Abstract
The Eocene Sokor1 Formation is proven oil reservoir rocks in the Termit sub-basin. These sandstone intervals are deeply buried, highly heterogeneous in character and characterized by Low Contrast Low Resistivity (LCLR) log responses. Petrophysical and quantitative well-based rock physics interpretations were integrated for property estimations, fluid and lithology typing in reservoir characterization. Six (6) reservoir sandstone intervals were identified, delineated and correlated across five (5) wells. The estimated petrophysical properties showed that the Eocene Sokor1 sandstones have averagely good reservoir properties with sand_5 interval exhibiting exceptional reservoir properties. Vp/Vs vs. AI and μρ vs. λρ elastic cross-plots color coded with reservoir properties (Vsh and Φ), show distinct and well separated data clusters signifying hydrocarbon bearing sandstones, brine sandstones and shales/mudstones in the 3D crossplot planes with varying seismic elastic property values in each well thereby, enhancing reservoir characterization and providing information’s about the burial history, reservoir quality and property distribution in the sub-basin. The analysis suggests that, although the reservoir interval has averagely good petrophysical properties in all wells, the seismic elastic crossplots show that these properties are much better distributed in wells 2 and 3 than in wells 4, 5 and 9. Therefore, sand_5 reservoir interval in wells 2 and 3 is likely to be more hydrocarbon bearing and productive than wells 4, 5 and 9 in the sub-basin.
Highlights
Hydrocarbon reservoir rocks are distinguished based on their quality and exceptional petrophysical properties
Petrophysical and quantitative well-based rock physics interpretations were integrated for property estimations, fluid and lithology typing in reservoir characterization
The analysis suggests that, the reservoir interval has averagely good petrophysical properties in all wells, the seismic elastic crossplots show that these properties are much better distributed in wells 2 and 3 than in wells 4, 5 and 9
Summary
Hydrocarbon reservoir rocks are distinguished based on their quality and exceptional petrophysical (reservoir) properties. The quality of the reservoir is dependent on the rock type, environment of deposition and burial history, which determines their specific character and properties Reservoir properties such as lithology, porosity, clay volume, grain size, fluid saturation, permeability among many others, are essential for the characterization of hydrocarbon reservoirs. These properties are derived from core analysis, they can be estimated through petrophysical evaluation from well log measurements. The ability to adequately characterize hydrocarbon reservoirs with complex sedimentary properties and heterogeneities from well logs remains a great challenge. These types of reservoirs exhibit Low Contrast Low Resistivity (LCLR) log responses. Discriminating reservoir sands from shales and hydrocarbon sands from brine sands as well as accurately evaluating the distribution of relevant reservoir properties are complicated and tasking in LCLR reservoirs from petrophysics alone
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