Modelling the hydrodynamic regime of the Metegero-Ichersky aquifer after resumption of the exploitation of the “Mir” deposit

Abstract

Introduction: The Metegero-Ichersky aquifer complex (MIAC) provides about 95% of the groundwater inflow to the Mir deposit. It is also used for the re-injection of brines into the Earth’s interior. Technical solutions used during the exploitation of the field led to significant changes in the MIAC and technogenic pressure on it. The piezometric surface of the Metegero-Ichersky aquifer complex experienced considerable changes over the long period of mining of the large diamond deposit. The resumption of the deposit exploitation will lead to technogenic pressure on the geological environment and will have a great impact on the hydrodynamic regime of the aquifer. Methodology: To study the hydrodynamic regime of the Metegero-Ichersky aquifer within the quarry field and the associated re-injection nodes, we applied conventional methods used in the study of groundwater dynamics. The creation of the hydrogeological model involved determining the filtration parameters of reservoirs, which was carried out using the results of observations during experimental, individual, and cluster pumping tests conducted over the last 5 years. The forecast of changes in the hydrodynamic regime was carried out following the calibration of the constructed model using a hydrogeological modelling program (Modflow software). Results and discussion: The conducted work allowed obtaining data regarding the changes in the hydrodynamic regime of the Metegero-Ichersky aquifer. The results include schematic pressure distribution maps for a possible resumption of the pre-drying system. The modelling of the re-injection process involved determining the best operating mode for wells located in the zone of dynamic impact of the Eastern Fault. The maximum injection rate, in case of maintaining a phreatimetric regime, is between 2000 m3/hour (during the first year of resumption) and 1400 m3/hour (in the following years). The modelling allowed us to conclude that to guarantee a 100% dewatering in the quarry field in the period between 2038 and 2045, it is necessary to perform additional exploitation of the injection site in the dynamic zone of the East Appainsky Fault. As a result, the configuration of the piezometric surface will become even more complex. Conclusion: The conducted work allowed studying changes in the level regime of the Metegero-Ichersky aquifer complex caused by the exploitation of the Mir field, as well as forecasting the dynamics of subsequent changes depending on the additional technogenic pressure on the geological environment. Further reconstruction of the quarry should use the pre-drying principle, i.e. pumping out of all types of water entering the pit bowl, as well as the volumes accumulated at the quarry water marks. The injection of such amount of water might require not only the modernisation of the existing dewatering system in the area of the Eastern Fault, but also the construction of a new dewatering system in the dynamic zone of the East Appainsky Fault.