Remediation of water and hydrocarbon phase trapping problems in low permeability gas reservoirs

Aqueous and hydrocarbon phase traps can occur in porous media when water- or oil-based fluids come into contact with a formation which exhibits a "subirreducible" initial liquid saturation of the phase of interest. This commonly occurs with water-based fluids in many low permeability desiccated gas bearing formations and in depleted conditions in rich gas retrograde condensate; reservoirs. This paper documents how phase traps are induced by direct displacement, countercurrent imbibition or depletion effects, and presents techniques for diagnosing whether a reservoir is B candidate for an aqueous phase trapping problem. Techniques to minimize problems with aqueous and hydrocarbon phase trapping are reviewed, followed by discussion of methods to reduce or remove the effect of existing phase traps, such as increased drawdown, alteration of IFT, alteration of pore geometry or direct removal methods. A brief discussion of laboratory techniques used to screen the optimum process for selection are also presented.