Abstract

In 1993, Conoco discovered the first commercial hydrocarbon reservoir in Lodgepole Waulsortian mounds in North Dakota, Delineation, based on 2D seismic and proximity to successful wells, and then unitization of the Dickinson Lodgepole Unit (DLU), quickly followed. Conoco and other operators acquired several 3D seismic surveys in and around the Dickinson area following the discovery. However, the play did not expand until almost two years later, when Duncan Oil completed a second Lodgepole discovery just three miles from the DLU.

The Dickinson area now has nine productive Lodgepole fields. This has been a highly competitive play, because the lP of a Lodgepole well can exceed 1000 BOPD, usually water-free, and individual wells can produce more than 1 million barrels of oil.

Production is from low porosity (5%) Waulsortian mounds, which range between 250 to 320 ft. thick and have oil columns up to 180 ft. These reservoirs have a heterogeneous internal architecture, related both to original depositional geometry and facies, as well as diagenetic alteration. The mounds in the Dickinson subsurface have been through multi-stage diagenesis and fracturing, which has created an excellent dual porosity system. The mounds' internal architecture is therefore difficult to predict. However, the location and gross morphology of the mounds can be determined fairly well from 3D seismic, which is a very good tool for both exploration and development.

These reservoirs are excellent candidates for secondary recovery. All of the Dickinson area Lodgepole reservoirs are either currently under waterflood, or are in the process of being unitized so that water injection can begin in the near future, Primary recovery has been estimated at approximately 28%, and secondary recovery is likely to be 13% or higher. With total original oil-in-place estimates of 70 to 100 million barrels for the Dickinson area mounds, the Lodgepole presents a very attractive exploration target.

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