A New-Generation LWD Tool With Colocated Sensors Opens New Opportunities for Formation Evaluation
- Thomas James Neville (Schlumberger) | Geoff Weller (Schlumberger) | Ollivier Faivre (Schlumberger) | Haitao Sun (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- April 2007
- Document Type
- Journal Paper
- 132 - 139
- 2007. Society of Petroleum Engineers
- 5.2 Reservoir Fluid Dynamics, 1.6.1 Drilling Operation Management, 1.6.7 Geosteering / Reservoir Navigation, 1.12.5 Real Time Data Transmission, 3.3.2 Borehole Imaging and Wellbore Seismic, 5.8.7 Carbonate Reservoir, 5.6.1 Open hole/cased hole log analysis, 1.2.3 Rock properties, 1.11 Drilling Fluids and Materials, 1.6 Drilling Operations, 6.3.6 Chemical Storage and Use, 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 1.6.9 Coring, Fishing, 3.3.6 Integrated Modeling, 5.3.4 Integration of geomechanics in models, 2.4.3 Sand/Solids Control, 1.12.2 Logging While Drilling
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A new logging-while-drilling (LWD) tool that combines traditional measurements of gamma ray, propagation resistivity, gamma-gamma density, and thermal-neutron porosity with measurements unique to the LWD arena, including neutron capture spectroscopy and capture cross section, opens up new opportunities for formation evaluation on LWD.
The compact design of the new-generation LWD tool greatly increases the likelihood that measurements will be made before the onset of significant invasion. The colocation of resistivity- and neutron-based sensors also means that key measurements are being made at the same depth at the same time and on a similar volume of the formation. These features ensure that all measurements are essentially seeing the same amount of invasion, thus removing a major complication in conventional LWD interpretation.
A new-generation LWD tool has been developed that integrates measurements of gamma ray, propagation resistivity, gamma-gamma density, and thermal-neutron porosity with additional measurements unique to the LWD arena, including neutron capture spectroscopy and measurement of formation capture cross section (Weller et al. 2005). The EcoScope multifunction LWD service integrates all of these measurements in a single collar optimized to:
- Minimize measurement distance to bit.
- Improve real-time data-transmission rates.
- Improve service reliability.
- Minimize use of chemical nuclear sources.
The new-generation LWD tool is currently available in a 6¾-in. collar size, with a total length of 26 ft (Fig. 1). The tool is rated to operate at up to 20,000 psi and 300°F. Other collar sizes are also under development to allow the tool to be deployed in a wider variety of hole sizes.
Array propagation resistivity measurements and neutron-based measurements, including neutron porosity, neutron capture spectroscopy, and formation capture cross section, are colocated in the top half of the tool, with the highest measure point being less than 16 ft above the bottom of the tool.
The conventional stabilized gamma-gamma density measurement is located within 8 ft of the bottom of the tool; this provides average and quadrant values and 16-sector images of bulk density and photoelectric factor. Stabilizers are available to support use in hole sizes ranging from approximately 8 to 10 in. Future developments of the tool will extend this range. Adjacent to the stabilizer are two diametrically opposed ultrasonic standoff sensors. These provide a 16-sector ultrasonic borehole image when the tool is rotating and allow for a caliper measurement even when sliding.
Finally, an azimuthal gamma ray measurement device, capable of producing 16-sector gamma ray images as well as quadrant and average gamma ray measurements, is located only 5 ft above the bottom of the tool. The gamma ray detector uses a very large sodium iodide crystal to achieve high count rates, and owing to a focused design, the measurement has good azimuthal sensitivity; this enables gamma ray images to be acquired.
Efforts to address the four objectives described above have led to the design of a tool with unprecedented application for formation evaluation. We will discuss here the application of the rich data set produced by this tool for the evaluation of lithology and mineralogy, porosity, and fluid saturations.
Evaluation of these properties using a similar suite of measurements acquired while using wireline-logging tools has been presented previously (Herron et al. 2002). However, the suite of measurements available with this new tool, and the fact that many of the measurements are colocated, has allowed this methodology to be extended and enhanced. In addition, recent enhancements in data-transmission rates allow all of these measurements to be accessed in real time, thus bringing the possibility to use advanced formation-evaluation results to make while-drilling decisions.
|File Size||2 MB||Number of Pages||8|
Herron, M.M. and Herron, S.L. 1998.Quantitative Lithology: Open and Cased Hole Application Derived from IntegratedCore Chemistry and Mineralogy Data Base. In Core-Log Integration, ed.P.K. Harvey and M.A. Lovell, Special Publication 136, 81-95. London: TheGeological Society.
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