This paper discusses the physical parameters involved in the slow flow of high molecular weight polymer solutions in porous media. The interacting erects of polymer properties and porous media properties on flow performance are considered. Experiments were conducted with the polyethylene oxides, with molecular weights ranging from 200,000 to over 5,000,000. Frontal advance velocities ranged from 1 to 30 ft/day. The porous matrix consisted of a flow cell packed with glass beads. Polymer solutions were characterized by viscosity and normal stress measurement. Under certain condition, unexpectedly high Row resistance was observed. This behavior was observed to be a function of flow rate, pore size, polymer molecular weight and concentration. The polymer solutions exhibit "dilatant" flow behavior in porous media in contrast with the pseudo plastic behavior in simple flow systems. A theoretical explanation of such behavior is presented. Introduction The use of polymers in the injected water of a waterflood increases oil displacement efficiency by reducing the mobility (kw/uw) of the driving phase. A reduced driving phase mobility results in improvements in the areal sweep efficiency and in the vertical coverage in stratified reservoirs. This mobility reduction may be achieved by a permeability reduction, a viscosity increase or by a combination of the two. Early attempts at increasing the injected water viscosity were not successful because of the poor economics involved. The use of such materials as glycerin, sugar or glycols to increase water viscosity was not economically feasible. Attempts in using certain naturally occurring polymers were not too successful because of the high polymer losses to the rock. A high molecular weight, partially hydrolyzed polyacrylamide was introduced 3 years ago as a waterflood additive. Initial work by Pye indicated that the presence of these polymers in dilute concentrations decreases the water mobility 5 to 20 times more than would be expected from measurements of the solution viscosity. Such an effect would be of obvious economic value since only a small polymer concentration would be required to accomplish a large reduction in water mobility. This research was designed to study the basic flow mechanisms of polymer solutions in porous media. The interacting effects of polymer properties and porous media properties on flow performance are considered. This study indicates some of the conditions under which these interactions can lead to significant mobility effects. DEFINITION OF PROBLEM The Darcy equation ........................................(1) is valid only for Newtonian fluids. For polymer solutions and other non-Newtonian fluids the equation must be modified to consider that viscosity is a variable quantity. Modification of the Darcy equation to include non-Newtonian effects has been the subject of several recent investigations. The modifications generally adopt a rheological model, such as an Ellis or power law model, to porous media by defining some characteristic channel radius. Most of these studies showed the porous media flow behavior to be predictable from viscometric data. Investigations involving the flow of high molecular weight polyacrylamide solutions through cores have generally encountered the high flow resistances reported previously by Pye. This high flow resistance has generally been attributed to an in-depth permeability reduction, as evidenced by a reduced permeability to water which has displaced polymer solution from the porous media. Marshall and Metzner report high flow resistances, which they attribute to viscoelastic effects. In this paper, the effects of polymer molecular weight. pore size, flow rate and concentration are considered. The polymers used are the polyethylene oxides known as Polyox. This class of polymers was used because of its availability in a wide range of molecular weights and because of its known ability to propagate well through porous media. THEORY PHYSICAL PROPERTIES OF POLYMER SOLUTIONS The polymer molecule dissolves in water by means of hydrogen bonding, but retains some of its own structural identity while in solution. Nonionic polymers, such as polyethylene oxide, are generally considered to have a random coiling configuration. This type of molecule has the ability to "sequester" or hold a large volume of solvent within its coils in a manner similar to that of a sponge. JPT P. 1065ˆ

Laboratory core tests show that small polymer-driven micellar slugs displace tertiary oil, polymer-driven micellar slugs displace tertiary oil, efficiently. Surfactant adsorption studies reveal nonclassical behavior. Polymer requirements are decreased by permeability-reducing micellar/clay interaction and by reduced losses behind a micellar slug. The required volume of polymer slug increases when the pore volume that is inaccessible to the polymer increases. Long-core tests with multiple polymer increases. Long-core tests with multiple pressure taps reveal the existence of a high-mobility pressure taps reveal the existence of a high-mobility oil-water bank and a low-mobility oil-micellar mixing zone. Introduction Micellar fluids that use petroleum sulfonate surfactants have been tested by several organizations as potential candidates for secondary and