Fractured oil reservoirs, which are among the most technically complicated oil and gas reservoirs, often trap significant amounts of recoverable oil within the matrix. Extraction of this oil requires a better insight of the main displacement physics controlling matrix-fracture interactions. Immiscible gas injection, for example, is one of the common techniques used to improve oil recovery from fractured reservoirs. However, the presence of fractures in such reserves as a high permeable path impacts the displacement physics and consequently the oil recovery, especially where three phases (i.e., brine, oil, and gas) coexist.

In this study, I performed a set of two- and three-phase experiments under tertiary gas injection using spreading oil on a fractured 10-mm diameter limestone rock sample by utilizing micro-CT imaging technique. The aim is to compare pore fluid occupancies under a wide range of oil saturations within the pore space and the fracture openings. Interpretation of the micro-scale images helps to capture a detailed map of the fluid arrangements within the pore space in the matrix and the fracture. These maps clearly demonstrated the relevance of spreading phenomena to fluid displacements in the fracture undergoing three-phase flow processes.

The saturation profile over the course of the gas injections showed that brine was predominately produced first since it was the most well-connected phase. After increasing the gas flow rate, the gas obtained sufficient capillary pressure to invade areas containing trapped oil at which point oil layers began to form and re-connect the oil phase. The oil layers allowed the further production of oil with each incremental increase in gas flow rate. Oil layers were seen to be thicker at lower flow rates and became progressively thinner with increased capillary number. Overall, it was found that, at higher oil saturations, the displacement of oil was predominantly achieved by the connectivity of the bulk oil after the evolution of the reconnected trapped oil blobs in the matrix, whereas at lower oil saturations, the displacement of oil was governed by the stability and the hydraulic connectivity of the spreading oil layers that maintained the continuity of the oil phase from the matrix to the fracture.

You can access this article if you purchase or spend a download.