Real-time detection of dielectric anisotropy or isotropy in unconventional oil-gas reservoir rocks supported by the oblique-incidence reflectivity difference technique

Abstract

Current geological extraction theory and techniques are very limited to adequately characterize the unconventional oil-gas reservoirs because of the considerable complexity of the geological structures. Optical measurement has the advantages of non-interference with the earth magnetic fields, and is often useful in detecting various physical properties. One key parameter that can be detected using optical methods is the dielectric permittivity, which reflects the mineral and organic properties. Here we reported an oblique-incidence reflectivity difference (OIRD) technique that is sensitive to the dielectric and surface properties and can be applied to characterization of reservoir rocks, such as shale and sandstone core samples extracted from subsurface. The layered distribution of the dielectric properties in shales and the uniform distribution in sandstones are clearly identified using the OIRD signals. In shales, the micro-cracks and particle orientation result in directional changes of the dielectric and surface properties, and thus, the isotropy and anisotropy of the rock can be characterized by OIRD. As the dielectric and surface properties are closely related to the hydrocarbon-bearing features in oil-gas reservoirs, we believe that the precise measurement carried with OIRD can help in improving the recovery efficiency in well-drilling process.

Three-dimensional quantitative fracture analysis of tight gas sandstones using industrial computed tomography

“…High-resolution fractures can also be identified by SEM imaging analysis 56 . Thin sections, which were impregnated with blue epiflourescent epoxy, were analyzed under plane-polarized and cross-polarized light to determine intergranular and intragranular pores at Houston Advanced Technology Center of Core Laboratory.…”

“…Scanning electron microscope (SEM) analysis was conducted on the fresh surfaces of the core plug samples which are coated with gold to help detect the micropores associated with authigenic clay minerals. High-resolution fractures can also be identified by SEM imaging analysis 56 . Thin sections, which were impregnated with blue epiflourescent epoxy, were analyzed under plane-polarized and cross-polarized light to determine intergranular and intragranular pores at Houston Advanced Technology Center of Core Laboratory.…”

Ultraviolet laser-induced voltage in anisotropic shale

“…The shale sample used in the LIV measurement was cored in the horizontal direction with a cylindrical plug from a whole specimen of a shale formation at the depth of 3325.4 m. The diameter and height of the core was 25 and 60 mm, respectively. Optical microscopy images and SEM pictures of the core sample used here were shown in our previous study [25], in which the orientational arrangement of the particles and crevices could be observed by the SE morphology contrast and BSE images. Besides, the layered distribution of the dielectric properties in the shale sample were also identified, and the width of the adjacent main beddings was measured as ~100-300 μm, as well as the secondary laminations ~30-50 μm.…”

“…Optical methods, which are insensitive to harsh physical environment, can be served as an appropriate method to promote the development of unconventional oil-gas industry. In our previous study [25], the anisotropy of shale was clearly observed in the OIRD images, and such method is proved promising in surface anisotropy detection in rock. Here in this work, LIV is employed to study the electrical anisotropy of shale, and periodic variation of V p was observed with the angle.…”

“…With the advantages of non-interference with the earth magnetic fields, optical measurements have been proved effectively to evaluate petroleum resources [22], especially for properties of unconventional reservoirs [23,24]. In our previous study, the oblique-incidence reflectivity difference (OIRD) technique was initially employed to characterize the layered distribution of the dielectric properties in shales, showing that directional changes of the dielectric and surface properties were resulted by the micro-cracks and particle orientation [25]. Dielectric responses of anisotropic oil shales in the terahertz (THz) range were studied by THz-time domain spectroscopy (THz-TDS), and the refractive index anisotropies of the oil shales were plotted as a function of the oil yield, indicating that the increase of organic matter has promoted the degree of anisotropy [26].…”