The impact of faults on the water inflow and gas content of the deep levels of the Aikhal pipe (Republic of Sakha (Yakutia))

Abstract

Introduction: During the development of the primary diamond deposit of the Aikhal pipe using underground mine workings, the sub-permafrost upper Cambrian water-bearing complex was opened, which influences the water inflow of treatment, permanent, and mining operations. Ensuring the safety of further work at the deposit sets one of the main tasks which is the study of the hydrogeological conditions of the deep levels of the pipe, conducted in such detail that allows performing all the necessary calculations for the forecast of inflows of natural brines and crude gases. Methodology: To study the filtration parameters, calculate the main hydrodynamic and gas-dynamic characteristics, and determine the engineering-geological properties of the host rocks, test boring was performed in 2018 to conduct an entire set of hydrogeological studies. The studies included the selective determination of changes in the consumption of natural brines and crude gases, selection of samples to determine their chemical composition, and engineering-geological core documentation. In total, over 102 samples of natural brines, crude gases, and core were taken from the test wells to determine the composition of caustobiolites and their physical and mechanical characteristics. 53 compression tests and 12 admissions were also made. Full-scale experiments were conducted selectively in the underground mine operations of the Aikhal mine. Results and discussion: The result of the conducted work was the information presented in this article on the hydrogeological and gas-dynamic conditions of the deep levels at lev. -100/-400 m, (700–1000 m from the daylight surface) of the Aikhal pipe. A brief hydrogeological description of natural brines of the opened sub-permafrost upper Cambrian aquifer complex, which is dominant in the composition of the drainage waters of the Aikhal mine, is presented. The chemical composition of crude gases and the nature and intensity of gas emissions were determined. The aspects and special features of the influence of tectonic disturbances on the hydrodynamic and capacity properties of the reservoirs of the upper Cambrian aquifer complex, as well as the intensity and duration of the outflow of highly mineralised formation waters from lowdensity fractured reservoirs. The section was zoned by caustobiolite saturation. Conclusions: The conducted work allowed studying the hydrogeological conditions of the deep levels of the Aikhal pipe. The characteristics required for the design and preparation for the development of the resources of the deposit were obtained. The correlation between tectonic disturbances, gas saturation, and host rock abundance of water, as well as the water transmissivity coefficient, was analysed. This allows taking into account negative factors during the headway of the underground mine workings and identifying the areas which are potentially characterised by large water and gas inflows. Consideration of the abovementioned factors is primarily aimed at ensuring the safety of further development of the deposit and the construction of an underground mine.