Perforation strategies for multi-layered gas condensate and dry reservoirs

Abstract

Multilayered gas and gas condensate reservoirs in the Gulf of Thailand are generally limited in extent and dissected by numerous faults. A single area may consist of a large number of individually distinguished reservoirs. The method to gain production is to perforate the layers in the right sequence. In this study, the system of interest consists of dry gas and gas condensate reservoirs. Seven different perforation strategies are analyzed in order to maximize condensate and gas production. For two-layer reservoirs with depletion-drive gas-condensate reservoir on top and dry-gas reservoir at the bottom having permeability of 500 mD and thickness of 100 ft, the best perforation strategy to maximize condensate production and barrel of oil equivalent is to perforate the top reservoir first until gas production rate reaches half of initial production rate and then perforate the bottom layer while keeping the top zone open. As the thickness of the gas condensate and dry gas reservoir decreases, we should delay the perforation of the lower zone in order to preserve the amount of gas in the lower reservoir to be used to lift condensate at late times in order to maximize condensate production. However, in term of barrel of oil equivalent, stand alone perforation is best for thickness of 50 ft. As the permeability of the gas condensate and dry gas zones decreases, we should also delay the perforation of the lower zone in order to maximize condensate production and barrel of oil equivalent.