Experimental Study of Controlled Gravity Drainage in Fractured Porous Media

Abstract

Oil production from a fractured reservoir with a gas cap and an oil zone usually takes place at a constant withdrawal rate until gas breakthrough; thereafter, the pumping rate is influenced by the presence of gas. Knowing the effect of pumping rate on production performance before gas breakthrough and selecting optimum pumping rates are necessary. In this paper, the concept of "critical production rate" (CPR) is introduced; it is the production rate at which a porous medium has a recovery factor (RF) equal to that for higher rates before gas enters into the production well, and is also the rate above which the difference between liquid levels in the fracture and matrix remains unchanged. One may use the CPR to choose a lower pumping rate to increase RF before gas breakthrough and to aid in understanding the physics of pumping from fractured media in real cases.Flow visualization experiments were performed using rectangular unconsolidated-packed models with two fractures on the sides. Sensitivity analyses were performed on the effects of different system parameters on the CPR, the maximum possible withdrawal rate (MPWR), RF at gas breakthrough, and gas-liquid (G-L) interface behaviour in both matrix and fractures. Results show that as long as the porous medium is drained with a constant liquid withdrawal rate below CPR, the height difference between G-L interfaces in the matrix and fracture remains constant. CPR and RF can also be related to other system parameters using dimensionless numbers, such as fracture/matrix permeability ratio and Bond number.

Free fall and controlled gravity drainage processes in fractured porous media: Laboratory and modelling investigation

“…[52] However, for this case, the wettability was considered to be constant during the tests. [16,19] Given the matrix threshold pressure and by using the J-function, fracture threshold pressure was set to 100 Pa. A matrix pore size distribution index was chosen as 2, based on usual values in the literature for glass beads; this parameter for the fracture was set to 4 for proper modelling of the fluid front behaviour and capillary force in the fracture. [53] …”

“…[13][14][15] Several experimental studies for different types of gravity drainage processes were conducted in unconsolidated models. [16][17][18][19] However, accurate determination of the parameters requires mathematical modelling of this process. There are some mathematical models in the literature, [5,10,15,20] though most previously proposed models have many simplifying assumptions, because of the complexities associated with the gravity drainage process and non-linearity of the governing equations.…”

Finger Thickening during Extra-Heavy Oil Waterflooding: Simulation and Interpretation Using Pore-Scale Modelling

“…They found that the rate of finger growth was largely independent of the type of heterogeneity and that the level of bypassed oil decreased linearly with increasing dimensionless distance travelled by the front. Zendehboudi et al [6] performed an experimental study of controlled gravity drainage in fractured porous media and studied the sensitivity to several system parameters. They found that the critical production rate and recovery factor could be correlated to the fracture/matrix permeability ratio and Bond number.…”

Gravity Drainage Effects on Compositional Displacements in Fractured Reservoirs

“…They attributed this difference to variations in the experimental features such as the permeability heterogeneity at the matrix-fracture boundary (Firoozabadi and Tan 1994). Zendehboudi and Chatzis (2011) have recently conducted an experimental work to understand and investigate the interactions between capillary and gravity forces of controlled gravity drainage in NFRs. They used unconsolidated glass bead packs surrounded by two vertical fractures on the sides.…”