CHARACTERIZATION OF A THIN BEDDED RESERVOIR IN CALIFORNIA USING 3-D RESISTIVITY MEASUREMENTS

The Puente formation of offshore California contains thin-bedded turbidite sands. Geologic and petrophysical evaluation of these zones has historically underestimated their net pay and hydrocarbon saturation parameters. The use of advanced logging technology has allowed an enhanced understanding and quantification of this reservoir. Wireline resistivity imaging techniques were used to identify the nature of the bedding and to quantify the bed thickness distribution. It was recognized that bed thickness less than 2” were common in some subzones and that the resulting net pay and saturation calculations were pessimistic. The under-estimation comes in part from the averaging of the low-resistivity shale beds with the higher-resistivity pay sands, measured in a vector parallel to the logging tool. A new 3-D resistivity tool was utilized which employs an array of 3-axis, co-located coils, which provide horizontal (Rh) and vertical (Rv) resistivity measurements, corrected for bedding dip and hole angle. The thin bedded zones in the study field demonstrated resistivity anisotropy showing substantial differences between the vertical and horizontal measurements, which are typical in thin bedded pay zones. The use of this 3-D resistivity data resulted in the calculation of lower water saturations and increased net pay attributed to the thin bedded zones.