REAL-TIME QUANTIFICATION OF OBM FILTRATE CONTAMINATION DURING OPENHOLE WIRELINE SAMPLING BY OPTICAL SPECTROSCOPY

摘要

Acquisition of representative hydrocarbon samples from downhole formations is extremely important to assess reservoir value. Accurate fluid analysis needs to be performed in order to properly estimate reserves and determine optimal production strategies. It is critical to identify the fluids coming from the formation during openhole sampling because fluid analysis quality is adversely affected by sample contamination. This is especially true for oil samples taken in oil-based or synthetic-based mud (OBM) wells, as estimation of OBM filtrate contamination can be difficult and qualitative. In this Paper, we describe a new technique utilizing visible - near-infrared (NIR) spectroscopy which enables quantitative estimations of OBM contamination as a function of sampling time. Significant improvement in sampling efficiency is made possible by analyzing NIR data; prediction of contamination levels can be made by extrapolation of sampling time. Sampling can be terminated early and moved to another depth if high contamination levels are predicted, resulting in significant rig time savings and improved sample quality. We describe methods to use NIR data to give quantitative OBM contamination as a function of sampling time. Several field examples are shown and the significant improvement in sampling efficiency is discussed.