Hydrocarbon Generative Windows Determination Using Geomathematical Model: Case Study from Ogbogede Field, Niger Delta, Nigeria

Oil and gas generative windows of source rocks in Niger Delta have been determined by applying a mathematical model to geotemperature data from the wells of Ogbogede oil field. GR and Resistivity log signatures show that the Benin and Agbada Formations comprises massive sands with clay intercalations while the Agbada Formation comprises alternate sequence of sandstones and shales. The geothermal gradients for the field range from 1.4oC/100m to 2oC/100m with an average of 1.8oC/100m and standard deviation of 0.2oC/100m. Geotemperature analysis of shales of the Agbada Formation varies from 58.92oC-107.6oC, indicating that they are thermally mature and within the oil generative window, at depths varying approximately from 1833.30 m to 5166.67m. The gas window occurs from 5166.67 m to 11000 m. This work has provided a mathematical method of source rock evaluation to compliment geochemistry. The outcome is a very important tool, which can be applied to other fields and sedimentary basins in hydrocarbon exploration. Keywords: Hydrocarbon Generative Windows, Geotemperature dat

Lithofacies and Pebble Morphogenesis: Keys to Paleoenvironmental Interpretation of the Nkporo Formation, Afikpo Sub-Basin, Nigeria

The Nkporo Formation in the Afikpo Subbasin, Nigeria, is dominantly shaly but contains two sandstone members within it. These sandstones host vein quartz pebble beds and dispersed clasts which have been used for pebble morphometric analysis. As independent functions and dependent variables, pebble morphometric indices of Coefficient of Flatness, Elongation Ratio, Maximum Projection Sphericity, Oblate-Prolate Index, Roundness and Form suggest deposition of the sandstones in fluvio-deltaic to littoral settings. Lithofacies analysis identified six lithofacies, grouped into estuarine delta and marine offshore lithofacies associations. These include trough cross-bedded sandstone, ophiomorpha burrowed, wave/rippled and planar cross-bedded lithofacies, Inclined heterolithic lithofacies, fine grained, silty sandstone, lignite/coals, shales/mudstone, interbedded with limestones and oolitic ironstones lithofacies. The estuarine lithofacies association shows a tripartite subdivision into meandering estuarine and tidal point bars overlain by estuary funnel tidal creek sandstones, carbonaceous beds; and estuary mouth tidal and barriers bars and shallow marine shales in a drowned incised valley. The fining upwards lithofacies pattern suggests deepening and transgression of the sea in a tidal estuarine setting. Keywords: Lithofacies, Lithofacies association, Pebble morphogenesis, Paleoenvironments, Tidal estuar

Tide-generated Sedimentary Structures, Lithofacies and Particle Size Distribution: Proxies to the depositional setting of the Ajali Sandstone in the Anambra Basin, Southeastern Nigeria.

Herringbone cross stratification, mud draped foresets, reactivation surfaces, tidal bundles, flaser beddings, ripple and horizontal laminations were identified on the Ajali Sandstone studied. The biogenic structures occur as dominantly vertical to sub-vertical and u -tubed burrows of the Skolithos ichnofacies commonly Skolithos verticalis and Ophiomorpha nodosa. Occasional Thalassinoides and Teichichnus isp burrows of the Cruziana Ichnofacies also occur. Three lithofacies were identified and these include; the medium to coarse grained cross bedded sandstone lithofacies, Fine grained cross bedded sandstone lithofacies and the mudstone lithofacies. The paleocurrent pattern from cross bed azimuths shows a bimodal – bipolar pattern indicative of tidal process. The grain size frequency histograms indicate both unimodal and bimodal asymmetrical patterns with shifting modes. The cumulative frequency curves suggest traction, saltation and suspension as the mechanisms of the sediment transport. The bivariate plots of the discriminant functions (Y1, Y2 and Y3) for the sands suggest deposition in a shallow agitated marine environment. Intertidal to subtidal shallow marine depositional setting is proposed for the Ajali Sandstone. Key word: Tide, Sedimentary structures, Particle size, Lithofacies, Subtidal, Depositional settin