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Results
Abstract The most important parameters in the calculation of the rate and extent of gas dissolution during solvent-based heavy oil recovery processes are diffusion coefficient and solubility. However, there is a lack of sufficient experimental data on these parameters. Further, significant differences associated with reported values of diffusivities because of various nonphysical approximations made in development of the models used for calculation of this coefficient from the pressure-decay tests. This paper presents an inverse solution technique for determining solubility, diffusion coefficient and interface mass transfer coefficient of gases in liquids (bitumens) using pressure-decay data. The approach, which is based on modeling the rate of pressure decline in response to gas diffusion, couples gas mass balance equation with the diffusion equation. Analytical solution for the forward problem is obtained by assigning physically meaningful initial and boundary conditions. Then, the forward solution is utilized to develop an interpretation technique for simultaneous determination of the equilibrium solubility, diffusivity and interface mass transfer coefficient of gas into oil. To evaluate the validity of the proposed technique, literature pressure-decay data of CH4 and CO2 dissolution in Athabasca bitumen at two different temperatures (50 and 90 ยฐC) and initial pressure of 8 MPa were used. The simultaneous estimation of the three mass transfer parameters is the main advantage of the new methodology over the existing ones. Additionally, the calculation method doesnโt depend on empirically-defined unknowns such as Henryโs constant, density of solvent-bitumen mixture and etc. Eventually, the effect of neglecting gas-bitumen interface resistance on the predicted values of gas solubility and diffusivity was investigated.
- North America > United States (0.46)
- North America > Canada (0.29)
Abstract Vapour Extraction (VAPEX), a process to recover heavy oil by injecting vapourized solvent into a reservoir, has been extensively studied through small-scale 1-D and 2-D laboratory tests. Recently, a series of large-scale 3-D tests have been conducted by Saskatchewan Research Council (SRC). In this study, 2-D tests were conducted under the same conditions as those for the 3-D tests; then, numerical simulation models were investigated to reduce the uncertainty in upscaling the results from 2-D tests to 3-D tests. This helps to better understand the uncertainty in predicting the field-scale VAPEX performance. Plover Lake heavy oil was used in the tests, and the sandpack permeability was about 4.4 Darcy. In each test, the initial waterflooding was conducted prior to the subsequent solvent injection. Then, a numerical model was established to simulate the 2-D test. History match of the 2-D test was conducted by tuning the uncertainties such as the relative permeability, capillary pressure, solubility, and the wall effect in sand-packing. Afterwards the tuned parameters were applied to predict the 3-D test performance. Through comparison of the predicted and experimental results in the 3-D test, the capability of predicting up-scaled VAPEX processes through numerical simulation was examined, and the differences between physical and numerical modeling were identified. The results show that the waterflooding performance can be successfully predicted, whereas the uncertainty in upscaling the VAPEX process is large. In the waterflooding period, the predicted oil recovery factor was 25.78% compared with 23.4% in the 3-D test. In the VAPEX process, the difference between the predicted and measured oil recovery factors was in the range of 0.75โ25.14%, depending on the different combination of uncertain parameters. This fact indicates that different scales of physical modeling are required in order to reduce the uncertainties in predicting the field-scale VAPEX performance.
- North America > United States (0.68)
- North America > Canada > Saskatchewan (0.24)
- North America > Canada > Alberta (0.16)
Abstract The dissolution of gas in both water and bitumen as a mechanism contributing to gas production in SAGD is studied. The contribution of this mechanism to the production of gas in SAGD is evaluated through the implementation of appropriate thermodynamic models into a series of numerical simulations in order to more accurately represent the physics of gas behavior inside the SAGD chamber. Methane, carbon dioxide and hydrogen sulphide are considered. It is observed from the numerical simulation results that the production of a gas in SAGD is directly proportional to the solubility of that gas in the liquid phases being produced. Additionally, these results lead to the conclusion that gas dissolution is an important mechanism in gas production. Results from this study also confirm the findings observed by other researchers that gas will accumulate at the front and top of the SAGD chamber, thus reducing SOR and oil production rates. The degree of such accumulation of gas depends, among other operational and reservoir conditions, on the solubility of that gas in the liquid phases under the temperature and pressure conditions inside the steam chamber.
Abstract Many authors have published effects of Non Condensable Gas (NCG) injection during steam assisted gravity drainage (SAGD) operation, on one hand it provides an insulation blanket to the steam chamber and avoids heat loss to the over burden and improves the economics of the project, but on the other hand it can stall the steam chamber growth in the middle of high pay zone, provided the reservoir has high solution gas. All the commercial simulators predict the accumulation of the gas blanket ahead of steam front. However, field operations have proved that the NCG are produced along with bitumen and water and doesn't accumulate, but simulators are unable to predict the right amount when it comes to history matching and accurate predictions. This paper is focused on numerically findings of the gas transport mechanism in the SAGD operations. Many possible mechanisms were considered and found that most of the commercial simulators lack the function of gas production due to viscous liquid drag, which contributes a lot towards gas production especially during early years of SAGD. Solubility exclusion of the two major NCG i.e. CO2 and CH4 in both water and oil phases is another reason for under-estimating the gas production. Along with the above two mechanisms, interestingly, the constraints on the production wells in the simulators also account for a great deal of NCG production. Now instead of using a fraction of GOR, simulation engineers can include the complete GOR of the Alberta bitumen reservoirs to history match and predict the correct amount of bitumen and gas production.