Geophysical and transport properties of salt rocks subjected to loading/unloading, and during dissolution

The dataset contains data from a dual experiment conducted to study (i) the stress dependence of ultrasonic (elastic) waves and permeability of salt rocks, and (ii) the dissolution of an intact and a cracked halite samples using geophysical methods.

The tests were run in the high-pressure room-temperature (20°C) experimental setup for flow-through tests at the National Oceanography Centre, Southampton (NOCS) (Falcon et al. 2016). The rig consists of a triaxial vessel equipped with (i) ultrasonic sensors that allow measuring P- and S-wave velocities and their attenuation factors using the pulse echo method (McCann and Sothcott, 1992), and (ii) two rigs of electrodes embedded into the rubber sleeve of the pressure vessel for collecting electrical resistivity data that can be used to build up an electrical tomography of the sample (North el al. 2013). The rig has automatic control of both confining and pore pressure (ISCO EX-100D system). For the operating conditions and in homogeneous samples, the bulk electrical resistivity error is <1% for bulk resistivities <100 Ω m, increasing up to 5% with the degree of heterogeneity and above this resistivity value, at frequencies 1–500 Hz (North et al., 2013). Regarding the ultrasonic data, the technique and instrumentation used in this experiment provide velocity precision of ± 0.1% and accuracy of ± 0.3% (95% confidence), and attenuation accuracy of ± 0.1 dB cm-1 within the frequency range 300-1000 kHz (Best, 1992). The dataset presented here show the ultrasonic data at a single frequency of 600 kHz, obtained from Fourier analysis of broadband signals.

Permeability to water and to N2 can be both determined with the aid of integrated flowmeters and pore pressure sensors both up- and downstream of the rock sample.

The rock samples include: Pre-Cambrian salt (unknown well, Pakistan (source: www.likit.co.uk/)), Cambrian salt (unknown well, Tunguska Basin, Russia), Triassic salt (Arm Hill #1 well, NW Lancashire, UK), and Messinian salt (3A GN3 S02 well, core # 19, near Marianopoli, Sicily). 2.5 cm length, 5 cm diameter core plugs were extracted from precursor rocks, composition estimated by X-ray diffraction analysis, and connected porosity by He-pycnometry.

Falcon-Suarez, I., North, L., Amalokwu, K., Best, A., 2016. Integrated geophysical and hydromechanical assessment for CO2 storage: shallow low permeable reservoir sandstones. Geophysical Prospecting 64, 828-847, http://doi.org/10.1111/1365-2478.12396.

McCann, C., Sothcott, J., 1992. Laboratory measurements of the seismic properties of sedimentary rocks. Geological Society, London, Special Publications 65, 285-297, https://doi.org/10.1144/gsl.sp.1992.065.01.22.

North, L., Best, A.I., Sothcott, J., MacGregor, L., 2013. Laboratory determination of the full electrical resistivity tensor of heterogeneous carbonate rocks at elevated pressures. Geophysical Prospecting 61, 458-470, https://doi.org/10.1111/j.1365-2478.2012.01113.x.