CO2 Flooding Process Research Articles

Technical Feasibility of CO2 Flooding in Weyburn Reservoir - A Laboratory Investigation

Abstract Miscible or near-miscible flooding with CO2 or hydrocarbon gases will significantly increase, and extend the production life of, Saskatchewan light and medium oil reserves. These pools are approaching their economic limit of production under conventional technology (primary and secondary recovery methods). Responding to industry needs, a comprehensive study by Saskatchewan Research Council is assessing the suitability of the CO2 flooding process for reservoirs in southeast Saskatchewan. This paper presents the details of a laboratory study to evaluate the applicability of CO2 flooding for a southeast Saskatchewan reservoir, Weyburn. The evaluation is based on the measurement of CO2 minimum miscibility pressure for the Weyburn reservoir fluid, of PVT properties for reservoir fluid CO2 mixtures, and of oil recovery behaviour from core flood tests conducted in the near-miscible region. Laboratory studies showed that the tertiary CO2 injection at over 12 MPa into the waterflo'oded reservoir is expected to produce miscible flooding conditions. At this pressure of injection, over 60 mol % CO2 was dissolved in the reservoir fluid. This reduced the viscosity of the fluid nearly fourfold to 0.70 mPa.s and swelled the oil about 45%. Coreflood studies indicated that the microscopic displacement efficiency of the process increased with injection pressure in the near-miscible region. It is believed that the geology of the Weybum reservoir will prove advantageous for near-miscible operation. However, this aspect needs to be further investigated. Introduction Most of Saskatchewan's light and medium oil (LMO) reservoirs have reached their economic limit of production under conventional technology. Primary and secondary methods together recover about 21% of the initial oil-in-place (IOlP). Although the remaining light and medium oil-in-place in Saskatchewan is 1,373 million cubic metres(1) the remaining reserves producible under primary and secondary recovery are only 59 million cubic metres. This latter number would rise by 20 million cubic metres if medium oil in southwest Saskatchewan, not considered here, were included(1). The development of tertiary recovery techniques is, therefore, essential to increase the production life of these reservoirs and to maintain current production. Application of the miscible or near miscible oil displacement process using CO2, hydrocarbon or other gases as injection fluids is expected to increase the LMO reserves threefold and extend the production life of these pools by two decades(2). Miscible (or near-miscible) flooding with carbon dioxide or hydrocarbon solvents is considered to be one of the most effective enhanced oil recovery (EOR) processes applicable to LMO reservoirs. A comparison of effectiveness of CO2 and hydrocarbon gases as miscible solvents has been discussed(3). CO2 floods minimize gravity segregation compared with the hydrocarbon solvents. In addition, CO2 generally costs less than hydrocarbon miscible solvents in the United States(3). There is a limited supply of CO2 in Saskatchewan and Alberta for EOR purposes. However, CO2 can be imported from the U.S. to be implemented in miscible displacement projects in Canada. Current industry interest in CO2 miscible flooding is high, as evidenced by the growing level of activity in field testing(4) and increasing production from this method worldwide.

Linear Model Studies of the Immiscible CO2 WAG Process for Heavy-Oil Recovery

Summary This paper presents experimental work that quantifies the effect of water-alternating-gas (WAG) variables on the immiscible CO2 flooding process for moderately viscous heavy oils. The results may be used to determine such parameters as total CO2-slug size, WAG ratio, and number of WAG slugs. Analysis of the relative efficiency of each WAG slug is discussed.

Immiscible CO2 Process for the Salt Creek Field

Summary An immiscible CO2 flooding process was investigated for use at the Salt Creek field, WY. This proposed process with CO2 slug and 100% carbonated chase water may recover an incremental 8.6% original oil in place (OOIP). However, tertiary recovery of this light crude is sensitive to the reservoir crude composition, temperature, and pressure. Initial studies and simulations led to a proposed process pilot.

Carbon Dioxide Flooding-applJications

Abstract This is the second part of a two-part paper and will deal with the reservoir engineering aspects of field applications. First, certain criteria which may be useful in identifying a good candidate reservoir for C02 flooding together with the limitations of the so-called screening procedures are discussed. Second, calculations for CO2 slug size are given, and the following factors dealt with: diffusion, dispersion and solubility phenomena; injection/ production rates and their effect on pressure distribution and maintenance of miscibility in the reservoir; the rate of advance of the displacement front and stability considerations; and oil recovery efficiency. Finally, recommended ways of testing the CO2 flooding process are detailed. Introduction Carbon dioxide flooding is generally regarded as the most promising enhanced oil recovery process(l). At present, there are about forty field applications underway, most having been started in the past few years. The United States leads in the number of field applications. There are no CO2 floods in Canada at the moment. Although the Judy Creed Beaver hill Lake A Pool was proposed and approved for CO2 flooding, the economics appear to have caused cancellation of that project(2). Husky Oil Ltd. is conducting CO2 stimulation/soak in a few wells. The first CO2 flood in Canada may well be in the Joffre Viking Pool and will be undertaken by Vikor Resources Ltd.(3). An earlier paper dealt with the fundamentals and the research considerations of carbon dioxide flooding(4). In this paper, selection of reservoirs suitable for CO2 flooding, determining the CO2 requirements, injection and production strategies, problematic areas in the field and recommendations regarding pilot testing are presented. Selecting a Suitable Reservoir A number of screening criteria have been suggested in order to select a reservoir that is best suited for carbon dioxide flooding(5). Although screening criteria serve some purpose and usefulness in looking at a large number of reservoirs from which one must choose the best candidates for CO2 flooding, the use of such criteria in itself has many pitfalls and does not mean that a successful field application would result. If one has but only a few reservoirs to consider, then some standard reservoir engineering considerations are far superior to any general screening criteria. The first reservoir engineering consideration has to do with whether the displacement is to be miscible or immiscible CO2 flooding. In light and medium-gravity oils one would aim at miscible CO2 displacement and laboratory experiments would have already indicated whether or not the miscibility can be achieved within realistic pressure ranges. Especially old pools should not be subjected to high injection pressures which may cause casing or cement failure, premature breakthrough of the injected fluids due to viscous fingering or coning problems. If the miscibility is not the object, but rather swelling of the oil, reduction of oil viscosity and interfacial effects are the principal phenomena which may lead to increased oil recovery, the reservoir to be selected could have different properties than one which may have been suitable for a miscible displacement process.

