Emily L Stoudt1,
Michael A Raines1
(1) Texaco North American Producing, Midland, TX
Abstract: Reservoir characterization in the San Andres formation of Vacuum field, Lea County, New Mexico - another use of the San Andres Algerita outcrop model for reservoir description
Detailed studies of San Andres outcrops on the Algerita Escarpment, Guadalupe Mountains, Texas and New Mexico have produced excellent 2 dimensional facies, porosity, and flow unit models for skeletal and oolitic/peloidal packstone and grainstone reservoirs developed in Permian (ice-house) climates. Salient elements of the model include: (1) evolution from open shelf skeletal wackestones and packstones to fusulinid pack/grainstones, to peloidal pack/grainstones and finally into tight, tidal flat capped cycles, (2) “object modeling” of porous/permeable reservoir facies within fusulinid and peloidal lithologies, and (3) identification of major sequence boundaries and associated karst features.
Examination of 2,000+ feet of core cut in the San Andres formation in Vacuum field, Lea County, New Mexico, reveals strong similarities to the published San Andres outcrop model. In ascending depth order, major depositional units included bryozoan/sponge/pelmatozoan wackestones and boundstones, fusulinid/peloid pack/grainstones, ooid/peloid pack/grainstones, and tidal flat capped cycles. A probable third order sequence boundary, marked by deposition of the Lovington Sand, is correlative to the “Brushy Canyon Bypass” surface, identified as a major sequence boundary in the San Andres formation on the Algerita Escarpment.
Numerous karst features are comparable to the same features seen on outcrop. They include dissolution, cave development, collapse structures, and sandstone infiltration. Infiltrated sands are often mistaken for depositional sandstones on logs, resulting in erroneous lateral correlations.
Tidal flat capped cycles are tight, and function as local vertical and lateral permeability barriers. Use of the outcrop analog enables prediction of the 3 dimensional distribution of tight cycles and their impact on reservoir continuity.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana