THE FIRST EXPERIENCE OF SALINE DRAINAGE WATERS DISPOSAL FROM THE UDACHNAYA PIPE QUARRY INTO PERMAFROST
ALEXEEV, SERGEY V.. Institute of the Earth's Crust SB RAS, 664033, Irkutsk, Russia.
Drozdov, Alexander V.. Udachny GOK JSC "ALROSA", 678189, Udachny, Russia .
Drozdova, Tatyana I.. Udachny GOK JSC "ALROSA", 678189, Udachny, Russia .
Alexeeva, Ludmila P.. Institute of the Earth's Crust SB RAS, 664033, Irkutsk, Russia.
The Udachnaya kimberlite pipe is one of the main diamond suppliers in Russia. It's situated on the Siberian platform in the central part of the Yakutian diamond province (Fig. 1). At present the exploitation of kimberlite deposit of the Udachnaya pipe is complicated by the influx of chloride magnesium-calcium subpermafrost brines into the quarry. The influx is 75-85 m3/hour. The ground water mineralization reaches 350 g/L, bromine and chlorine contents are hundred and thousand times the acceptable limiting concentrations. Therefore discharge of drainage waters into the river network is prohibited.
For the last 15 years the open water drainage from the Udachnaya pipe quarry has been used. Brines are disposed into the Cambrian frozen rocks at the depths, which are lower than the local base level of erosion 150-250 m. The acting Octyabrskiy disposal polygon is situated on the watershed 3.5 km to the west from the quarry in the regional fault zone. The frozen strata here are broken into blocks, which is a result of step-like displacement of rock layers.
The method of waste isolation is grounded in the ability of high-mineralized water to melt structure-forming ice at wide range of negative temperature (Pinneker et al., 1989). The live capacity of the permafrost massif, used for drainage brines disposal, is dependent on a) 9% release of additional space at ice melting caused by brines in fractures and caverns, b) presence of the thick tectonic crush zone, along with open vertical and subvertical joints 10-15 cm wide and ice-free cavernous and porous rock with potentially high filtration properties, c) presence of large quantity (up to 5% from volume) of gas includes in the ground ice. The thickness of permeable rock strata and blocks varies from 10-20 cm up to 10-20 m (Alexeev, 2000).
Drainage system of the kimberlite deposit works the following way: drainage waters from the artificial reservoirs situated in different horizons are dumped into the inverted wells in the Oktyabrskiy polygon. Wastewater disposal into the wells is done by free filling without pressure on the well mouth. In summer brine temperature is +5...+8, in winter it decreases down to -15...-25 (C. At the disposal into permafrost the descending and lateral migration of technogenic water takes place. Firstly brines move along vertical and subvertical joints down to the lower part of strata. Then plane filtration along the interlayer joints occurs. Injection of the indicator (fluorescein) into the inverted wells demonstrates that the hydraulic conductivity coefficient of technogenic waters in the massif reaches 1-1.5 m/day.
During the period 1985-2001 over 10.000,000 m3 of brines were buried into the permafrost of Oktyabrskiy polygon. Some part of technogenic solutions returns to the quarry, which is proved by numerous icings observed in the quarry slopes (Fig. 2). Closed talik has formed inside the frozen massif. Technogenic waters are spread within the distance of 6-8 km. A recent hydrogeological survey concluded that the massif capacity in the Octyabrskiy polygon would allow containing about 2.000,000 more m3 of brines in the nearest future. There has been also a change in thermal condition of the rock massif: before the disposal system was exploited the rock temperature at the depth of 200 m was -2 (C. After a 5-year brine disposal it decreased down to -5 (C. The most cooled layers are at the depth of 160-240 m accordingly to the technogenic aquifer. Deposit exploitation in spring and in summer is rather complicated by atmospheric precipitation inflowing to the quarry. Its volume reaches up to 300,000-400,000 m3 during the period of June - the end of August. Additional reservoirs on the berms were created to intercept surface water. Accumulating waters have sulfate-chlorine magnesium-calcium composition. Their mineralization is 10-30 g/L and bromine content is 0.2-0.3 g/L. of Such technogenic solutions are discharged into the river network only if previously significantly diluted, which requires not less than 300-400.000.000 m3 of fresh water, but there is no such amount in the immediate vicinity.
In this relation the necessity arose to search reliable storages for large volumes of salty drainage waters, inflowing in the quarry in spring and summer. The acting Oktyabrskiy polygon seemed the most ecologically safe and technico-economical profitable. A technological scheme of salty water disposal in the Oktyabrskiy polygon in summer was worked out. Both freezing temperature of different mineralized technogenic solutions and thermal condition of permafrost were taken into account. The essence of the method is alternating discharge of salty surface water and drainage brines into inverted wells. At the first stage salty waters are discharged. Coming in the massif, they are mixed with cryopegs within closed talik and supply resources of the technogenic aquifer. Meanwhile wastewater mineralization decreases and wastewater further freezes. Salty waters are discharged into the disposal polygon until intensity of their absorption is fixed. At the second stage brines are discharged. Brines with positive temperature and high mineralization gradually melt newly formed ice in reservoirs and move deep into the massif. When brine absorption intensity becomes stable, discharge stops and salty water discharge is renewed. And so on.
To estimate the scale of geochemical processes at mixing of different types of technogenic waters, the physico-chemical simulation was carried out. The simulation was conducted using software HydrGeo designed at the Tomsk Department of the Institute of Petroleum and Gas Geology SB RAS (Bukaty, 1997). The average results of the analyses of drainage brines and salty surface water are used as initial data. The simulation and estimation of solution composition change were made at the mixing of technogenic water under the real PT conditions (T= -5, 0, +5 oÑ and Ð=2.5 ÌPà). Calculations were made for the proportions of solution in the mixture from 90:10 to 10:90 %. It's been established that all obtained mixtures have different levels of saturation of the calcite, dolomite and gypsum; moreover the unsaturation degree increases with growth of mixed water mineralization, i.e. with the growth of the drainage water amount in the mixture. Under the layer conditions the dilution of interactive solutions will only occur without modification of water chemical composition. Therefore there are no causes for precipitation and filtration properties decrease of the rock massif.
In summer 1997 an experimental discharge of technogenic salty water and brines into the inverted wells was carried out. The intensity of brine absorption in each well was not less than 100 m3/hour. The alternating waste disposal was carried out 16-50 hours without pressure on the well mouth. Ultimately during the natural experiment 59 000 m3 of salty water and 73 280 m3 of drainage brines were discharged into the massif on the Oktyabrskiy polygon.
The obtained results confirm groundness of technological scheme of salty drainage water disposal in the Oktyabrskiy polygon. Realization of the elaborated method will provide long non-stoppage work of the Udachnaya diamond mining quarry.
The study has been carried out with the financial support of Russian Fund for Basic Research (grant's number 01-05-64012).
Alexeev, S.V., 2000. The cryogenesis of groundwaters and rocks (on an example of the Daldyn-Alakit region of Western Yakutia). SPC UIGGM, Novosibirsk (in Russian).
Bukaty, M.B., 1997. "The working out of the software in the petroleum-gas geology." J. Razvedka i ohrana nedr. N 2, 37-39 (in Russian).
Pinneker, E.V., Alexeev, S.V., and Borisov, V.N., 1989. The interaction of brines and permafrost. In WRI-6 International Symposium, 1989, Proceedings: Rotterdam, Balkema, pp. 557-560.
Figure 1. Position of the Udachnaya kimberlite pipe
Figure 2. Icings of salty technogenic waters in the Udachnayalale pipe quarry
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