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Abstract Chemical flooding methods hold particular attraction for recovering the "residual oil" left in the reservoir after waterflooding. This paper describes and compares the results for two promising methods, viz. micellar flooding and alkaline-surfactant-polymer (ASP) flooding processes. Both of these methods have been tested successfully in the field, notably micellar flooding. Laboratory results are described for micellar floods in consolidated sandstone cores as well as in unconsolidated sand packs, including a two-dimensional model, equipped with horizontal or vertical wells. Floods were also carried out in unconsolidated cores using combinations of an alkali, surfactant and a polymer. Individual slugs were injected sequentially in some of the experiments, while the three components were mixed and injected as a single slug in other experiments. Oil recoveries in the two cases were similar. Results for the two processes are compared and contrasted, showing that on the basis of oil volume recovered per unit mass of the chemical used, the two processes are similar, with micellar flooding having an edge. However, on the basis of total oil recovery micellar flooding is the superior process, with oil recoveries ranging from 50 to 80% of the oil left in the porous medium after a waterflood. Practical implications of the results are discussed. Introduction Among chemical flooding methods, micellar flooding and alkaline-surfactant-polymer (ASP) flooding processes are particularly effective for recovering a large fraction of the conventional oil (25 °API, or higher) left in the reservoir after a waterflood - which could be as much as 60% of the original oil in place. Many field tests of the micellar flooding process and several of ASP have established the effectiveness of these methods for mobilizing waterflood residual oil. The present laboratory study compares and contrasts the two processes, based on tertiary floods in sand packs and Berea sandstone cores. A number of investigators have noted the use of an alkali for reducing the divalent ion content and increasing the negative charge of the rock with a view to reducing chemical loss. Surkalo reported the alkaline-surfactant- polymer (ASP) process as an alternative to micellar flooding. Several field tests have also been reported. THE PROCESS Chemical flooding methods are based on improving the mobility ratio, i.e. making the mobility of the displacing flood less than or equal to the mobility of the displaced fluid, and increasing the capillary number, mainly by making the interfacial tension (IFT) between the displacing and the displaced phases as small as possible. Other effects are also present, such as formation of macro- and microemulsions, formation of precipitates, wettability changes, relative permeability shifts, etc. Macroemulsions may improve mobility ratio through drop entrainment and entrapment. At the same time, surfactant adsorption occurs on the rock surface. This is the principal limitation of most chemical flooding methods. The micellar and ASP processes address this problem somewhat differently. A brief description follows. ALKALINE-SURFACTANT-POLYMER (ASP) FLOODING This process is a combination of the three processes, viz. alkaline, surfactant and polymer flooding, in that three slugs are used in a sequence.
- North America > Canada > Alberta (0.29)
- North America > United States > West Virginia (0.25)
- North America > United States > Pennsylvania (0.25)
- (2 more...)
