NEW RESERVES IN AN OLD FIELD, THE NIOBRARA RESOURCE PLAY IN THE WATTENBERG FIELD, DENVER BASIN, COLORADO
Wattenberg straddles the Denver Basin synclinal axis and is regarded as a basin-center petroleum accumulation. The Niobrara is overpressured and drilling depths are 6200 to 7800 ft. The Wattenberg area is a “hot spot” or positive temperature anomaly. Temperature gradients range from 16 – 18oF/1000 ft on the edges of the field to about 28 to 29oF/1000ft in high GOR areas.
The Niobrara consists of four limestone (chalk) units and three intervening marl intervals. The lower limestone is named the Fort Hays and the overlying units are grouped together as the Smoky Hill member. The chalk units are referred to in descending order as the A, B, C, and Fort Hays. Erosional unconformities exist at the top and base of the Niobrara. The upper unconformity removes the upper chalk bed in some areas of the Wattenberg Field. The B and C chalks are the main focus of horizontal drilling by operators in the field. The underlying Codell Sandstone/Fort Hays is also targeted with horizontal wells.
Recent horizontal completions have initial production of approximately 100 to 700 BOPD with a GOR of 500 to 10,000 cu ft per barrel. Estimated ultimate recovery per well is greater than 300,000 BOE. The Wattenberg area has a resource estimate from the Niobrara of 3-4 billion barrels equivalent. The combined technologies of horizontal drilling and multistage fracture stimulation have brought significant new life into this 43 year old field.