Critical Oil Rates in Naturally Fractured Reservoirs to Minimize Gas and Water Coning: Case History of a Mexican Carbonate Reservoir

Abstract

Abstract This study extends Birks (1963) coning method by defining various options for calculation of the critical oil rate in naturally fractured reservoirs through an explicit use of the radial pressure gradient in the fracture, ∂P/∂R. The study aims at minimizing gas and water coning, and introduces methodologies for estimating fixed and variable radius of drainage, as well as an iterative procedure for calculating the critical oil rate and the drainage radius within the fracture. The methodology has been used with good practical results, allowing optimization of oil production, in various naturally fractured carbonate reservoirs in the southeast of Mexico. Determining a critical or maximum efficient oil rate in naturally fractured reservoirs is very important in those cases where oil productivity can decrease significantly due to increases in water/oil and/or gas/oil ratios. Imposing a critical oil rate is also related to the capacity of fluids handling in surface installations and reservoir management when gas and/or water injection projects are being conducted in the reservoir. It is concluded that the methodology, which is not developed with the idea of replacing detailed coning simulation studies, can be used quickly, easily and with a good level of certainty in naturally fractured reservoirs.