Technical Paper: New Formation Tester Probe Design for Low Contamination Sampling

Society: SPWLA
Paper Number: 2006q
Presentation Date: 2006


The use of third-generation wireline formation testers (WFT) to acquire fluid samples has gradually been accepted as a valid alternative to acquiring samples with a drillstem test or production test. In the offshore and especially deepwater environments, this has resulted in considerable cost savings for operating companies. In addition, the WFT allows acquisition of samples at multiple depths and in multiple zones, thus giving considerable flexibility in characterizing fluids. Also, the newly emerging field of downhole fluid analysis (DFA) has allowed us to execute WFT sampling programs that ensure optimum sample acquisition to properly characterize the reservoir fluids.

In spite of all these advances, however, one significant obstacle remains: acquiring valid samples and good DFA data in the presence of miscible filtrate. This problem presents itself when sampling water in wells drilled with water-base mud and when sampling hydrocarbons in wells drilled with oil-base mud. In traditional WFT sampling operations, the filtrate is sampled with the reservoir fluid, resulting in a sample that is irreversibly contaminated. This results in laboratory or DFA measurements that will, at best, have high uncertainty or at worst be unusable.

The traditional approach to dealing with this problem has been to pump for extended periods of time. However, this is a suboptimal solution. Long on-station pumping times are rig-time expensive and carry an increased chance of mechanical failure and tool sticking.

In this paper we will present a new focused sampling apparatus that features a newly designed WFT probe with concentric flow areas for the Schlumberger MDT1. As a result of this geometric arrangement, we are able to achieve very low contamination results in much shorter pump times and smaller pumped volumes. Results from several field jobs will be presented that demonstrate the success of the technique.

1 MDT, LFA and Quicksilver are Schlumberger marks. The ability to perform DFA measurements on lowcontamination fluids reduces the uncertainty associated with them. We will demonstrate how the functionality of existing spectroscopic and fluorescence measurements can be greatly increased now that we are measuring fluids that will be reliably cleaner.

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