This paper describes efforts in an experimental search for polymers that are sufficiently soluble in dense CO 2 that· they could serve as mobility control agents. The operation of the apparatus designed and built for the measurement of solubility in condensed gases is described. A modified version of this apparatus has been used to measure viscosity by timing the fall of a cylinder in a tube.More than a dozen polymers have been found that are soluble at least in the parts-per-thousand (ppt) range in liquid and in dense supercritical CO 2 , As pressures and temperatures are varied, the solubilities of these polymers generally are found to increase with increasing CO 2 density. Certain generalizations have been made concerning the influence of various polymer properties on their solubility in dense CO 2 , These properties include structure, stereochemistry, and molecular weight. Although the viscosity enhancements of the solutions measured thus far are insufficient for purposes of mobility control, they provide clues that point toward those features of polymer molecules that yield greater thickening properties.Also discussed are considerations involved in the application of direct thickeners in the mobility control of CO 2 floods and the advantages in the use of such CO 2 -soluble polymers in place of methods that involve the injection of water.
Theoretical considerations and mathematical tools to analyze multidimensional transient infiltration from a trickle source have been developed. Two mathematical models were considered: (i) a plane flow model involving the Cartesian coordinates x and z; and (ii) a cylindrical flow model described by the cylindrical coordinates r and z. The diffusion‐ type water flow equation in unsaturated soil was solved numerically by an approach that combines the noniterative ADI difference procedure with Newton's iterative method. The numerical results have been compared with Wooding's solution for steady infiltration from a circular pond and with a simple one‐dimensional solution. These comparisons indicate that the method is reliable and can be used with confidence. Typical results are demonstrated to show the effect of trickle discharge on the water content field, the saturated water entry zone, and the water flux at the soil surface.
The solubilities of several organic compounds in dense carbon dioxide (both liquid and supercritical) have been determined. Our data supplements earlier work by Francis. Based on these two sets of data, the structural features that either limit or enhance the solubility of different groups of compounds are identified. By use of this approach, some general structure-carbon dioxide solubility relationships have been developed and are illustrated by examples in the case of hydrocarbons, alcohols, phenols, aldehydes, ethers, esters, amines, and nitro compounds. These relationships can be used in qualitative predictions about the solubilities of substances in carbon dioxide; such information would be useful in enhanced oil recovery operations, supercritical fluid chromatography, and supercritical fluid extraction.
The problem of nonlinear pseudo-steady-state parameter estimation for tubular reactors is addressed. It is shown that constant-gain, nonlinear, Kalman filters are feasible tools for estimating catalyst activity and the heat-transfer coefficient. Inclusion of a concentration measurement in addition to temperature measurements brought a large improvement in the correlation of the estimates of two parameters. An adaptation algorithm is presented to estimate one parameter for cases where process and measurement noises are unknown. It finds the optimal filter gain from data of suboptimal filter performance.
Summary This paper summarizes new and previous high-pressure experiments measuringthe mobility of CO2 foam in porous rock, including both sandstones andcarbonates, with permeabilities ranging from less than 1 md to hundreds ofmillidarcies. Foam mobility is defined here as the ratio of the combined flowrate per unit superficial area to the pressure drop required for simultaneousflow of dense CO2 and brine/surfactant through the sample and can be expressedin units of millidarcies per centipoise. The measured results, which can alsobe expressed in terms of the apparent viscosity of the CO2 foam, give aquantitative basis for the belief that this displacing fluid should beparticularly effective in heterogeneous formations. From a macroscopicviewpoint, the CO2 foam acts like a single fluid with a viscosity equal to theratio of the rock's brine permeability to the measured mobility. According toour results, the permeability to the measured mobility. According to ourresults, the apparent viscosity depends on rock permeability in a nonlinearfashion, increasing from a minimum of about 2 cp for the tightest rocks to anapparent maximum of about 1,000 cp for Berea. Individual mobility measurementswere made at steady-state conditions; this is justified by consideration ofoilfield operational constraints. Results of auxiliary experiments are givenand the methods described. These include measurements of essential surfactantcharacteristics, such as durability against coalescence of the dense CO2 bubbles in brine/ surfactant solution. Results given also show the influence ofother factor s, such as surfactant concentration and type, flowing fraction ofthe dense gas, and overall rate, on foam mobility. Introduction The increased use of CO2, flooding for EOR within the past decade has beenrelated directly to the availability of sufficient quantities of relativelyinexpensive CO2 and has occurred principally in the Permian Basin of west Texasand southeastern New Mexico. These facts might lead skeptics to conclude thatthe efficiency and economics of the process justify its use only under suchspecial circumstances. The inference is partly justified by experience. Although CO2 floods have been profitable and more oil has been recovered thanwould have been by waterfloods alone, things could be better. On the basis of laboratory displacements in slim tubes, at pressures abovethe minimum miscibility pressure, a developed pressures above the minimummiscibility pressure, a developed miscibility flood could be expected toproduce a large fraction of the oil remaining in the formation. Instead, although field experience with CO2 floods has been considerably better thanexperience with early liquified petroleum gas and other solvent floods, mosthave been subject to early breakthrough and have yielded (or are expected toyield) overall recoveries of only 10 to 20% of the original oil in place, representing less than half the oil remaining after waterflood. Among the reasons for these somewhat disappointing results, two stand out. First, the reservoir is heterogeneous, containing preferential" channels" along which the injected fluid can be conducted preferential" channels" along which the injected fluid can be conducted more rapidlyto the producing wells than along other paths. Second, because of the lowviscosity of even dense CO2, the mobility ratio is usually 20 or higher, andthe consequent frontal instability leads to viscous fingering that also causespreferential flow. Both factors, which may be intensified by their interaction, lead to the "bypassing" of substantial quantities of oil. Much of thisoil will remain in the reservoir at the economic limit of production andconstitutes the target for enhanced mobility-controlled CO2 floods. The data presented here show that simultaneous injection of dense CO2 and anaqueous solution of suitable surfactant will produce a foam-like dispersion inreservoir rock. The mobility of this foam is substantially lower than that of CO2 alone. Furthermore, the apparent viscosity of this CO2 foam is not constantbut depends in a favorable way on the permeability of the rock through which itis flowing. The experiments from which these data were derived were designed tomeasure the mobility of the foam in sections of the reservoir that lie farbehind the displacement front. At the front, in the displacement region itself, the dense CO2 (which issupercritical above 88 degrees F) can mobilize residual oil by generation of a Hutchinson-Braun, developed-miscibility zone. If the integrity of the zone canbe maintained by stabilizing the front against the nonuniform flow discussedabove, its graded composition can displace almost all the oil in the pathsalong which it flows. While the displacement itself is accomplished in thefrontal region, the stabilization of the front requires mobility control in themuch larger portion of the reservoir that lies between the front and theinjection well. With effective mobility control in the field, a greaterfraction of the oil remaining after either primary recovery or waterflood canbe expected to be recovered.
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