Summary
The mobility and flow distribution of liquid injected after foam control the effectiveness of foam/acid matrix well-stimulation treatments and the injectivity of liquid in many foam improved-oil-recovery processes. We present a computed-topography (CT) study of liquid injection following foam, in which both mobility and the sweep of liquid are determined directly, the latter by CT imaging. Earlier experimental work is extended in that the effects of foam quality, foam-injection rate, post-foam liquid-injection rate, and core heterogeneity on liquid mobility and displacement pattern are observed directly. CT images show that liquid fingers through foam rather than displacing it evenly. As a result, 1D models for the displacement cannot represent the process accurately. The formation of the finger is at least partly stochastic: In different experiments in the same core, with similar initial foam states, the liquid finger took markedly different paths through the core. Liquid injected after foam does not follow simply the path of mobile gas in the foam. In these experiments, post-foam brine injection was not qualitatively less effective than post-foam surfactant injection, though there were differences in both post-foam mobility and fingering pattern. Implications of field application of foam-acid diversion in matrix-stimulation treatments are discussed.
