New Methods for Estimating Parameters of Low Permeability Reservoirs

Abstract

Abstract The use of simultaneously measured downhole pressure and flow rate may not completely eliminate wellbore storage or afterflow effects when there is considerable additional wellbore volume below the pressure gauge and flowmeter. This paper presents new interpretation methods with or without measured wellbore flow rate, taking the additional wellbore volume into account. A diagnostic method is also presented for the determination of the correct logarithmic convolution straight line. It is shown that a simple deconvolution (β-deconvolution) is possible when the wellbore flow rate increases (drawdown) or decreases (buildup) exponentially. For partially penetrated wells, it is also shown that the vertical permeability can be obtained from either the onset of the semilog straight line if it evolves or the simultaneous use of the deconvolution and the convolution associated with non-linear estimation. New solutions are presented for infinite-conductivity vertically fractured wells with wellbore storage (including the fracture storage, which may be important even if the flow rate is measured at the wellbore) and skin effects. Two examples are presented to demonstrate the use of the new interpretation methods for both drawdown and buildup tests.