Investigation of Wettability Alteration Following Scale Inhibitor Adsorption onto Carbonate and Clastic Reservoir Core Material - Static Tests and ESEM Studies

In this paper, we make an assessment and comparison of scale inhibitor/ rock interactions onto carbonate (calcium carbonate and dolomite) and clay-rich (illite-rich and kaolinite-rich) core materials. This is compared using both non-solvent cleaned and solvent cleaned (increased water wetness) reservoir chips of the same core material. In order to investigate the wettability alteration following the interaction with scale inhibitor solutions, ESEM studies were carried out on the pre-and post treatment reservoir chips. The interaction of two generic scale inhibitor chemicals penta-phosphonate (DETPMP) and phosphino-polycarboxylic acid (PPCA) with various un-cleaned and solvent-cleaned core substrates at pH 2 and pH 5.5 have been examined under static conditions. The bulk differences in the inhibitor-rock interactions have been assessed by the comparison of cation (Ca, Mg) and scale inhibitor (SI) concentrations of pre- and post treatment core chips. ESEM observations and EDAX analysis of the pre- and post treatment core chips have then allowed for the investigation of wettability alteration following the interaction with various scale inhibitor solutions. In summary, quite distinct inhibitor/rock interactions and wettability alterations are observed at different mineral surfaces. Under certain conditions, excessive surface precipitate of pseudo scale (inhibitor/calcium complex) can occur as a result of mineral dissolution and consequential localized increase in pH and cation concentration. In addition, the adsorption/precipitation of SI onto certain minerals under specific conditions have been found to reverse the original wettability state of the reservoir chips. The results therefore help to explain relative permeability issues associated with scale inhibitor treatments both in core flood experiments and field treatments. Moreover, the hot solvent cleaning process has made the initial mineral surface more water wet.