The wireline formation tester (WFT) is a well-developed technology used to collect representative downhole fluid samples. Collecting low-contamination downhole samples in wells drilled with miscible oil-based mud (OBM) is challenging because the process must balance the need to acquire a sample with the desired level of contamination while using the minimum rig time.
The authors introduce a simple but effective method for monitoring WFT sampling when targeting the low levels of contamination needed for asphaltene-onset-pressure analysis.
Flow-assurance problems caused by asphaltene deposition are common reasons for lost and deferred production in Gulf of Mexico Miocene reservoirs. High-quality samples are needed to measure the asphaltene-onset pressure and manage related flow-assurance problems. The asphaltene-onset pressure varies with the level of OBM contamination. The rise of asphaltene-related flow-assurance issues encourages operators to acquire high-quality downhole samples with the lowest possible OBM contamination.
To reduce OBM contamination, operators have to pump out fluid from the formation to the borehole before filling the samples at the desired OBM-contamination level. There is not a standard procedure to determine a sample’s contamination level during the pump-out. Engineers sometimes rely on empirical evidence and previous experience to determine contamination levels. This study introduces a practical method to estimate the contamination level from real-time fluid-analyzer data. A discussion of methods used to predict contamination is provided in the complete paper....
Method for Monitoring Mud Contamination in Wireline-Formation-Tester Sampling
26 October 2016