Experimental investigation of CO2 huff and puff in a matrix-fracture system

The purpose of this experimental study is to evaluate the efficiency and performance of cyclic CO2 injection on recovery of heavy oil from a matrix-fracture system and to study the feasibility of carbon storage in a fractured medium. In this study; different laboratory experiments on one of the Iranian heavy oil and brine reservoir samples were performed. The Minimum Miscibility Pressure (MMP) between the oil sample and carbon dioxide at reservoir temperature (80 degrees C) was estimated using Vanishing Interfacial Tension (VIT) technique (2424 Psi). In order to perform the cyclic CO2 injection tests; two sets of six 8.6 cm diameter and 15 cm long tight carbonate core samples have been prepared and saturated with reservoir oil at initial brine saturation conditions. The saturated cores were placed in a long vertical sleeveless core holder, which has been specially designed to simulate fluid flow in a matrix-fracture system. The total number of two CO2 huff and puff tests, 4 cycles each, with 24 and 48 h soaking periods were performed on the system at reservoir temperature conditions. The results of experiments confirmed the effectiveness of this method for stimulating heavy oil saturated matrix-fracture system; furthermore it is concluded that longer soaking period will result in the higher oil recovery. This difference is pronounced at early cycles. The results also indicated that additional 24 h soaking period will result in approximately 10% increase in oil recovery. (C) 2015 Elsevier Ltd. All rights reserved.