Laboratory Study of Gas Trapping in Foam-Acid Diversion

摘要

A series of Berea coreflood experiments modeled the processof foam-acid diversion for well stimulation. Foam wasinjected to steady state, followed by injection of liquid torepresent acid. Pressure gradient was monitored along the coreand average liquid saturation was determined by weighing thecore continuously during the experiments. This approachprovides direct data on liquid saturation and liquid relativepermeability during foam injection and liquid injectionafter foam.Water saturation increased by a larger amount during postfoamliquid injection than estimated in previous studies. Theliquid relative-permeability function krw(Sw) obtained duringfoam injection was reasonably accurate during post-foamliquid injection, until gas dissolution into the injected liquidbecame significant. The ultimate trapped-gas saturation duringliquid injection appears to depend on previously injected foamquality; this may require a revision of models for the aciddiversionprocess.It appears that a sufficiently high foam quality (injectedgas fraction) can eliminate the detrimental decline in pressuregradient observed during liquid injection in earlier studies.This may alter previous ideas about the optimal foam qualityfor foam-acid diversion.