New Wireline Formation Testing Tool With Advanced Sampling Technology

Abstract

Summary A recently introduced wireline formation-testing tool incorporates new digital-control technology that significantly improves formation fluid sampling and pressure testing. A primary focus of the new technology is improving the quality of reservoir fluid samples. An innovative pumpout design using a digital-control feedback system enables the tester to continuously monitor the fluid sampled and to make precise adjustments to the rate and pressure at which the fluid is withdrawn from the formation and injected into a sample chamber. The tool design incorporates a powerful pumpingsystem motor and an efficient hydraulic system. Consequently, invaded fluids surrounding the probes, such as mud filtrate, can be flushed 50% faster than other wireline test tools whose capabilities have been made public.1,2 Faster flushing enables quicker sampling of virgin formation fluids. Sample chambers can be filled against hydrostatic pressure to help ensure that pressure-volume-temperature (PVT) characteristics of the samples are not corrupted. Furthermore, additional pressure can be applied to minimize phase changes that might otherwise occur because of temperature gradients in the borehole. The new system also can be used to perform a closed-chamber PVT test for the bubblepoint of the fluid sampled. Closely spaced dual probes are deployed simultaneously for pressure testing and fluid sampling. Besides increasing tool reliability through redundancy, the two probes allow for advanced pressure-testing techniques. For example, formation anisotropy can be determined with an interference test between the two probes. Alternatively, a new pressure-pulsing technique can be used, which uses time delays between the probes' measured pressures to determine additional hydraulic-diffusive properties of the formation. The drawdowns can be rate- or pressure-controlled from either probe. The new tester is combinable with existing openhole logging tools, and tester tool sections are interchangeable. This combinability permits a complete wireline tool string to be configured to meet particular openhole formation-evaluation and testing needs in a single trip into the well. Current tool sections for the new tester include a dual-probe section (DPS), flow-control pumpout section (FPS), precision quartz gauge section (QGS), chamber valve section (CVS) for two sample chambers (1 to 5 gallons), and a multichamber section (MCS) with 1,000-cm3 chambers. The MCS chambers are compatible with hydrogen sulfide (H2S) with Natl. Assn. Of Corrosion Engineers-approved materials and have an exemption with the U.S. Dept. of Transportation (DOT) for common-carrier transportation. This paper details operational features of the new tester and introduces new pressure-testing and sampling-interpretation techniques. Field-test results are used to demonstrate these features and techniques.