Acoustic Properties of Ancient Shallow-Marine Carbonates: Effects of Depositional Environments and Diagenetic Processes (Middle Jurassic, Paris Basin, France)
Acoustic Properties of Ancient Shallow-Marine Carbonates: Effects of Depositional Environments and Diagenetic Processes (Middle Jurassic, Paris Basin, France)
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DOI：
10.2110/jsr.2010.071
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发表时间：
2010-09
影响因子：
2
通讯作者：
B. Brigaud;B. Vincent;C. Durlet;J. Deconinck;P. Blanc;A. Trouiller
中科院分区：
文献类型：
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作者：
B. Brigaud;B. Vincent;C. Durlet;J. Deconinck;P. Blanc;A. Trouiller
摘要：对巴黎盆地东部中侏罗统碳酸盐岩的 250 多个岩心塞进行了岩石物理性质（声速、孔隙度、渗透率和密度）和岩石学特征（结构、相组成和成岩作用）的研究，为控制相对低孔隙度碳酸盐岩（Φ < 20%）的声速参数提供了见解。孔隙类型观测揭示了粒间大孔样品和面下微晶粒微孔样品中不同的声速，因此在给定的孔隙度范围（15-20%）下，微孔泥岩-砂岩（泻湖）沉积物中的速度大于大孔颗粒岩（浅滩）样品中的速度。标准 Wyllie 和 Raymer 变换非常适合泥岩或泻湖相的声速和孔隙度之间的线性回归。被解释为泻湖相的泥灰岩和细粒沉积物包括速度和孔隙度之间统计上显着的相关性（r = 0.9）。然而，数据表明，粒岩的速度-孔隙度关系的广泛分散并不是不同分选、粒度、孔隙类型、白云石含量或粘土含量的结果。相反，早期胶结作用极大地影响了成岩过程中的声学特性，并被解释为在给定孔隙度范围内速度的高变化性的原因。具体来说，在给定的孔隙率下，未经历早期胶结的压实颗粒岩中的声速高于早期胶结颗粒岩中的声速。岩石学观察表明，早期胶结作用限制了机械压实，从成岩作用的最早阶段就形成了一种非均质介质（不接触颗粒，保留了粒间大孔隙，这些孔隙被后来的块状方解石胶结物部分或完全填充）。粒岩中的泥晶化鲕粒、早期胶结物边缘和块状方解石之间丰富的界面可能会引起显着的波衰减。因此，标准时均方程无法预测早期胶结作用等成岩特征对声速的影响。相反，缺乏早期胶结有利于机械压实、颗粒间接触和缝合。其结果是形成均匀的微晶化颗粒支撑网络，可以促进波的传播。通过论证早期胶结作用在解释声学性质变异性中的关键作用，本研究的结果说明了影响碳酸盐岩速度变换的复杂因素（Wyllie 和 Raymer），即预测储层性质的经典工具。这些关于 Vp 解释和粒岩单元速度-孔隙度变换细化的见解可能广泛适用于加强碳酸盐岩层序中基于地震的勘探。
Abstract Examination of petrophysical properties (acoustic velocity, porosity, permeability, and density) and petrographical characteristics (texture, facies composition, and diagenesis) of more than 250 core plugs from the Middle Jurassic carbonates of the eastern Paris Basin provides insights into the parameters controlling acoustic velocities in relatively low-porosity carbonate rocks (Φ < 20%). The pore-type observations reveal distinct acoustic velocities in samples with intergranular macropores and samples with micropores in subhedral micrite, such that velocities in microporous mudstone–wackestone (lagoonal) deposits are greater than in macroporous grainstone (shoal) samples, at a given porosity range (15–20%). The standard Wyllie and Raymer transforms fit very well with the linear regression between acoustic velocity and porosity from mudstone or lagoonal facies. Marls and fine-grained deposits interpreted as lagoonal facies include statistically significant correlation (r = 0.9) between velocity and porosity. However, the data suggest that the wide scatter in velocity–porosity relationship from grainstones are not the result of different sorting, grain size, pore type, dolomite content, or clay content. Instead, early cementation greatly influences acoustic properties during diagenesis, and are interpreted to account for the high variability of velocities over a given porosity range. Specifically, at a given porosity, acoustic velocities in compacted grainstone that did not undergo early cementation are higher than in early-cemented grainstone. Petrographic observations suggest that early cementation limits mechanical compaction, creating a heterogeneous medium from the earliest stages of diagenesis (non-touching grains, preservation of intergranular macropores that are partially to totally filled by later blocky calcite cement). The abundant interfaces between micritized ooids, early cement fringes, and blocky calcites in grainstones may induce significant wave attenuation. As a result, the standard time-average equations fail to predict the effect of diagenetic features such as early cementation on sonic velocity. Conversely, an absence of early cementation favors mechanical compaction, grain-to-grain contact, and suturing. The result is a homogeneous micritized grain-supported network that may facilitate wave propagation. Through demonstration of the key role of early cementation in the explanation of variability in acoustic properties, the results of this study illustrate the complicated factors influencing velocity transforms in carbonates (Wyllie and Raymer), i.e., classical tools for predicting reservoir properties. These insights on the interpretation of Vp and the refinement of velocity–porosity transforms in grainstone units may be broadly applicable to enhancing seismic-based exploration in carbonate successions.