Production from Valley-Fill Deposits, Morrow Sandstone, Southeast Colorado: New Exploration Challenges and Rewards

Robert J. Weimer, Stephen A. Sonnenberg, Lee T. Shannon

New exploration success in southeast Colorado indicates opportunities for future discoveries from the Morrow sandstones of many fields in the 10 million to 40 million bbl recoverable reserve category. Drilling depths from 5,000 to 6,000 ft and estimated per well recoveries averaging 200,000 bbl of oil in several fields provide favorable economics, even in times of depressed oil prices. In the past, major problems have been low discovery ratios in exploration wildcat drilling for elusive narrow channel sandstones and predictability of reservoirs in development drilling. Thus, a major challenge is to improve predictability of trends and traps through refinement of geologic and seismic models. This improvement is possible through analysis of existing fields by use of cores, amples, logs, and integrated seismic.

Four widely scattered areas illustrate typical fields in the Morrow play. These are McClave, Sorrento-Clifford, and Smokey Hill fields and the state line area extending from Stockholm field to Arapahoe field. Data needed for each producing area are structure, stratigraphy, sedimentology, reservoir characteristics, and production history.

Production in all four areas is from coarse-grained channel sandstones in the Morrow formation that are interspersed between marine black shales or marine gray shale and limestone. The channels are part of several valley-fill sequences that were deposited during major sea level changes during the Early Pennsylvanian.

AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988