Contrasting diagenetic evolution patterns of platform margin dolostone and limestone in the Lower Triassic Feixianguan Formation, Sichuan Basin, China
Contrasting diagenetic evolution patterns of platform margin dolostone and limestone in the Lower Triassic Feixianguan Formation, Sichuan Basin, China
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四川盆地下三叠统飞仙关组台缘灰岩和白云岩成岩演化模式对比
DOI：
10.1016/j.marpetgeo.2017.10.029
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发表时间：
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影响因子：
4.2
通讯作者：
Li Yin Pan
中科院分区：
文献类型：
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作者：
Lei Jiang;Richard H. Worden;Chun Fang Cai;An Jiang Shen;Xun Yue He;Li Yin Pan
四川盆地下三叠统飞仙关组深层碳酸盐岩储层蕴藏着丰富的天然气资源。这些储层主要发现于鲕滩中，其中泥质化带的储层质量高于未风化灰岩对应物。在这里，我们提出了岩相学，同位素，流体包裹体和定量孔隙度数据的组合，以了解和预测的成岩过程，影响白云岩和石灰岩的储层质量。由于方解石胶结作用，石灰岩的孔隙度已降低至107.5%，而鲕粒白云岩的孔隙度不与方解石胶结，通常具有1023.5%的孔隙度。白云石化和同时早期成岩石膏的增长发挥了至关重要的作用的发展和保存的高孔隙度的鲕粒白云岩，首先通过稳定岩石组构，以抑制孔隙度的损失在埋藏过程中，其次通过产生新的孔隙度的碳酸盐和硬石膏溶解。δ 18 O和盐度值（<3.5wt.从石灰岩中成岩方解石胶结物中的流体包裹体测得的100%的孔隙度表明，与大气降水有关的成岩作用在破坏石灰岩储层质量方面起着关键作用。早期充油似乎对白云岩中碳酸盐岩储层质量产生了积极影响，因为石油侵位抑制了方解石胶结作用。随后，热化学硫酸盐还原（TSR）发生，主要发生在白云岩中，如TSR方解石胶结物所示，具有高度负的δ 13 C值（δ-20 ‰ VPDB）和δ 18 O值（δ-10 ‰ VPDB）以及升高的方解石沉淀温度（>110 °C）。TSR很可能是导致白云岩中孔隙度增加0.2%的扩大溶洞形成的原因：i）硬石膏溶解，ii）大量水的产生导致地层水相对于方解石和白云石不饱和，iii）H2S和CO2的产生，以及H2S与方解石和白云石中菱铁矿（FeCO 3）组分的后续反应。这项研究表明，成岩作用的重要性，在形成深埋，高品质的储层中的影响的存在下的鲕粒岩为主的颗粒岩。我们的研究结果将有助于指导未来的勘探和油藏开发在类似的古地理和成岩环境。
Deeply-buried carbonate-reservoirs from the Lower Triassic Feixianguan Formation in the Sichuan Basin of China host extensive natural gas resources. These reservoirs are predominantly found in oolitic shoals, with the reservoir quality of dolomitized zones being higher than that of undolomitized limestone counterparts. Here we present a combination of petrographic, isotopic, fluid inclusion, and quantitative porosity data in order to understand and predict the diagenetic processes that have impacted the reservoir quality of dolostones and limestones. The porosity of limestones has been reduced to ∼7.5% due to calcite cementation, whereas the porosity in oolitic dolostones is not cemented with calcite and typically has ∼23.5% porosity. Dolomitization and concurrent early-diagenetic gypsum growth played crucial roles on the development and preservation of high porosity in the oolitic dolostone, first by stabilizing the rock fabric to inhibit loss of porosity during burial, and secondly through the generation of new porosity by dissolution of carbonate and anhydrite. A negative shift of δ18O and salinity values (<3.5 wt. %) measured from fluid inclusions in diagenetic calcite cement in limestones suggest that diagenesis associated with meteoric water played a key role in destroying limestone reservoir quality. Early oil charge seems to have had a positive effect on carbonate reservoir quality in the dolostones, since oil emplacement inhibited calcite cementation. Subsequently, thermochemical sulfate reduction (TSR) occurred, predominantly in the dolostones, as shown by TSR calcite cement with highly negative δ13C values (∼−20‰ VPDB) and δ18O (∼−10‰ VPDB) together with elevated calcite precipitation temperatures (>110 °C). It is likely that TSR was responsible for the formation of enlarged dissolution vugs that increased porosity by ∼2% in dolostones due to: i) anhydrite dissolution, ii) production of significant amounts of water resulting in formation water undersaturated with respect to calcite and dolomite, iii) generation of H2S, and CO2, and the consequent reaction of H2S with the siderite (FeCO3) component in calcite and dolomite. This study demonstrates the importance of diagenesis in the formation of deeply-buried, high-quality reservoirs in ooid-dominated grainstones influenced by the presence of evaporites. Our results should be useful for guiding future exploration and reservoir developments in similar paleogeographic and diagenetic settings.