Two phase flow in reservoirs is strongly dependent on wettability. Determination of the in situ wettability conditions is crucial for the evaluation of both core and log data. With the increasing use of oil-based muds in the industry, a thorough laboratory examination of the possible wettability alteration in the flushed zone is needed to infer the original wettability from its altered state. This study provides data for the wettability and permeability alterations caused by most commonly used oil-based mud components and whole muds for carbonates and for water-wet and oil-wet sandstones.

Eighteen components were evaluated in this study. Both the capillary pressure behavior and contact angle measurements were used to measure the wettability alteration. The capillary pressure tests consisted of primary and secondary imbibition and drainage cycles. A combined Amott / USBM method which allowed the calculation of both the Amott and USBM indices were used as indicators for the wettability alteration. These tests were run on strongly water-wet Berea sandstone, asphaltene treated fractional-wet cores, and chemically treated oil-wet cores. As an independent wettability index, contact angles were measured on calcite and quartz crystals and on asphaltene coated glass slides.

The components used in this study include surfactants, inorganic salts, and base oils. All the components with the exception of the base oils and barite tend to make the cores more oil-wet cores.with the surfactants having the most dramatic effect. Most components reduced the permeability significantly. For the contact angle measurements, significant alterations (from the water-wet to oil-wet) were caused by diesel and most of the components prepared with diesel. Conversely, only the components prepared in brine affected the oil-wet asphaltene coated surfaces.