Generation of isotopically and compositionally distinct water during thermochemical sulfate reduction (TSR) in carbonate reservoirs: Triassic Feixianguan Formation, Sichuan Basin, China

Jiang, Lei; Worden, Richard H.; Cai, Chunfang

doi:10.1016/j.gca.2015.05.033

Cited by 57 publications

(20 citation statements)

References 51 publications

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“…, , ; Worden & Smalley ; Jiang et al . ). Salinities from the two‐phase inclusions reached relatively high values.…”

Section: Discussionmentioning

confidence: 97%

“…; Jiang et al . , ,b). The seawater‐like REE+Y and marine δ 13 C values suggest that the fabric‐obliterative dolomite resulted from seawater‐derived fluids (Nothdurft et al .…”

Section: Discussionmentioning

confidence: 99%

“…The lowest d 18 O values also indicate that it formed at high temperatures (Al-aasm et al 2002;Zhang et al 2009;Conliffe et al 2010). The d 13 C values of saddle dolomite cement are similar to those of fabricretentive dolomites and fabric-obliterative dolomites, which suggests that it was also derived from contemporaneous seawater and that no carbon was sourced from thermochemical sulphate reduction (Machel 1987;Krouse et al 1988;Heydari & Moore 1989;Worden et al 1995Worden et al , 2000Jiang et al 2015b). Salinities from the two-phase inclusions reached relatively high values.…”

Section: Origin Of the Dolomitesmentioning

confidence: 99%

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Origin of dolomites in the Cambrian (upper 3rd‐Furongian) formation, south‐eastern Sichuan Basin, China

et al. 2016

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The origin of large‐scale ancient dolomite is one of the most hotly debated topics in sedimentology. The Loushanguan group of the upper 3rd‐Furongian Cambrian series on the south‐eastern margin of the Sichuan Basin consists of numerous dolomites, and the origins of these dolomites have never been reported previously although they are probably good hydrocarbon reservoirs. Based on a systematic analysis of petrology, fluid inclusions, carbon and oxygen isotopes, trace elements and rare earth elements (REEs), this study provides some unique insights into the origins of the dolomites. Four dolomite types have been identified in the study area: dolomicrite, fabric‐retentive oolitic dolomite, fabric‐obliterative dolomite and saddle dolomite cement. In the dolomicrite and fabric‐retentive oolitic dolomite, high Sr contents (with respect to the fabric‐obliterative dolomite) and the lack of two‐phase aqueous inclusions suggest that they formed at shallow‐to‐intermediate burial depths at low temperatures (<50–60°C). Carbon and oxygen isotopes and seawater‐like REE+Y characteristics of the dolomicrite and fabric‐retentive oolitic dolomite indicate that the dolomitizing fluids were evaporated seawater or slightly modified seawater. The obliteration of the original sedimentary fabric and relatively low δ18O and Sr values compared to the fabric‐retentive dolomite indicate that fabric‐obliterative dolomite formed at intermediate‐to‐deep burial diagenesis. The chemical composition approaches pure dolomite and the REE+Y characteristics are similar to those of the fabric‐retentive dolomite, indicating that the fabric‐obliterative dolomite was formed due to the recrystallization of the previously formed fabric‐retentive dolomite at elevated burial depths and temperatures. High fluid inclusion homogenization temperatures (115–150°C), low δ18O values, nonplanar‐a crystals and seawater‐like REE+Y characteristics suggest that saddle dolomite cement formed by reprecipitation of dolomite that related to seawater‐driven and deep burial fluid. In the study area, dolomicrite and fabric‐retentive oolitic dolomite may have been formed by penecontemporaneous or seepage‐reflux dolomitization during early‐stage diagenesis. Subsequently, during progressive burial, most of the fabric‐retentive dolomite was converted into fabric‐obliterative dolomite by recrystallization. This study confirms that fabric‐obliterative dolomite was the main dolomite type, and although deeply buried, these Cambrian dolomites most likely have preserved coeval seawater geochemical signals.

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“…, , ; Worden & Smalley ; Jiang et al . ). Salinities from the two‐phase inclusions reached relatively high values.…”

Section: Discussionmentioning

confidence: 97%

“…; Jiang et al . , ,b). The seawater‐like REE+Y and marine δ 13 C values suggest that the fabric‐obliterative dolomite resulted from seawater‐derived fluids (Nothdurft et al .…”

Section: Discussionmentioning

confidence: 99%

Section: Origin Of the Dolomitesmentioning

confidence: 99%

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Origin of dolomites in the Cambrian (upper 3rd‐Furongian) formation, south‐eastern Sichuan Basin, China

et al. 2016

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“…B), precluding the possibility of meteoric water influx. During deep burial, water associated with anhydrite dissolution and thermochemical sulphate reduction (TSR) generated water commonly have relatively depleted δ 18 O VSMOW values compared with the evolved connate formation water (Worden et al ., ; Jiang et al ., ,c). Abundant anhydrite in the presence of petroleum, H 2 S concentrations up to 11% (Worden & Smalley, ; Cai et al ., ) and temperatures >110°C all show that TSR has occurred in the Lower to Middle Cambrian dolostones.…”

