Mineralogical Controls on Rock Fluid Properties--The Delaware Mountain Sandstones, Waha Field, West Texas

Abstract

Reservoir rocks of the Guadalupian Delaware Mountain Group in Waha field, Reeves Co., Texas are very fine-grained, subarkosic sandstones interbedded with organic-rich siltstones and thin limestones. Shales and detrital clays are notably rare. The Delaware Mountain Group, including in descending order the Bell Canyon, Cherry Canyon, and Brushy Canyon formations, are currently buried at depths of 4,500-8,000 ft in this area. Production is primarily from the Bell Canyon and Cherry Canyon formations. Diagenesis of the Delaware Mountain Sandstones is unique in several aspects: The lack of shale in the sequence precludes significant changes associated with shale diagenesis. Abundant organic matter within the formations may have played an important role in diagenetic processes. Pore fluids migrating from the overlying Castile evaporite sequence are a likely source of early halite cement in the Delaware Mountain Group. Large scale dissolution subsequently removed cement and detrital material, creating abundant secondary porosity. In the study area, reservoir porosities generally range from 20 to 25%. However, permeabilities are low (usually less than 50 md) and water saturations are high due to the presence of pervasive porelining chlorite. Reservoir quality of these sandstones has been controlled to a large extent by diagenetic processes.