Summary
An areas near Elat was investigated for the purpose of identifying suitable sites for the construction of mined underground petroleum storage caverns. The area of study is located at the northern tip of the Arabo-Nubian Precambrian Massif, close to the big geo-suture known as the Syrian-African Rift Valley.
The Precambrian basement is built mainly of schist, gneiss, and variable types of granite. The area has undergone plastic and ruptural deformations accompanied by phases of basic and acidic dyke intrusions. The goal of the investigation was to study very carefully the complicated, a priori untavourable structure and rock characteristics near Elat, in order to locate a site where underground man-made cavities could be economically designed and constructed.
A combination of detailed geological mapping and core drilling was used to evaluate the body of rock selected for study. Geological mapping included the preparation of a series of joint frequency overlay maps to portray distribution patterns of the principal joint sets.
Comparison of structural features, including the frequency of jointing, in drill holes with that mapped on the surface led to the conclusion that the structural details observed on the surface can be projected downward with reliability. It appears that detailed geological mapping in this area can eliminate a substantial amount of expensive explorat ory core drilling.
A preferred orientation for caverns has been established in the study area and it, is suggested that surface geology be projected down to one or more horizontal planes at the proposed cavern level below the water table to allow final selection of optimum cavern construction sites within the least disturbed blocks of granite.
Résumé
Les environs d'Eilat ont été étudiés dans le but de déterminer des endroits convenables pour le creusement de cavités en vue d'un stockage souterrain de pétrole. La région étudiée est située en bordure nord du massif précambrien arabo-nubien, tout près d'un sillon profond connu sous le nom de «vallée du rift syro-africain».
Le soubassement précambrien consiste principalement en schistes, gneiss et granites divers. La région en question a subi au Précambrien supérieur des déformations plastiques et des ruptures accompagnées par des phases intrusives sous forme de dikes acides et basiques. Il y a eu, aussi, fracturation pendant la période tertiaire.
L'objectif de cette étude était de déterminer les détails d'une structure a priori défavorable, ainsi que les caractéristiques de la roche près d'Eilat afin de trouver un site dans lequel on pourrait construire économiquement des cavités souterraines.
La région considérée est faite de rochers arides sans végétation. Malgré une croûte altérée, la lithologie et la structure sont bien conservées en surface et peuvent être facilement reportées sur la carte. On a dressé une carte de base lithogénétique en même temps que trois cartes juxtaposées montrant les principaux systèmes de joints. Une d'elles indique les fissures de tension à angle élevé de la phase de consolidation. Une seconde montre des joints N-S plus récents à grand angle et plus ou moins parallèles aux principaux dikes. Une troisième carte montre des diaclases à faible angle ainsi que des décollements obliques.
La comparaison entre ces différents cartes facilite le choix d'un site favorable. On conclut que les cavernes les plus stables doivent être localisées parallèlement et entre les principaux dikes et, de plus, perpendiculaires à la principale direction des joints.
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Flexer, A., Braun, M., Lasman, N. et al. Selection of optimum underground petroleum storage cavern sites by detailed geotechnical mapping (Syrian-African Rift Valley, Elat, Israel). Bulletin of the International Association of Engineering Geology 19, 205–216 (1979). https://doi.org/10.1007/BF02600477
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DOI: https://doi.org/10.1007/BF02600477