Claudio Delle Piane

Infrared Attenuated Total Reflectance Spectroscopy: An Innovative Strategy for Analyzing Mineral Components in Energy Relevant Systems

The direct qualitative and quantitative determination of mineral components in shale rocks is a problem that has not been satisfactorily resolved to date. Infrared spectroscopy (IR) is a non-destructive method frequently used in mineral identification, yet challenging due to the similarity of spectral features resulting from quartz, clay, and feldspar minerals. This study reports on a significant improvement of this methodology by combining infrared attenuated total reflection spectroscopy (IR-ATR) with partial least squares (PLS) regression techniques for classifying and quantifying various mineral components present in a number of different shale rocks. The developed multivariate classification model was calibrated using pure component mixtures of the most common shale minerals (i.e., kaolinite, illite, montmorillonite, calcite, and quartz). Using this model, the IR spectra of 11 real-world shale samples were analyzed and evaluated. Finally, the performance of the developed IR-ATR method was compared with results obtained via X-ray diffraction (XRD) analysis.

Further developments in measurement of low‐frequency seismic attenuation in laboratory

The study of wave attenuation in partially saturated porous rocks over a broad frequency range provides valuable information about the fluid system of reservoirs, which are inherently multiple phase fluid systems. Until now, not much laboratory data have been collected in the seismically relevant low frequency range and existing literature data on experimental measured partially saturated rock are very limited. The main goal of our work is to experimentally measure the bulk seismic attenuation on fluid-bearing rocks, using natural rock samples in an efficient way at in situ conditions and employing linear variable differential transformers (LVDTs). Bench-top results are promising and show consistency with reported experimental data for dry, partially, and fully fluid saturated rocks. Measurements with the machine are accurate and precise. We are able to detect a wide range of attenuation values, from nearly elastic materials, like aluminum, up to very well characterized viscoelastic material, such as Plexiglas. This can be considered the end-members for a saturated rock in the low frequency range at different degrees of saturation.

Geomechanical and rock physics properties of an Australian Northwest shelf shale

Shales are the most abundant sedimentary rock type, and have a very important role in oil and gas drilling operations, where they make up for a great part of all the drilled sections. Few experimental are available reporting their mechanical and rock physics characteristics. This study aims at characterizing a preserved shale recovered from the Northwest shelf of Australia in terms of composition, microstructure, mechanical and rock physics properties, plus evolution of ultrasonic anisotropy under triaxial loading. Preserved shale specimens cored normal and parallel to bedding were tested to evaluate the evolution of the ultrasonic wave velocities with increasing stress conditions and how anisotropy is affected by different loading angle with respect to the bedding plane. An array of ultrasonic transducers allowed us to measure five independent wave velocities on a single core plug, which were used to calculate the full elastic tensor of the shale assuming it to be a transversely isotropic medium. Results indicate that Pand S-wave velocities vary monotonically with increasing mean effective stress. The shale has small intrinsic P-wave anisotropy which tends to increase up to 5% with increasing mean effective stress, while S-wave anisotropy decreases from ~40% to ~30% over the same stress increment. Intrinsic anisotropy is related to the initial composition and fabric of the sediment and the presence of microfratures, while changes in elastic anisotropy result from the applied stresses, their orientation to the rock fabric and the degree of stress anisotropy.

Organic matter network in post mature Marcellus Shale: Effects on petrophysical properties

Shale samples of the Marcellus Shale from a well drilled in northeastern Pennsylvania were used to study diagenetic effects on the mineral and organic matter and their impact on petrophysical response. We analyzed an interval of high gamma ray and anomalously low electrical resistivity from a high thermal maturity (mean maximum vitrinite reflectance > 4%) part of the shalehgas play. A suite of microanalytical techniques was used to study features of the shale down to the nanoscale and assess the level of thermal alteration of the mineral and organic phases. The samples are organic rich, with total organic carbon contents of 3–7 wt. %; the vast majority of the organic matter was identified as highly porous pyrobitumen. Matrix porosity is also present, especially within the clay aggregates and at the interface between rigid clasts and clay minerals. Mineral- and organic-based thermal maturity indices suggest that during burial the sediment had been exposed to temperatures as high as 285°C (545°F). Under these conditions, the residual, migrated organic matter assumed a partially crystalline habit as confirmed by the identification of turbostratic structures via electron microscopy imaging. Experimental dielectric measurements on organic matter–rich samples confirm that the anomalous electrical properties observed in the wire-line logs can be ascribed to the presence of an electrically conductive interconnected network of partially graphitized organic matter. The preservation of porosity suggests that this organic network can contribute not only to the electrical properties but also to the gas flow properties within the Marcellus Shale.

Generation of amorphous carbon and crystallographic texture during low-temperature subseismic slip in calcite fault gouge

Identification of the nano-scale to micro-scale mechanochemical processes occurring during fault slip is of fundamental importance to understand earthquake nucleation and propagation. Here we explore the micromechanical processes occurring during fault nucleation and slip at subseismic rates (∼3 × 10−6 m s–1) in carbonate rocks. We experimentally sheared calcite-rich travertine blocks at simulated upper crustal conditions, producing a nano-grained fault gouge. Strain in the gouge is accommodated by cataclastic comminution of calcite grains and concurrent crystal-plastic deformation through twinning and dislocation glide, producing a crystallographic preferred orientation (CPO). Continued wear of fine-grained gouge particles results in the mechanical decomposition of calcite and production of amorphous carbon. We show that CPO and the production of amorphous carbon, previously attributed to frictional heating and weakening during seismic slip, can be produced at low temperature during stable slip at subseismic rates without slip weakening.