Estimation of concentration-dependent diffusion coefficient in pressure-decay experiment of heavy oils and bitumen

2011 ◽  
Vol 305 (2) ◽  
pp. 132-144 ◽  
Author(s):  
Seyyed M. Ghaderi ◽  
S. Hamed Tabatabaie ◽  
Hassan Hassanzadeh ◽  
Mehran Pooladi-Darvish
Keyword(s):  
Diffusion Coefficient ◽  
Heavy Oils ◽  
Pressure Decay

Estimation of Solubility and Diffusivity of Gases in Heavy Oils by Use of Late-Time Pressure-Decay Data: An Analytical/Graphical Approach

SPE Journal ◽  
2015 ◽  
Vol 20 (04) ◽  
pp. 717-728 ◽  
Author(s):  
Francisco J. Pacheco-Roman ◽  
S. Hossein Hejazi
Keyword(s):  
Diffusion Coefficient ◽  
Gas Phase ◽  
Time Pressure ◽  
Early Time ◽  
Late Time ◽  
Heavy Oils ◽  
Time Data ◽  
Henry's Constant ◽  
Pressure Decay ◽  
Phase Pressure

Summary Solubility and diffusivity of gases in heavy oils, quantified by Henry's constant (Hij) and the diffusion coefficient (D), respectively, are essential properties for the design of recovery processes that require the injection of gas or vapor solvents into the reservoir. Data, obtained from various experimental procedures such as the pressure-decay technique (PDT), are used to estimate these two parameters. The PDT uses a pressure/volume/temperature (PVT) cell where the gas-phase pressure declines as gas diffuses into heavy oil following an early- and a late-time regime. Current approaches to analyze data from the conventional PDT are either graphical techniques based on early-time data or full numerical simulation. Early-time data, when the diffusing gas has not reached the bottom of the PVT cell, do not provide enough information to simultaneously estimate both the diffusion coefficient and Henry's constant. Hence, existing graphical procedures are limited to diffusion-coefficient estimation. In this paper, we propose a novel graphical technique to estimate the diffusion coefficient and Henry's constant by use of the late-time data from pressure-decay experiments. Our method is derived from the modeling of gas-phase pressure decay by use of Fick's second law and gas-phase mass-balance equations. We use the integral method to provide an approximate analytical solution to the set of equations. In addition, by use of the resultant solution, we develop a simple graphical method to directly estimate both the diffusion coefficient and Henry's constant. The estimated parameters through the proposed technique for methane/bitumen and carbon dioxide/bitumen experiments are in close agreement with those reported in the literature.

A Power-Law Mixing Rule for Predicting Apparent Diffusion Coefficients of Binary Gas Mixtures in Heavy Oil

2017 ◽  
Vol 140 (5) ◽  
Author(s):  
Hyun Woong Jang ◽  
Daoyong Yang ◽  
Huazhou Li
Keyword(s):  
Diffusion Coefficient ◽  
Apparent Diffusion Coefficient ◽  
Heavy Oil ◽  
Diffusion Coefficients ◽  
Gas Mixtures ◽  
Gas Diffusion ◽  
Gas Mixture ◽  
Mixing Rule ◽  
Heavy Oils ◽  
Apparent Diffusion

A power-law mixing rule has been developed to determine apparent diffusion coefficient of a binary gas mixture on the basis of molecular diffusion coefficients for pure gases in heavy oil. Diffusion coefficient of a pure gas under different pressures and different temperatures is predicted on the basis of the Hayduk and Cheng's equation incorporating the principle of corresponding states for one-dimensional gas diffusion in heavy oil such as the diffusion in a pressure–volume–temperature (PVT) cell. Meanwhile, a specific surface area term is added to the generated equation for three-dimensional gas diffusion in heavy oil such as the diffusion in a pendant drop. In this study, the newly developed correlations are used to reproduce the measured diffusion coefficients for pure gases diffusing in three different heavy oils, i.e., two Lloydminster heavy oils and a Cactus Lake heavy oil. Then, such predicted pure gas diffusion coefficients are adjusted based on reduced pressure, reduced temperature, and equilibrium ratio to determine apparent diffusion coefficient for a gas mixture in heavy oil, where the equilibrium ratios for hydrocarbon gases and CO2 are determined by using the equilibrium ratio charts and Standing's equations, respectively. It has been found for various gas mixtures in two different Lloydminster heavy oils that the newly developed empirical mixing rule is able to reproduce the apparent diffusion coefficient for binary gas mixtures in heavy oil with a good accuracy. For the pure gas diffusion in heavy oil, the absolute average relative deviations (AARDs) for diffusion systems with two different Lloydminster heavy oils and a Cactus Lake heavy oil are calculated to be 2.54%, 14.79%, and 6.36%, respectively. Meanwhile, for the binary gas mixture diffusion in heavy oil, the AARDs for diffusion systems with two different Lloydminster heavy oils are found to be 3.56% and 6.86%, respectively.

Suggesting a numerical pressure-decay method for determining CO2 diffusion coefficient in water

2015 ◽  
Vol 211 ◽  
pp. 31-39 ◽  
Author(s):  
Yasin Gholami ◽  
Reza Azin ◽  
Rouhollah Fatehi ◽  
Shahriar Osfouri
Keyword(s):  
Diffusion Coefficient ◽  
Pressure Decay ◽  
Co2 Diffusion

scholarly journals Measurement of CO2 diffusion coefficients in both bulk liquids and carven filling porous media of fractured-vuggy carbonate reservoirs at 50 MPa and 393 K

RSC Advances ◽  
2021 ◽  
Vol 11 (32) ◽  
pp. 19712-19722
Author(s):  
Zhixing Wang ◽  
Jirui Hou
Keyword(s):  
Porous Media ◽  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Carbonate Reservoirs ◽  
Pressure Decay ◽  
Co2 Diffusion

Herein, the pressure decay method was improved to obtain the CO2 diffusion coefficient in fractured-vuggy carbonate reservoirs at 393 K and 50 MPa and obtained good correlation results between bulk and porous media by porosity and tortuosity.

