Stratigraphic Trapping Mechanisms in the Iles Formation, Piceance Basin, Colorado

Compartmentalization within shoreface and deltaic reservoirs is key to trapping gas in the Iles Formation of the southern Piceance Basin. There are two types of reservoirs: 1) compartmentalized gas-saturated Corcoran and Cozzette sandstones, and 2) continuous water-saturated Rollins sandstones. Compartmentalized sandstones are interpreted to have been deposited during a time of relatively low accommodation with relatively low sediment supply while more connected sandstones were deposited during a time of relatively high accommodation and a much higher sediment supply. The compartmentalization is due to 1) location within the overall parasequence stacking pattern; 2) facies variability within the deltaic and wave-dominated deposits; and 3) further partitioning due to the superposition of multiple types of erosion surfaces ultimately related to low accommodation rates. The continuous sandstones are more connected because they were apparently deposited during a period of time when rates of progradation were more regular and overall accommodation and sedimentation were higher.