(610i) Adsorption of Chemicals on Minerals during Enhanced Oil Recovery Processes

Abstract

Chemical enhanced oil recovery processes have been in general less than satisfactory due to loss of chemicals by adsorption on minerals present on the reservoir rock surfaces, precipitation, which results in changes in rock wettability. Adsorption and wettability changes are determined mainly by the chemical structure of the minerals and mix of the surfactants, surface properties of the rock, composition of the oil and reservoir fluids, nature of the polymers added and solution conditions such as salinity, pH and temperature. The mineralogical composition of reservoir rocks plays an important role in determining interactions between reservoir minerals and externally added exotic fluids (surfactants/polymers) and their effects on solid–liquid interfacial properties such as surface charge and wettability. Some of the reservoir minerals can be sparingly soluble causing precipitation and changes in wettabilty as well as loss of surfactants/polymers. Most importantly, the effect of surfactants on wettability depends not only how much is adsorbed but also on how they adsorb. A water wetted rock surface that is beneficial for displacement of oil can be obtained by manipulating the orientation of the adsorbed layers. New surfactants capable of tolerating harsh conditions created by extremes of pH, temperature or inorganics and capable of interacting favourably with inorganics and polymers are promising for enhanced oil recovery. In many cases, mixed surfactants perform much better than single surfactants due to synergetic effects and ability to alleviate precipitation. Also, addition of inorganics such as silicates, phosphates and carbonates and polymers such as lignins can be used to control the adsorption and the wettability. In this paper, use of specialty surfactants and their mixtures is discussed along with the mechanisms involved with the minerals present in the reservoir rock.