Porosity and Lithology Prediction in Eve Field, Niger Delta Using Compaction Curves and Rock Physics Models

M. T. Olowokere, J.S. Ojo

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DOI: 10.4236/ijg.2011.23039                

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 varies with shale being parabolic in form, and sands with linear and exponential in nature. Plots of sonic porosity 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 relationship 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

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	L. F. Athy, “Density, Porosity and Compaction of Sedimentary Rocks,” AAPG Bulletin, Vol. 14, No. 1, 1930, pp. 1-24.
[2]	B. Baldwin and C. O. Butler, “Compaction Curves,” AAPG bulletin, Vol. 69, No. 4, 1985, pp. 622-626.
[3]	K. Bj?rlykke, “Clay Mineral Diagenesis in Sedimentary Basins—A Key to the Prediction of Rock Properties; Examples from the North Sea Basin,” Clay Minerals, Vol. 33, No. 1, 1998, pp. 15-34.
[4]	S. N. Ehrenberg, “Relationship between Diagenesis and Reservoir Quality in Sandstones of the Garn Formation, Haltenbanken, Mid-Norwegian Continental Shelf,” AAPG Bulletin, Vol. 74, No. 10, 1990, pp. 1538-1558.
[5]	Z. Haung and F. Gradstein, “Depth-Porosity Relationship from Deep Sea Sediments,” Scientific Drilling, Vol. 1, 1990, pp. 157-162.
[6]	R. R. Hills, “Quantifying Erosion in Sedimentary Basins from Sonic Velocity in Shales and Sandstone,” Exploration Geophysics, Vol. 24, 1993, pp. 561-566. doi:10.1071/EG993561
[7]	C. E. Hottman and R. K. Johnson, “Estimation of Formation Pressures from Log-derived Shale Properties,” Journal of Petroleum Technology, Vol. 17, No. 6, 1965, pp. 717-722. doi:10.2118/1110-PA
[8]	H. H. Haldorsen, and L. W. Lake, “A New Approach to Shale Management in Field-Scale Simulation Models,” The Journal of Petroleum Technology, Vol. 24, No. 4, 1984, pp. 447-457.
[9]	D. R. Issler, “A New Approach to Shale Compaction and Stratigraphic Restoration, Beaufrt-MackenZie Basin and Mackenzie Corridor, Northern Canada,” AAPG Bulletin, Vol. 76, No. 8, 1992, pp. 1170-1189.
[10]	P. Japsen, “Influence of Lithology and Neogene Uplift on Seismic Velocities in Denmark: Implications for Depth Conversions of Maps,” AAPG Bulletin, Vol. 77, No. 2, 1993, pp. 194-211.
[11]	G. Korvin, “Shale Compaction and Statistical Physics,” Geophysical Journal of the Royal Astronomical Society, Vol. 78, No. 1, 1984, pp. 35-50. doi:10.1111/j.1365-246X.1984.tb06470.x
[12]	D. K. Larue and H. Legarre, “Flow Units, Connectivity, and Reservoir Characterization in a Wave-Dominated Deltaic Reservoir: Meren Reservoir, Nigeria”, AAPG Bulletin, Vol. 88, 2004, pp. 303-324. doi:10.1306/10100303043
[13]	G. Liu and E. Roaldset, “A New Decompaction Model and it Applications to the Northern North Sea,” First Break, Vol. 12, 1994, pp. 81-89.
[14]	K. Magara, “Thickness of Removed Sedimentary Rocks, Paleopore Pressure, and Paleotemperature, Southwestern Part of Western Canada basin,” AAPG Bulletin, Vol. 60, 1976, pp. 554-566.
[15]	K. Magara, “Comparison of Porosity-Depth Relationships of Shale and Sandstone,” Journal of Petroleum Geology, Vol. 3, No. 2, 1980, pp. 92-102. doi:10.1111/j.1747-5457.1980.tb00981.x
[16]	Schlumberger, “Log Interpretation Principle and Applications,” Schlumberger education Services, Houston, 1989, p. 46.
[17]	J. W. Schmoker and R. B. Halley, “Carbonate Porosity versus Depth: A Predictable Relation for South Florida,” AAPG Bulletin, Vol. 66, No. 12, 1982, pp. 2561-2570.
[18]	J. G. Sclater and P. A. F. Christie, “Continental Stretching: An Explanation of Post Mid-Cretaceous Subsidence of the Central North Sea,” Journal of Geophysical Research, Vol. 85, No. B7, 1980, pp. 3711-3739. doi:10.1029/JB085iB07p03711
[19]	R. C. Selley, “Porosity gradient in the North Sea oil-bearing sandstones,” Journal of the Geological Society of London, Vol. 135, No. 1, 1978, pp. 119-132. doi:10.1144/gsjgs.135.1.0119
[20]	B. F. M. Stam, G. P. Lloyd and D. Gillis, “Algorithm for Porosity and Subsidence History,” Computers and Geosciences, Vol. 13, No. 4, 1987, pp. 317-349. doi:10.1016/0098-3004(87)90006-9
[21]	J. M. Weller, “Compaction of Sediments,” AAPG Bulletin, Vol. 43, No. 2, 1959, pp. 273-310.
[22]	M. R. Wyllie, J. A. R. Gregory and G. H. F. Gardner, “An Experimental Investigation of Factors Affecting Elastic Waves Velocities in Porous Media,” Geophysics, Vol. 23, 1958, pp. 459-493. doi:10.1190/1.1438493