Publisher: Bachudo Science Co. Ltd

Effects of Clay On Resistivity Index Thin Bed: Case Study From Western Niger Delta

Dulu Appah
KEYWORDS: Resistivity, saturation, clay


Certain clays produce micro-porosities that retain a relatively thick water layer and enhance the path for conductivity of electric ,currents through capillary forces. Saturation exponent (n) in clay-rich fields is less than the value of 2, usually assumed in well-logging. Accurately determined clay-corrected saturation exponent ("n") and resistivity index are needed for better reserve estimation. A clay inclusion study of saturation-resistivity relationships from thin and laminated beds is carried out in the laboratory. Saturation exponents (n) are measured on a number of core samples from several wells in a Niger Delta field Cation exchange capacity (CEC) technique is used to detect clay in the rocks CEC values are in the ranges of 0.0278 and 0.0078 for the interval 5456-5574ft and 0.0025 - 0.0166 for 8600 to 8695ft. A correlation of the resistivity index and saturation indicates deviations, from 'normal', caused by the effect of clay minerals such as kaolinite, montmorillonite and smectite. Clay presence produces a curve towards low saturation point., The average field "n" is 1.83 and acceptable;CEC tolerance in heterogeneous formations is within a depth of 0.2ft. The larger the CEC, the greater the suppression of downhole resistivity and active clays such as montmorillonites have greater influence on log response than kaolinite.

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