Acquiring low-contamination samples and valid testing data
Following an initial run of the MDT modular formation dynamics tester
employing conventional probes, the lower mobility reservoir sections were
investigated using the MDT tester in combination with the Saturn 3D radial
probe. Sampling efficiency was greatly improved by using the Saturn probe to
collect three oil samples and six water samples at mobilities as low as 0.3
mD/cP. For example, the conventional probe collected a hydrocarbon sample in a
zone with 2.4-mD/cP mobility after 5 h of pumping that contained 17-wt% OBM
filtrate. When the Saturn probe extracted fluid from 5 m lower in the same
formation at 0.6 mD/cP, the drawdown was about half of that from the single-
probe sampling and after only 6 h of pumping the contamination had been reduced
to 5 wt%.
The toolstring also incorporated an observation probe at a 1.23-m
interval from the Saturn probe for conducting vertical interference tests to
evaluate permeability and permeability anisotropy and to estimate the flow
potential. All four vertical interference tests returned valid, interpretable
reservoir responses at the probes, with particularly good data acquired in a
zone with 120-mD/cP mobility. High-quality pretest pressure measurements were
made at all Saturn probe stations, in mobility as low as 0.3 mD/cP.