How burial diagenesis of chalk sediments controls sonic velocity and porosity
How burial diagenesis of chalk sediments controls sonic velocity and porosity
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DOI：
10.1306/06230301113
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发表时间：
2003-11-01
期刊：
影响因子：
3.5
通讯作者：
Fabricius, IL
中科院分区：
文献类型：
--
作者：
Fabricius, IL
基于纵波速度和密度数据，建立了白垩沉积物的新弹性模型。该模型允许构建一系列等框架（IF）曲线，每条曲线代表对固体框架做出贡献的矿物相的恒定部分。IF曲线可以与白垩埋藏成岩作用的进展相关，其修订如下：新沉积的碳酸盐软泥和混合沉积物的孔隙度范围为60%至80%，具体取决于空心微化石的普遍程度。尽管孔隙率很高，但这些沉积物并不处于悬浮状态，如 0.1 或更高的 IF 所反映的那样。埋藏后，沉积物通过机械压实失去孔隙率，同时方解石颗粒再结晶成逐渐更均匀的形状。高压实率可以使颗粒保持相对运动，而低压实率则允许形成接触水泥，由此IF增加并形成白垩。岩石力学测试表明，当压实需要的压力大于原位应力时，孔隙度的降低就会受到抑制。在随后的埋藏过程中，由于持续的再结晶，晶体和孔隙的尺寸会增大。在此过程中孔隙度损失的缺乏证明了方解石-方解石压力溶解不存在化学压实作用，以及接触胶结作用的孔隙度保持作用。在足够的埋藏应力下，缝合线的存在表明方解石和硅酸盐之间发生压力溶解，并且根据孔隙水化学和温度，可能在相对较短的深度间隔内发生孔隙充填胶结作用。石灰岩和混合沉积岩形成，孔隙率可降至20%以下。等框架增加到0.6以上。在北海白垩岩油气藏中，发现了相对较高的孔隙度和较高的IF。原因可能是重结晶和保孔接触胶结作用进展，而充孔胶结作用较小，可能是因为沿着缝合线的压力溶解被抑制。压力溶解可能因两个原因而被阻止：（1）烃的引入导致有效埋藏应力下降，以及（2）极性烃在硅酸盐上的吸附可以保护方解石免受硅酸盐的影响。
Based on P-wave velocity and density data, a new elastic model for chalk sediments is established. The model allows the construction of a series of isoframe (IF) curves, each representing a constant part of the mineral phase contributing to the solid frame.The IF curves can be related to the progress of burial diagenesis of chalk, which is revised as follows:Newly deposited carbonate ooze and mixed sediments range in porosity from 60 to 80%, depending on the prevalence of hollow microfossils. Despite the high porosity, these sediments are not in suspension, as reflected in IFs of 0.1 or higher.Upon burial, the sediments lose porosity by mechanical compaction, and concurrently, the calcite particles recrystallize into progressively more equant shapes. High compaction rates may keep the particles in relative motion, whereas low compaction rates allow the formation of contact cement, whereby IF increases and chalk forms. Rock mechanical tests show that when compaction requires more than in-situ stress, porosity reduction is arrested.During subsequent burial, crystals and pores grow in size as a consequence of the continuing recrystallization. ne lack of porosity loss during this process testifies to the absence of chemical compaction by calcite-calcite pressure dissolution, as well as to the porosity-preserving effect of contact cementation.At sufficient burial stress, the presence of stylolites indicates that pressure dissolution takes place between calcite., and silicates, and depending on pore-water chemistry and temperature, pore-filling cementation may occur over a relatively short depth interval. Limestone and mixed sedimentary rock form, and porosity may be reduced to less than 20%. Isoframe increases to more than 0.6.In hydrocarbon reservoirs in North Sea chalk, relatively high porosity and high IFs are found. The reason may be that recrystallization and porosity-preserving contact cementation progress, whereas pore-filling cementation is small, probably because pressure dissolution along stylolites is arrested. Pressure dissolution may be arrested for two reasons: (1) the introduction of hydrocarbons causes a fall in effective burial stress, and (2) adsorption of polar hydrocarbons on the silicates may shield calcite from the silicates.