Reservoir characteristics analysis in the onshore Cawthorne Channel (CAWC) oil field, Niger Delta is here presented. The aim of the research was to assess reservoir properties and their relationships. A suite of geophysical logs comprising gamma ray, resistivity, neutron and density logs from eight wells were used in the analysis. Three reservoirs sands were delineated and linked across all eight wells. The litho-stratigraphy correlation section revealed that each of the sand units spreads over the field are differs in thickness with some units occurring at greater depth than their adjacent unit, that is possibly an evidence of faulting. The results show volume of shale values range from 11% to 17% indicating that the fraction of shale in the reservoirs is quite low. The total porosity of the reservoirs ranges from 0.22 to 0.39 indicating a very good reservoir quality and reflecting probably well sorted coarse-grained sandstone reservoirs. The permeability of the reservoirs ranges from 288 mD to 1250mD and this suggests good reservoir horizons. The hydrocarbon saturation of the reservoirs ranges from 0.59 to 0.71 indicating that the proportion of void spaces occupied by water is low consequently high hydrocarbon production. Sand-shale lithology was calculated, with sandstone volume decreasing with increasing depth, while shale volume increases with depth. Porosity and permeability showed decreasing trend with depth for both sandstone and shale units in all wells with few exceptions. This could be as a result of low compaction by overburden pressure from overlying rocks. Plot of lithology versus depth reveals that shale lithology increases with depth, while sandstone decreases. Lithology versus porosity plots show an inverse relationship between permeability and shale volume and direct relationship between permeability and volume of sand. Lithology versus permeability shows that permeability and shale volume have an inverse relationship whereas permeability and volume of sand have a direct relationship. Permeability decreases exponentially with decrease in porosity in rock matrix made up of intercalation of sandstone and shale. The modelled equation of permeability and porosity is given by K = 0.053e 32.934Ф. This implies that in the absence of core and well-log data, permeability can be estimated using only porosity data. The results of this work can be used as an exploration tool for the identification of prospective areas and also for feasibility studies during an appraisal activity.
The chemical mobility of heavy metal pollutants (Cu, Pb, and Ni) is fundamental to the understanding of their environmental accessibility, toxicity and geochemical behaviour to be able to account for the safety and vulnerability of the groundwater resource in the study area. In this work, EDXRF spectrometer was used to determine the total concentration of the metals in the samples and the concentrations left in the residual fractions after extraction. FAAS was used for the chemical analysis of the test sample extracted. The results show that the concentrations of the mobilized fractions are well within the permissive limit, and more of the concentrations of about 60% to 80% of the total concentrations of the pollutants are in the residual phase that keeps the pollutants in their inert state as such posed no threat to the environment and man, and particularly rendering the groundwater resource less vulnerable to the presence of these pollutants. There remobilization is very possible under favourable conditions as therefore, constant monitoring of human activities should be put in place with regular evaluation of pollution status of the environment for the good of all.
A comparative analysis of porosity values computed from sonic and neutron-density logs obtained from the same well is here presented. The aim is to identify the more reliable logging tool between sonic and neutron-density in the estimation of porosity values in a formation. Two wells from different parts of Niger Delta were logged for Transit times, bulk density and hydrogen index of the formation as a function of depth. The analysis of sonic, density and neutron porosity values shows a conventional trend of decrease in porosity with depth. Sonic porosity values of well A, and well B varies from 1 to 17%, and 27 to 60% respectively while Neutron-Density Porosity values of well A, and well B varies from 24 to 45%, and 21 to 37% respectively. The Coefficient of Variation for sonic porosity data are 56%, and 23%of well A, and well B respectively , similarly the Coefficient of Variation for Neutron-Density porosity data are 15%, and 14% of well A, and well B respectively. Coefficient of variation of Neutron-density log derived porosities is less than sonic log derived porosities; therefore Neutron-density log derived porosity is more reliable tool for porosity data estimation than sonic log derived porosity. Neutron and density logging tool is here recommended for determination of a reliable porosity value of a formation.
In this paper, composite well log (gamma ray, sonic and density) was used to identify thin layers of different lithologies and the lithologic boundaries at various depths by the signature records of the logs, and checkshot data were used to check and/or validate the integrated time and sonic derived velocities. The results show that acoustic velocities are very much affected by different lithologic properties and depth; porosity decreases more in shale than sandstone and velocity increases more in shale than sandstone all with respect to depth. The result further showed that there was normal parametric trend for both wells from 120m to about 3450m depth beyond which overpressure sets in.
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