ABSTRACT

Cedar Hills Field is an Ordovician Red River "B" field located on the southwest flank of the Williston Basin just down-dip of the Cedar Creek Anticline (CCA). The CCA is a 100 mile (161 kilometres) long, faulted anticline that has produced over 400 MMBO (63.6 x 106 m3) from multiple fields along the crest of the structure. The majority of the Cedar Hills Field is located in Bowman County, ND, although portions of the northwest part of the field extend into Slope County, ND and Fallon County, MT.

Cedar Hills Field has been developed entirely through the use of horizontal drilling technology. Horizontal drilling has turned an uneconomic project into a highly economic and successful project with significant secondary recovery potential. The horizontal drilling direction (NE-SW) is parallel to the preferential permeability direction to increase sweep efficiency in the secondary recovery process. The field is fully developed on a primary basis with over 180 wells.

The Red River "B" reservoir interval is a 10-foot (3-metre) thick, finely-crystalline dolomite bounded above by a thin anhydrite and below by a tight limestone. Although several different facies can be distinguished in the "B" interval from detailed core and petrographic work (Longman, 1998; Coringrato and Canter, 1998), only 2 of these have been consistently identified on logs. These two units are informally known as the Upper and Lower Red River "B" and are separated by a thin silica-cemented zone informally called the "hard streak". Exploiting the Upper "B" is critical to the economic success of each well. Mudlog data (drill time, gas shows, sample description, and geometry) are used to determine where the well is drilling (Upper "B" versus Lower "B").

The Red River "B" reservoir is unique in the fact that the porosity and thickness are consistent and uniform over the entire field area and have little affect on well performance. Permeability in the Upper and the Lower Red River "B" zones is the single most important factor affecting well performance, due to the extreme permeability variability across the field. Oil saturation is the other critical reservoir property affecting well performance in this field.