Real-Time Determination of Filtrate Contamination During Openhole Wireline Sampling by Optical Spectroscopy

Abstract

Abstract The key objectives of openhole wireline sampling are to identify desired fluids and to collect representative formation samples. Optical methods such as visible – near-infrared spectroscopy (NIR) are used to identify and quantify mixed oil, water, and gas flows in-situ during wireline logging. In wells drilled with oil based muds (OBM) or synthetic based muds (SBM), differentiating crude oil from the filtrate base fluid is critical. The widely used current practice is to measure the increase in fluid coloration (by NIR) vs. time to qualitatively assess the increasing fraction of crude oil with pumping time. Here, we describe new methods of utilizing NIR log data to provide quantitatively during sampling the %-OBM contamination in the extracted fluid. In addition, these methods allow prediction of contamination at future times during the sampling job, thereby determining the effectiveness of further pumping. The significant improvement in sampling efficiency is demonstrated with several log examples. Finally, using our methods, mud performance in the downhole environment can be monitored and optimized in subsequent jobs.