Comparison of stress-dependent geophysical, hydraulic and mechanical properties of synthetic and natural sandstones for reservoir characterization and monitoring studies
Comparison of stress-dependent geophysical, hydraulic and mechanical properties of synthetic and natural sandstones for reservoir characterization and monitoring studies
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DOI：
10.1111/1365-2478.12699
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发表时间：
2019-05-01
影响因子：
2.6
通讯作者：
Best, Angus I.
中科院分区：
文献类型：
--
作者：
Falcon-Suarez, Ismael Himar;Amalokwu, Kelvin;Best, Angus I.
当用于实验室岩石物理性质研究时，合成岩石样品可以提供优于天然岩石样品的优势，前提是它们作为天然类似物的成功是众所周知的。合成岩石模拟弹性波、电和流体输运性质的天然应力依赖性的能力是主要的兴趣。因此，我们比较了四个石英砂岩样品（孔隙度范围20-25%），包括两个合成和两个天然（Berea和Corvio）样品，后者广泛用作岩石物理研究的标准实验室多物理测量的一致性。我们同时测量超声波（P-和S-波）的速度和衰减，电阻率，渗透率和轴向和径向应变在很宽的压差范围内（围压15-50 MPa;孔隙压力5-10 MPa）的四个盐水饱和样品。尽管一些明显的物理差异所造成的合成制造过程中，如硅胶结和各向异性，结果显示只有很小的差异，应力之间的依赖关系的合成和天然砂岩的所有测量参数。应力依赖性分析的干样品使用各向同性的有效介质模型的球形孔和硬币形裂纹，连同颗粒凝聚力模型，提供证据的裂纹闭合机制在天然砂岩中，看到在合成砂岩的程度要小得多。较小的粒度，较大的水泥含量，以及在oedometric条件下的胶结作用特别影响合成砂岩的流体输运性质，从而导致对于类似孔隙度的较低渗透率和较高电阻率。有效应力系数，确定为每个参数，与文献中报道的数据一致。我们的研究结果表明，特定的合成材料进行了测试，合成砂岩可以作为良好的代理天然砂岩的弹性和力学性能的研究，但应小心使用的传输性能的研究。
Synthetic rock samples can offer advantages over natural rock samples when used for laboratory rock physical properties studies, provided their success as natural analogues is well understood. The ability of synthetic rocks to mimic the natural stress dependency of elastic wave, electrical and fluid transport properties is of primary interest. Hence, we compare a consistent set of laboratory multi-physics measurements obtained on four quartz sandstone samples (porosity range 20-25%) comprising two synthetic and two natural (Berea and Corvio) samples, the latter used extensively as standards in rock physics research. We measured simultaneously ultrasonic (P- and S-wave) velocity and attenuation, electrical resistivity, permeability and axial and radial strains over a wide range of differential pressure (confining stress 15-50 MPa; pore pressure 5-10 MPa) on the four brine saturated samples. Despite some obvious physical discrepancies caused by the synthetic manufacturing process, such as silica cementation and anisotropy, the results show only small differences in stress dependency between the synthetic and natural sandstones for all measured parameters. Stress dependency analysis of the dry samples using an isotropic effective medium model of spheroidal pores and penny-shaped cracks, together with a granular cohesion model, provide evidence of crack closure mechanisms in the natural sandstones, seen to a much lesser extent in the synthetic sandstones. The smaller grain size, greater cement content, and cementation under oedometric conditions particularly affect the fluid transport properties of the synthetic sandstones, resulting in lower permeability and higher electrical resistivity for a similar porosity. The effective stress coefficients, determined for each parameter, are in agreement with data reported in the literature. Our results for the particular synthetic materials that were tested suggest that synthetic sandstones can serve as good proxies for natural sandstones for studies of elastic and mechanical properties, but should be used with care for transport properties studies.