Experimental investigation of tertiary oil gravity drainage in fractured porous media

The amount of residual oil trapped in the matrix of a fractured reservoir after water drive, either natural water drive or water injection, depends on the wettability of the matrix rocks. Gas oil gravity drainage (GOGD) has been proposed as the tertiary oil recovery process for this type of oil reservoir. The current work focuses on experimental investigation of tertiary GOGD in fractured porous media under different types of matrix wettability. Results of a set of experiments performed in artificial porous media composed of sand packs and glass beads of different wettability have been used to check the GOGD rate and the ultimate oil recovery for previously waterflooded models. A novel experimental setup to study flow behavior in fractured artificial porous media was designed to perform the GOGD process. Results show that tertiary gravity drainage increases oil recovery efficiency from a fractured matrix block, which also depends on the post-waterflood residual oil saturation and the wettability of the medium. Observation of the gas front location and oil recovery profile with time during the tertiary recovery stage reveals that the oil recovery of post-waterflood residual oil in a fractured matrix block starts before stabilization of the gas-liquid front. Oil recovery mechanisms similar to those presented in tertiary GOGD recovery in a conventional reservoir are proposed to explain the gradual drainage of matrix blocks in a naturally fractured stratum.