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Thomas A. Ryer1, Chet Ozgen2, Nidia Rios3
(1) Schlumberger, Houston, TX
(2) Nitec, LLC, Denver, CO
(3) YPF, Buenos Aires, Argentina

Abstract: Deterministic and stochastic, object-based models for a complex, fluvial reservoir in the Jurassic Barrancas Formation, Lunlunta-Carrizal field, Cuyo Basin, Argentina

A 60-m section of predominantly sandy and conglomeratic strata of the Middle Jurassic Barrancas Formation has produced approximately 4.2 million m3 of oil and 112 million m3 of associated gas from a north-trending anticlinal structure at Lunlunta-Carrizal field.

The Barrancas Formation consists mostly of flat-bedded sandy conglomerate and flat-bedded to cross-stratified sandstone and pebbly sandstone deposited in low-sinuosity channels. Porous sandstone and conglomerate make up 50 to 70% of the formation. The sandstone and conglomerate beds generally have abrupt basal contacts. Many beds are massive; some display upward fining of grain size, grading upward into sandy mudstone deposited in interchannel areas.

Beds of sandstone and conglomerate in the Barrancas Formation, as identified in core and on wireline logs, range from 1 m to 17 m in thickness. Beds ranging between 1 and 4 m in thickness are interpreted to represent individual channel bodies; thicker beds are interpreted to represent multi-storied or compound channel deposits. Detailed correlation of beds in two representative, 5-m-thick intervals suggest that the trends of the channel sandstone bodies vary widely. The mean direction of flow was northward. Channel belts, as mapped deterministically, are generally 250 m to 500 m in width, ranging up to a maximum of about a km.

Paleogeographic interpretations provided input for a computer program that stochastically populated the reservoir volume with similar channel bodies. Three horizontal wells drilled since completion of the study indicate that the stochastically generated model adequately represents this complex fluvial reservoir.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana