A Predictive Model of Reservoir Continuity in Fluvial Sand Bodies of a Lacustrine Deltaic System, Colton Formation, Utah

Abstract

Abstract The Paleocene/Eocene Colton Formation of east-central Utah is interpreted to be a fluvial-dominated lacustrine deltaic sequence that prograded from the southeast into ancient Lake Uinta. Predictability of reservoir continuity is based largely on understanding the nature of impermeable mudstone drapes within multilateral and multistory sandstone bodies. Fluvial sandstones are categorized into three systems according to associated facies, channel morphologies, and percent sandstone found within the section. Suspended-load systems dominate the western distal end of Colton exposures and are characterized as follows: meandering to sinusoidal fluvial systems, abundant multilateral accretion sets, and low sandstone percent (< 30%). Reservoir characteristics include poor porosity (< 9%) and permeability (< 0.6 md), poor reservoir continuity, small reservoir size, and good potential for development of numerous hydrocarbon traps. Mixed-load systems are typified by sinusoidal fluvial channels, large multilateral accretion sets, and intermediate sandstone percent (25-45%). Reservoirs display good porosity (approx. 18.5%) and permeability (< 50 md), intermediate reservoir continuity, intermediate to large reservoir size, and good potential to develop numerous hydrocarbon traps. Bed-load systems are characterized by relatively straight channels, very few point bar sequences, and high sandstone percent (< 45%). Reservoir characteristics display very good porosity (19.6-22.6%) and permeability (0.133-2.657 darcies), good reservoir continuity, large reservoir size, and less potential for hydrocarbon trap development. Distributary mouth bar sandstones display excellent reservoir characteristics including good porosity (20%) and the most homogeneous permeability (< 200 md) of the four volumetrically important sandstone facies. Recognition criteria of the four reservoir sandstone facies include sandstone percent in the section, grain size, thickness of the sandstone body, thickness of the sandstone interval, porosity and permeability of sandstones, and the nature of mudstone drapes between multilateral and multistory sandstone bodies. Improved technology in horizontal drilling may be used to link large noncommunicating multilateral accretion sets.