The fate of CO2 derived from thermochemical sulfate reduction (TSR) and effect of TSR on carbonate porosity and permeability, Sichuan Basin, China
The fate of CO2 derived from thermochemical sulfate reduction (TSR) and effect of TSR on carbonate porosity and permeability, Sichuan Basin, China
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DOI：
10.1016/j.earscirev.2014.12.001
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发表时间：
2015-02-01
影响因子：
12.1
通讯作者：
Cai, Zhongxian
中科院分区：
文献类型：
--
作者：
Hao, Fang;Zhang, Xuefeng;Cai, Zhongxian
本文讨论了甲烷在热化学硫酸盐还原（TSR）中的作用、TSR 衍生的 CO2 的去向以及 TSR 对储层孔隙度和渗透率的影响，以及四川盆地东北部下三叠统酸性碳酸盐岩气藏异常高孔隙度和渗透率的原因。下三叠统碳酸盐岩储层埋藏深度约7000m，在被抬升到现今深度4800～5500m之前，经历了最高温度220℃，但其孔隙度仍高达28.9%，渗透率高达3360md。现今的干燥气藏是由古石油聚集演化而来，并经历了不同程度的 TSR 改变，丰富的富硫固体沥青以及不同的 H2S 和 CO2 浓度就证明了这一点。 TSR 主要发生在石油和凝析油/湿气窗口内，液态烃和湿烃气体作为主要还原剂，负责硫酸盐还原、富硫固体沥青和 H2S 生成以及方解石沉淀。以甲烷为主的 TSR 是一个相当晚的事件，在改变储层方面发挥的作用不太重要。 TSR 过程中大量生成 H2S 和 CO2，导致方解石胶结而不是碳酸盐溶解，这意味着 TSR 过程中产生的水量在体积上微不足道。烃氧化产生的贫 C-13 CO2 优先与 Ca2+ 反应形成同位素轻方解石胶结物，剩余 CO2 与富 C-13 水岩系统重新平衡，其 δ C-13 迅速接近母岩的值，这解释了观测到的重且相对恒定的 CO2 δ C-13 值。碳酸盐岩储层因 TSR 涉及的固体沥青生成以及 TSR 引起的方解石和黄铁矿沉淀而遭受差异孔隙度损失。强化TSR显着降低了预计硫酸盐含量相对较高的层段（蒸发台白云岩和紧邻蒸发带下方的台缘浅滩白云岩）的孔隙度和渗透率。早期的石油充注和有限的 TSR 蚀变强度，加上非常低的页硅酸盐含量和早期的白云石化，是古油/水界面上方储层中异常高孔隙度得以保存的原因。封闭系统似乎在保持古油/水接触面以下气层储层的高孔隙度方面发挥了特殊作用。封闭体系不利于深埋碳酸盐岩的溶蚀和次生孔隙的生成，但有利于深埋碳酸盐岩早期形成孔隙的保存。尤其是蔗糖质和孔洞白云岩具有保留此类孔隙度的巨大潜力。 (C) 2014 Elsevier B.V. 保留所有权利。
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 degrees 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 H2S generation, and 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 rather than carbonate dissolution, which implies that the amount of water generated during TSR was volumetrically insignificant. C-13-depleted CO2 derived from hydrocarbon oxidation preferentially reacted with Ca2+ to form isotopically light calcite cements, and the remaining CO2 re-equilibrated with the C-13-enriched water-rock systems with its delta C-13 rapidly approaching the values for the host rocks, which accounted for the observed heavy and relatively constant CO2 delta C-13 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 fades). 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 porosity in the gas zone reservoirs below the paleo-oil/water contact. The closed system, which is unfavorable for deep burial carbonate dissolution and secondary porosity generation, was favorable for the preservation of early-formed porosity in deeply buried carbonates. Especially sucrosic and vuggy dolostones have a high potential to preserve such porosity. (C) 2014 Elsevier B.V. All rights reserved.