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The AAPG/Datapages Combined Publications Database

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Abstract


 
Chapter from: M 63:  Unconformities and Porosity in Carbonate Strata 
Edited By
D.A. Budd, A.H. Saller, P.M. Harris

Authors
S.W. Tinker, J.R. Ehrets, and M.D. Brondos

Carbonate Reservoirs

Published 1995 as part of Memoir 63
Copyright © 1995 The American Association of Petroleum Geologists.   All Rights Reserved.
 
Chapter 11

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Multiple Karst Events Related to Stratigraphic Cyclicity: San Andres Formation, Yates Field, West Texas

S. W. Tinker
Marathon Oil Company 
Petroleum Technology Center
Littleton, Colorado, U.S.A.
J. R. Ehrets
Consulting Geologist
Boulder, Colorado, U.S.A.
M. D. Brondos
Marathon Oil Company 
Petroleum Technology Center
Littleton, Colorado, U.S.A.


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ABSTRACT

Open caves and solution-enhanced joints influence porosity distribution and fluid flow in Yates field. Therefore, applying an accurate model for cave formation, describing the distribution of cave and karst features, and quantifying the contribution of caves to total pore volume is important in order to characterize the reservoir. Prior work showed that karst and caves in Yates field were formed by meteoric processes acting on subaerially exposed islands following San Andres deposition, and predicted that the number of open caves should decrease with depth below the top of the San Andres Formation. The current work addresses three related issues: the possibility of multiple karst events in the San Andres of Yates field and the relationship of these events to stratigraphic cyclicity, the 3-D distribution of caves in the reservoir and the areas where future well deepenings might encounter caves in the field, and the effect of subaerial exposure on porosity and permeability.

There is a relationship between cave distribution and sequence stratigraphy in Yates field. Sequence-stratigraphic interpretation indicates that four major cycles aggraded and prograded from west to east. Each major cycle has a clinoformal geometry, shoals upward overall, and was capped by a subaerially exposed island complex. On these exposed islands separate cave lenses formed as a result of meteoric processes. Because the clinoforms and their associated island complexes aggraded and prograded from west to east, deeper drilling in Yates field should encounter additional caves to the west of known shallower caves in the east.

 

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