Vízügyi Közlemények, 1972 (54. évfolyam)
4. füzet - Rövidebb közlemények és beszámolók
(82) THE CHARACTERISTICS AND MECHANISM OF POROUS DEEP AQUIFERS UNDER THE HUNGARIAN PLAINS By Dr. Korim, Kálmán, Geologist (For the Hungarian text see pp. 369) Owing to the particular geology and structure of the Hungarian Basin surrounded by the Carpathians, a considerable volume of water is stored at great depths in young Tertiary porous formations. Exploration thereof has been started around 1920 and water from the deep (800 to 2500 m) porous aquifers is still withdrawn at increasing rates, especially in areas, where geological and hydrological conditions are favourable. The water in these deep aquifers is partly fossile in character, in that it has been excluded from the hydrological cycle. The overwhelming majority of these resources is not renewed, no recharge reaches these aquifers and any withdrawal results in a diminution of supplies. The volume of water that can be produced economically depends on the magnitude of formation energy accumulated in these aquifers in the course of geological times. The mechanism controlling the operation of the deep waterbearing layers in Hungary depends primarily on the geological and reservoir conditions. Indeed, within various sub-basins successive sand-sandstone layers have been perforated, which arc large in extension, but of moderate thickness and which tend to form closed reservoir systems with several horizons and formations. The petrophysica properties are also important factor (Section 1 )• The flow of water at these great depths is influenced greatly by the physical and chemical properties of the water itself, these being in several respects different from those in layers near the surface and at shallow depths. Owing to the great depth of these aquifers, the extraordinarily high géothermie gradient in the Hungarian Basin, further to the dissolved gas content, a considerable quantity of natural energy has become stored. Of these kinds of energy the content of dissolved gases (CH, CO., and N.) further thermal expansion arc most important, whereas the clastic expansion of the compressed water- and rock masses is of but minor significance. The role of gravity is apparently unimportant in these closed-type aquifer systems (Section 2 and 3 ). The waterbearing formations at great depth are generally "infinite" in extension. Composite, multi-unit storage systems represent discrete hydraulic units, although the type of flow in them and their behaviour are largely identical. The release of potential energy in the deep aquifers tapped by deep boreholes causes the water and the gases dissolved therein to expand (Section 4). The prerequisite for the reasonable production of water from these quifers is the exploration of the mechanics of these reservoirs and the assessment of the hydraulic conditions dominating their behaviour. The advanced methods to be used for these explorations involve on the one hand basic observations in water wells (formation pressure, formation temperature, capacity, flow measurement and physical-chemical water analyses), on the other hand special studies into reservoir mechanics, such as interference between wells, well recovery, calculation of water resources. Detailed reservoir-engineeiing investigations have thus far been completed in South—East Hungary, in the regions of Szeged and Szentes (Section 5 ). The limited supply in the deep aquifer systems calls for deliberate, rational management of formation energy, optimum production methods and operation practices, as envisaged in the relevant orders issued by the Hungarian National Water Authority (Section 6). THE ACTIVE LENGTH OF WELL SCREENS By Dr. Kovács, György, Civ. Engr., ac. Dr. (For the Hungarian text see pp. 393) Discharge measurements performed at different depths over the screened length of operating wells have shown the inflow to be unevenly distributed over the length of the screen. Once the reduction of inflow with depth has been recognised