Sedimentology and Permeability Distribution of the Ajali Sandstone around Odugbo, North Central Nigeria

摘要

Ajali Sandstone around Odugbo, North Central Nigeria was studied in order to determine its sedimentological characteristics and permeability distribution. The study involves both field mapping, samples collection from different outcrops locations and laboratory analyses. Grain size analysis revealed that the sandstones are composed of medium grained (av. 1.50 ?), poorly sorted (av. 1.60 ?) and sub-angular to sub- rounded grains which indicate deposition close to the source area. Permeability values deduced from an empirical formula are generally low with an average value of 46.76md indicating that the sandstones have poor flow characteristics. The low permeability is considered to have resulted from weathering and grained dissolution during the formation of hematite cement. Petrographic study shows that the sandstones are composed of mainly quartz (av. 95.08%), feldspar (av. 2.55%) and mica plus rock fragments (1.19%), and suggests texturally mature and mineralogically mature quartz arenite. This study also presents the trend suggestive that sedimentary structures and depth of burial can be considerable factors affecting sandstone permeability.