Ocjene, prikazi i skupovi

Ocjene knjiga/zbornika radova/skupova: Josip Matasović i paradigma kulturne povijesti: zbornik radova znanstvenog skupa održanog u Slavonskom Brodu 23.-24. studenoga 2012., ur. Suzana Leček, Slavonski Brod, Zagreb: Hrvatski institut za povijest, Podružnica za povijest Slavonije, Srijema i Baranje, Hrvatski državni arhiv Društvo za hrvatsku povjesnicu, 2013., 446. str.; Josip Glaurdić, Vrijeme Europe: Zapadne sile i raspad Jugoslavije, Zagreb: Mate d.o.o., 2011., 453.str.; 21. godišnja konferencija Euroclia – „Kako podijeliti naše kulturno nasljeđe“ Skopje-Ohrid, 31. ožujka -5. travnja 2014

Experimental observation of water saturation effects on shear wave splitting in synthetic rock with fractures aligned at oblique angles

Fractured rocks are known to exhibit seismic anisotropy and shear wave splitting (SWS). SWS is commonly used for fractured rock characterization and has been shown to be sensitive to fluid type. The presence of partial liquid/gas saturation is also known to affect the elastic properties of rocks. The combined effect of both fractures and partial liquid/gas saturation is still unknown. Using synthetic, silica-cemented sandstones with aligned penny-shaped voids, we conducted laboratory ultrasonic experiments to investigate the effect fractures aligned at an oblique angle to wave propagation would have on SWS under partial liquid/gas saturation conditions. The result for the fractured rock shows a saturation dependence which can be explained by combining a fractured rock model and a partial saturation model. At high to full water saturation values, SWS decreases as a result of the fluid bulk modulus effect on the quasi-shear wave. This bulk modulus effect is frequency dependent as a result of wave-induced fluid flow mechanisms, which would in turn lead to frequency dependent SWS. This result suggests the possible use of SWS for discriminating between full liquid saturation and partial liquid/gas saturation

Joint elastic-electrical rock physics properties dataset: a laboratory study

Deliverable of Rock Solid Images (formerly OHM Ltd) sponsored Upscaling Projec

Effects of fluids and dual-pore systems on pressure-dependent velocities and attenuations in carbonates

The effects of fluid substitution on P- and S-wave velocities in carbonates of complex texture are still not understood fully. The often-used Gassmann equation gives ambiguous results when compared with ultrasonic velocity data. We present theoretical modeling of velocity and attenuation measurements obtained at a frequency of 750 kHz for six carbonate samples composed of calcite and saturated with air, brine, and kerosene. Although porosities (2%–14%) and permeabilities (0–74 mD) are relatively low, velocity variations are large. Differences between the highest and lowest P- and S-wave velocities are about 18% and 27% for brine-saturated samples at 60 and 10 MPa effective pressure, respectively. S-wave velocities are measured for two orthogonal polarizations; for four of six samples, anisotropy is revealed. TheGassmann model underpredicts fluid-substitution effects by <2% for three samples and by as much as 5% for the rest of the six samples. Moreover, when dried, they also show decreasing attenuation with increasing confining pressure. To model this behavior, we examine a pore model made of two pore systems: one constitutes the main and drainable porosity, and the other is made of undrained cracklike pores that can be associated with grain-to-grain contacts. In addition, these dried rock samples are modeled to contain a fluid-filled-pore system of grain-to-grain contacts, potentially causing local fluid flow and attenuation. For the theoretical model, we use an inclusion model based on the T-matrix approach, which also considers effects of pore texture and geometry, and pore fluid, global- and local-fluid flow. By using a dual-pore system, we establish a realistic physical model consistently describing the measured data

Relationships among low frequency (2Hz) electrical resistivity, porosity, clay content and permeability in reservoir sandstones

