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首页> 外文期刊>AAPG Bulletin >New insights into the formation mechanism of high hydrogen sulfide-bearing gas condensates: Case study of Lower Ordovician dolomite reservoirs in the Tazhong uplift, Tarim Basin
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New insights into the formation mechanism of high hydrogen sulfide-bearing gas condensates: Case study of Lower Ordovician dolomite reservoirs in the Tazhong uplift, Tarim Basin

机译：高含硫化氢气体凝析物形成机理的新见解：以塔里木盆地塔中隆起下奥陶统白云岩储层为例

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摘要

Huge, high gas-oil ratio, hydrogen sulfide (H2S)-bearing gas condensate accumulations were recently discovered in the Ordovician carbonate reservoirs of the Tazhong uplift in the Tarim Basin, northwest China. Distinct differences exist between the eastern and western condensates in terms of chemical and isotopic compositions. Condensates from the western part of the uplift were characterized by high dibenzothiophenes (generally >500 mu g/g), a high H2S concentration (similar to 7%, vol./vol.), and relatively depleted C-13 methane (delta C-13(1) = -55.5 parts per thousand to -36 parts per thousand). The H2S concentration in the Tazhong gas condensates shows a positive correlation to Mg2+ concentration in the formation water. Formation water in Lower Ordovician-Cambrian strata in the Tazhong uplift is rich in Mg2+, which facilitates the thermochemical sulfate reduction (TSR) of sulfate contact ion pairs (CIPs) to produce H2S and dibenzothiophenes. A detailed comparison of the chemical compositions of the formation waters in different strata indicates that a high H2S concentration in the Tazhong gas condensates originates from the TSR of sulfate CIPs in the Lower Ordovician Cambrian strata, where a primary oil accumulation may have existed. The concentrations of 3- and 4-methyldiamantanes in the western condensates (80 to 150 mu g/g) are relatively lower than those from the eastern part of the uplift. Also, the delta C-13(1) in the western H2S-bearing gas condensates was more negative, and the delta C-13(2)-delta C-13(1) value was larger than that from typical TSR-altered gases. These features indicate that the western Tazhong samples had just entered the initial stage of TSR. According to the pressure, volume, temperature (PVT) phase diagram, the lower Paleozoic section was quickly buried after the Tortonian. High-H2S hydrocarbon inclusions formed during the last 10 m.y. when paleotemperatures reached 140 degrees C (284 degrees F). Because the reaction rate of the sulfate CIPs oxidation was relatively slower than that of H2S autocatalysis during the entire TSR process, advanced TSR has not been accomplished yet. It is also inferred that the Tortonian was the key period for accumulation of secondary H2S-bearing gas condensates, resulting from abundant gas washing along deep fractures and charging in the early reservoirs. An increased aromaticity parameter (toluene-heptane) and an increased fractionation index from east to west indicate an intensified degree of gas washing. Different gas-washing intensities in the eastern and western gas condensates led to diverse PVT states as well. Deep strata in the Tazhong uplift were characterized by multiple charges and mixing, coupled with periodic TSR, leading to the occurrence of variable H2S-bearing gas condensates.
机译：最近在中国西北塔里木盆地塔中隆起的奥陶系碳酸盐岩油藏中发现了巨大的，高油气比的硫化氢（H2S）气藏。在化学和同位素组成方面，东部和西部凝析油之间存在明显差异。隆起西部的凝析油的特征是二苯并噻吩含量高（通常> 500μg / g），H2S浓度高（约7％（体积/体积））和相对贫乏的C-13甲烷（δC）。 -13（1）= -55.5千分之至-36千分之三。塔中气凝析物中的硫化氢浓度与地层水中的Mg2 +浓度呈正相关。塔中隆起区下奥陶统-寒武系地层中的地层水富含Mg2 +，这促进了硫酸盐接触离子对（CIPs）的热化学硫酸盐还原（TSR）生成H2S和二苯并噻吩。对不同地层中地层水化学成分的详细比较表明，塔中气凝析物中的高H2S浓度源自下奥陶纪寒武纪地层中硫酸盐CIPs的TSR，那里可能已存在一次石油聚集。西部凝析物中3-和4-甲基二金刚烷的浓度（80至150μg / g）相对低于隆升东部地区的浓度。同样，含H2S的西部凝析气中的δC-13（1）更加负，并且δC-13（2）-δC-13（1）的值比典型的TSR改变的气体大。这些特征表明，塔中西部的样品刚刚进入TSR的初始阶段。根据压力，体积，温度（PVT）相图，在Tortonian之后，下古生界被迅速掩埋。在最后10 y年形成了高H2S烃包裹体。当古温度达到140摄氏度（284华氏度）时。由于在整个TSR过程中，硫酸盐CIPs氧化的反应速率相对于H2S自催化的反应速率相对较慢，因此尚未完成先进的TSR。还可以推断，Tortonian是次生含H2S凝析气聚集的关键时期，这是由于沿深裂缝的大量气洗和早期储层中的充注所致。芳香度参数（甲苯/正庚烷）增加和分馏指数从东向西增加表明气体洗涤程度增强。东部和西部凝析气中不同的气体洗涤强度也导致了不同的PVT状态。塔中隆起深层地层的特征是多次充注和混合，再加上周期性的TSR，导致了含H2S的气体凝析油的变化。

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