effect of TSR on carbonate p
Fang Hao a,b,⁎, Xuefeng Zhang c, Cu
Jianzhang Liu a, Zhongxian Cai a a Key Laboratory of Tectonics and Petroleum Resources, the b State Key Laboratory of Petroleum Resources and Prospect c Oil & Gas Institute, School of Earth and Space Sciences, Pek d CNOOC Research Institute, Beijing 100027, China e Exploration Southern Company, Sinopec, Chengdu 610041 f Department of Earth Sciences, Zhejiang University, Hangzh a r t i c l e i n f o
Sichuan Basin than carbonate dissolution, which implies that the amount of water generated during TSR was volumetrically em, which is unfavorable le for the preservation of dolostones have a high r B.V. All rights reserved.
Earth-Science Reviews 141 (2015) 154–177
Contents lists available at ScienceDirect
Earth-Science Reviews j ourna l homepage: www.e lsev ie r .com/ locate /earsc i revporosity in the gas zone reservoirs below the paleo-oil/water contact. The closed syst for deep burial carbonate dissolution and secondary porosity generation, was favorab early-formed porosity in deeply buried carbonates. Especially sucrosic and vuggy potential to preserve such porosity. © 2014 Elsevieinsignificant. 13C-depleted CO2 derived from hydrocarbon oxidation preferentially reacted with Ca2+ to form isotopically light calcite cements, and the remaining CO2 re-equilibrated with the 13C-enriched water–rock systems with its δ13C rapidly approaching the values for the host rocks, which accounted for the observed heavy and relatively constant CO2 δ13C values. The carbonate reservoirs suffered from differential porosity loss by TSR-involved solid bitumen generation and TSR-induced calcite and pyrite precipitation. Intensive TSR significantly reduced the porosity and permeability of the intervals expected to have relatively high sulfate contents (the evaporative-platform dolostones and the platform-margin shoal dolostones immediately underlying the evaporative facies). Early oil charge and limited intensity of TSR alteration, together with very low phyllosilicate content and early dolomitization, accounted for the preservation of anomalously high porosities in the reservoirs above the paleo-oil/water contact. A closed system seems to have played a special role in preserving the high⁎ Corresponding author at: Key Laboratory of Tectonics
E-mail addresses: email@example.com (F. Hao), zhang firstname.lastname@example.org (H. Zou), email@example.com (Y. Z http://dx.doi.org/10.1016/j.earscirev.2014.12.001 0012-8252/© 2014 Elsevier B.V. All rights reserved.2 calcite precipitation. Methane-dominated TSR was a rather late event and had played a less significant role in altering the reservoirs. Intensive H2S and CO2 generation during TSR resulted in calcite cementation ratherArticle history:
Received 8 July 2014
Accepted 2 December 2014
Available online 8 December 2014
Thermochemical sulfate reduction
Anomalously high porosity
Carbonate reservoirsthermochemical sulfate reduction (TSR) and orosity and permeability, Sichuan nwu Wang d, Pingping Li b, Tonglou Guo e, Huayao Zou b, Yangming Zhu f,
Ministry of Education, China University of Geosciences, Wuhan 430074, China ing, China University of Petroleum, Changping, Beijing 102249, China ing University, Beijing 100871, China , China ou 310027, China a b s t r a c t
This article discusses the role of methane in thermochemical sulfate reduction (TSR), the fate of TSR-derived CO2 and the effect of TSR on reservoir porosity and permeability, and the causes of the anomalously high porosity and permeability in the Lower Triassic soured carbonate gas reservoirs in the northeast Sichuan Basin, southwest
China. The Lower Triassic carbonate reservoirs were buried to a depth of about 7000 m and experienced maximum temperatures up to 220 °C before having been uplifted to the present-day depths of 4800 to 5500 m, but they still possess porosities up to 28.9% and permeabilities up to 3360 md. The present-day dry gas reservoirs evolved from a paleo-oil accumulation and experienced varying degrees of TSR alteration as evidenced from the abundant sulfur-rich solid bitumens and varying H2S and CO2 concentrations. TSR occurred mainly within the oil and condensate/wet gas windows, with liquid hydrocarbons and wet hydrocarbon gases acting as the dominant reducing agents responsible for sulfate reduction, sulfur-rich solid bitumen and H S generation, andThe fate of CO2 derived fromand Petroleum Resources, the Ministry of Education, China University of Geosciences, Wuhan 430074, China. firstname.lastname@example.org (X. Zhang), email@example.com (C. Wang), firstname.lastname@example.org (P. Li), email@example.com (T. Guo), hu), firstname.lastname@example.org (J. Liu), email@example.com (Z. Cai). . . . . . . . . . . . . . . . . . . . . . n? . . . . . qu oirs . . . . en . . . . . . . . 155F. Hao et al. / Earth-Science Reviews 141 (2015) 154–177prohibits carbonate cementation. Dixon et al. (1989) proposed that
CO2 production by TSR in the siliciclastic Upper Jurassic Norphletet al., 2014). These studies have significantly improved our understanding about the conditions, rates, processes, and products of TSR.
Nevertheless, several aspects of the physicochemical processes and effects of TSR have not yet beenwell documented and remain controversial (Bildstein et al., 2001; Machel, 2001; Mougin et al., 2007; Zhang et al., 2007). CO2 in TSR-altered gas reservoirs is usually believed to be one of the major products of TSR, and the ratio of CO2/(CO2 + ΣCn) has been used as a parameter to reflect the extent of TSR (e.g., Krouse et al., 1988; Worden and Smalley, 1996). However, a number of studies show that CO2 in TSR-altered gas reservoirs may be isotopically much heavier than predicted for an organic origin (e.g., Hao et al., 2008; Mankiewicz et al., 2009; Huang et al., 2010; Liu et al., 2013; Cai et al., 2014).
A relevant issue is the effect of TSR on reservoir porosity and permeability. At least four conflicting opinions have been proposed in the literature. (1) TSR has insignificant effect on reservoir porosity. Machel and Buschkuehle (2008) suggested that, since competing processes such as anhydrite removal versus calcite and dolomite cementation are involved, the overall changes in porosity and permeability of carbonate reservoirs in the Southesk–Cairn Carbonate Complex of the