Objective:
The aim of the work was to identify and visualize changes in the internal structure of samples of the GZH / Zh and OS brands of coal as a result of PPT using the XT method.
Key features:
- Series of XT scans were performed of coal samples before and after the implementation of PPT.
- The samples comprise of 9 samples of coal brands of various sizes.
- The study allowed a comprehensive comparison of XT scans before and after the implementation of PPT.
Significance:
- XRT is a non-destructive technique to analyse the coal samples and detect any changes that might have occurred in the rock matrix due to the implementation of PPT. The study will yield a comprehensive results of microcracks that were created due to the stimulation technique (PPT).
- The detection of these microcracks will further play a role in determining the increase in secondary permeability, which is the primary objective of PPT.
Methodology:
- Key components of any CT scanner comprise of the source of X-Rays, the subject of the study (coal samples), a detector of X-Rays which records the level of radiation absorbed by the object.
- As the X-Rays passes through the sample, the intensity is measured by forming a two-dimensional image. This image is known as shadow projection. (Refer to figure 1)
- Multiple shadow projections are recorded from various angles of the sample (Refer to figure 2)
- The primary principle is to place the sample in the field of view of the detector, followed by multiple iterations of sample rotation around its axis. In this way, multiple images are recorded, each signifying a unique angle of the sample.
- Therefore, in contrast to the classical X-ray radiography, in addition to the X-ray projection of the sample, information is recorded on the spatial position of the object under study, source, and detector.
Fig 1: Schematic setup of mutual positions of the system and the sample while making shots
Fig 2: The scheme for obtaining a set of shadow projections
Results:
Fig 3: Coal brand: “GZh / Zh”
Formation thickness: 2 m & 1.5 m
Coal density: 1.2 t/m3
Fig 4: Coal brand: “OS”
Formation thickness: 8.5 m
Coal density: 1.34 – 1.43 t/m3
Conclusions:
- It is evident that PPT has an effect on the internal structure of the coal.
- The crucial change in the internal structure is the formation of cracks, which was observed in both the possible scenarios, i.e., creating new cracks and the opening of previously existing cracks.
- It was also observed that the cracks were formed in accordance with the pre-existing order, following the block structure of the rock and connecting the system of natural cracks.
- The formation of microcracks further signify the enhancement of permeability of the coal seam.