Well Test Analysis of Gas Condensate Reservoirs from Pressure Build Up and Draw Down Tests

Abstract

Condensate drops out around the wellbore in the gas condensate reservoirs when the well bottomhole pressure falls below the dew-point. In these reservoirs interchanges in fluid from single phase to multiphase in the near-wellbore region, causes three different mobility regions in the reservoir. At the outer region, Away from the well, pressure is still above the dew-point with initial liquid saturation and there is only gas existed (Region 3). Next, there is an intermediate region in which the pressure is below the dew-point with increasing in liquid saturation and the condensate drops out of the gas phase (regions 2). Finally, increasing in the liquid saturation reaches above critical value and both gas and condensate are mobile and flow together into the wellbore (region1). This paper presents well test challenges on the gas condensate reservoirs. It demonstrates phase redistribution, double porosity, capillary number effects, partial penetration or composite behaviors. Many reservoirs in all around the world are affected by gas condensate behavior. For example, the Karachaganak field in Kazakhstan, the Cupiagua field in Colombia, the North Field in Qatar and the South Pars field in Iran. Consequently, many researches have been conducted since the 1950's to understand the behavior of the gas condensate reservoirs below the dew point pressure to determine the main controlling parameters. To sum up, the draw down flow periods are extremely complex to interpret. Hence, it shows that the condensate banking effect can be removed completely with an excellent fracturing job in place, even though the well is depleted below the reservoir's dew point pressure. Along increasing the skin; it is important to note that the composite behavior is represented. Our studies have been performed mainly on build-up data, because draw down data depends on flow rate fluctuations due to noise; especially in the gas condensate wells. Before the final radial flow stabilization, Humping skin effect is observed and the dual porosity does not disappear immediately.