Abstract Design of micellar floods is largely based on laboratory experiments, which are usually un-scaled. This paper describes scaling criteria for the process, derived from the basic flow equations, using Dimensional Analysis and Inspectional Analysis. The derivations are based on three phase (oleic, emulsion. and aqueous), six-component (oil, water, surfactant, polymer, monovalent ion, and divalent ion) flow in a porous medium. The general scaling criteria were simplified for core floods, and verified by micellar floods in scaled models. Model and prototype were geometrically scaled Berea cores. Prototype performance was predicted using the model results and compared with the actual prototype results. Good agreement was obtained in most cases between the actual and predicted oil production histories, showing the validity of the scale-up. The scaling criteria derived can be used for designing a micellar flood. Implications of partial scaling are discussed for field applications. Introduction Micellar flooding process is one of the proven chemical recovery methods for the tertiary recovery of light oils. The process consists in injecting a micellar solution slug (5–10% rock pore volume) and a polymer buffer (40–50% pore volume), followed by continuous injection of water (drive water). Micellar solutions are surfactant stabilized oil-water micro emulsions. Often, they also contain co-surfactants, such as alcohols, for viscosity control, and salts to improve solution properties. Micellar solutions are effective in increasing the Capillary Number, which is crucial for the mobilization and recovery of tertiary oil. Polymer buffer, usually a dilute polymer solution (about 500 ppm), provides mobility control behind the displacement front so that most of the residual oil is mobilized and banked before the drive water dissipates the micellar slug. The process has been evaluated in thirty field tests and was found to be technically successful, having a process efficiency (oil recovered-to-slug volume ratio) of 3–4. Recently, Thomas et al. showed that process efficiency can be improved to 12–15 through the use of multiple slugs and graded slugs instead of a single micellar slug. Economics of the process remain unattractive, mainly due to the cost of chemicals and the initial expense in the development of the process for a particular field, as well as low oil prices (< $20/bbl). Chemicals that is better adapted to reservoir conditions, and laboratory studies representative of field conditions will improve the economic feasibility of the process. Laboratory results based on scaled model experiments will reduce the risk in extending them to field. Scaling criteria derived for the process were discussed in a previous paper. MATHEMATICAL MODEL The micellar flooding process can be described mathematically for simplified situations, e.g. considering the oil (o) to be one component, surfactant (s) another, and water (w), polymer (p), monovalent ions (m), and divalent ions (d) similarly single components. The concentration of a particular component in a given phase is expressed as a mass fraction phase, component. Diffusion and dispersion is assumed to occur in the case of surfactant (s), polymer (p), monovalentions (m), and divalent ions (d). It is assumed that the coordinate axes are oriented in the direction of flow.
- North America > Canada > Alberta (0.31)
- North America > United States > Texas > Clay County (0.24)
Abstract The importance and application of emulsions in the oil recovery has received considerable attention. This is a first attempt to simulate macro emulsion flooding performance compositionally by including the physical property changes that occur simultaneously during multiphase displacement. Since emulsion flooding is a complex EOR process involving several mechanisms that occur at the same time during displacement, simulation of oil recovery by emulsion flooding requires an understanding of the flow mechanics of emulsions in porous media. With this end in view, the present study was carried out to achieve a better mechanistic understanding of emulsion flow and its mathematical representation. In the first phase of this research, the physical mechanisms were observed during stable emulsion flow in a porous medium. Particularly, emulsion rheology and droplet capture for the system of comparable drop and pore sizes were investigated comprehensively. These mechanisms, namely emulsion rheology, droplet capture, and surfactant adsorption, were then represented mathematically and incorporated into a one-dimensional, three-phase (oleic, aqueous, and emulsion) mathematical model which accounted for interactions of surfactant, oil, water, and the rock matrix. The simulator was validated by comparing the simulation results with the results from linear core floods performed in the laboratory. The comparison was made using different physical property models and testing various mechanisms to determine which combination best followed the core flood observations and measurements. It was found that a multiphase non-Newtonian rheological model of an emulsion with interfacial tension-dependent relative permeabilities and time-dependent capture gave the best match of the experimental corefloods. Introduction Since emulsions play an important role in many EOR processes, attempts have been made to simulate these processes with increasingly complex compositional simulators. These require a detailed understanding of the mechanisms involved during the displacement process. Therefore, there is a need to understand the physics controlling the flow of an emulsion in a porous medium. However, very little research has been carried out in the area of the flow mechanics of emulsions in porous media. Additionally, emulsion rheology and drop capture have been investigated separately for certain conditions. These conditions restrict the model to specific applications. This leads to the question of how emulsion transport occurs in a porous medium in the case where emulsion drop size and the pore size are comparable, which is often the case. Therefore, the present study investigates these subjects to achieve a better mechanistic understanding of emulsion flow and its mathematical representation. This will provide information that can be applied in any EOR process involving emulsion flow. EXPERIMENTAL WORK Physical Mechanism Observations A number of experimental core floods were conducted in this study to observe the physical mechanisms that occurred during stable emulsion flow in a porous medium. These are described in Ref. 1. The observations found from this study can be summarized as follows:Observations were made of the rheological behavior of the caustic and surfactant emulsions for the system of comparable drop to pore size for both Berea sandstones and Ottawa sand packs. Rheological similarities were seen when the emulsions flowed in porous media and in a viscometer with slight differences probably due to an interaction between drops and pores.