Section: Discussionmentioning

confidence: 99%

Multiphase dolomitization of deeply buried Cambrian petroleum reservoirs, Tarim Basin, north‐west China

et al. 2016

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Cambrian dolostone reservoirs in the Tarim Basin, China, have significant potential for future discoveries of petroleum, although exploration and production planning is hampered by limited understanding of the occurrence and distribution of dolomite in such ancient rocks buried to nearly 8 km. The study herein accessed new drill core samples which provide an opportunity to understand the dolomitization process in deep basins and its impact on Cambrian carbonate reservoirs. This study documents the origin of the dolostone reservoirs using a combination of petrology, fluid‐inclusion microthermometry, and stable and radiogenic‐isotopes of outcrop and core samples. An initial microbial dolomitization event occurred in restricted lagoon environments and is characterized by depleted δ13C values. Dolomicrite from lagoonal and sabkha facies, some fabric‐retentive dolomite and fabric‐obliterative dolomite in the peloidal shoal and reef facies show the highest δ18O values. These dolomites represent relatively early reflux dolomitization. The local occurrence of K‐feldspar in dolomicrite indicates that some radiogenic strontium was contributed via terrigenous input. Most fabric‐retentive dolomite may have precipitated from seawater at slightly elevated temperatures, suggested by petrological and isotopic data. Most fabric‐obliterative dolomite, and medium to coarse dolomite cement, formed between 90°C and 130°C from marine evaporitic brine. Saddle dolomite formed by hydrothermal dolomitization at temperatures up to 170°C, and involved the mixing of connate brines with Sr‐ enriched hydrothermal fluids. Intercrystalline, moldic, and breccia porosities are due to the early stages of dolomitization. Macroscopic, intergranular, vuggy, fracture and dissolution porosity are due to burial‐related dissolution and regional hydrothermal events. This work has shown that old (for example, Cambrian or even Precambrian) sucrosic dolomite with associated anhydrite, buried to as much as 8000 m, can still have a high potential for hosting substantial hydrocarbon resources and should be globally targeted for future exploration.

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“…In domestic and overseas investigations, high concentrations of H 2 S have generally been attributed to the thermochemical sulfate reduction (TSR) between anhydrite and hydrocarbons (Worden et al 2000;Jiang et al 2015), during which liquid hydrocarbons are enriched with sulfur and the drying coefficient of gas reservoirs may exceed 99%. In actual geological conditions, the formation water could act as the reaction agent of TSR.…”

Section: Introductionmentioning

confidence: 99%

Impact of formation water on the generation of H2S in condensate reservoirs: a case study from the deep Ordovician in the Tazhong Uplift of the Tarim Basin, NW China

Jin

Wang

et al. 2017

Pet. Sci.

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A number of condensate reservoirs with high concentrations of H 2 S have been discovered in the deep dolomite reservoirs of the lower Ordovician Yingshan Formation (O 1 y) in the Tazhong Uplift, where the formation water has a high pH value. In the O 1 y reservoir, the concentrations of Mg 2? and SO 4 2-in the formation water are higher than those in the upper Ordovician formation. The concentration of H 2 S in the condensate reservoirs and the concentration of Mg 2? in the formation water correlate well in the O 1 y reservoirs of the Tazhong Uplift, which indicates a presumed thermochemical sulfate reduction (TSR) origin of H 2 S according to the oxidation theory of contact ion-pairs (CIPs). Besides, the pH values of the formation water are positively correlated with the concentration of H 2 S in the condensate reservoirs, which may indicate that high pH might be another factor to promote and maintain TSR. Oil-source correlation of biomarkers in the sulfuretted condensates indicates the Cambrian source rocks could be the origin of condensates. The formation water in the condensate reservoirs of O 1 y is similar to that in the Cambrian; therefore, the TSR of sulfate-CIPs likely occurred in the Cambrian. High H 2 S-bearing condensates are mainly located near the No. 1 Fault and NE-SW strikeslip faults, which are the major migration pathway of deep fluids in the Tazhong Uplift. The redox between sulfateCIPs and hydrocarbons is the generation mechanism of H 2 S in the deep dolomite condensate reservoirs of the Tazhong Uplift. This finding should be helpful to predict the fluid properties of deep dolomite reservoirs.

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Generation of isotopically and compositionally distinct water during thermochemical sulfate reduction (TSR) in carbonate reservoirs: Triassic Feixianguan Formation, Sichuan Basin, China

Cited by 57 publications

References 51 publications

Origin of dolomites in the Cambrian (upper 3rd‐Furongian) formation, south‐eastern Sichuan Basin, China

Origin of dolomites in the Cambrian (upper 3rd‐Furongian) formation, south‐eastern Sichuan Basin, China

Multiphase dolomitization of deeply buried Cambrian petroleum reservoirs, Tarim Basin, north‐west China

Impact of formation water on the generation of H2S in condensate reservoirs: a case study from the deep Ordovician in the Tazhong Uplift of the Tarim Basin, NW China

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