesting that most of the sulfur in the solid bitumen is derived from isotopically heavy H2S of TSR origin (from+12.0‰ to+13.7‰). Interestingly, two gases produced from gas to water transition zones during drill stem testing (DST) show significantly lighter δ34S values (+3.3‰ and+4.1‰) than the H2S from gas-producing intervals. The isotopically light H2S may be genetically linked to fracture-filling isotopically heavy anhydrite with δ34S values from+38.5‰ to+39.6‰, which are significantly heavier than those of coeval seawater sulfate (+11.8‰ to+21.7‰) as measured for bedded anhydrite. The link may have resulted from reduction of part of the dissolved sulfate by hydrocarbons under sulfate-limited conditions. Source rock kerogens show a secular change in δ34S values relative to source rock age. A dramatic decrease and then increase in δ34Skerogen was found toward the Permian/Triassic boundary for the first time in the East Sichuan Basin.
AB - Solid bitumen, H2S, pyrite and anhydrite samples from the Lower Triassic Feixianguan Formation and Upper Permian Changxing Formation, and source rock kerogen samples from the Cambrian, Ordovician, Silurian and Permian in the East Sichuan Basin were analyzed for their sulfur content and δ34S values, to determine if the measurements were consistent with a thermochemical sulfate reduction (TSR) origin of the produced H2S and solid bitumen. The results show that the solid bitumen samples have sulfur contents from 2.6 to 12.5wt.% and δ34S values from+13.4‰ to+22.1‰. The δ34S values are significantly heavier than those of potential Upper Permian source rock kerogens that average+1.3‰ (n=3), suggesting that most of the sulfur in the solid bitumen is derived from isotopically heavy H2S of TSR origin (from+12.0‰ to+13.7‰). Interestingly, two gases produced from gas to water transition zones during drill stem testing (DST) show significantly lighter δ34S values (+3.3‰ and+4.1‰) than the H2S from gas-producing intervals. The isotopically light H2S may be genetically linked to fracture-filling isotopically heavy anhydrite with δ34S values from+38.5‰ to+39.6‰, which are significantly heavier than those of coeval seawater sulfate (+11.8‰ to+21.7‰) as measured for bedded anhydrite. The link may have resulted from reduction of part of the dissolved sulfate by hydrocarbons under sulfate-limited conditions. Source rock kerogens show a secular change in δ34S values relative to source rock age. A dramatic decrease and then increase in δ34Skerogen was found toward the Permian/Triassic boundary for the first time in the East Sichuan Basin.
UR - http://www.scopus.com/inward/record.url?scp=77956192203&partnerID=8YFLogxK
U2 - 10.1016/j.orggeochem.2010.03.009
DO - 10.1016/j.orggeochem.2010.03.009
M3 - Article
VL - 41
SP - 871
EP - 878
JO - Organic Geochemistry
JF - Organic Geochemistry
SN - 0146-6380
IS - 9
ER -