Parametric Pulsing of Oil and Gas Reservoirs-An Evaluation of the Merits
Authors: May R.A. , Chase C.A. 
Published: December 2007

Analytical and numerical results show, that, for single-phase flow, reservoir performance is not enhanced by alternating production and shut-in periods, contrary to recently published information.

Introduction

It is the reservoir engineer's responsibility to produce a reservoir in the most efficient manner possible. This responsibility requires a continual evaluation of the merits of new methods that are proposed. Tek and coworkers have recently suggested that the performance of a reservoir can be improved by parametric pulsing. Parametric pulsing is a cyclic operation whereby a well Parametric pulsing is a cyclic operation whereby a well or wells are alternately produced and shut in for specified periods of time. The cumulative delivery by parametric pulsing has been claimed to be as much as 95 parametric pulsing has been claimed to be as much as 95 percent greater than the cumulative delivery by continuous percent greater than the cumulative delivery by continuous production. production. The conclusions of Tek et al. regarding the benefits derived from parametric pulsing are based on limited empirical data and simplified analytical expressions coupled under assumptions that might not be justified. They have presented no theoretical analysis or simulation studies for a complete cycle. In this paper we investigate the merits of parametric pulsing for the case of single-phase flow. parametric pulsing for the case of single-phase flow. Both analytical. and numerical methods are used. The performance of a reservoir in which production rates of performance of a reservoir in which production rates of some or all of the wells are pulsed can be compared by analytical methods with that of a reservoir in which wells are produced continuously by maintaining bottom-hole pressures at their lowest possible values. The analysis shows that the cumulative recovery at any time is greater for continuous production than for parametrically pulsed production. This result depends only on the parabolicity of the flow equation and is independent of such factors as permeability and porosity variations in space and permeability and porosity variations in space and time or with pressure, anisotropy, nondarcy flow, pressure-dependent properties of the gas, or reservoir pressure-dependent properties of the gas, or reservoir geometry. Thus, if parametric pulsing can improve production it must be due to some mechanism other than production it must be due to some mechanism other than the phenomenon of single-phase flow in the reservoir. For example, it could be due to sonic multiphase phenomenon caused by condensate fallout, or it could phenomenon caused by condensate fallout, or it could be caused by reservoir mechanics combined with the effects of tubing flow or of surface gathering facilities. To examine an actual case from the viewpoint of the reservoir alone, a compressible-fluid numerical simulator was used to compare production performance of the two methods. For the conditions considered, the calculations confirm that parametrically pulsed production is less efficient than continuous production is less efficient than continuous production, as predicted theoretically. production, as predicted theoretically. Parametrically pulsed and continuous production of a single well are compared schematically in Fig. 1. For continuous operation the bottom-hole pressure is maintained at the minimum possible value p*BH. A typical production-decline curve for constant-BHP production is indicated by the solid curve. The production is indicated by the solid curve. The bottom-hole pressure and production histories for parametrically pulsed production are indicated by the parametrically pulsed production are indicated by the dashed curves. The total cycle period is T days. The well is produced for a fraction, of the period with the bottom-hole pressure maintained at the minimum value p*BH.

JPT

P. 85