The nature and origin of quartz, clay mineral, and carbonate cement in the Upper Ordovician Mamuniyat Formation, Concession NC174, Murzuq Basin, SW Libya

This project reports an investigation to determine controls on the distribution of quartz over growth cement and other pore filling authigenic minerals in the Ordovician Mamuniyat Formation reservoir, NC174 concession, Murzuq Basin, Libya. A case study was undertaken using samples of Mamuniyat sandstone collected from 7 wells to characterise subsurface relationships between authigenic minerals and porosity. Diagenetic features were characterised using electron microscopy, fluid inclusion analysis, cathodoluminesence, stable isotope analysis, and x-ray diffraction. The sandstone samples were mainly very fine to coarse-grained quartz arenites with minor subarkose and sublithic arenite. Detrital mineralogy is dominated by monocrystalline and minor amounts of polycrystalline quartz grains, feldspar grains, lithic fragments, and mica (muscovite). The texture is grain or grain cement supported and both packing and compaction are generally low to medium. Authigenic minerals m the sandstone include quartz and siderite, ferroan dolomite/dolomite, kaolinite, illite and pyrite. The dominant authigenic cement phase is quartz overgrowths cement (up to 13% by volume) and is the major mechanism for porosity reduction. Authigenic quartz was mainly sourced internally from the pressure solution and possible dissolution of detrital grain and where externally sourced was from the overlying Tanezzuft shale (with the silica released from clay mineral during diagenetic processes). Kaolinite and illite were present as gram coating clay minerals and resulted from mechanical infiltration. Authigenic kaolinites and authigenic illite were sourced mainly from dissolution of K-feldspar. Kaolinite is related to sedimentary facies with water saturation the main control on the volume of kaolinite precipitation. IIlite formation was related to sedimentary facies.EThOS - Electronic Theses Online ServiceGBUnited Kingdo