![]() ![]() Moreover, the pore-filling shale trend straddles the clean sandstone trend and meets the load-bearing shale trend between 100 and 150 apparent formation factors. In resistivity–velocity space, the resistivity of load-bearing shale increases with increasing velocity which form a more distinct trend with steeper gradient compared to those for partial pore-filling shale and clean sandstones. This scheme in particular allowed us to distinguish between pore-filling and load-bearing shale distributions according to idealized definitions, which provides new insight into the joint ultrasonic properties and resistivity behaviour for shaly sandstones. ![]() The distribution of volumetric shale content was classified by comparing the calculated dry P-wave modulus to the modified Upper Hashin–Shtrikman bound for quartz and air mixtures, assuming pore-filling shale. All the data were collected using the ultrasonic (700 kHz) pulse-echo measurement technique for P- and S-wave velocities ( V p, V s), attenuations ( Q p −1, Q s −1), and a four-electrode method for resistivity under elevated hydrostatic confining pressures between 10 and 50 MPa (pore fluid pressure 5 MPa). We investigated the effect of shale distribution on the joint elastic wave and electrical properties of shaly reservoir sandstones using a dataset of laboratory measurements on 75 brine-saturated (35 g/L salinity) rock samples (63 samples from the literature, 12 newly measured samples).
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