Critical Gas Saturation and Relative Permeability During Depressurization in the Far Field and the Near-Wellbore Region

Abstract

Depressurization of a virgin or waterflooded oil reservoir results in the appearance of a solution gas saturation. Above a saturation threshold, this gas becomes mobile and can be produced. Knowledge of the critical gas saturation (S gc ) and the subsequent relative permeabilities (K r ) in the far field and the near-wellbore region has a tremendous impact on gas and oil production forecasts.The present paper provides a new methodology to obtain representative K r and S gc values for a depressurization process. Specific experiments are presented in which undersaturated oil was injected upstream at a fixed rate whereas downstream the pressure was controlled in order to reproduce a drawdown. Evolution of pressure was recorded and in-situ gas saturations measured by CT-scanner. Two initial conditions were considered, fully oil saturated and at irreducible water saturation. Influence of the drawdown scheme was also explored. Transient evolution of the gas saturation profile in the core is clearly shown. Kr are deduced from history matching. They are finally compared to the K r derived from gas injection experiments.It is demonstrated that gas/oil K r shape is strongly affected by the way the gas appears and is distributed in the porous medium. For solution gas drive, oil relative permeability is higher and gas relative permeability is smaller than for gas injection. Concerning critical gas saturation, the experiments show two types of gas mobility depending on the operational conditions: mobility threshold attained from connection of bubbles or from mobilization of a population of separate bubbles. For the first type, S gc can be linked to the values obtained through static experiments at fixed depletion rate.

Evolution of gas saturation and relative permeability during gas production from hydrate‐bearing sediments: Gas invasion vs. gas nucleation

“…During external drive, gas gradually invades the largest interconnected pores advancing from one boundary into the medium. In contrast, internal gas nucleation takes place at independent pores and results in separate and disconnected bubbles before they coalesce to form continuous gas patches [Poulsen et al, 2001;Egermann and Vizika, 2001]. The initial distribution of dissociated gas is spatially correlated with the distribution of the hydrate phase in hydrate-bearing sediments.…”

Relative Permeability Measurements during the Exsolution and Dissolution of Hydrogen Gas Produced by the Hydrolysis of Sodium Borohydride

“…Other studies, however, have shown little difference in the aqueous relative permeability following internal drainage compared with external drainage (Poulsen et al, 2001;Jang and Santamarina, 2014), despite differences in gas relative permeability. Furthermore, those studies that have reported aqueous relative permeability differences (Egermann and Vizika, 2000;Zuo et al, 2012) have shown similar aqueous relative permeabilities at low gas saturations (e.g., less than approximately 5%).…”

Gas production and transport during bench-scale electrical resistance heating of water and trichloroethene

“…Internal drainage has been discussed in the context of solution gas drive, carbon dioxide sequestration and geothermal reservoir applications. It can result in different distributions of gas, and different constitutive relationships, than during external drainage due to gas which nucleates and becomes trapped in pores that are not part of the most conductive channel network (Counsil and Ramey, 1979;Egermann and Vizika, 2001;Jang and Santamarina, 2014;Kamath and Boyer, 1995;Poulsen et al, 2001;Sheng et al, 1999;Zuo et al, 2012).…”