- North America > Canada > Alberta (0.31)
- North America > United States > West Virginia (0.25)
- North America > United States > Pennsylvania (0.25)
- (2 more...)
Abstract A novel steam-CO2 combination flooding process for oil recovery hasbeen investigated systematically using a specially designed experimentalsystem. Numerous experiments have been performed using both non-fractured and fracturedsandstone cores. The experimental results from non-fractured and fracturedsandstone cores are very encouraging. The oil recovery increased as much as 20%for non-fractured cores and 18% for fractured cores of original oil in place bysteam-CO2 process compared to steam-alone process. In addition to the effects of injection temperature and injection rates on oilrecovery and irreducible oil saturation, the ratio of steam overCO2, a dimensionless number, was found to dominate the oil recoveryprocess. In non-fractured sandstone cores, there exists an optimum ratio ofsteam over CO2 which yields a maximum oil recovery with the lowestirreducible oil saturation. The ratio does not depend on injection temperatureand injection rates. In fractured cores, there still exits an optimumsteam-CO2 ratio which yields a maximum oil recovery with lowestirreducible oil saturation. However, it depends on injection temperature. The theory to explain this novel steam-CO2 flooding process stillneeds further study, some fundamental mechanisms which contribute to theprocess have been investigated in our research. Introduction Naturally fractured carbonate reservoirs represent a unique target for theapplication of enhanced oil recovery (EOR) technology. High divalent ionconcentrations in reservoir water and extensive fracture networks discouragethe use of chemical and miscible processes with possible exception of miscible CO2. Because of channeling of injected air, in-situ combustion wouldbe difficult to sustain. For non-fractured eservoirs steam floodingis a proven and commercially process for oil recovery (especially heavy oil).Its recovery mechanisms are so well identified that design and operation ofthese methods are successfully implemented. The state of understanding andtechnology is quite controversial in case of using the process for fracturedreservoirs. Recently, at the University of Wyoming laboratory studies of this littleexplored research area of steam flooding in fractured reservoirs with thepurpose of understanding the basic mechanisms that control the recoveryprocesses were performed, , , .The results obtained from these studies have been very encouraging n terms ofanswering the questions about the important process mechanisms controlling therecovery oil from fractured sandstone cores. For homogeneous (non-fractured) reservoirs, laboratory studies and fieldreports, , , , ,, indicated that the use of certain additives(carbon dioxide nitrogen, flue gases, caustic, etc.) with steam could resultin improvement in oil recovery. These observations lead us to believe that theeffects of additives to steam flooding of fractured reservoirs would be veryuseful investigations for improving the success of steam flooding processes infractured reservoirs. The existing steam flooding system was combined with facilities of injectingadditives (CO2Nitrogen, etc.), By using this new experimentalapparatus, numerous experiments were performed both in the non-fractured andfractured sandstone cores. This paper summarizes the related research and fieldtest results. The experimental details as well as the results ofsteam-CO2 flooding in fractured
- North America > Canada (0.31)
- North America > United States > Wyoming (0.26)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.70)
- Geology > Petroleum Play Type > Unconventional Play (0.56)
- Well Drilling > Drilling Operations > Coring, fishing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Carbonate reservoirs (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery (1.00)
