Because of the importance of chemical flooding operations, the mechanisms of chemical dispersion and adsorption in porous media are of increasing interest to the petroleum industry. This paper presents a mathematical model for simulating presents a mathematical model for simulating chemical transport phenomena in porous rocks; these phenomena include dispersion and either Langmuir phenomena include dispersion and either Langmuir equilibrium or rate-controlled adsorption. The accuracy of this numerical model was verified by comparing the calculated results with those obtained by analytical solutions for a number of limiting cases. The effects of dimensionless dispersion, adsorptive capacity, flow rate, and kinetic rate groups controlling dispersion/adsorption mechanisms were investigated. The utility of the model was demonstrated further by matching experimental results. When adsorption of a chemical is rate-controlled or time-dependent, core flood data obtained at times much shorter than reservoir residence times can lead to a serious underestimation of chemical requirements for the field projects. Introduction Chemical dispersion and adsorption in porous media are of increasing interest to the petroleum industry because of the increasing importance of chemical flooding operations. While dispersion causes mixing and dissipation of a chemical slug, adsorption can result in a real chemical loss to the reservoir; the ultimate success of a chemical recovery process is controlled by the nature and magnitude of the loss. Although diffusion and dispersion have been studied extensively during the past two decades, publications on the adsorption of chemical recovery publications on the adsorption of chemical recovery agents have been limited. The relatively simple case of adsorption of a gas on a clean, homogeneous, solid surface illustrates the complexity of the adsorption phenomenon. The adsorption can be purely physical, purely chemisorption, a combination of physical, purely chemisorption, a combination of both, or an intermediate type. The adsorption of polymer and surfactant solutions on porous rocks is polymer and surfactant solutions on porous rocks is complicated by the physiochemical properties of the solutions and rocks and by the nature of the pore structure of the rock matrix. Nevertheless, adsorption from dilute aqueous-phase solutions can be described by the Langmuir equilibrium isotherm for a variety of chemicals, including many surfactants and polymers. These chemicals can sometimes exhibit adsorptions that are significantly rate-controlled or time-dependent rather than instantaneous. The classical model for rate-controlled adsorption was proposed by Langmuir. This paper presents numerical solutions to the transport equations for dispersion and adsorption in porous media, considering Langmuir equilibrium porous media, considering Langmuir equilibrium adsorption as well as Langmuir rate-controlled adsorption. The effects of various process parameters on adsorption also were investigated. parameters on adsorption also were investigated. Model Development Transport Equations A chemical transport equation chacterizing dispersion and adsorption of a chemical solution flowing through a porous medium can be derived by a mass balance as follows. 2C q C C 1- CrD ----- - ---- --- = ----- + ---- pr -----.x2 A x t t...................................(1) The dispersion coefficient, D, can be expressed as qD= (---)= u.................................(2)A SPEJ P. 129
Reliable data on chemical retention in the reservoir is vital for designing chemical floods. A multiwell pilot can provide the needed information; however, such a project is expensive and time-consuming. Experience has shown that a chemical flood pilot can fall short of the predicted performance using the laboratory data and mathematical performance using the laboratory data and mathematical model studies. An alternative approach for obtaining retention under the reservoir condition is from a short duration, low cost field test using only a single well. The proposed technique entails multiple cycles of injection of a tertiary chemical solution containing a non-adsorbing tracer, soaking and production from the same well. The concept initially production from the same well. The concept initially was verified by tests conducted in laboratory core cells. A mathematical model also was developed for simulating the cyclic test. Finally, a field test was carried out in a well in the Manvel Field, Brazoria County, Texas, where a pilot chemical flood was underway. This paper presents the results of the aforementioned investigation. It is concluded that the single well cyclic test is a potentially viable, short term, low cost technique for determining chemical retention in situ. The test may bridge the gap between the laboratory and pilot floods. Data obtained from such a test could yield scale-up criteria for designing and implementing a full scale pilot, or in determining the feasibility of even pilot, or in determining the feasibility of even undertaking a project. Introduction Reliable data on chemical retention in the reservoir are vital for designing chemical floods. These data are usually obtained from laboratory core floods, but they do not account for many factors controlling chemical retention by formation matrices and fluids. Conversely, a multiwell pilot flood can provide the needed information; however, such a project is expensive and time-consuming, and it may not perform according to the laboratory based retention parameters used in the pilot design. An alternative approach for obtaining retention data is from a short duration, low cost field test using only a single well. Froning and Leach reported single well tests to determine loss of wettability alternation chemicals in a Gallup Sandstone reservoir and in a Clearfork Lime. A single injection-production cycle was employed in both tests. The proposed technique of the subject investigation differs from the above referenced method in two significant aspects. First, the subject method employs multiple injection-soak-production cycles and secondly, it can provide more accurate retention data based upon the actual reservoir volume retaining the injected chemical. The previous investigators obtained chemical retention based upon an assumption that the reservoir pore volume retaining the chemical is the same as the pore volume retaining the chemical is the same as the pore volume contacted by the injected liquid. This pore volume contacted by the injected liquid. This assumption is erroneous when sufficient chemical is not injected to satisfy retention requirement of the reservoir volume contacted by the injected liquid. When this situation arises, calculated retention will be lower than the actual value. The proposed procedure entails injecting a relatively small quantity of tertiary chemical solution containing a non-adsorbing tracer. The well is then shut in for a few days residence time to approach chemical equilibrium. Finally, the well is put back in production and the produced chemical and tracer concentrations are measured. The injection soak-production cycle is then repeated. The chemical retention values are determined by material balances on the injected and produced chemical and tracer. This concept initially was verified by tests conducted in laboratory core cells. A mathematical model also was developed for simulating the cyclic test. Encouraged by the good agreement between the laboratory and simulated results, a field test was conducted in a well in the Manvel Field, Brazoria County, Texas. This paper presents the results of this investigation.
American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract A numerical simulation is developed to determine the temperature profiles and oil production for an inverted 5-spot pattern subjected to dry or wet in situ combustion. The basic equations required for the simulation are derived and discussed. The simulation takes into consideration the heat of combustion, the reservoir heat capacity, the conduction and convection of heat through the reservoir, and the conduction of heat between the reservoir and the cap and base rocks. Oil production is calculated through the use of the temperature-oil saturation relationships, a production delay factor and a well-capturing factor. Examples of temperature profiles and oil production for the dry and wet combustion processes are presented. The features of the temperature profiles produced from the simulation appear to produced from the simulation appear to be in agreement with those reported by others in the literature. For the same injection rate of steam or water simultaneously with air there is not much difference in the temperature profiles ahead of the combustion front. However, behind the front there is definitely a better utilization of heat (i.e., heat scavenging effect) in the case of water injection. Introduction In situ combustion is one of the promising techniques for the recovery of promising techniques for the recovery of heavy oil. With this process, air is injected into the formation to burn a part of the oil in-place. Heat part of the oil in-place. Heat generated by combustion is used to heat up the formation and its contents. The increase in temperature reduces the oil viscosity and thus increases its mobility. Ahead of the combustion front, the formation water is vaporized and together with water generated by combustion produces a steam zone. Further ahead, this steam condenses and produces a hot condensate zone. Hence, the in situ combustion process includes both steam and water flooding mechanisms. Many processes for in situ combustion have been studied and reported in the literature. Among these are forward combustion, reverse combustions and wet combustion.
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