Quantitative Monitoring of Cleaning Time and Wettability Alteration of Carbonate Rocks During Soxhlet Cleaning

Abstract

Summary Core analysis is one of the most important steps in formation evaluation. The availability of routine–core–analysis (RCAL) and special–core–analysis (SCAL) data results in a better characterization of reservoirs and prediction of their behaviors. Unfortunately, the process of running core experiments, in both RCAL and SCAL phases, is very time consuming. Because all plug samples should be cleaned during the RCAL phase, finding a solvent that can speed up this process is desirable. The cleanliness of a core sample during Soxhlet extraction is usually determined by monitoring the color of solvents qualitatively. The main contribution of this study is to propose a methodology during RCAL to determine the best solvent during the Soxhlet–cleaning experiments. By introducing a novel quantitative method, the cleaning time of different solvents (i.e., tetrachloroethene, acetone, toluene, chloroform, xylene, and n–hexane) is investigated. This quantitative method is based on turbidity measurement of the solvent that siphons periodically from the Soxhlet extractor. Moreover, the wettability alteration of the implemented solvents is monitored by contact–angle measurements. To perform the analysis, two crude–oil samples (a heavy oil and a light oil with different asphaltene/resin fractions) and carbonate rocks from two Iranian formations are implemented. The results show that the polar solvents can speed up the cleaning process while altering the wettability of the carbonate samples toward more–water–wet conditions. The introduced methodology of measuring the cleaning time can be implemented as a routine screening tool in RCAL projects to determine the proper solvent that can reduce the Soxhlet–cleaning time.