The improved interpretation of marine controlled source electromagnetic (CSEM) data requires knowledge of the inter-relationships between reservoir parameters and low frequency electrical resistivity. Hence, the electrical resistivities of 67 brine (35 g/l) saturated sandstone samples with a range of petrophysical properties (porosity from 2% to 29%, permeability from 0.0001 mD to 997.49 mD and volumetric clay content from 0 to 28%) were measured in the laboratory at a frequency of 2 Hz using a four-electrode circumferential resistivity method with an accuracy of ± 2%. The results show that sandstones with porosity higher than 9% and volumetric clay content up to 22% behave like clean sandstones and follow Archie's law for a brine concentration of 35 g/l. By contrast, at this brine salinity, sandstones with porosity less than 9% and volumetric clay content above 10% behave like shaly sandstones with non-negligible grain surface conductivity. A negative, linear correlation was found between electrical resistivity and hydraulic permeability on a logarithmic scale. We also found good agreement between our experimental results and a clay pore blocking model based on pore-filling and load-bearing clay in a sand/clay mixture, variable (non-clay) cement fraction and a shaly sandstone resistivity model. The model results indicate a general transition in shaly sandstones from clay-controlled resistivity to sand-controlled resistivity at about 9% porosity. At such high brine concentrations, no discernible clay conduction effect was observed above 9% porosity

Observations of fluid-dependent shear-wave splitting in synthetic porous rocks with aligned penny-shaped fractures

P- and S-wave velocity and attenuation coefficients (accurate to ±0.3% and ±0.2 dB/cm, respectively) were measured in synthetic porous rocks with aligned, penny-shaped fractures using the laboratory ultrasonic pulse-echo method. Shearwave splitting was observed by rotating the S-wave transducer and noting the maximum and minimum velocities relative to the fracture direction. A block of synthetic porous rock of fracture density 0.0201 ± 0.0068 and fracture size 3.6 ± 0.38 mm (measured from image analysis of X-ray CT scans) was sub-sampled into three 20–30 mm long, 50 mm diameter core plugs oriented at 0?, 45? and 90? to the fracture normal (transversely isotropic symmetry axis). Full waveform data were collected over the frequency range 500–1000 kHz for both water and glycerin saturated cores to observe the effect of pore fluid viscosity at 1 cP and 100 cP, respectively. The shear-wave splitting observed in the 90? core was 2.15 ± 0.02% for water saturated and 2.39 ± 0.02% for glycerin saturated, in agreement with the theory that suggests that the percentage splitting should be 100 times the fracture density and independent of the saturating fluid. In the 45? core, by contrast, splitting was 0.00 ± 0.02% for water saturation and ?0.77 ± 0.02% for glycerin saturation. This dependence on fracture orientation and pore fluid viscosity is consistent with the poro-visco-elastic theory for aligned, meso-scale fractures in porous rocks. The results suggest the possible use of shear- or converted-wave data to discriminate between fluids on the basis of viscosity variations

An anisotropic model for the electrical resistivity of two-phase geologic materials

Electrical and electromagnetic surveys of the seafloor provide valuable information about the macro and microscopic properties of subseafloor sediments. Sediment resistivity is highly variable and governed by a wide range of properties including pore-fluid salinity, pore-fluid saturation, porosity, pore geometry, and temperature. A new anisotropic, twophase, effective medium model describes the electrical resistivity of porous rocks and sediments. The only input parameters required are the resistivities of the solid and fluid components, their volume fractions and grain shape. The approach makes use of the increase in path length taken by an electrical current through an idealized granular medium comprising of aligned ellipsoidal grains. The model permits both solid and fluid phases to have a finite conductivity useful for dealing with surface charge conduction effects associated with clay minerals and gives results independent of grain size hence, valid for a wide range of sediment types. Furthermore, the model can be used to investigate the effects of grain aspect ratio and alignment on electrical resistivity anisotropy. Good agreement was found between the model predictions and laboratory measurements of resistivity and porosity on artificial sediments with known physical properties