Abstract Oil recovery from depleted light oil reservoirs (after a waterflood, with overone-half of the oil still in place) requires a large increase in the drivingfluid capillary number and a decrease in its mobility. These often conflictingrequirements are approached in a number of oil recovery methods, three of which- micellar, surfactant and caustic flooding techniques - are discussed in thispaper, in the light of the authors' laboratory experiments. Under optimalconditions, a 5% pore volume slug of micellar solution can recover as much as90% of the residual oil left after a waterflood. Surfactant floods are aboutone-half as effective, and caustic floods tend to be still less effective. Theproblem of scale-up to field conditions has to be faced also. The paper considers the three processes and the governing capillary number and mobility ratio variations. Related processes arementioned also. Each process involves complex interactions leading to changingdisplacement regimes. Experimental data obtained on consolidated sandstone cores is discussed, presented in a form where the essential features of the three processes can becompared. Two Alberta crude oils were tested in such cores under similar conditions. Oilrecovery, chemical consumption and process efficiency were evaluated for eachcase. Introduction In most light oil reservoirs, over one-half of the oil originally in placeremains unrecovered even after a waterflood. Some of this oil may be recoveredby an appropriate enhanced oil recovery (EOR) method, such as chemicalflooding, miscible displacement, or carbon dioxide flooding. In rarecircumstances, even thermal methods may be applicable, although they are bettersuited for heavy oils. Chemical methods have great promise for the future inthe context of light oils. This paper looks at two such methods. Chemical EOR methods have been the subject of many laboratory studies and fieldtests and include such methods as polymer, surfactant, micellar, emulsion, andalkaline looding techniques and their combinations. Although many field testshave been carried out, chemical floods have not performed as wellin the field as in the laboratory, partly because the experiments are usuallyunscaled. Scaling criteria for chemical floods have been obtained, but are difficult to satisfy; consequently, laboratory results. such as oilrecovery vs. pore volumes injected, are not directly applicable to fieldsituations. The extent of reliability of laboratory data for field use dependson the process under consideration. Our experience shows that laboratoryresults for micellar flooding are more indicative of field performance thanthose for caustic or surfactant floods, where the injected chemicals are lostto the rock and fluids in many ways, and are the principal cause of the lack ofsuccess in the field. Displacement Efficiency The microscopic efficiency of oil displacement within the pores of a rockdepends on mobility ratio and the capillary number which vary with time at anypoint during a chemical flood. Other factors may be present also, such as phasetransitions. Mobility ratio, M, is usually defined as the mobility ?ing (=k/ µ, where k is effective permeability and µ is viscosity) of the displacing fluiddivided by the mobility ?ed of the displaced fluid (assumed to beoil in this discussion).
Abstract Typically, when an oil reservoir becomes uneconomic to produce -- after primary and secondary methods have been exhausted -- over two-thirds of the original oil is still in the reservoir. Many chemically based oil recovery methods have been proposed and tested in the laboratory and field. Indeed, chemical oil recovery methods offer a real challenge in view of their success in the laboratory and lack of success in the field. This paper examines this question, looking at the field test results for selected chemical oil recovery methods, and comparing them with laboratory response. The answer lies in the inadequacy of laboratory experiments on one hand, and the very limited knowledge of the reservoir characteristics on the other. Field test performances of polymer, alkaline, and micellar flooding methods are examined for nearly 50 field tests, results for which are tabulated. The oil recovery performance of micellar floods is the highest, followed by polymer floods. Alkaline floods have been largely unsuccessful. The reasons underlying success or failure are examined, and research needs for the future are outlined. Introduction Over two-thirds of the original oil is left unrecovered in a typical oil reservoir when it reaches economic limit (i.e. after primary and secondary -- waterflood -- recovery). Many methods - often called "tertiary recovery" -- have been proposed for recovering this "unrecoverable" oil. The class of "chemical methods" is of particular interest, because it largely permits the use existing oilfield equipment and facilities. The interest in tertiary oil recovery, and particularly the field activity, rises and falls with the prospect of increasing or decreasing oil prices, and also with the perceived foreign oil supply situation and government incentives. Thus economics dominate much of the oil recovery activity reflected by the extensive field project surveys published by the Oil & Gas Journal every two years (Moritis ). The large number