Role of Clays in the Enhanced Recovery of Petroleum From Some California Sands
Authors: Somerton W.H. , Radke C.J. 
Published: December 2007

Summary
Many oil-producing formations contain significant amounts of clay. Because of the large surface area and the high reactivity of such surfaces. the response of the formations to various recovery processes may be dominated by the reactions of the clays. Thus, the success or failure of enhanced oil recovery (EOR) methods may be controlled to a large extent by the amount and type of clays in the formations to which the methods are being applied. This paper evaluates the type and amounts of clays and clay minerals present in typical oil-producing formations that may be candidates for application of EOR methods. After identification of the clay minerals present, tests are run on the extracted clay fractions to determine cation-exchange capacities (CEC's), surface areas, and chemical-loss characteristics. Flood tests are run on core samples to evaluate the magnitude of chemical loss and to note the change in flow characteristics while different fluids, which might be used in EOR operations, are flowed through the core. This background material is used to test predictive equations developed for screening reservoirs for EOR applications and for optimizing process variables. Techniques to counter the effects of rock/fluid interactions are considered.

Introduction
Because of the large effective surface areas of clays contained in oil reservoir formations and because of the high degree of reactivity of such surfaces, clays may play a disproportionate role in the success or failure of EOR techniques. Clays adsorb many substances that may be injected into the reservoir to improve oil recovery. In many cases. surfactants and polymers adsorb on clay surfaces in sufficient amounts to make the recovery process uneconomical. The ion-exchange capacity of clay minerals may have two detrimental effects:release of divalent ions can cause surfactant precipitation, increased surfactant oil solubility, loss of ultralow interfacial tension, and polymer degradation;ion-exchange reactions with concomitant surface-charge effects may cause structural damage to the formation.
Clay swelling and migration of fines also may result from causes other than changes in the system chemistry. For example, rate effects are important in fines migration. Rapid changes in flow rate, salinity, or temperature may cause plugging, whereas only negligible plugging may result if the rates of change are decreased. Many oil reservoir formations contain substantial amounts of fines including considerable amounts of clay minerals. Screening tests must be conducted on object formations to provide information on potential problems and to suggest means of minimizing their effects. There also are possibilities that certain clay mineral components can be used advantageously in mobility control. This is particularly important in heterogeneous formations containing viscous residual oils.

Test Program
The overall objectives of this research program are to evaluate the effects that clays present in typical oil-producing formations have on the failure or success of EOR operations. Methods of dealing with the detrimental effects of clays and enhancing the favorable characteristics of clays, if any, are explored.
JPT
P. 643^