Mechanical compaction and ultrasonic velocity of sands with different texture and mineralogical composition

Abstract

A B S T R A C TThis study presents the results of experimental compaction while measuring ultrasonic velocities of sands with different grain size, shape, sorting and mineralogy. Uniaxial mechanical compaction tests up to a maximum of 50 MPa effective stress were performed on 29 dry sand aggregates derived from eight different sands to measure the rock properties.A good agreement was found between the Gassmann saturated bulk moduli of dry and brine saturated tests of selected sands. Sand samples with poor sorting showed low initial porosity while sands with high grain angularity had high initial porosity. The sand compaction tests showed that at a given stress well-sorted, coarse-grained sands were more compressible and had higher velocities (Vp and Vs) than finegrained sands when the mineralogy was similar. This can be attributed to grain crushing, where coarser grains lead to high compressibility and large grain-to-grain contact areas result in high velocities. At medium to high stresses the angular coarse to medium grained sands (both sorted sands and un-sorted whole sands) showed high compaction and velocities (Vp and Vs). The small grain-to-grain contact areas promote higher deformation at grain contacts, more crushing and increased porosity loss resulting in high velocities. Compaction and velocities (Vp and Vs) increased with decreasing sorting in sands. However, at the same porosity, the velocities in whole sands were slightly lower than in the well-sorted sands indicating the presence of loose smaller grains in-between the framework grains. Quartz-poor sands (containing less than 55% quartz) showed higher velocities (Vp and Vs) compared to that of quartzrich sands. This could be the result of sintering and enlargement of grain contacts of ductile mineral grains in the quartz-poor sands increasing the effective bulk and shear stiffness. Tests both from wet measurements and Gassmann brine substitution showed a decreasing Vp/Vs ratio with increasing effective stress. The quartz-rich sands separated out towards the higher side of the Vp/Vs range.The Gassmann brine substituted Vp and Vs plotted against effective stress provide a measure of the expected velocity range to be found in these and similar sands during mechanical compaction. Deviations of actual well log data from experimental data may indicate uplift, the presence of hydrocarbon, overpressure and/or cementation. Data from this study may help to model velocity-depth trends and to improve the characterization of reservoir sands from well log data in a low temperature (<80-100 o C) zone where compaction of sands is mostly mechanical.

Clastic compaction unit classification based on clay content and integrated compaction recovery using well and seismic data

“…The initial porosity is affected not only by grain size, sorting, sphericity, roundness, and filling of sediment, but it also involves grain assemblage and consolidation (He et al 2002). The initial porosity can be obtained through direct experimental measurements (Atkins and McBride 1992;Beard and Weyl 1973;Pryor 1973) or numerical simulations (Zaimy and Rasaei 2013;Fawad et al 2011;Alberts and Weltje 2001;Harbaugh et al 1999;Syvitski and Bahr 2001); however, this is a time-consuming process. In industrial practice, He et al (2002) proposed a method in which the initial porosity is assigned to fall within a reasonable range of values.…”

Ultrasonic compaction of granular geological materials

“…In this secondary compaction phase, the relative motion between particles is very high and particle packing is thereby enhanced [12]. For the compaction processes studied in this paper, the critical stress under different operational conditions of compaction is of interest.…”

“…However, the influence of the physical characteristics of the granular geological materials is also very important. Although it has been reported that particle mineralogy and shape both affect the performance of an ultrasonic compaction 3 process [12,13], the influence of geological materials is unclear. There has been conflicting evidence between different studies with respect to the influence of vibrations on densification [14], and it has been proposed that significant differences between the physical properties of the particles, such as grain size and density, are contributory factors.…”

“…Porosity is a property of a material which is closely related to the density, and reduces as the density increases. It is known that the porosity within a sample of granular material depends on the particle size and shape, the material composition, and also the distribution of the particles [12].…”

Inverting Dynamic Elastic Moduli of a Granular Pack to Get Shear Modulus of the Grain

“…Jenkins et al (2005) presented a combination of Walton rough and smooth model to get the effective moduli of a granular pack that has a mixture of rough and smooth surface grains. A compilation of effective granular medium models from different studies can be found at Wang and Nur (1992) and Mavko et al (2009). Fawad et al (2011 experimented on some samples of different textures (grain size, shape, sorting and mineralogy) of the granular packs and found noticeable correlation between texture and ultrasonic velocities.…”