Influence of the Western Donbass share dislocation zone on the formation of gas accumulations in coal-bearing sediments

https://doi.org/10.23939/jgd2018.01.027
Received: January 10, 2018
Revised: February 20, 2018
Accepted: March 12, 2018
1
M. S. Polyakov’s Institute of geotechnical mechanics of National academy of sciences of Ukraine
2
Institute of geotechnical mechanics of the National Academy of Sciences of Ukraine
3
Institute of geotechnical mechanics of the National Academy of Sciences of Ukraine

Purpose. The objective of the work is to develop the concept of geodynamic evolution of the Western Donbass (WD) shear dislocation zone on the basis of determining the natural gas content results analysis with the help of Svidovska site example using modern information processing and visualization facilities; the establishment of the main regularities for influence of shear tectonics on the formation of gas accumulations in coal-bearing sediments of WD. Methodology. For the structural-geological information analysis methods of digital geological mapping, mining-geometric modeling, and geological-structural analysis (diagnostic geometry of the discontinuous structures paragenesis) were applied. A set of methods for statistical data processing of tectonic disturbance was used, which is an estimate of azimuth ruptures orientations occurrence frequency calculated using the method of rose diagrams. A complex analysis was used to reveal structural elements in the coal seam, which include morphometric and morphostructural studies of deformation processes that are a trend analysis of the soil surface of coal horizons and the rate of deformation in local areas using gradient analysis of the residue surface through excluding the regional background was estimated. When processing and analyzing definitions of natural gas content using KA 61 core gas samplers, performing coal seam tests by the KII-65 seam tester, gas logging, we used interpolation methods for the initial data of the coal seams’ natural methane content and the visualization of the surfaces of gas contour line. The studies were conducted on 134 wells in 8 coal seams (с1, с42, с5,, с6в, с7н, c8в, c8н, c10в) and accounted for 102 samples of gas coal. Results. We propose a model for formation of a principled Western Donbass dislocation zone under conditions of transtension, which caused the forming of shear-expansion along the transform fault of the submeridional strike – the formation of a pull-apart, followed by the development of “domino” structures as a result of the left-lateral shear activation. It was revealed that faults of the northwestern orientation (the azimuth of the strike is 340°) of the eastern wing of the Dniprovska mine and the Svidovskoy section form a single tectonobande, oriented parallel to the Krivorozhskiy‑Pavlovskiy suture zone and we can observe a right-handed shift along the plane displacement. The allocated tectonobande divides the Central block of the Samara block into two almost equal parts. Within Svidovskoy the WD terrain there have been delineated zones of low and abnormally high gas contents. These were caused by a presence of, respectively, small displacement faults represented by sinistral R1 shears and fault related fold structures, which axes appeared to be subparallel to principal strikes of normal faults of the region. A total set of subsidiary structures has been formed in sinistral strike-slip zone triggered by interplay of compressive-tensile environments. Originality. For the first time, we propose a formation model of WD dislocation zone under conditions of transtension, which caused the forming of shear-gapping along the transform rupture of the submeridional strike – the formation of a pull-apart, followed by the development of “domino” structures as a result of the left-lateral shear activation, which had a direct effect on the gas content of sediments in zones of tectonic bands which have a shear nature. For the first time, it was ascertained that zones with reduced values of the natural gas content of the northeastern strike which were revealed within the coal seams, arise from the presence of a tectonic band in the rock massif, represented by a series of low-amplitude tectonic disturbances, morphologically shifts are represented by left synthetic Riedel shears R1 that are traced within Zahidno-Donbaska and Pavlogradska mining concessions. Practical significance. The regularities of shear tectonics effecting on the formation of gas accumulations in coal seams of the WD, established in the work, are important not only for clarifying the mechanism of tectonogenesis and the nature of coal formation and gas deposits, but also for optimizing the search for gas-bearing structures, objects and conditions for their formation and localization in a coal-bearing massif. Structural-tectonic analysis in conjunction with the actual data analysis of the natural gas content from mining territories’ coal seams can reduce the cost of finding promising (profitable) plots with high methane content, as well as in the case of coal deposits exploitation, it is possible to sustainably predict structurally-tectonic inhomogeneity.

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