Evaluating the Effectiveness of Rock Cleaning

Core cleaning is a fundamental step in laboratory core analysis since it affects the interpretation of core data, thus its applications. For example, the thoroughness of core cleaning is an essential factor for characterizing reservoir rock wettability (Ma and Amabeoku, 2015). Although well-established core cleaning methods exist, characterizing the effectiveness of these methods continues to be a challenge. In this study, we present an innovative method based on NMR T_2 measurements at 100% water saturation (S_W1). Since T_2 of the water phase is sensitive to oil coating on solid surface, the shift in T_2 log-mean (T_2LM ) for water after cleaning provides a direct measurement for detecting rock surface cleanliness. The effectiveness of two standard cleaning protocols are evaluated on ten outcrop cores including sandstone, dolomite, limestone, and chalk. Rock surface cleanliness after each cleaning stage is characterized by the ratio of (T_2LM^end)⁄(T_2LM^start ) at S_W1, where (T_2LM^end)⁄(T_2LM^start )<1 indicates increased cleanness or more water wetness. Therefore, a method is developed for characterizing the effectiveness of cleaning and can be used to select optimal and economical means for cleaning reservoir core samples or cuttings.