ABSTRACT: Naturally Fractured Reservoir Description Through Well Cutting Analysis. A Case Study: Block IX, Lago de Maracaibo, Venezuela

Xiomara Marquez

The recognition of variations in sedimentary facies can improve exploration and development strategies for naturally fractured carbonate reservoirs.

The evaluation of millimeter-size drill cuttings in well SVS-176 shows that the Cretaceous carbonate sequence consists of five coarse-grained facies: micritized grainstone (G1), algae grainstone (G2), oolitic grainstone (G3), mollusk grainstone (G4), and skeletal packstone (Pl), all deposited in a shallowing-upward carbonate sand sequence.

The presence of millimeter-size, partly filled fractures and abundant, tiny, euhedral calcite crystals on smooth surfaces of some cuttings indicates that facies G3 is the most prone to have open fractures. This fact was proven by electrical logs, production behavior, drilling lost zones, and drifting rate information.

Sedimentological, petrophysical, and production and drilling data concurrently support that facies G3 controls the presence of open fractures. This information, which confirmed the earliest prediction, was used to propose drilling of well SVS-225.

Results obtained with this approach show that by combining independent lines of evidences it is possible to derive an objective and quantitative methodology for naturally fractured reservoir characterization.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990