Gas-Oil Gravity Drainage and Reinfiltration in Naturally Fractured Reservoirs

Abstract

The prediction of production performance in naturally fractured reservoirs is dependent on reinfiltration and capillary continuity phenomena. In fractured reservoirs, reinfiltration and capillary continuity phenomena have been the major setback during gas-oil gravity drainage. The oil contained within the matrix of the gas invaded zone begins to drain down into the fracture system and into the lower matrix blocks, due to the force of gravity. Some of the oil that is drained out of the upper matrix blocks can reinfiltrate into the lower matrix blocks from the top or side surfaces and can flow down through the areas of contact between blocks. To evaluate the effect of reinfiltration in gravity drainage mechanism and fractured reservoir parameters: fracture width (b f ) and storativity capacity () on reinfiltration process, a fractured porous media was modeled with ECLIPSE-100 Simulator. The base-case simulation runs (SIM-1 and SIM-2) showed that 55.14% and 53.40% of the oil in-place in the modeled fractured porous media were recovered by gas-oil gravity drainage mechanism without reinfiltration and with reinfiltration, respectively. Furthermore, the sensitivity study of the aforementioned fractured reservoir properties on gas-oil gravity drainage and reinfiltration with simulation runs (SIM-3 through SIM-10) indicate that fracture porosity as well as storativity capacity influence the ultimate oil recovery in naturally fractured reservoirs. Additionally, the fracture width has no influence on gas-oil gravity drainage and reinfiltration in the modeled fractured reservoir. Therefore, gravity drainage recovery mechanism proliferation is affected by oil reinfiltration within the matrix blocks that resulted in 3.173% production reduction. Hence, fracture porosity and storativity capacity are considerable factors in reinfiltration mechanism in naturally fractured reservoirs.

Performance Quantification of Enhanced Oil Recovery Methods in Fractured Reservoirs

“…Gravitational and capillary forces have the leading roles in capillary continuity and reinfiltration processes. In the case of the stack of matrix blocks, capillary continuity and reinfiltration phenomena occur due to block-to-block interactions, which might lead to oil recovery reduction [5,6]. In the reinfiltration process, drained oil from upper blocks can be reimbibing into lower blocks through the liquid bridges and film flow across contact points between vertical blocks.…”

“…Re-infiltration is affected by capillary and gravity forces. Conversely, capillary continuity in the vertical direction between matrix blocks can improve the oil recovery [5,6].…”

“…Although gravitational and viscous effects are the main forces affecting flow in conventional porous media, gravitational and capillary forces are dominated in the fracture-matrix system. Moreover, viscous and gravitational forces can be active in fracture under a particular state, such as the foam injection process [6,8,9].…”

“…Gravitational forces drive the oil displacement in the vertical direction between matrix blocks due to capillary continuity and reinfiltration. However, the oil reinfiltration between the matrix blocks can reduce oil recovery [6]. Under gas injection, gravitational forces dominate the viscous force, and the gravitational-dominated flow regime controlling the oil drained to fractures.…”

Experimental and Modelling Study of Gravity Drainage in a Three-Block System

“…Gravity drainage modelling can be categorized as analytical (Bech et al 1991;Di Donato et al 2006;Abbasi et al 2018), numerical (Schechter and Guo 1996;Chow and Butler 1996;Saedi et al 2015;Udoh et al 2015;Dejam 2018;Rahmati and Rasaei 2019) and empirical-experimental (Li and Horne 2003;Zendehboudi et al 2011) models. Some researchers investigated the gravity drainage mechanisms in tight rocks by introducing film flow phenomena (Nenniger and Storrow 1958).…”