Effective stress, porosity, p-wave velocity and mineral composition of ODP Hole 174A-1073A sediments

Porosity, permeability, and compressional (P-wave) velocity were measured as a function of stress on sediments from Ocean Drilling Program Site 1073, U.S. Mid-Atlantic continental slope. Thin sections, scanning electron microscopy, and X-ray diffraction analyses provided mineralogical characteristics of the samples. Uniaxial strain boundary conditions were imposed on the samples during consolidation tests with the maximum effective axial stress reaching 13 MPa. The maximum effective radial stress necessary to maintain uniaxial strain was 7.6 MPa. Over an effective axial stress interval of 0 to 5.2 MPa, Sample 174A-1073A-26X-2, 82-89 cm (226.65 meters below seafloor [mbsf]), exhibited the largest decrease in porosity (51% to 41%), whereas Sample 71X-1, 2-8 cm (644.70 mbsf), exhibited the smallest decrease in porosity (48% to 45%). All samples showed negligible porosity increases during unloading. The permeability (on the order of 1 x 10-17 m**2) of Sample 174A-1073A-71X-1, 2-8 cm, was twice that measured on Sample 8H-1, 23-26 cm (63.75 mbsf), even though the former was considerably deeper and older. The differences in porosity-stress behavior and permeability between shallow and deep samples is related to lithologic, mineralogic, and diagenetic differences between the sediments above and below the Pliocene-Pleistocene to Miocene unconformity. P-wave velocity for Samples 174A-1073A-41X-5, 97-103 cm (372.35 mbsf), and 71X-1, 2-8 cm, increased with decreasing porosity, but did not change significantly during unloading.

本数据集针对美国中大西洋大陆斜坡大洋钻探计划（Ocean Drilling Program）1073站位的沉积物，测定了孔隙度、渗透率及纵波（P波）速度随应力的变化规律。通过薄片分析、扫描电子显微镜（scanning electron microscopy，SEM）与X射线衍射（X-ray diffraction，XRD）分析，获取了样品的矿物学特征。固结试验过程中对样品施加单轴应变边界条件，试验最大有效轴向应力达13 MPa，维持单轴应变所需的最大有效径向应力为7.6 MPa。
在有效轴向应力区间0~5.2 MPa范围内，样品174A-1073A-26X-2（井段82~89 cm，海底以下226.65米，meters below seafloor，缩写为mbsf）的孔隙度降幅最大，由51%降至41%；而样品71X-1（井段2~8 cm，海底以下644.70 mbsf）的孔隙度降幅最小，由48%降至45%。所有样品在卸荷过程中孔隙度增幅均可忽略不计。
尽管样品174A-1073A-71X-1（井段2~8 cm）埋藏更深、形成年代更久远，但其渗透率（量级约为1×10^-17 平方米）是样品8H-1（井段23~26 cm，海底以下63.75 mbsf）的两倍。浅部与深部样品的孔隙度-应力响应特征及渗透率差异，与上新世-更新世至中新世不整合面上下沉积物的岩性、矿物学及成岩作用差异密切相关。
样品174A-1073A-41X-5（井段97~103 cm，海底以下372.35 mbsf）与样品71X-1（井段2~8 cm）的纵波速度随孔隙度降低而升高，但在卸荷过程中无显著变化。