Contact angle measurements on conventional and unconventional reservoir cores

Wettability measurements can be used to assess primary, secondary, and tertiary recoveries. In this study, wettability alteration during: (1) variable salinity waterflood, (2) variable salinity water with surfactant flood, (3) variable salinity water with CO₂ flood, and (4) variable salinity water with surfactant and CO₂ flood scenarios were investigated using contact angle measurements. Drop shape analyzer equipment was used to measure the contact angle between conventional/unconventional reservoir core discs and oil-droplets. Low-permeability carbonate core from Middle East reservoir, medium-permeability Berea Sandstone core, and ultra-low permeability cores from the Three Forks formation are the core discs used in this study. Contact angle was measured after the core discs were aged in 32 API gravity oil for eight weeks at reservoir temperature. Contact angle measurements on cleaned and unaged core discs from adjacent core plugs were also performed. For the variable salinity water with CO₂ flood and variable salinity water with surfactant and CO2 flood scenarios, the crude-aged core discs were kept for two days at 2,500 psia in brine-CO₂ and brine-surfactant-CO₂ fluid mixtures prior to contact angle measurements. Details of the experimental procedure, results, and discussions will be presented, and the following are some of our observations: (a) the wettability of crude-aged carbonate and Three Forks core discs altered from oil-wet to intermediate-wet with decreasing salinity; whereas, crude-aged Berea sandstone core disc wettability was altered from intermediate-wet to water-wet; (b) the wettability of crude-aged carbonate core discs alter from intermediate-wet to water-wet with decreasing salinity of brine in presence of 1,000 ppm surfactant; (c) addition of surfactant alters the wettability of crude-aged or cleaned un-aged core discs towards more water-wet. The degree of water-wetness achieved by surfactant solution depends on salinity level; (d) introduction of surfactant, CO2, or surfactant-CO2 into the system altered wettability of carbonate, sandstone, and Three Forks cores toward hydrophilic conditions; (e) cleaned un-aged carbonate, sandstone, and Three Forks core were water-wet.