New Wireline Formation Testing Tool With Advanced Sampling Technology
- Mark A. Proett (Halliburton Energy Services) | Gregory N. Gilbert (Halliburton Energy Services) | Wilson C. Chin (Halliburton Energy Services) | Myrick L. Monroe Jr (Halliburton Energy Services)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- April 2001
- Document Type
- Journal Paper
- 76 - 87
- 2001. Society of Petroleum Engineers
- 5.2 Reservoir Fluid Dynamics, 2.2.2 Perforating, 4.3.4 Scale, 5.5.11 Formation Testing (e.g., Wireline, LWD), 5.6.1 Open hole/cased hole log analysis, 4.1.5 Processing Equipment, 5.2.1 Phase Behavior and PVT Measurements, 4.2.3 Materials and Corrosion, 4.1.2 Separation and Treating, 2 Well Completion, 4.5.3 Floating Production Systems, 5.1 Reservoir Characterisation, 5.6.4 Drillstem/Well Testing, 1.7.5 Well Control, 4.2 Pipelines, Flowlines and Risers, 1.15 Fundamental Research in Drilling, 1.6 Drilling Operations
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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continuously monitor the fluid sampled and to make precise adjustments to the rate and pressure at which the fluid is withdrawn from the formation and injected into a sample chamber.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 pumping-system 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.
Wireline formation testing tools have been available since the mid-1950's and have undergone generations of evolutionary changes. Early tools were conceived as simple sampling devices with a single probe that established formation-fluid flow with a bullet perforation charge.3 Strain-gauge pressure transducers quickly followed, adding a new dimension to wireline formation evaluation.4 In the 1970's, dual chambers and pressure sensing were followed by the next generation of hydraulically powered tools with repeated pressure-testing capabilities and high-resolution quartz gauges.5,6 Multiple probes, pumps, and fluid sensors were added in the late 1980's to early 1990's to purge the zone near the wellbore of filtrate while monitoring sample quality.7 Only recently have sample-chamber-filling techniques been improved to reduce the shock experienced when the chamber is opened and filled.8
High-quality samples continue to be the driving force for each new advancement. Advances in downhole microprocessor digital-control technology combined with modern hydraulic servo systems can extend the level of sampling control and improve sample quality. Even when a sample is drawn carefully into the tool, if it is not kept in a single phase in the chamber before it is retrieved to the surface, its quality can be corrupted. A complex sequence of events transpires during the pumping of the formation fluid, filling of a sample chamber, and bringing of the sample to the surface. The events must be monitored and controlled precisely to ensure that a single-phase PVT-quality sample is delivered.
Though sample quality is considered a priority, wireline testers have continued to advance in formation-evaluation techniques. The first function performed by a wireline tester is a pretest, an experiment to evaluate the zone's potential. After the probe is sealed against the borehole wall, a small volume of fluid is drawn into the tool. A drawdown-buildup sequence follows, mimicking a miniature well test. The pore pressure is determined from the buildup and has been the most important measurement of the zone's potential. If the flow rate can be controlled and the sandface flow rate reaches a steady-state condition, the formation mobility (i.e., md/cp) can be determined easily. Unfortunately, the volume of the pretest is too small (5 to 10 cm3) to affect a significant zone of investigation. Furthermore, the flow rate may not be well controlled, and the compressibility of fluid in the flowlines of the tool can further modify the sandface flow rate and dominate the transient-pressure response.
While these effects can be corrected with improved transient-analysis techniques, the validity of the measurement is questioned. As a result, mobility and permeability estimates have not been regarded as primary measurements for wireline testers. If a high degree of control can be applied to the pretest experiment, the analysis technique is simplified and accuracy is improved. Additionally, if the pumpout flow rates can be controlled in a real-time dynamic manner, the cleaning action of the pump can be monitored with changes in permeability. Pumping can remove more than 40 gallons of formation fluids, increasing the depth of investigation. The net result is a more accurate measurement of permeability in real time during pumping and sampling.
The paper demonstrates how improvements to sampling and pressure-testing control can improve the quality of wireline formation testing. A new tool design is introduced with a short description of its functions and capabilities. Simulations of the tool's behavior illustrate how its design parameters were derived for testing and sampling over a wide range of formation conditions. Finally, log examples demonstrate the applications of the new testing tool.
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