Feasibility of foamed acid treatment in upper stimulation of fractured-vuggy dolomite reservoirs with bottom water

Abstract

Bottom water breakthrough, which is posed by the failure in an initial water control during acid treatment, is a complex problem in fractured-vuggy dolomite reservoirs with bottom water. To analyze the feasibility of upper stimulation during foamed acid treatment, various experiments were performed, including the analysis of acid flow and etching exclusively in fractures and that in fractures between caves (or reservoirs). The results confirm the abilities of the retarding and upper stimulation of foamed acid. Foamed acid penetrates into the upper fractures and replaces the oil in this part of the reservoir, whereas thickened acid invariably displaces into fractures present in the lower part. During treatment with foamed acid, the displacement rate of oil increases with an increase in the upper fracture connectivity. Furthermore, upper stimulation is suitable for reservoirs with developed upper and undeveloped lower fractures. For field applications, the flow rate should not be extremely high when using foamed acid for upper stimulation of fractured-vuggy dolomite reservoirs with bottom water, and should be maintained at the minimum while ensuring construction efficiency; otherwise, it might result in bottom water breakthrough.