Philip L. Moses, Core Labs, Inc
Most so-called gas reservoirs which produce liquid in the ratio of ten barrels per million or more are actually retrograde condensate reservoirs. As retrograde condensate reservoirs, they exhibit a dew point and condense liquid in the formation upon reduction in reservoir pressure. This liquid condensation in the reservoir adversely affects the production of liquid and gas at the surface. In extreme cases this retrograde condensation in the reservoir may result in the loss of as much as 75 to 80 per cent of the stock tank condensate initially contained in the reservoir fluid. With a knowledge of how the producing well stream characteristics may be expected to behave as reservoir pressure declines, several alternatives are available to minimize the effect of this retrograde loss. The decisions to be made are largely economic decisions based upon an accurate projection of both gas and condensate production over the life of the reservoir for various operating methods. This paper describes the type of study needed on the reservoir fluid to make intelligent decisions regarding the method of operation of the reserve, including decisions regarding the method of operation of the reserve, including decisions regarding the pressure maintenance versus pressure depletion and choice of surface separation equipment. In addition, the data are furnished to calculate the economics of gasoline plant operation considering either pressure maintenance or pressure depletion with lease separation of full well stream processing. With proper data, the reserve may be operated to obtain the maximum economic return.