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Permeability Evolution During Non-linear Viscous Creep of Calcite Rocks

机译：方解石岩石非线性蠕变过程中的渗透率演化

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摘要

Permeability, storage capacity and volumetric strain were measured in situ during deformation of hot-pressed calcite aggregates containing 10, 20, and 30 wt% quartz. Both isostatic and conventional triaxial loading conditions were used. The tests were performed at confining pressure of 300 MPa, pore pressures between 50 to 290 MPa, temperatures from 673 to 873 K and strain rates of 3 × 10−5 s−1. Argon gas was used as the pore fluid. The initial porosities of the starting samples varied from 5% to 9%, with higher porosity correlated to higher quartz content. Microstructural observations after the experiment indicate two kinds of pores are present: 1) Angular, crack-like pores along boundaries between quartz grains or between quartz and calcite grains and 2) equant and tubular voids within the calcite matrix. Under isostatic loading conditions, the compaction rate covaries with porosity and increases with increasing effective pressure. Most of the permeability reduction induced during compaction is irreversible and probably owes to plastic processes. As has been found in previous studies on hot-pressed calcite aggregates, permeability, k, is nonlinearly related to porosity, ϕ. Over small changes in porosity, the two parameters are approximately related as k ∝ ϕ n . The exponent n strongly increases as porosity decreases to a finite value (from about 4 to 6% depending on quartz content), suggesting a porosity percolation threshold. When subjected to triaxial deformation, the calcite-quartz aggregates exhibit shear-enhanced compaction, but permeability does not decrease as rapidly as it does under isostatic conditions. During triaxial compaction the exponent n only varies between 2 and 3. Non-isostatic deformation seems to reduce the percolation threshold, and, in fact, enhances the permeability relative to that at the same porosity during isostatic compaction. Our data provide constraints on the governing parameters of the compaction theory which describes fluid flow through a viscous matrix, and may have important implications for expulsion of sedimentary fluids, for fluid flow during deformation and metamorphism, and melt extraction from partially molten rocks.
机译：在包含10％，20％和30％（重量）石英的热压方解石聚集体变形过程中，就地测量了渗透率，储存能力和体积应变。等静压和常规三轴加载条件都被使用。试验是在300 MPa的围压，50到290 MPa的孔隙压力，673到873 K的温度以及3×10-5 s-1 的应变速率下进行的。氩气用作孔隙流体。起始样品的初始孔隙率在5％至9％之间变化，孔隙率越高，石英含量越高。实验后的微观结构观察表明存在两种孔隙：1）沿着石英晶粒之间或石英与方解石晶粒之间的边界的角状裂纹状孔隙，以及2）方解石基质中的等效和管状空隙。在等静载荷条件下，压实率随孔隙率变化，并随有效压力的增加而增加。压实过程中引起的大多数渗透率降低是不可逆的，可能归因于塑性过程。正如在先前对热压方解石骨料的研究中发现的那样，渗透率k与孔隙率ϕ非线性相关。在孔隙率有微小变化的情况下，这两个参数大致相关，即k ϕ n 。指数n随着孔隙率降低至有限值（取决于石英的含量，从约4％到6％）而急剧增加，表明存在孔隙率渗滤阈值。当经受三轴变形时，方解石-石英聚集体表现出剪切增强的压实，但是渗透率没有像在等静压条件下那样迅速下降。在三轴压实过程中，指数n仅在2和3之间变化。非等静变形似乎降低了渗流阈值，实际上，与等静压过程中相同孔隙度的渗透率相比，渗透率提高了。我们的数据为压实理论的控制参数提供了约束条件，压实理论描述了通过粘性基质的流体流动，并且可能对排出沉积流体，变形和变质过程中的流体流动以及部分熔融岩石中的熔体提取具有重要意义。

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  • 来源
    《Pure and Applied Geophysics》 |2006年第10期|2071-2102|共32页
  • 作者

    Xiaohui Xiao; Brian Evans; Yves Bernabé;

  • 作者单位

    Department of Earth Atmospheric and Planetary Sciences Massachusetts Institute of Technology;

    Department of Earth Atmospheric and Planetary Sciences Massachusetts Institute of Technology;

    Ecole et Observatoire des Sciences de la Terre de Strasbourg Université Louis Pasteur;

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  • 原文格式 PDF
  • 正文语种 eng
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  • 关键词

    Permeability; porosity; viscous creep; compaction;

    机译：渗透率;孔隙率;粘滞蠕变;压实;

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