Accueil > Documentations scientifiques > Revues récentes > Madamines > 201601.Madamines, volume 3, 2016, ISSN 2220-0681 > GEOLOGICAL ANALYSIS OF OIL SANDS CORES ZONE VI BEMOLANGA OIL (...)

    Madamines, volume 3, juillet 2016, ISSN 2220-0681

    Auteurs : Simon Rakotoarison, Roger Randrianja, John W. Kramers, Baholy Robijaona

    Key words : geological, geochemical, mining, Zone VI, Driez quarry, bitumen, dykes, Isalo, Karroo, sandstones, lithologs.

    The province of Alberta – Canada owns the biggest non conventional hydrocarbon fossils in the world. Named the Athabasca oil sand deposit, Canada may be self sufficient in petroleum consumption with oil crude from Alberta. The reserve assessment as well as the mining production, bitumen extraction process using the hot water process is well developed for the Athabasca oil sands since 1970.
    Bemolanga deposit has been estimated to more than 250 km². Geological and mining study was mainly carried out by the French Petroleum Company (SPM) since 1950 in the zone VI of about 6 km². This zone VI with its DRIEZ quarry seems the most interesting zone because of its high bitumen content (up to 12% by weight).
    The probable bitumen reserve was estimated for 3 billion tons for the entire zone and on 1960, feasibility study for producing non conventional crude was undertaken by the SPM using hot water process but the project didn’t get through and replaced by the Tamatave refinery which imported crude from everywhere (Algeria, USSR, etc.), starting to process light crude from middle east to end up with medium crude from Russia. Since that time, Madagascar have always imported his crude oil to be treated in that refinery and self sufficient in white products such as gasoline, gasoil, jet fuel and heavy products (fuel oil and bitumen). The excess heavy products such as fuel oil were sold to La Reunion, to Mauritius and to Comoros.
    On 1980, the Malagasy government decided to undertake for his own the Bemolanga project in the aim of producing crude from tar sand bitumen. The studies were focused on the zone VI and concern the geological, geochemical and the mining aspect for the future exploitation.
    All the analyses were carried out at the High School of Polytechnic in Antananarivo, at OMNIS and at the Alberta Research Council-Canada laboratories in Edmonton.
    Thus this paper is related to geological and geochemical assessment of the four wells drilled into the zone VI to understand the source rocks behavior and to get better knowledge of the geology of the bituminous sands deposit within the Bemolanga area.
    Cores from four wells drilled in zone VI of Bemolanga oil sands deposit are described on lithologs which one example is attached in this paper.
    The average oil saturation (w/w) from the four wells is as follows :
    ANK 140 bis : 5,32 %
    ACD 141 bis : 7,79 %
    SACD 142 bis : 6,43 %
    NPA 143 : 6,87 %
    None of the wells penetrated the entire thickness of the oil saturated section. The bitumen is contained in predominantly fine to medium gained, cross-bedded, lithified sandstones of the basal Isalo II sandstones.
    Palynological examination of two shale beds indicates an upper Triassic (Rheatic) age for the sandstones. In the cores and outcrops examined, the predominant cementing agent are calcite and carbonate in the large modules and small patches ; clay minerals in small paths and/or as a general cement binding the rock together ; and silica, mainly in the form of quartz overgrowths on sand grains.
    NNW-SSE trending dykes cut through the oil sands. These dykes post-date the emplacement of the oil in the sandstones. .
    It is thought that the Isalo II sandstone were deposited in a fluviatil sandstone, which by its very nature produces a complex facies pattern that is characterized by a lack of lateral continuity of individual sands on shale unit.
    None of the sand bodies found in the core could be correlated from one well to another. Because of the nature of depositional environment of the Isalo II sandstones, delineation drilling for future mine exploitation as to be carried out on smaller grid pattern.
    Based on the overall study we have carried out, followings are suggestions for the future prospection on Bemolanga oils sand deposit :
    -  4 to 5 km grid in essential non explored areas, mainly in the northern of the deposit
    -  2 km grid in the areas known to be underlain by oil sands
    -  150 m grid for main planning and ore body delineation.
    -  All cores should be fully cored and logged with geophysical well logs.
    -  A detailed depositional model should be established for the Isalo II sandstones.
    -  A detailed mapping program should be undertaken to map the dykes that cut the oil sands.
    -  Further geological and geochemical study should be undertaken on the available cores to get better knowledge of the geology of the Bemolanga oil sands and Tsimiroro deposits.


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