Browsing by Subject "Gas flooding"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Advances in calculation of minimum miscibility pressure(2011-05) Ahmadi Rahmataba, Kaveh; Johns, Russell T.; Bryant, Steven L.; DiCarlo, David; Dindoruk, Birol; Sepehrnoori, KamyMinimum miscibility pressure (MMP) is a key parameter in the design of gas flooding. There are experimental and computational methods to determine MMP. Computational methods are fast and convenient alternatives to otherwise slow and expensive experimental procedures. This research focuses on the computational aspects of MMP estimation. It investigates the shortcomings of the current computational models and offers ways to improve the robustness of MMP estimation. First, we develop a new mixing cell method of estimating MMP that, unlike previous "mixing cell" methods, uses a variable number of cells and is independent of gas-oil ratio, volume of the cells, excess oil volumes, and the amount of gas injected. The new method relies entirely on robust P-T flash calculations using any cubic equation-of-state (EOS). We show that mixing cell MMPs are comparable with those of other analytical and experimental methods, and that our mixing cell method finds all the key tie lines predicted by MOC; however, the method proved to be more robust and reliable than current analytical methods. Second, we identify a number of problems with analytical methods of MMP estimation, and demonstrate them using real oil characterization examples. We show that the current MOC results, which assume that shocks exist from one key tie line to the next may not be reliable and may lead to large errors in MMP estimation. In such cases, the key tie lines determined using the MOC method do not control miscibility, likely as a result of the onset of L₁-L₂-V behavior. We explain the problem with a simplified pseudo-ternary model and offer a procedure for determining when an error exists and for improving the results. Finally, we present a simple mathematical model for predicting the MMP of contaminated gas. Injection-gas compositions often vary during the life of a gasflood because of reinjection and mixing of fluids in situ. Determining the MMP by slim-tube or other methods for each possible variation in the gas-mixture composition is impractical. Our method gives an easy and accurate way to determine impure CO₂ MMPs for variable field solvent compositions on the basis of just a few MMPs. Alternatively, the approach could be used to estimate the enrichment level required to lower the MMP to a desired pressure.Item Development of a four-phase flow simulator to model hybrid gas/chemical EOR processes(2015-05) Lotfollahi Sohi, Mohammad; Pope, Gary A.; Delshad, Mojdeh; Sepehrnoori, Kamy; Mohanty , Kishore K; Johnston, Keith PHybrid gas/chemical Enhanced Oil Recovery (EOR) methods are such novel techniques to increase oil production and oil recovery efficiency. Gas flooding using carbon dioxide, nitrogen, flue gas, and enriched natural gas produce more oil from the reservoirs by channeling gas into previously by-passed areas. Surfactant flooding can recover trapped oil by reducing the interfacial tension between oil and water phases. Hybrid gas/chemical EOR methods benefit from using both chemical and gas flooding. In hybrid gas/chemical EOR processes, surfactant solution is injected with gas during low-tension-gas or foam flooding. Polymer solution can also be injected alternatively with gas to improve the gas volumetric sweep efficiency. Most fundamentally, wide applications of hybrid gas/chemical processes are limited due to uncertainties in reservoir characterization and heterogeneity, due to the lack of understanding of the process and consequently lack of a predictive reservoir simulator to mechanistically model the process. Without a reliable simulator, built on mechanisms determined in the laboratory, promising field candidates cannot be identified in advance nor can process performance be optimized. In this research, UTCHEM was modified to model four-phase water, oil, microemulsion, and gas phases to simulate and interpret chemical EOR processes including free and/or solution gas. We coupled the black-oil model for water/oil/gas equilibrium with microemulsion phase behavior model through a new approach. Four-phase fluid properties, relative permeability, and capillary pressure were developed and implemented. The mass conservation equation was solved for total volumetric concentration of each component at standard conditions and pressure equation was derived for both saturated and undersaturated PVT conditions. To model foam flow in porous media, comprehensive research was performed comparing capabilities and limitations of implicit texture (IT) and population-balance (PB) foam models. Dimensionless foam bubble density was defined in IT models to derive explicitly the foam-coalescence-rate function in these models. Results showed that each of the IT models examined was equivalent to the LE formulation of a population-balance model with a lamella-destruction function that increased abruptly in the vicinity of the limiting capillary pressure, as in current population-balance models. Foam models were incorporated in UTCHEM to model low-tension-gas and foam flow processes in laboratory and field scales. The modified UTCEM reservoir simulator was used to history match published low-tension-gas and foam coreflood experiments. The simulations were also extended to model and evaluate hybrid gas/chemical EOR methods in field scales. Simulation results indicated a well-designed low-tension-gas flooding has the potential to recover the trapped oil where foam provides mobility control during surfactant and surfactant-alkaline flooding in reservoirs with very low permeability.Item Evaluation of EOR Potential by Gas and Water Flooding in Shale Oil Reservoirs(2013-05) Chen, Ke; Sheng, James; Menouar, Habib K.; Heinze, Lloyd R.The demand for oil and natural gas will continue to increase for the foreseeable future; unconventional resources such as tight oil, shale gas, shale oil will pose an irreplaceable role in oil and gas industry to fill the gap between demand and supply. With the relatively modest natural gas price, producing oil from unconventional shale reservoirs, which are less common and less well understood than conventional sandstone and carbonate reservoirs, has attracted more and more interest from oil operators. Through many tremendous efforts on the development of shale resources, the horizontal well-drilling with multiple transverse fractures has proven to be an effective method for shale gas reservoirs exploitation and it has also been used in extracting oil from shale reservoirs by some operators. However, the oil recovery is very low (5-10%). For the important role of shale resources in future oil and gas industry, more stimulation and production strategies must be considered and tested to find better methods to improve oil production from shale reservoirs. Gas flooding and water flooding, relatively simple and cheaper EOR techniques, which have been successfully implemented in conventional and some unconventional tight oil reservoirs for a long time, are considered in our work. A black-oil simulator developed by Computer Modeling Group Ltd was selected in our work. We build a reservoir model of 200ft long, 1000ft wide and 200 ft thick two 1-ft wide ×1000-ft long hydraulic fractures to simulate gas flooding and water flooding in shale oil reservoirs. We first validate a base model, and discussed the determination of miscibility parameter and injection pressure. Production behavior and oil recovery of different plans are discussed through sensitivity studies. Simulation results of primary production, gas injection and water injection are compared in this thesis. Results show that miscible gas injection has better effect on improving oil recovery from shale reservoirs than water injection. Solvent injected into the reservoirs above MMP can be fully miscible with oil, reducing oil viscosity greatly, and can lead a better sweep efficiency besides pressure maintenance. Our simulation results indicate that the oil recovery can be increased up to 15.1% by using gas injection in a hydraulically fractured shale reservoir, compared with the original 6.5% recovery from the primary depletion. This thesis provides a preliminary analysis to regarding the EOR potentials by gas and water flooding in shale oil reservoirs. The results show that miscible gas flooding could be a good prospect in future development of shale oil resources.