Showing papers by "Sonatrach published in 1992"

Carbonate metasomatism in the lithospheric mantle: peridotitic xenoliths from a melilititic district of the Sahara basin

Abstract: The petrological and geochemical study of harzburgitic and dunitic xenoliths from the melilititic district of In Teria (Algerian Sahara) shows that the lighospheric mantle of this region has been affected by a multi-stage metasomatism. The first metasomatic event is related to the injection of alkali silicated (basaltic or kimberlitic) melt and was responsible for the crystallization of phlogopite at depths ranging between 80 and 100 km and the crystallization of amphibole at about 60 km. During this first event, carbonate probably precipitated in the garnet stability field. In a second stage, the spinal peridotites suffered strong mineral changes resulting in an extensive formation of high-Cr endiopside and leading to conversion of harzburgite and dunite into lherzolite and wehrlite. These changes are associated with an enrichment in the most incompatible trace elements including light REE (rare-earth elements), Ta, Th and variable values of ratios such as Th/La and Ta/La. This second event is atributed to the injection (under conditions of decarbonatation and release of CO2) of a carbonatitic melt resulting from incipient melting of the garnet peridotites, which were previously carbonated. This interpretation is corroborated by the calculation of a diffusion-percolation model which reproduces well the observed distribution of incompatible trace elements in the spinel peridotites. Given the proposed sequence of events, it appears that most of the specificities of the In Teria xenoliths can be explained by the successive geochemical modifications induced within the lithospheric mantle during reheating.

Le gisement de Rhourde el Baguel (Algérie) : modélisation de la fracturation naturelle

Abstract: Le Gisement de Rhourde el Baguel produit de l'huile a partir d'un reservoir greseux du Cambro-Ordovicien aux qualites matricielles mediocres. La fracturation naturelle joue un role important sur la productivite. L'intensite de la fracturation parait liee davantage aux parametres lithologiques qu'a des variations d'epaisseur des bancs. Les directions des fractures relevees sur les carottes orientees d'un sondage ne sont pas en accord avec la direction des grandes failles proposee jusqu'ici. Les fractures et les blocs delimites par celles-ci sont presentes sous trois formes : un bloc diagramme simplifie qui montre la complexite du reseau et la faible representativite d'un sondage a l'echelle du gisement; des blocs matriciels en trois dimensions a partir de l'utilisation d'un logiciel preexistant; une hauteur moyenne de bloc matriciel calculee a partir de l'application d'un modele probabiliste.

Experimental Design: Application to the Development of a Treatment to Inhibit the Deposition of Barium Sulfate Liable to Be Formed in Enhanced Oil Recovery by Waterflooding

Abstract: For technical and economic reasons, waterflooding is the most widely-used method in enhanced oil recovery [1]. In many situations, unfortunately, the formation water is incompatible with the injection water. The deposits and corrosion induced by the various reactions of this incompatibility cause irreversible damage, which is especially dangerous for the reservoir rock and the downhole and surface production facilities. This study is concerned exclusively with barium sulfate deposits liable to occur in surface production facilities by the mixing of injection water loaded with sulfate (1300 mg. 1 to the power of (-1)) with a formation water with a high barium concentration (1200 mg. 1 to the power of (-1)) [2].