Abstract: Increasing Reserves Through Improved Evaluation of Low Contrast Pay Sands: Lower Lagunilias, Bloque IV, Lake Maracaibo

I. D. Bryant, M. Herron, A. Matteson, R. Ramamoorthy, C. Coll, H. Gamero, M. Frass, R. Casco

Pay sands have traditionally been defined in the Lower Lagunillas reservoir by applying porosity and saturation cutoffs following a Waxman-Smits evaluation. This strategy has proven useful to identify sands which historically provided prolific production when completed over multiple zones in vertical wells. However, zones that were not attractive completion targets in vertical wells have been shown to be attractive targets for dedicated horizontal infill wells.

The mineralogy of samples from old cores has been determined by Fourier Transform infrared spectroscopy. This mineralogical model has been implemented to provide improved evaluations of the shaly sands. This evaluation suggests that in-place oil volumes may be up to 23% higher. In new infill wells, FMI logs indicate that non-traditional pay zones comprise thinly laminated sands and shales. Incorporation of the these high resolution logs into high resolution petrophysical evaluations yields further increases in evaluated oil volumes of 44% in these zones. A recently drilled infill well has established that these zones can produce oil at economic rates in a horizontal drainhole.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela