Critical Gas Saturation and Supersaturation in Low-Permeability Rocks

Abstract

The~aboratory methodology for determining critical gas saturation, SgC' m field depletion processes is still uncertain. Through measurements. on low-permeability rocks, we explore some of the key issues affectmg laboratory determination of Sgc. Differences between laboratory depletion and external gasdrive experiments are measured and analyzed. We also investigate the relationship between average Sgc from material balance and true Sgc, source of supersaturation, gas nucleation conditions, and dynamics of gas bubble growth in d~pletion drive experiments. We assess the use of low-bubblepoint Olls to reduce experiment time. Finally, we suggest some improvements to laboratory procedures.

Visualization and simulation of bubble growth in pore networks

“…The critical gas saturation, corresponding to the onset of gas flow in the production outlet, was found to be slightly higher in the experiment involving a lower pressure decline rate. This trend is opposite to recent experimental results (Kortekaas and Poelgeest, 1989;Firoozabadi et al, 1989;Kashchiev and Firoozabadi, 1993b), although it must also be noted that Kamath and Boyer (1993) observed no significant effect of the pressure decline rate in their low rate experiments. This discrepancy is due to the following: For an unambiguous definition, a critical gas saturation should be identified with the value at which a sample-spanning cluster forms (in a manner similar to a percolation cluster, although here growth also occurs from multiple sites and mass transfer is an additional factor, Satik et al (1995); Li and Yortsos (1995).…”

“…The onset of growth occurs from various nucleation sites, which become activated at different stages of the process, usually after a certain supersaturation level was reached. A wide range of supersaturations for different systems has been reported in the literature (Kamath and Boyer, 1993;Kennedy and Olson, 1952;Stewart et al, 1954;Wieland and Kennedy, 1957). In our glass micromodel experiments, we observed supersaturations varying from 5 to 30 psi (35 to 207 kPa).…”

“…In solution-gas drive processes, which are of main interest here, these include the value of the critical gas saturation, Sgc, denoting the minimum gas volumetric content before the onset of bulk gas flow and the effect of pressure decline rate on growth (De Swaan, 1981;Firoozabadi et al, Correspondence concerning this article should be addressed to Y. C. Yortsos. 1989; Li and Yortsos, 1993). Their consideration is important for the optimal design of various oil recovery methods, particularly in fractured systems, where the solid matrix has low permeability (Kamath and Boyer, 1993). Analogous problems exist in boiling.…”

Formation of natural gas hydrates in marine sediments: 1. Conceptual model of gas hydrate growth conditioned by host sediment properties

“…At thermodynamic equilibrium, the requirement for the chemical potential of dissolved methane to equal that within small bubbles of the gas phase leads to an increase in the concentration of methane in water. This effect, which has been discussed by Kamath and Boyer [1995], Claypool [1996] and Makogon [1996], is termed capillary supersaturation. The thermodynamic potentials of the various chemical components change according to the internal pressures of the phases that they are in (interfacial curvature of the bubble and gas fugacity inside it are related by the Kelvin equation), so changes in the gas capillary pressure will influence the hydrate-forming reactions.…”

Venezuela-MEM/USA-DOE Fossil Energy Report IV-11: Supporting technology for enhanced oil recovery - EOR thermal processes

“…A recent work on critical gas saturation and supersaturation is presented by Kamath & Boyer (1995). They separate the supersaturation in two components.…”