--> ABSTRACT: Yates Formation of North Ward-Estes and South Ward Fields, Permian Basin of Texas-New Mexico: Part II: Clastic Reservoir Characterization, by S. Dronamraju, R. Johnson, W. M. Ahr, J. M. Mazzullo, and T. A. Blasingame; #91021 (2010)

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Yates Formation of North Ward-Estes and South Ward Fields, Permian Basin of Texas-New Mexico: Part II: Clastic Reservoir Characterization

DRONAMRAJU, S., R. JOHNSON, W. M. AHR, J. M. MAZZULLO, and T. A. BLASINGAME

This study describes the petrography and reservoir properties of clastic facies in the Yates Formation on the Central Basin Platform of the Permian basin. The Yates is a sequence of carbonates, clastics and evaporites which was deposited in fluvial, deltaic, eolian, sabkha, and shallow marine environments. It contains two highfrequency sequences (HFS) and 18 parasequences, each of which is characterized by an "upward-drying" transition from shallow marine to continental facies.

The best quality Yates reservoirs are found in the well sorted, fine-grained fluvial-deltaic sandstones which are preserved in the IVFs at the bases of the HFSs; in the thick eolian sandstones within the prograding units at the tops of HFSs; and in the thin eolian sandstones within aggrading and retrograding parasequence sets. The permeabilities (k) of these sandstones range from 1 to 250 md and their porosities (phi) range from 5 to 27%. The porosity is largely secondary in origin, formed by the dissolution of intergranular cement and feldspars. The poorest quality reservoirs, with phi = 1% and k < 0.2 md, are found in the dolomite- and evaporite-rich clastics which accumulated in sabkhas and coastal environments. The anhydrite-cemented sabkha facies and subtidal carbonates act as vertical flow barriers.

Oil production from the clastic reservoirs is characterized by early depletion and water influx, leaving 60% of the oil unrecovered. Careful selection of perforation intervals and selective isolation can improve the recovery by suitable flooding mechanism, even in mature field area. This study is expected to serve as a model for flooding Yates reservoirs on a larger scale.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.