Abstract
The exploratory borehole Megiddo-Jezre’el 1 (MJ1) was drilled in Israel, in the Bet She’an Valley which branches out from the Central Jordan Rift. It reached the depth of 5060 m and bottomed within the Upper Triassic Mohilla Fm. Following the increase of groundwater exploitation, the Cl- concentrations increased and ionic ratios changed indicating inflow of Ca2+-Cl- brines, the origins of which were hitherto unknown. Data from the new MJ1 borehole revealed that rock porosities decrease with depth. Lowermost values of about 3% were interpreted from logs in Lower Jurassic and Triassic strata. The highest shut-in pressures were measured in the Upper Jurassic sequence raising the water much higher than the ground surface. Along the drilled section, there is a continuous downward increase in Cl- concentrations in the range of 12-186 g Cl-/l and a very clear stratification of brines. Data from the MJ1 borehole and from other exploration wells indicate that in the subsurface of the area, there are two definite source brines: Triassic brine and the Late Tertiary (so-called) Rift brine. Brines encountered in Jurassic and Cretaceous beds represent ancient mixtures of the two source brines involving various water-rock chemical transformations. Evidence of very high pressures in deep boreholes Devora 2A, Rosh Pinna 1, and MJ1 revealed the existence of a mechanism in which the deep brines are “piston-driven” upwards and possibly also laterally. The ongoing salinization of groundwater in the area is due to the inflow of the Late Tertiary Ca2+-Cl- Rift brines and not that of the Jurassic or Triassic brines. The hydrogeological and hydrochemical data from borehole MJ1 is of major importance for the management of groundwater resources in the Central Jordan Rift Valley and in the adjacent geologically connected areas.
Highlights
One of the major causes of the water crisis in Israel is the ongoing contamination of its groundwater resources by saline water bodies
The main deteriorating process occurring in groundwaters of the Jordan-Dead Sea Rift Valley and in adjacent connected areas is the upflow and migration of highly pressurized thermal Ca-chloride brines penetrating into fresh groundwater bodies [1]
The hydrogeological and hydrochemical data collected during the drilling of wildcat Megiddo-Jezre’el 1 (MJ1) significantly improved the understanding of groundwater salinization in the Rift and in the structurally connected areas
Summary
One of the major causes of the water crisis in Israel is the ongoing contamination of its groundwater resources by saline water bodies. The newly established groundwater flow regimes have facilitated the further migration of saline groundwater bodies, their participation in the active hydrological cycle, and the progressive contamination of fresh groundwater [2]. These processes were not anticipated by planners and water resources managers because there was no sufficient information about the Geofluids occurrence and the physical regimes controlling the migration of the brines. A common feature of all groundwater bodies flowing in the Jordan-Dead Sea Rift Valley is that these are mixtures of low salinity or freshwater bodies with a Ca2+-Cl- saline brine, otherwise known as the “Rift brine.”. The saline Ca2+-Cl- component, i.e., the “Rift brine” [3], is identified by its high salinity and by typical ionic ratios such as Q < 0:5, and
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