ABSTRACT: Log Facies and Outcrop Analyses of Weathered Crust Formation

Syngaevsky, Pavel E¹ and Sergey F Khafizov²
(1) Louisiana State University, Baton Rouge, LA
(2) Tyumenskaya Neftyanaya Kompaniya (TNK), Moscow, Russia

Outcrop analyses are commonly used to characterize various facies observed on log diagrams and in cores. Most outcrop studies focus on the description of sand-shale sequences, their grain-size variations, morphology and reservoir properties. In West Siberia Basin majority of such studies are concentrated on deep water (K 1) or shallow-marine/alluvial plain (J 1-3) analogs. Less attention is being focused on Weathered Crust formation (J 2 - T 2-3). This paper main purpose is to show how ancient depositional environments could be reconstructed by interpreting wireline log diagrams in such complex and to certain extend "exotic" reservoir.

The objectives of this paper are to: 1) Review and compare several outcrop examples; 2) Characterize zones, which are identified on log diagrams and core; 3) Evaluate reservoir properties of Weathered Crust zones;

Our three years detailed study of Arkansas, Wyoming, Central and Polar Ural outcrops, logs and core from more that 300 wells documents five main lithofacial units of Weathered Crust formation that could be recognized on wireline diagrams. A detailed petrographical and petrophysical characterization of these zones allow to identify them and to define a correct boundary between the sedimentary cover and the basement, as well to predict the sequence of facial zones in the section. Similar signatures of well log diagrams (Log Facies) were recognized in various oil-gas bearing basins: Trans-Ural, Pre-Caspian, West and East Siberia.

Such approach also could be successfully used in other parts of the World, especially were there is limited core material available to support well log interpretation.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia