International Journal of Geosciences, 2011, 2, 366-372 doi:10.4236/ijg.2011.23039 Published Online August 2011 (http://www.SciRP.org/journal/ijg) Copyright © 2011 SciRes. IJG Porosity and Lithology Prediction in Eve Field, Niger Delta Using Compaction Curves and Rock Physics Models M. T. Olowokere, J. S. Ojo Department of Applied Geophysics, Federal University of Technology, Akure, Nigeria E-mail: olowo_mt@yahoo.com Received January 8, 2011; revised May 10, 2011; accepted June 12, 2011 Abstract The primary objective of this study is to investigate the porosity-depth trends of shales and sands and how they affect lithologies. Compaction curves from well logs of five wells were determined using interval transit time from sonic logs. The depth of investigation lies between 1087 m and 2500 m. Based on the shale and sand trend modeling, the study intends to determine the model to be used for lithology prediction at various depths given the interplay between shale and sand compaction. The improved understanding of the physical properties of shales and sands as a function of burial depth was demonstrated, in conjunction with a good understanding of how compaction affects lithology. The compaction curve for shale and sand lithologies var- ies with shale being parabolic in form, and sands with linear and exponential in nature. Plots of sonic poros- ity against depth show great dispersion in porosity values while plotting porosity values against depth for different lithologies produced well-defined porosity trends. This shows decrease in porosity with depth. The negative porosity trend is less marked in sandstones, and faster in shale which suggests that it is possible to make accurate porosity predictions using compaction trend. The porosity trend showed exponential relation- ship at small depth less than 2500m. The linear and exponential models are not dependable at large depth. The result shows that the compaction models applicable for sandstones do not necessary apply for shales. Keywords: Compaction Trend, Lithology, Porosity, Reservoir Characteristic, Velocity Logging, Sand–Shale 1. Introduction Various authors have proposed different theoretical mo- dels to show the fluid-solid interaction in reservoir rocks for the purposes of both porosity and lithology prediction and fluid substitution (e.g. Bjørlykke, 1998; and Ehren- berg, 1990). However, these models can only be applied under certain conditions because the theories have some limitations. Athy, (1930); Magara, (1976a); Sclater and Christie, (1980), Magara (1980) Liu and Roaldset (1994) and Selley (1978)) have proposed a variety of models that shows the relationship between porosity and depth. Magara (1980) and Selley (1978) used linear porosity- depth relationship to describe diagenetic changes affect- ing compaction. A parabolic relationship has been pro- posed by Liu and Roaldset (1994). Exponential curves were probably first introduced by Athy (1930) to des- cribe porosity in shale. Sclater and Christie (1980) used exponential curves for porosities in sandstone, siltstone and chalk in the Central Graben of the North Sea, but their exponential curve for shale was criticized by Bald- win and Hutler (1985) who proposed a power-law curve for shale compaction (although they agreed with Sclater and Christie’s sandstone compaction curve). Schmokker and Halley (1982) proposed an exponential curve for carbonate after their work in South Florida Basin. Using exponential curves to describe normal compaction in shale were also favoured by Korvin, (1984); Magara, (1980); Selley, (1978); and Haung and Gradstein (1990). Issler, 1992 used the time-average equation of Wyllie et al. (1956) to estimate porosity and clay content in con- solidated formations. This paper is a unique study of porosity prediction in the Niger Delta using compaction curves to improve re- servoir modelling and production. In this study, we derive the local shale and sand com- paction trend for the Eve (gas-and-oil) field by inte- grating rock physics modeling with well-log and seismic data analysis. This model is based on the calibration of core and well-log data. Based on the compaction trend modeling, we demonstrate that improved understanding of the physical properties of shales as a function of burial