Evgeny M. Chesnokov

Elastic Properties of Four Shales Reconstructed From Laboratory Measurements At Unloaded Conditions

Summary The elastic properties of four shales (Barnett, Woodford, Muscogee, and Caney) are studied on 11 samples at the room conditions with the help of specially developed and constructed apparatus, allowing us to measure the elastic wave velocities (VP, VSH, and VSV) in different directions relative to the axis of cylindrical sample. The difference in the angular behavior of the velocities is attributed to the different mineral composition and microfabric of the shales. The stiffness tensors of shales are reconstructed from the measurements taking into account the experimental errors in velocities and rotation angle and possible disorientation of the sample axis relative to the elastic symmetry axis. The closest VTI stiffness tensors are inverted for all shale samples, and the accuracy of such an approximation is given in terms of relative average errors between experimental and theoretical velocities. These errors are shown to vary from 0.5% to 8%. These errors can be decreased if the tensor is approximated by the monoclinic symmetry in the laboratory coordinate system.

Gas shale; relationships between permeability and intrinsic composition

The quantitative mineralogical data, TOC and porosity were used to increase understanding there relationships to permeability, and permeability anisotropy of gas shale based on lab measurements. Four different productive gas shales were used to study these relationships. There is a general increase in permeability with increase gas-felling porosity. At the same time, all samples, regardless of the flow direction, show a nonlinear reduction in permeability with increase of effective pressure (up to 3 orders of magnitude), with large variations from sample to sample and flow direction. This is more consistent with the microcracks model than with the capillary tube one. This reduction in permeability is found to follow a cubic k- law and explained by preferential flow through pore likecracks. There is a good relationship between permeability and mineralogical composition of the studied samples where the quartz-rich samples are more permeable than carbonate–rich samples, and permeability increases with increasing quartz content. Also permeability shows an increase when pyrite content is higher. On the other hand, permeability shows a decrease with increase carbonate and clay minerals especially illite. While the microstructure studies show a lot of microand nano-pores within the TOC, there is no clear relationship between TOC and permeability or porosity. Further intensive studies to establish these relationships are needed.

Measuring Gas Shale Permeability Tensor In the Lab Scale

Permeability tensor measurements for three different gas shale samples were done using quasi-steady flow technique in specially designed apparatus in which confining pressure, upstream pore pressure, downstream pore pressure and temperature are independently controlled. The initial pressure difference between upstream and downstream changes only after the pressure pulse passes across the whole sample. Using the quasi-steady flow technique gives the ability to measure axial permeability of three different oriented plugs simultaneous at the same pressure temperature conditions. Measured intrinsic permeability anisotropy ratio in gas shale was 25 % in average. The anisotropy ratio remains almost constant with increasing effective pressure, however permeability magnitudes decrease by almost two orders. This reduction in permeability was described by a cubic k- law and explained by preferential flow through pore like-cracks. The anisotropy ratios response suggested a presence of this type of pores both parallel to and perpendicular to bedding which close upon increasing confining pressure. The pore like-crack throats could be small as the test fluid kinetic molecular diameter (e.g. 0.381 nm for natural gas “Methane”).

Eq uations of wave propagation in nonlinear elastic anisotropic media

Summary This paper presents a theoretical investigation of wave propagation in randomly heterogeneous anisotropic media, such as granulated materials or porous media, in the vicinity of areas with large initial stress. The authors have obtained an exact expression for the mean value of elastic constants of a deformed medium. The Feynman diagram technique developed in quantum field theory was used for operating with diverging infinite series. The dependency of vibration spectra on the stress state of the medium is also shown in this paper.

Relating Pore Geometry to Seismic Properties

The combined effects of pore geometry and saturation are simulated using effective media models. Static and dynamic models are considered for penny-shaped and cylindrical-shaped pores containing gas or brine. The static and dynamic solutions are compared in terms of their usefulness for distinguishing the pore geometry effects from the saturation changes. Penny-shaped and cylindricalshaped inclusions are considered. Frequency-dependent effects are shown to be critical for some aspects of the separation.