Depositional facies and platform architecture of microbialite-dominated carbonate reservoirs, Ediacaran-Cambrian Ara Group, Sultanate of Oman
Depositional facies and platform architecture of microbialite-dominated carbonate reservoirs, Ediacaran-Cambrian Ara Group, Sultanate of Oman
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DOI：
10.1306/02271412063
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发表时间：
2014-08-01
期刊：
影响因子：
3.5
通讯作者：
Al-Rawahi, Zuwaina
中科院分区：
文献类型：
--
作者：
Grotzinger, John;Al-Rawahi, Zuwaina
埃迪卡拉纪寒武纪Ara群的盐内碳酸盐岩构成了阿曼盐内“细脉”成藏带的重要储集元素，在该成藏带中，碳酸盐岩被包裹在3至7 km（1.9至4.3 mi）深处的盐中。这些储层碳酸盐具有显著的微生物影响。虽然阿拉组储层大多是最新的前寒武纪，这里开发的模型可能适用于年轻的微生物为主的碳酸盐岩储层在较高的盐度的盆地时，更高的生物被排除在外，在湖泊环境中，钙化的无脊椎动物不是碳酸盐的重要来源，或在动物群恢复之前的大规模灭绝时期。广泛的碳酸盐相提供了背景，在其中了解的微生物为主的储层的起源，跨越斜坡和镶边陆棚配置文件。主要的相组合包括碳酸盐-蒸发岩过渡带、深斜坡和斜坡、潮下微生物岩、碎屑结构碳酸盐和局限的潮缘碳酸盐。微生物岩可细分为许多相，这些相在理解环境历史和储层性质方面都具有重要意义，并有助于预测储层航道的位置。受微生物影响的相包括具有大量凝块结构和非常高的初始孔隙度（>50%）的浅潮下带血栓岩、具有厘米级叶片形态变化的浅潮下带脓疱纹层岩、显示毫米级叶片形态变化的较深潮下带褶皱纹层岩以及显示毫米至厘米级簇状结构的潮间簇状纹层岩。其他储集相为更常规的粒状碳酸盐岩，包括涟漪状交错层状颗粒岩-包岩、丘状交错层状颗粒岩-包岩、扁平卵石砾岩、卵状和内碎屑颗粒岩-包岩以及Cloudina颗粒岩-包岩。这些相几乎都是泥化的，并且都具有中等至极好的储集层质量。这些相包括碳酸盐台地，在盐构造过程中破碎，厚度可达160米（525英尺），在盐运动之前横向延伸数十至50公里（31英里）。储集相的分布遵循层序地层学预测，微生物岩出现在每个可容纳空间剖面中。晚期高位和早期海侵体系域有利于凝块岩建造的横向扩展，而晚期海侵到早期高位体系域有利于建造储集相的横向不连续性和划分。脓疱纹层与凝块岩堆积密切相关，但在海侵晚期到高水位晚期形成横向扩展的岩片。褶皱纹层形成于海侵晚期到早期高位体系域，当碳酸盐沉积物的通量大大减少，使远洋来源的有机物积累时，可能代表最大的洪水间隔。
Intrasalt carbonates of the Ediacaran Cambrian Ara Group constitute a significant reservoir element of the intrasalt "stringer" play in Oman, in which dolomitic carbonates are encased in salt at depths of 3 to 7 km (1.9 to 4.3 mi). These reservoir carbonates have significant microbial influences. Although Ara Group reservoirs are mostly latest Precambrian, the models developed here may be applicable to younger microbially dominated carbonate reservoirs in basins of higher salinity when higher organisms are excluded, in lacustrine settings where calcified invertebrates are not a significant source of carbonate, or after periods of mass extinction before faunal recovery. A broad range of carbonate facies provides the context in which to understand the origin of the microbialite-dominated reservoirs developed across both ramp and rimmed shelf profiles. Major facies associations include carbonate-evaporite transition zone, deep ramp and slope, subtidal microbialites, clastic-textured carbonates, and restricted peritidal carbonates. Microbialites are subdivisible into a number of facies that all have significance in terms of understanding environmental history as well as reservoir properties, and that help in predicting the location of reservoir fairways. Microbially influenced facies include shallow subtidal thrombolites with massive clotted textures and very high initial porosities (>50%), shallow subtidal pustular laminites with cm-scale variability of lamina morphology, deeper subtidal crinkly laminites that show mm-scale variability of lamina morphology, and intertidal tufted laminates that show mm- to cm-scale tufted textures. Other reservoir facies are more conventional grainy carbonates including ripple cross-stratified grainstone-packstone, hummocky cross-stratified grainstone-packstone, flat pebble conglomerate, ooid and intraclast grainstone-packstone, and Cloudina grainstone-pack: stone. These facies are almost invariably dolomitized and all have moderate to excellent reservoir quality. These facies comprise carbonate platforms, broken up during salt tectonics, that range up to 160 m (525 ft) in thickness and extended laterally, prior to halokinesis, for tens to over 50 km (31 mi). The distribution of reservoir facies follows sequence stratigraphic predictions, with microbialites occurring in every accommodation profile. Late highstand and early transgressive systems tracts favor greater lateral extent of thrombolite build-ups, whereas later transgressive to early highstand system tracts favor greater lateral discontinuity and compartmentalization of buildup reservoir facies. Pustular laminites occur in close association with thrombolite buildups but form laterally extensive sheets in late transgressive to late highstand periods. Crinkly laminites form during late transgressive to early highstand systems tracts and may represent maximum flooding intervals when the flux of carbonate sediment was greatly reduced allowing pelagically derived organics to accumulate.