An experimental investigation of the diversion characteristics of foam in Berea sandstone cores of contrasting permeabilities

Foam has been used successfully in the field as a diverting agent for matrix acidizing when layers of contrasting permeabilities are present. However, the mechanisms governing the diversion performance of foam are still not properly understood and only a handful of foam diversion papers can be found in the literature. This paper discusses the results from several dual-core experiments using 11- and 22-in. (27.9 and 55.9 cm) long and 1.5-in. (3.8 cm) diameter fired Berea sandstone cores (permeability range: 10–1000 md) in which parameters such as foam quality, total injection rate, foam slug size, etc., are varied systematically for different permeability contrasts. Each experiment consists of a gas-free surfactant injection phase, followed by a foam injection phase, which is then followed by a brine injection phase simulating the post-foam acid injection stage. The pressure data along each core at four locations and the weight of the liquid effluents for each core are recorded continuously. An attempt is made to quantify the diversion performance by the introduction of various diversion factors. The effect of variables such as foam quality, injection rate, slug size, etc., on the diversion factors are then compared for different permeability contrasts. Results show strong dependence of the diversion performance on permeability contrast, foam quality and total flow rate. This study provides important guidelines for designing acid jobs for different permeability contrasts and ranges when foam is used as a diverting agent.