Determination of Recovery and Relative Permeability for Gas Condensate Reservoirs

摘要

Coreflood experiments on gas condensate flow behavior were conducted for a Libyan gas condensate reservoir. The objectives were to investigate the effects of rock and fluid characteristics on critical condensate saturation (CCS), gas and condensate relative permeability’s, hydrocarbon recovery and trapping by water injection, and incremental recovery by subsequent blowdown and vaporization by dry gas injection. rnThe water/gas relative permeability data were generated using implicit historical matching simulator which uses a reverse history matching technique to generate a full suite of relative permeability curves over the range of interest. The results of the tests on the reduction in gas permeability due to retrograde condensate accumulation demonstrated that, in general, the effective permeability to gas decreased significantly at pressures below the dew point pressure due to the condensate trapping effect for all the stacks investigated in this study. Permeability continues to drop at very low pressures even though theoretically condensate should be revaporizing. The recoveries of the liquid condensate during the vaporization by dry gas injection at pressures below the dew point pressure were generally high. The recovery ranged from 66% to 70% for the high permeability core stack and 86% to 98% for the lower permeability core stack. In theory, it is possible for all of the condensate to be revaporized into the methane gas stream. However, in practice, the recovery is usually less than 100% due to macroscopic sweep efficiency limitations and mass transfer limitations within the rock matrix. rnPoor mobility ratio and viscous fingering during the methane injection characterize the re-vaporization of gas condensate by methane gas. This results in early breakthrough of the methane gas and very high gas/liquid ratios during the test. The volume of methane gas injection required to recover a significant amount of the condensate liquid in the core is a function of temperature, pressure, composition of the gas, heterogeneity and especially the permeability of the core sample.