tertiary oil recovery operations. Typically, a micellar flood consists of a brine preflush to condition the formation, a bank of micellar fluid (5 to 40 percent PV) that displaces the oil, a mobility buffer (polymer) bank to drive the micellar slug, and a chase-water bank. Micellar flooding is attractive as an improved oil recovery process because it is not severely affected by gravity segregation and is not limited by ultimate surfactant availability. DEVELOPMENT OF MICELLAR FLUIDS The micellar fluids that have been developed by our laboratory for miscible waterflooding are microemulsions of high water content (85 to 95 percent by weight). These fluids generally are percent by weight). These fluids generally are prepared with 4 to 10 weight percent oil-soluble prepared with 4 to 10 weight percent oil-soluble hydrocarbon sulfonate (with an equivalent weight, EW, from 350 to 475) and an oil- or water-soluble alcohol cosurfactant. The cosurfactant performs several functions. In many cases it aids the water solubility of the sulfonate. Gale and Sandvik reported that systems that do not use cosurfactants require sulfonates with a broad EW range. The low-EW sulfonates provide water solubility for the high-EW material. Since the systems discussed here use a cosurfactant to perform this function, the EW range of the sulfonates we used is much narrower. An additional benefit of the cosurfactant is that sulfonate adsorption by the rock surface is reduced. SCREENING PROCEDURE Before core testing, crude oils that are potential candidates for micellar flooding are screened qualitatively against a number of micellar compositions of varying surfactant/cosurfactant ratio, monovalent ion concentration, and water content. Divalent ion tolerance and temperature are also examined. Preliminary qualitative screening tests are used to visually examine the degree of miscibility between the crude oil and the micellar solution. If a micellar fluid shows potential for oil displacement and is economically attractive, a core testing program is initiated. Typically, tertiary floods are conducted at reservoir conditions in fresh 2-in.-diameter, 4-ft-long Berea sandstone cores mounted in Hassler holders. A small volume of micellar fluid (from 2.5 to 10 percent PV) is injected at a linear advance rate of percent PV) is injected at a linear advance rate of about 2 ft/D and is followed by a bank of low-salinity, polymer-thickened water. If the tertiary recovery is encouraging, the micellar fluid is evaluated in detail. This evaluation involves extensive adsorption studies to optimize the fluid composition and long-core tests to examine the propagation and interaction of the fluid banks. propagation and interaction of the fluid banks. MICELLAR FLUID DEVELOPMENT FOR A PARTICULAR RESERVOIR The Second Wall Creek reservoir of the Salt Creek field north of Casper, Wyo., has been selected as one of the potential candidates for micellar flooding. The reservoir has a temperature of 110 degrees F, a crude oil viscosity of 4.0 cp, and an average permeability of 50 md. Analyses of the Second Wall Creek formation water and the Madison Field water (to be used as the micellar and polymer bank makeup water) are shown in Table 1. Both waters produce stable one-phase micellar fluids since the produce stable one-phase micellar fluids since the total dissolved solids and divalent ion contents are low. SPEJ P. 633

By removing residual oil and organic skins from the vicinity of a well, water injection rates can be increased. The micellar compositions described here are highly effective for this purpose and are applicable under widely divergent field mixing and reservoir conditions. Introduction To achieve favorable oil productivity during a waterflood project, water injection rates must be maintained at a high level. Acidizing and fracturing are established techniques for increasing water injectivity. These treatments should be avoided, however, where a created fracture or channel might result in the bypassing of oil. Injectivity may be increased in some wells by removing organic deposits and residual oil from around the wellbore. Potentially y effective treatments are solvent-alcohol injection and micellar solution injection. The micellar compositions found most effective in improving injectivity are of the type described in the earlier work of Jones. These solutions, when used with special injection techniques, have been found to be effective under diverse reservoir conditions. We shall emphasize here the laboratory and developmental aspects, including both micellar composition studies and core displacement tests. Other literature discusses the use of micellar solutions in producing wells and in injection wells. Laboratory Evaluation The micellar solutions are composed of a hydrocarbon solvent (usually kerosene), a sulfonate surfactant, a cosurfactant (usually an alcohol or a modified alcohol), and water, which normally contains added amounts of an electrolyte such as sodium chloride. The micellar solutions normally are transparent and single phase. Laboratory tests show that a small slug of a micellar solution driven by water can displace all of the oil from a rock matrix. The micellar solution performs as a true solvent, similar in mechanism to that proposed by Morse. The