Joy of Searching for Eroded Ellenburger Traps
Terence L. Britt
The eroded Ellenburger dolomite play covers a large part of the Ozona arch and Eastern shelf structural subprovinces in the Permian basin. In these areas, the Ellenburger Group has been partially truncated by pre-Pennsylvanian erosion. Basinal organic shales of Pennsylvanian age were deposited on the eroded Ellenburger surface and probably are the source of the oil found in Ellenburger traps here. More than 80 oil fields, ranging in size from 0.1 to 40 million bbl recoverable oil, have been discovered within the subject area. Effective trapping mechanisms include simple anticlines, truncated flanks of anticlines, permeability barriers across anticlines, and locally fractured tight dolomites along faults and steep flexures.
Successful involvement in this play requires evaluating several simple geologic concepts that, when combined, form a complex problem with associated high degree of exploration risk. These concepts are paleotopography (including solution-collapse features), facies mapping, internal zoning of the Ellenburger for recognition of true structure, and fracture prediction.
Exploration techniques used are primarily subsurface geologic methods aided by seismic data. A complete technical evaluation should include (1) mapping the eroded Ellenburger surface, (2) mapping the "true" structure within the Ellenburger as defined by insoluble residue (IR) and/or seismic data, (3) creating a zone subcrop (paleogeologic) map for the Ellenburger, (4) identifying the IR zones most favorable for development of reservoir-quality rock, and (5) attempting to map any suspected facies-related permeability barriers within favorable IR zones.
Explorationists with a high capacity for geologic documentation, creativity, and perseverance will be rewarded by additional discoveries in the eroded Ellenburger play.
AAPG Search and Discovery Article #91034©1988 AAPG Southwest Section, El Paso, Texas, 21-23 February 1988.