Effect of Matrix Wettability CO2 Assisted Gas-oil Garvity Drainage in Naturally Fractured Reservoirs

Abstract

SUMMARYThe wettability behavior of the matrix block is one of the major factors controlling the effectiveness of the employed EOR methods in NFRs. Water injection in NFRs with mixed-wet or effectively oil-wet matrix blocks usually results in low oil recoveries. In this case, gas injection is considered to be an alternative process, where the process benefits from the gravity forces and the process is called gas-oil gravity drainage. In this study, the effect of matrix wettability on the efficiency of gravity drainage by CO2 injection is addressed. Laboratory experiments and numerical simulation were performed to analyze the process under different wettability conditions of the matrix. It is concluded that for a system with an effectively oil-wet matrix, water is the most non-wetting phase while CO2 is the intermediate-wetting phase. In the three phase setting, which includes carbon dioxide, this is considered favorable for oil production. However, with a strongly water-wet matrix, CO2 is always the least wetting phase. For this condition, it turns out that when water is displaced by the gravity drainage process part of the oil is also produced. It is observed that higher oil recoveries are achieved by CO2 injection in an oil-wet matrix block.

Review of studies on pore-network modeling of wettability effects on waterflood oil recovery

“…In gas assisted gravity drainage (GAGD) oil recovery is influenced by reservoir rock and fluid specific properties, such as heterogeneity of the formation, wettability, oil and gas density, oil and gas viscosity, viscous force, capillary force, gravity, gas injection rate, and gas-oil miscibility or interfacial tension (Catalan et al, 1994;Caubit et al, 2004;Parsaei and Chatzis, 2011;Wu et al, 2013;Ameri et al, 2015;Khorshidian et al, 2017) Parsaei and Chatzis (2011) through a systematic experimental study investigated the impact of reservoir wettability variations at the macroscopic scale on oil recovery efficiency in gravity-assisted inert gas injection (GAIGI) process for tertiary recovery of residual oil by waterflooding. Obtained experimental results showed that for a positive oil-spreading coefficient, the continuity of water-wet portions of the heterogeneous porous medium favors the tertiary oil recovery through the film flow mechanism.…”

“…In addition, owing to the high waterflood residual oil content of the heterogeneous media tested, the oil bank formation occurred much earlier and grew faster, resulting in a higher oil recovery factor. Also, Ameri et al (2015) carried out laboratory experiments and numerical simulation to study the effect of matrix wettability on the efficiency of gravity drainage by gas (CO 2 ) injection. They concluded that for a system with an effectively oil-wet matrix, water is the most non-wetting phase while CO 2 is the intermediate-wetting phase.…”