surfactant and cosurfactant act as coupling agents to create a single-phase solution from two otherwise immiscible fluids. This mechanism may be compared to adding a mutually soluble alcohol or other solvent to a mixture of water and oil to create a single-phase, homogeneous solution. The type and amount of ingredients must be carefully selected to formulate a stable micellar solution. The surface chemistry explaining the various physical phenomena exhibited by micellar solutions physical phenomena exhibited by micellar solutions is highly complex so we shall not discuss it here. Requirements for a Versatile Composition In order that one composition may be effectively applied in many different reservoirs, the micellar fluid should exhibit the following properties.The micellar slug driven by water should be able to miscibly displace crude oils from various types of reservoir rock.It is desirable that the micellar solution be able to dissolve organic deposits, such as paraffins and asphaltenes, and to disperse solids or emulsions.The micellar solution should remain as a single-phase, homogeneous fluid over the expected range of surface and reservoir temperatures.It should be possible to prepare solutions with the various fresh waters that may be available near the treatment site. JPT P. 614

The development of a lignosulfonate gel system for improving sweep efficiency is discussed. The gel mixture is injected as a low-viscosity fluid into a loose streak. After gelation occurs, subsequently injected fluids are diverted into lower-permeability intervals. The developed system is composed of 95 percent or More water, ammonium lignosulfonate, and a mixed activator of sodium dichromate and salt. Laboratory studies show that lignosulfonate gels exhibit the following properties:long gel times can be designed, e.g., gel times up to 2 1/2 months were obtained at 190 degrees F;gel strength can be controlled to produce the level of flow reductions required for a particular application. Controlled flow reduction, rather than complete flow blockage, is needed where the loose streak may contain appreciable amounts of oil recoverable by further waterflooding or by a miscible flood;available injection waters, even highly saline ones, can be used for mixing the gel solutions; andlignosulfonates, with no activator, gel when exposed to temperatures in the range of 300 to 450 degrees F. A fluid with these properties should be useful in controlling sweep in high-temperature reservoirs or steamfloods. Introduction Reservoir heterogeneities, such as loose streaks or fractures, may limit oil recovery in waterflood operations. The injected water may break through prematurely and producing wells abandoned because prematurely and producing wells abandoned because of high water cuts, even though much of the oil in the reservoir is left behind. In spite of sweep problems, many waterfloods have been successful problems, many waterfloods have been successful because water is inexpensive and can be cycled to displace oil gradually from the matrix or lower permeability regions. permeability regions. Recent papers have pointed out that good volumetric sweep efficiency is particularly important in miscible recovery operations. An expensive slug of gas solvent or micellar fluid recovers only the oil that is contacted on a single pass through the reservoir. Thus, it is important that the miscible fluid contact a significant portion of the reservoir. One suggested method for improving sweep to micellar fluid involves prepolymer injection. Because of the growing awareness of the importance of good sweep, greater emphasis is being placed on the diagnosis of reservoir heterogeneities and development of materials for correcting diverse sweep problems. Polymers in various forms have been proposed for improving volumetric sweep caused by a poor mobility ratio or by permeability contrasts. Gels are used for the more severe channeling problems caused by loose streaks. Solid fines and gels are used for fracture plugging. plugging. A previous paper discussed the development and application of alkaline silica gels for selective plugging. Silica gels have been and will continue plugging. Silica gels have been and will continue to be used where the need is to eliminate flow through high-capacity loose streaks. However, with continued application, it has become apparent the silica gels do have some limitations. These includeshort gel times at high temperatures (e.g., about 10 hours at 200 degrees F) that limit the volume of gel mixture that can be injected, andsensitivity to salts that necessitates the use of fresh water for mixing and preflushing and that causes premature gelation in formations containing soluble compounds (e.g, gypsum or anhydrite). This paper describes the development of lignosulfonate gels for improvement of sweep. These gels overcome some of the above limitations of silica gels and also offer additional advantages. DESCRIPTION OF THE SYSTEM This selected system is composed of 95 percent or more water, a lignosulfonate, and a mixed activator of sodium dichromate and salt. This system has evolved from a systematic evaluation of the known reaction of a lignosulfonate with dichromate. SPEJ P. 391

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