Determining Diffusion Coefficients for Carbon Dioxide Injection in Oil-Saturated Chalk by Use of a Constant-Volume-Diffusion Method

Abstract

Summary This paper presents a novel technique to determine multicomponent diffusion coefficients for carbon dioxide (CO2) injection in a North Sea chalk field (NSCF) in Norway at reservoir conditions. The constant-volume-diffusion (CVD) method is used, consisting of an oil-saturated-chalk core in contact with an overlying free space, which is filled with the CO2. The experimental data are matched with an equation-of-state (EOS) -based compositional model. Transport by diffusion controls the dynamics of the constant-volume system and, together with phase equilibria, allows a consistent estimation of diffusion coefficients needed to describe the observed changes in system pressure. We conduct two experiments at reservoir conditions: One uses a core plug saturated with live oil and the other with stock-tank oil (STO). Once the experiments are completed, EOS-based compositional simulation is performed to match the experimental data by use of the oil- and gas-diffusion coefficients as history-matching parameters. The modeling work is conducted with a commercial reservoir simulator by use of a 2D radial-grid model to describe the experimental setup. The experiment uses an outcrop chalk core mounted in a vertically oriented core holder. The chalk is shorter than the core holder, thus resulting in an overlying void space. The system is initially saturated with oil at reservoir conditions. CO2 is then injected from the top, forming an overlying CO2 chamber and displacing oil toward the bottom of the core holder. Once CO2 fills the overlying bulk space, the system is isolated with no further injection or production. The CO2 and oil reach and remain in equilibrium locally at the gas/oil interface throughout the test, beginning and maintaining the diffusion mechanism. Diffusion of CO2 into the oil results in a decreasing pressure, which is the main history-matching parameter. The multicomponent diffusion coefficients are found to match the model pressure/time prediction to the experimental data. This suggests the modeling work flow incorporates a representative EOS model and the main transport dynamics controlled by diffusion are being treated properly. Proper simulation of CO2 injection in fractured-chalk reservoirs requires the ability to model multicomponent diffusion accurately. The proposed CVD method provides such modeling capabilities. Our modeling and experimental work indicate the novelty of the CVD method to determine the diffusion coefficients of a system where diffusion is the dominant displacement mechanism. The fact that the oil is contained within a low-permeability-chalk sample reduces density-driven convection that could result because of nonmonotonic oil-density changes as CO2 dissolves into the oil.

Huff-n-Puff Technology for Enhanced Oil Recovery in Shale/Tight Oil Reservoirs: Progress, Gaps, and Perspectives

“…The direct upscaling strategy would be beneficial since the laboratory cores are subjected to a greater contact surface and a longer treatment period for the injected gas than may be the case in the field. Ghasemi et al 105 suggested a technique of constant volume diffusion for the CO 2 injection displacement process in the Chalk Field, North Sea. The tests performed with this methodology not only confirmed the significance of the diffusion process, but it also demonstrated that the reciprocal diffusion between gas and oil could reduce the convection influence initiated by the concentration variation.…”

The Effect of Oil Properties on the Supercritical CO2 Diffusion Coefficient under Tight Reservoir Conditions

“…Therefore, a full understanding of the behavior of CO 2 under reservoir conditions has always been one of the main interests of researchers and the petroleum industry. There are several processes involved in the CO 2 EOR, i.e., diffusion of CO 2 into the crude oil in the porous rocks [9][10][11][12][13][14][15][16][17][18][19], the chemical reaction of CO 2 with formation minerals [20,21], and rock mechanics caused by pore pressure changes [22]. Only the first process of CO 2 diffusion in porous media is considered in this study, which has theoretical importance and meaning for applications in the petroleum industry.…”

Oil Shale In Situ Production Using a Novel Flow-Heat Coupling Approach

“…According to previous research by Ghasemi et al, the average diffusivity of ethane and butane in the gas phase of stagnant tank oil and live oil is approximately 6 × 10 –5 and 6 × 10 –4 m 2 /day, respectively . Li et al and Jia et al reported that the diffusivity of CO 2 in porous media is on the order of 10 –5 m 2 /day. , Using these literature data as a reference, we tested the distance that the most mobile HCG would travel with diffusivity values of 5 × 10 –4 and 5 × 10 –3 m 2 /day.…”