Abstract
The mobility and flow distribution of liquid injected after foam controls the effectiveness of foam-acid matrix well-stimulation treatments and the injectivity of liquid in many foam IOR processes. We present a CT study of liquid injection following foam, in which both mobility and the sweep of liquid are directly determined, 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 directly observed. CT images show that liquid fingers through foam rather than displacing it evenly. As a result, one-dimensional models for the displacement cannot accurately represent the process. 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 simply follow 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 for field application of foam-acid diversion in matrix stimulation treatments are discussed.
