oil-in-placeremains bypassed either in the deepeat regions of the resexvoir (gravityoverride case) orExperiments were run to Investigatethe effect in the lower permeabilityzones (channelingcaae). of surfactant concentration, injection rate, foam quality, oil saturation, and rock absolute perme-Because of the high fuel coat to generate the ability on the formation and propagation of foama injected steam, research efforts by the oil indusin Berea aandstoneaand Ottawa sandpacks. try have recently been directed toward overcoming First, both gravity override and channeling effects.One constant pressure unsteady-stategaaliquid relative periueability experiments were con-of tha moat promisingmethods being investigatedis ducted in Berea sandstone for varying residual the injection of surfactantswith steam to form a saturations of synthetic oil. It was found that resistive foam which can divert steam into bypassed high oil saturation can hinder the formation of zones.foam (no substantialdecreaae in the gas phaae relative permeability). In such casea, some of the When a mixture of surfactant,steam, and nonoil must firat be displaced from the core before a condensablegas is injected into a well, a foam is foam can form. generated either in the tubing ox at the sand face. In order to be effective in the diversion of steam, Other experiments were parformed by flowing the foam must not only penetrate into the stes?= preformed foams into cores at varioua conditions. swept zones, but must also propagate away from the The foama were preformed at high ratea repreaentawellbore. This is necessary to prevant the followtive of tubing or sandface rates. They were injecup steam from flowing back into the swept zone ted into the porous medium at J.ower ratea repreaen-beyond the foam plug a few feet away from the welltativa of near wellbore conditions (1.5-5m from bore. tha wellbore) but not of in-depth reservoir conditions. Raaults showed that the foam propagation Foattta are gaa-liquid emulaiona that exhibit a rate was significantlyaffected by rock permeabil-VISCOUS behavior in porous media.2 Several authors ity and injected foam texture. In high permeability have proposed mechanisms or obeened flow patterna sandpacks (40-50 darciaa), the foam propagated at pertinent to the viacoua behavior of foams in the same rate as the liquid phasa. Foam propagaporous media. Fried3 proposed that foam moves tion rates decreased substantiallyin lower parme-through pore spaces aa a body. Helm proposed that ability media. gaa flows aa a discontinuous phase separated by liquid lamellaeQ and that the lamellae break and INTRODUCTION reform as gaa passea through pore channels. Hiraaaki and Lawaon5 concluded that a foam's flow Foama are currently used to improve steam regime and its viscous behavior in capillary tubea aweep efficiency in both cyclic and drive oparationa.l 'ho types of reservoirproblems raduce the can be correlated to the ratio of bubble sfze to capillary radiue. This ratio determines whechar a effectiveness of staam applicationsgravity bulk ...

Laboratory experiments were performed to determine the effects of a residual oil phase to hot nitrogen flood on the propagation of surfactant foam in Berea sandstone rocks.Static phase behavior-type tests were performed in support of the displacement tests.In the static experiments, surfactant partitioning into the oil phase and thermal degradation losses were measured. The chemical and physical properties of the oil phase were varied by the employment of four crude oil and two synthetic oil samples. The chemical properties of the surfactant phase were varied by the employment of three different foaming sulfonate surfactants. Each oil was analyzed for composition and physical and interfacial properties were measured. The effect of the presence of an oil phase on foam propagation was found to be strongly surfactant-specific. Implications of the results on the mechanisms controlling oil production in reservoirs containing steam override zones and channels are discussed.

Laboratory experiments were performed to determine the effects of a residual oil phase to hot nitrogen flood an the propagation of surfactant foam in Berea sandstone rocks. Static phase behavior-type tests were performed in support of the displacement tests. In the static experiments, surfactant partitioning into the oil phase and thermal degradation losses were measured. The chemical and physical properties of the oil phase were varied by the employment of four crude oil and two synthetic oil samples. The chemical properties of the surfactant phase were varied by the employment of three different foaming sulfonate surfactants. Each oil was analyzed for composition and physical and interfacial properties were measured. The effect of the presence of an oil phase on foam propagation was found to be strongly surfactant-specific. Implications of the results on the mechanisms controlling oil production in reservoirs containing steam override zones and channels are discussed. Introduction Foams are used for steam mobility control in both steam drive and cyclic operations. Many mechanisms governing the flow of foam through porous media are not yet understood. One of these is the effect of oil on foam stability and consequently on foam flow in porous media where oil is present. Oil-foam, interactions are complex. The presence of oil can be detrimental to foams. First, the surfactant can preferentially partition into the oil phase, away from the gas-water interface, and destabilize the foam bubbles. Second, polar components, in the oil may adsorb at the gas-water interface instead of the surfactant. If these oil components have poorer foam-stabilizing properties than the surfactant, they will destabilize the foam. Third, oil could spread at the gas-water interface, resulting in a reduction of the local surface tension, thereby causing thinning and rupture of bubble lamellae by the Marangoni effect. Fourth, oil droplets can be located at strategic sites in the porous media where bubble snap-off is most likely to occur, thereby hindering generation or regeneration mechanisms. As the residual oil saturation is reduced, more channels can then be invaded by the foam bubbles. The requirement that foam coexists with high oil saturations depends on the application. In a mature steam drive, foam injection could reduce steam mobility in the oil-depleted zones (less than 15% Sor) of the reservoir (override or isolated channels Then, it could be undesirable to block the higher oil saturation regions with foam and reduce oil mobility in the reservoir. In other cases (channels resaturated by oil gravity drainage or override zones with higher oil saturations than found in mature steamfloods), it may be necessary to generate a foam in the presence of high oil saturation (less than 15%) to increase the resistance of steam in the charnels and override zones. In all cases, understanding the mechanisms of oil production in the reservoir will help in the selection of the best suited surfactant for a specific application. In this paper, foam propagation is investigated in Berea sandstone at residual oil saturation. Three surfactants with varying ability to foam in the presence of oil were studied. Four crude oil and two synthetic oil samples were used. P. 473^

The damage and residual strength of 7075-T6 aluminum panels exposed to caliber 0.50 AP M2 gunfire was found to vary with projectile velocity, impact angle, and target thickness. Maximum damage occurred at low velocities and high impact angles. The strength of thin panels agreed closely with fracture theory because of their predominant cracklike flaws; conversely, the strength of thick panels was close to the material ultimate tensile strength because of the blunt flaw shapes. Damage and residual strength prediction models were developed from the test data for monolithic panels. Alternate design concepts consisting of laminated, planked, and spar cap stiffened panels were investigated. The laminated panels exhibited extensive petaling and star-type cracking and low residual strength. Planked and spar cap stiffened panels provided damage alleviation and crack arrestment with high preload stresses.

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