G-2 and G-3 Reservoirs, Delta South Field, Nigeria: Part 2 - Simulation of Water Injection

Summary To date, laboratory experiments to evaluate a fieldprospect for CO2 flooding have concentrated on determining minimum miscibility pressure. Other experiments include core floods and single- and multiple-contact phase behavior studies. This paper discusses relationshipsbetween the various experiments in the light of current understanding of the mechanisms operating in the CO2-flooding process. Objectives and limitations ofeach experiment are discussed. Limitations on the use of the resulting data to estimate recovery from field CO2 floods also are reviewed. A new experimental procedure is described that permits rapid determination of phasebehavior and fluid properties of CO2 /crude-oil mixtures at reservoir conditions. The experimental procedure, which involves continuous contacting of the reservoirfluid with CO2, can be used efficiently to obtainphase-behavior and fluid-property data that would require difficult and time-consuming experiments if obtained bypreviously available techniques. Introduction Although CO2 flooding has been investigated since theearly 1950's, consensus has not developed as to thelaboratory experiments required for the evaluation of a CO2-flooding prospect. Laboratory experimentsperformed most often, however, fall into three generalareas:slim-tube displacements,core displacements, andhigh-pressure volumetric (PVT)and vapor/liquid equilibrium (VLE) experiments. Thethree types of experiments yield different information about a potential CO2 flood. This paper reviews brieflythe uses and limitations of the information obtained inthe various laboratory experiments. Design of any large-scale CO2 flood inevitably involves the use of numerical reservoir simulators. Those applicable to CO2 flooding also fall into three general groups:miscible simulators,compositional simulators, andhybrid miscible/compositional simulators. The type of data required to support a simulation effort depends (in part, at least) on the choice of the simulator. Miscible simulators based on the work of Todd and Longst afftreat CO2 as completely miscible with theoil, and require little more than the permeability, relative-permeability, capillary-pressure, viscosity, anddensity data common to black-oil simulators. Routine reservoir-fluid volumetric and fluid-property measurements, in addition to standard core characterizations (permeability, relative permeability, and capillary pressure), are adequateto support such simulations. JPT P. 888^

Carbon Dioxide Flooding-fundamentals

Introduction This is the first of two papers dealing with the fundamentals and application of carbon dioxide flooding. First, the basic mechanism involved is discussed. Then a laboratory experimental program as well as predictive techniques to determine the minimum miscibility pressure, swelling of oil, viscosity reduc tion, PVT properties, solution gas drive effect and increased injectivity are presented. Finally, laboratory tests directed toward the determination of residual oil saturation and the anticipated incremental oil recovery are discussed. Introduction Since 1950, the petroleum industry has been carrying out considerable research into the use of Carbon dioxide to increase the recovery of oil from underground hydrocarbon reservoirs(22). In the last few years, about a dozen new field applications have been initiated and more could come if economically priced CO2 supplies are found. Most petroleum research centers have projects relating to CO2 flooding, indicating the current interest in CO2 flooding and promising further innovations in the process. This paper deals with the fundamentals and the research aspects of carbon dioxide flooding. The basic mechanisms which may lead to an increased oil recovery, the data required to evaluate a potential application in the field, certain basic properties of CO2 and carbonated fluids, and the all-important considerations of residual oil and incremental oil recovery are described and discussed. A second paper covers the reservoir engineering aspects of field applications, such as selecting a reservoir suitable for CO2 flooding, determining the CO2 requirements, injection/production strategies and certain recommendations regarding pilot testing the process in the field. Basic Mechanisms Carbon dioxide flooding may be applied in the field as a secondary or tertiary process and would normally involve the injection of CO2 and some other fluids, either sequentially or in an alternating fashion. Generally, in reservoirs in which the displacement is horizontal or nearly so, the CO2 flooding process would involve alternating injection of CO2 and water to attempt to control the mobility of the fluids, whereas in vertical floods the various fluids would be injected sequentially. For example, in vertical downward displacement, the CO2 may be followed by a lighter gas to maximize the advantage of gravity segregation and minimize -viscous and gravity" fingering; in vertical upward displacement, CO2 would be followed by water, again taking advantage of the gravity segregation. Regardless of how CO2 flooding is applied in the field, the following factors may contribute to increasing the oil recovery:reduction of crude oil viscosity;swelling of crude oil;miscibility effects;increase of injectivity;internal solution gas drive. The effects of the foregoing on oil recovery have been discussed in the literature(12,22). Therefore, only the new and hitherto unrecognized aspects will be discussed here. With regard to swelling of crude oil, the additional oil recovery has generally been considered to be due to an increase in the oil formation volume factor so that the residual oil is smaller in volume at surface separator conditions.