Abstract

In order to consider the influence of variation of retrograde condensate saturation on well performance during production process in low permeability condensate reservoirs, this paper presents a new method to describe two-phase unsteady flow in formation around condensate well by using phase equilibrium and theories of unsteady flow through porous medium. The method takes into account the effect of retrograde saturation caused by phase behavior change on gas phase permeability and a new productivity prediction method by combining the variation has been offered. The method can be used to predict the distribution law of condensate saturation, pressure and relative permeability along radius direction as well as dynamic IPR curve and dynamic skin created by liquid saturation near wellbore in different production period. The method can also be used to predict effect of the dynamic skin on production. The application indicates that the method can reasonably describe the dynamic extension of retrograde condensate radius, the resistance effect of liquid dropping out on gas flow, and more rationally predict saturation variation near wellbore

Introduction

When we compare the general gas reservoirs with gas condensate reservoirs, there are many special factors which affect performance of gas condensate reservoir in exploitation process. For instance, the prediction on performance of gas condensate well is related to the law of gas condensate flow through the porous medium. In formation, the liquid will drop out from gas with pressure decline. It greatly affect the flowing feature through exploitation process. The condensate oil saturation around wellbore will be greater than that in the place far away from the wellbore due to the effect of the pressure distribution, the oil absorbed by rock, capillary forces and flowing feature. All of these will affect gas flow characteristics and change the property of well inflow performance. In these cases, not only the volume of dropping out liquid but also the flowing feature of it will play a part. Therefore, the existence of condensate oil will affect the gas condensate mixture flow to borehole, and its effect varies with time. We can more rationally and economically exploitate the oil-gas resources if these phenomena can be adequately described.

O'Dell and Miller presented a simple method based on steady-state flow concepts that can be used to estimate quickly the deliverability from the well. Results obtained using this method indicate that prediction of producing well rates will be presimistic if the average reservoirs pressure is below the saturation pressure of the in place fluid.

D.D. Fussell described the use of modified version of one-dimensional radial model developed by Rocbuck etc. to study the long term single-well performance.

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