Carbonate Rocks Wettability Changes Induced by Microbial Solution

Abstract

Abstract Contact angles are used to measure the wetting behavior of two immiscible fluids on a solid surface. Fluids are considered wettings if their contact angles with surface are less than 90°, and they are considered non-wetting, if their contact angles are greater than 90°. Because of its influence on other petrophysical properties of reservoir rocks, such as relative permeability, capillary pressure, and the residual oil saturation after a flood, wettability and its direct measure, the contact angle, play a significant role in affecting the recovery from both primary and improved recovery processes. In this work, contact angle alteration occurring in microbial enhanced oil recovery processes (MEOR) are quantififed and described, along with a study of the factors that would enhance such contact angle alteration. An experimental method for the measurement of contact angles has been developed in which the contact angle is measured as a function of time. Measurements of contact angle and interfacial tension for four different types of UAE crude oil and four different mineralogical rock composition over a range of microbial concentration, salinity, and temperature are reported. Results showed that contact angles for the studied systems increased with temperature, crude oil sulfur concentration and microbial concentration up to a certain concentration, beyond which the bacteria concentration exhibited no effect on the contact angle. Crude oils containing low asphaltene concentration produced a stable contact angle and oils containing high asphaltene concentration produced surfaces with unstable wettability. The mineralogical composition of limestone rocks had no effect on the contact angle of microbial-oil system. Introduction The wettability of porous media has been shown by a number of investigators to affect rock-fluid properties such as the capillary pressure and the relative permeabilities, and thus plays a big factor in determining the recoveries resulting from water floods1,2. Contact angles are commonly used to measure the wetting property of a solid surface with respect to two immiscible fluids. Young's equation provides a definition of contact angle in terms of a surface energy that interrelates the interfacial tensions of the three phases.sos=s ws+sow cos ? ow (1) The contact angle is a thermodynamic property and provides a definition of wettability. As the two main fluids in the reservoir are crude oil and brine, reservoirs are thus classified as either water-wet or oil-wet. Sandstone reservoirs are typically water-wet, while carbonate reservoirs, such as reservoirs in the U.A.E., are oil-wet. Water flood performance in water-wet reservoirs is much more efficient than in oil-wet reservoirs. Zisman3 has summarized a large body of air /liquid contact angle data measured on polymeric solids and on adsorbed organic monolayers laid down by the Langmuir-Blodgett technique on metal substrates. Treiber et al.4 measured the water advancing contact angle for 55 reservoirs with synthetic formation brine and observed a wide distribution of advancing contact angle.