Chemical Enhancement of Oil Production by Cyclic Steam Injection
Authors: Blair Charles M. , Scribner Richard E. , Stout Charles A. 
Published: December 2007

Members of a special class of interfacially active chemicals were injected into wells in Kern County, CA, immediately before and during the huff ‘n’ puff steaming cycle. The chemical treatment was found to give significant puff steaming cycle. The chemical treatment was found to give significant increases in oil production.

Introduction

Earlier work in this laboratory and in the field indicated that injection of water-soluble demulsifiers into the steam used in cyclic steam stimulation operations often gave improved oil production. This work extends this earlier application to the use of a broader range of compounds that we call thin film spreading agents (TFSA) and that, while still acting to prevent emulsification, are found to aid in oil displacement and water-wetting of rock surfaces. These compositions frequently have higher oil solubilities and higher oil/water distribution ratios than the formerly used products.

Mechanism of TFSA Action

Asphaltic or other semipolar constituents of petroleum adsorb rapidly at oil/water interfaces to form thick, viscous films that stabilize water-in-oil emulsions. Although the spreading pressures of these films are typically in the range of 15 to 30 dyne/cm (15 to 30 mN/m) and thus leave very substantial oil/water interfacial surface energies [25 to 40 dyne/cm (25 to 40 mN/m)] after adsorption, they create potential energy barriers that prevent coalescence of water droplets.TFSA compounds appear to destabilize emulsions by adsorbing at the oil/water interface, spreading somewhat more strongly than the asphaltic stabilizing agent and pushing it back into solution in the oil. Fig. 1 shows the relationships between spreading pressures and concentration for each of the two TFSA compounds used in this study when spread at interfaces between refined mineral oil and water. In these graphs, the concentration is expressed as the thickness of the TFSA film, with the assumption that all added material is adsorbed at the interface. The procedure of Ref. 4 was used for these measurements. The spreading pressure of TFSA rises rapidly with concentration, reaching pressures sufficient to displace asphaltenes back into oil solution at maximum thicknesses of about 4 to 10 A--around the diameter of a water molecule. TFSA lie flat at the interface, forming thin, mobile films that present almost no barrier to close approach of water droplets. This allows coalescence of water droplets and separation of oil and water into bulk phases.A further important property of a properly designed compound is that its spreading pressure reaches a limit as its concentration in the system increases or as the interfacial area decreases. TFSA in slight excess of that required to displace a hydrophobic interfacial film by a very thin, hydrophilic one appears to be dissolved in the oil phase, leaving an interfacial tension (IFT) in the range of 10 to 20 dyne/cm (10 to 20 mN/m) and a residual thermodynamic incentive for coalescence.In these respects as well as others, TFSA compounds differ sharply from ordinary surfactants and micelle-forming amphipathic agents. These latter agents generally undergo close packing at interfaces, forming thicker films and producing low IFT'S.

JPT

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