Measurement of Gas Diffusivity in Heavy Oils and Bitumens by Use of Pressure-Decay Test and Establishment of Minimum Time Criteria for Experiments

SPE Journal ◽  
2015 ◽  
Vol 20 (05) ◽  
pp. 1167-1180 ◽  
Author(s):  
Ram R. Ratnakar ◽  
Birol Dindoruk
Keyword(s):  
Oil Recovery ◽  
Accurate Determination ◽  
Experimental Studies ◽  
Gas Solubility ◽  
Heavy Oils ◽  
Gas Oil ◽  
Pressure Decay ◽  
Molecular Diffusivity ◽  
Decay Test ◽  
Long Time

Summary Molecular diffusion plays a very important role in various reservoir processes, especially in the oil-recovery processes where convective forces are not dominant or when direct frontal contact and mixing are not possible. For example, in heavy-oil and bitumen recovery, injected light hydrocarbons can diffuse into the oil beyond the potential fronts and/or convective zones and promote the effectiveness of the displacement process, reducing in-situ viscosities and in turn enhancing the oil recovery. Similarly, diffusive mixing can also be a dominant mechanism in the gas-redissolution process, even in lighter-hydrocarbon systems. For example, it controls how much gas will be dissolved in oil and how long it will take to dissolve, in the absence of mechanical/convective mixing, as in the case of reservoir repressurization. The extent of dissolution of a gas into oil is governed by its solubility, but the rate is controlled by both molecular diffusivity and solubility. Thus, accurate determination of these parameters is essential to design and understand displacement processes. Despite the significance of diffusion in various aspects of oil recovery, there are very few experimental studies available in the literature addressing the diffusion of gas in heavy oils. Experimental work is most commonly based on the pressure-decay concept. However, the parameter inversion in these tests relies on an error-function solution that neglects the transient processes at the gas/oil interface and assumes constant-saturation concentration. This assumption is not appropriate when decay in pressure is large because pressure in the gas cap changes continuously as gas is dissolved in the oil, and hence the gas solubility varies with time. One of the major issues related to this experimental process is that it takes a long time (order of several days to several months) to achieve steady-state (converged) solution to determine diffusivity. In this work, we have Experimentally investigated the diffusion of methane in heavy oils as well as light oils by use of a pressure-decay test Captured properly the variation in gas concentration in oil at the gas/oil interface with time by expressing gas solubility in terms of Henry's constant in the mathematical model Developed the exact solution of the 1D pressure-decay (transient-diffusion) model with pressure-dependent gas/oil-interface concentration and shown that after a long time, pressure decays exponentially in time with an exponent that depends on diffusivity as well as solubility Presented the inversion technique to determine the diffusivity and other parameters from late-transient-pressure data, and shown the convergence in their estimates (Most importantly) developed a cutoff criterion permitting us to stop the experiments while still being able to extract the converged diffusivity values (this is important in situations when the experiment is stopped prematurely for technical or other reasons)

Determination of Individual Diffusion Coefficients of Solvent/CO2 Mixture in Heavy Oil With Pressure-Decay Method

SPE Journal ◽  
2016 ◽  
Vol 21 (01) ◽  
pp. 131-143 ◽  
Author(s):  
Huazhou Li ◽  
Daoyong Yang
Keyword(s):  
Diffusion Coefficient ◽  
Gas Phase ◽  
Diffusion Model ◽  
Heavy Oil ◽  
Molecular Diffusion ◽  
Composition Analysis ◽  
Composition Change ◽  
Molecular Diffusion Coefficient ◽  
Pressure Decay ◽  
The Individual

Summary A novel methodology was developed to determine the molecular-diffusion coefficient for each component of the solvent/CO2 mixture in heavy oil under reservoir conditions on the basis of the pressure-decay theory. Experimentally, molecular-diffusion tests for the solvent/CO2/heavy-oil systems (i.e., pure-CO2/heavy-oil system, C3H8/CO2/heavy-oil system, and n-C4H10/CO2/heavy-oil system) are performed with a DBR pressure/volume/temperature system at constant temperature and decayed pressure. Theoretically, the Peng-Robinson equation of state combined with a 1D diffusion model is developed to describe the diffusion process of solvent/CO2 mixture in heavy oil. The composition analysis in the beginning and the end of pressure-decay experiments for the solvent/CO2/heavy-oil system indicate that the gas-phase solvent fraction decreases as diffusion proceeds, whereas the gas-phase CO2 fraction increases during the tests. One can determine the individual molecular-diffusion coefficient for each component in the mixture by minimizing the discrepancy between the measured composition change and the calculated composition change with the diffusion model. The newly developed methodology is successfully validated with the diffusion tests on the two solvent/CO2 mixtures: C3H8/CO2/heavy-oil system and n-C4H10/CO2/heavy-oil system. As for the solvent/CO2 mixtures tested, the molecular-diffusion coefficient of solvent in heavy oil is found to be significantly larger than that of CO2 in heavy oil. At similar test conditions, the C3H8/CO2/heavy-oil system ends up with a swelling factor of 1.058 after 168 hours of diffusion test, in comparison to 1.031 for the CO2/heavy-oil system.

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