In the application of horizontal well development to the Cadomin formation in the Deep Basin gas field of west central Alberta, control of formation damage to a low permeability, thin pay reservoir is of critical importance. Under the current fiscal regime the economics of the limited single well reserve potential does not allow for remedial operations after rig release. The horizontal well is, of necessity, the required stimulation to the reservoir and the drilling of the formation is the completion process.

The two primary formation damage mechanisms which must be controlled are aqueous fluid entrainment and drilling fines invasion which are significantly greater concerns in horizontal wells due to the intrinsically deeper reservoir penetration and longer exposure times. From laboratory studies, the Cadomin is undersaturated with respect to the capacity of the formation to retain water. Invasion of the zone by an aqueous phase doubles the irreducible water saturation within the reservoir severely reducing the relative permeability of the matrix to gas. Coupled with the entrainment of drilling fines, permeability can be impaired by an order of magnitude. In engineering for these conditions in the Cadomin, a viscosified clear diesel drilling fluid was designed incorporating sodium chloride as a bridging agent to permit near balanced drilling.

Reviewed in this paper is a case study describing a history of operations to characterize the formation and the field results of two Cadomin horizontal wells drilled with contrasting aqueous and diesel based fluid systems.

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