of field projects for a given method does not necessarily mean that the method is technically successful. Similarly, very few field tests of a particular process do not imply that the process is technically ineffective. Figure 1 shows a plot of the number of chemical flooding field projects by year, while Fig. 2 shows the total daily oil production for the projects. The peaks in 1986–88 correspond to special tax concessions introduced by the government for those years only. Eor - enhanced oil recovery Oil recovery methods can be broadly classified as non-thermal and thermal methods, depending on whether heat is employed in some form. Figure 3 shows a classification of EOR methods; the more promising methods from the commercial point of view are highlighted. Non-thermal EOR methods broadly consist of chemical and miscible processes. Chemical methods include polymer, surfactant, caustic and micellar/emulsion floods, and combinations thereof. The general features of these methods and field experience form the subject of this paper. Even though chemical floods have had limited success in the field, they hold promise for the future. Miscible methods include high pressure miscible drives, using a hydrocarbon gas nitrogen or carbon dioxide, as well as displacement by liquid hydrocarbons. Many variations are possible in the application of these processes, an important one being alternate injection of the miscible agent and water.
Abstract This research was designed to develop an efficient micellar/polymer flooding process for the tertiary recovery of selected light oils in Alberta. Two systems, specifically for Bonnie Glen crude and Provost crude, were developed to mobilize the waterflood residual oil. The effect of various types of preflushes on tertiary recovery and the process efficiency* was investigated. Effect of the multiplicity of micellar slugs as well as the graded micellar slugs on tertiary recovery were also studied. Over 100 core displacement tests were carried out in 5 cm diameter × 61 cm long Berea sandstone cores using a series of carefully formulated micellar slugs, with and without a preflush. A frontal velocity of ~1.3 m/day was employed. Tertiary recovery was sensitive to the type and slug size of the preflushes used. Significant increase in tertiary recovery was achieved by utilizing a suitable preflush such as sodium carbonate or EDTA. Suitably "tailored" composite micellar slugs were found to be far more effective than single slugs to enhance tertiary oil recovery. A graded composite slug proved to be superior to all other slug/polymer combinations employed, in improving the efficiency as well as the economics in both the systems developed. Introduction Micellar flooding is one of the very few processes, which have been shown to be successful in recovering oil from a watered-out light oil reservoir. Many large field tests conducted in the U.S. support the effectiveness of the micellar flooding process. The economics of the process remain dubious in view of the cost of the chemicals used and the small spacing usually employed in field tests. The purpose of this investigation was to develop micellar solutions for two Alberta crude oils (Bonnie Glen and Provost crudes). The emphasis was on improving process efficiency (i.e. volume of oil recovery per unit mass of sulphonate) by means of a number of strategies, including the use of preflushes and graded micellar solutions. Much work has been reported on the micellar flooding process by various investigators. The earliest papers by Gogarty and Tosch, Davis and Jones provide insight into the process mechanism. Recent work by Healy and Reed, Pope, Sayyouh and Farouq Ali, Enedy and Farouq Ali, Novasad et al. have been instrumental in finding ways of improving process efficiency. A current review of these and other papers on the subject is provided by Daharu. PROCESS DESCRIPTION Process efficiency of the micellar/polymer process can be defined as the tertiary oil recovery per unit volume of slug injected. Basic Process The micellar/polymer flooding process as an enhanced oil recovery method for a watered-out reservoir is increasingly being employed by the industry. Hydrocarbon, water/brine and surfactant are the basic components of a micellar solution. A small amount of alcohol is often used to improve solution stability, to adjust the viscosity, and to reduce surfactant loss due to adsorption on the reservoir rock. A suitably formulated micellar slug miscibly displaces the residual oil and improves tertiary recovery.
- North America > United States (1.00)
- North America > Canada > Alberta (0.93)