The inaccurate delineation of the sand intervals in well logs can significantly affect the porosity, permeability, pore-size geometry and net-to-gross ratio of the reservoir units. This study utilized well log cross-plots to accurately delineate the lithologic units and also used petrophysical evaluation methods to determine the reservoir properties of the sandstone intervals in three wells (L, M, N wells) of the Daura field, Niger Delta. The cross-plots of the gamma ray with density, gamma ray with sonic and gamma ray with depth were generated using the Hampson Russel software. The result of the cross-plot clusters shows two major lithologies of sandstone and shale with occasional intercalation of sand and shale units. Fluid detection analysis shows that reservoirs L3 (well L), M4-M5 (well M), and N2-N3 (well N) were found to contain oil, while reservoir M2 (well M) contains gas. The rest of the reservoir intervals in the three wells contain water, and the average porosity ranges from 14.23 to 28.01%. This study has shown that the cross-plots approach can be used to accurately delineate reservoirs for further formation evaluation. It therefore means that an outright estimation of petrophysical properties on wrongly delineated reservoirs can significantly affect the porosity, permeability, pore-size geometry and net-to-gross ratio of the reservoir units.

Geothermal gradients and present day heat flow values were evaluated for about seventy one wells in parts of the eastern Niger delta, using reservoir and corrected bottom – hole temperatures data and other data collected from the wells. The results showed that the geothermal gradients in the shallow/continental sections in the Niger delta vary between 10 - 18° C/km onshore, increasing to about 24° C/km seawards, southwards and eastwards. In the deeper (marine/paralic) section, geothermal gradients vary between 18 - 45° C/km. Heat flow values computed using Petromod 1–D modeling software and calibrated against corrected BHT and reservoir temperatures suggests that heat flow variations in this part of the Niger delta range from 29 – 55 mW/m2 (0.69 – 1.31 HFU) with an average value of 42.5 mW/m2 (1.00 HFU). Heat flow variations in the eastern Niger delta correspond closely to variations in geothermal gradients. Geothermal gradients increase eastwards, northwards and seawards from the coastal swamp. Vertically, thermal gradients in the Niger delta show a continuous and non-linear relationship with depth, increasing with diminishing sand percentages. As sand percentages decrease eastwards and seawards, thermal gradient increases. Lower heat flow values (< 40 mW/m2) occur in the western and north central parts of the study area. Higher heat flow values (40 - 55 mW/m2) occur in the eastern and northwestern parts of the study area. A significant regional trend of eastward increase in heat flow is observed in the area. Other regional heat flow trends includes; an eastwards and westwards increase in heat flow from the central parts of the central swamp and an increase in heat flow from the western parts of the coastal swamp to the shallow offshore. Vertical and lateral variations in thermal gradients and heat flow values in parts of the eastern Niger delta are influenced by certain mechanisms and geological factors which include lithological variations, variations in basement heat flow, temporal changes in thermal gradients and heat flow, related to thicker sedmentary sequence, prior to erosion and evidenced by unconformities, fluid redistribution by migration of fluids and different scales of fluid migration in the sub-surface and overpressures.

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The levels of biodegradation of five whole oil samples from five oil fields in the Niger Delta were assessed using a high-resolution gas chromatography. The results show that all the samples are at different levels of degradation ranging from slight to heavy. The crude oils from Fs, Bs and Qe fields had undergone extensive to heavy degradation, while those from Ai and Ea fields had undergone slight to moderate degradation. The low paraffinic content values in the samples suggest that the nparaffins have been degraded and reduced consistently. The aromatic fractions (C 14 -C 18 ) have been reduced slightly, though the 3-Methylhexane component was observed to show strong resistance to the bacterial attack even at deeper fields. These levels of biodegradation show indications that they could be caused by the degrading anaerobic bacteria present in the deep reservoir and/or by the influx of meteoric water, especially for the Bs crude, which is from an onshore field. As this degradation continues to deplete the light hydrocarbon components, the residual heavy components such as sulfur and asphaltenes are gradually concentrated, while the API gravity is consequently lowered.