Probe: Launches Reservoir Analysis Sonde, RAS, a Three-Detector Pulsed-Neutron Logging Tool

The RAS™, Reservoir Analysis Sonde, Probe’s three-detector pulsed-neutron logging tool was announced during this year’s Offshore Technology Conference. The tool uses sigma and carbon-oxygen (C/O) techniques to measure reservoir fluid saturation of oil, water and gas.

The ability to accurately and reliably monitor reservoir conditions is an ongoing challenge for operators and service companies alike. For years, the industry has relied on systems that employ pulsed neutron technology to measure reservoir fluids behind casing and well tubulars. This technology is applied to monitor fluid contacts in the reservoir, diagnose production problems and to locate bypassed pay zones.

Full-function pulsed-neutron reservoir monitoring tools that employ sigma logging and C/O spectroscopy have been available from the major wireline service companies. “Operators and smaller wireline service companies had no alternative but to use the tools offered by a few major players,” said Federico Casavantes, President & CEO of Probe, a leading supplier of cased-hole well logging and reservoir monitoring technology. “Consequently, demand for a full-function pulsed-neutron tool from an independent supplier, that could offer the same – or better – reservoir saturation data, continued to escalate. This demand was also being driven by market dynamics which greatly favored tool reliability, long-life and low total cost of ownership, all of which we are now able to fully address through our product offering.”

Probe’s Reservoir Analysis Sonde, RAS, an independent alternative

Specialists at Hunter Well Science, a subsidiary of Probe since December 2017, developed the tool to measure reservoir fluid saturation of oil, water and gas.

The tool operates in three basic modes:

Sigma: water saturation detected via thermal neutron decay

C/O: oil saturation detected with gamma spectroscopy

Water flow: water velocity from oxygen activation

In addition, in sigma mode, the three-detector array can be used to measure gas saturation. For wells with limited data, the tool can make standalone porosity and lithology measurements.

The shortest highly-adaptable pulsed-neutron tool in the industry

By using modern, ruggedized electronics, the RAS has been streamlined into a compact-robust device. The tool and telemetry-gamma ray casing collar locator together constitute the shortest reservoir analysis tool string in the industry, measuring a combined 16.9 feet (5.14m). “Its compact size makes it easier to deploy and reduces potential failure points,” said Casavantes. “It also means that it is very versatile and can be configured to suit different conveyance types and downhole conditions.”

At the center of the pulsed-neutron tool is a rugged neutron generator that operates in temperatures as high as 320°F (160°C) and has a typical service life of 1,000 hours—nearly double the lifespan of many other reservoir analysis tools.


With more than 500 successful runs completed primarily in the USA, Middle East-North Africa region, and China, it is a field-proven logging tool. It is used in a variety of applications, particularly in casedhole and openhole completions in surface read-out and memory-operating modes, on conventional tubing, e-Line, e-Coil, conductor and conventional slickline.

To help operators gather definitive saturation data, the pulsed-neutron tool is effective for the following applications:

1) Saturation logging of water, oil and gas

2) Time-lapse reservoir monitoring

3) Contact logging and time lapse contact logging

4) Oxygen activation (water flow) to determine water phase velocity

5) Openhole emulation

6) Wellbore performance (in combination with production logging)

As with all Hunter platform tools, the pulsed-neutron tool is designed for maximum flexibility. It is compatible with the company’s standard and array production logging technologies, spectral gamma ray and well integrity products in both surface read-out and memory-operating modes.

The pulsed-neutron tool, which is manufactured by Probe at its facility in Arlington, Texas, USA, is offered for purchase to oilfield service companies, NOC’s and IOC’s. The company provides thorough training and support, and frequently participates on-site during the first commercial use of the tool by a customer.