Interactions between solutes in displacement solutions and oil bearing rocks
Studies of adsorption of several surfactants from aqueous solution onto kaolin have been made, such as might be employed in an enhanced oil recovery process. Investigations of the surfactants were carried out with regard to pH, ionic strength, temperature, the addition of short chain aliphatic alcohols, the addition of sacrificial complexing agents and various ion-exchanged forms of kaolin. The various forms of kaolin were synthesised to simulate the effect of clay contact with sea water and/or formation water. To try and understand the surfactant solution more fully an attempt was made to determine the number of bound Ca2+ ions and A13+ ions using an ion-selective electrode and atomic adsorption spectroscopy techniques. The results of the adsorption experiments show that monolayer coverage of the kaolin takes place, and the minimum adsorption is favoured by the following conditions: high pH, low ionic strength and elevated temperatures. The presence of butan-l-ol and sodiwn citrate are also beneficial. In the presence of high ionic strength solutions, the anionic surfactant may also be lost due to salt formation with the metal ion present and hence be precipitated from solution. In the absence of the short chain alcohols the adsorption isotherms of the anionic surfactants can be said! at low concentrations « 10-3 mol dm-3), to be due to electrostatic interactions between the edge of the clay particles and the charged surfactant. At higher concentrations the adsorption becomes limited due to the formation of micelles. At concentrations> 10-2 mol dm-3 the surfactants appear to desorb into solution. This is due to the resolubilisation of the adsorbed surfactant-metal ion species by the excess micelles which exist at these surfactant concentrations. The determination of bound counter ions has been investigated and found to give acceptable results comparable to those that would be expected, However, slight reservations are made as to the total accuracy of the test method. This study has been able to define the conditions which will allow various anionic surfactants to be used in conjooction with other chemical species in enhanced oil recovery processes for both land or sea based wells.