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Downhole logging tools

Third Party Tools

Modular Temperature Tool (MTT)


The Modular Temperature Tool (MTT) is a flexible, general-purpose third party temperature logging tool developed for use in the Integrated Ocean Drilling Program by the Lamont-Doherty Earth Observatory Borehole Research Group. It replaces two previous temperature logging tools: 1) the Temperature-Acceleration-Pressure probe (TAP), which was limited to temperatures below 85°C and operated only in memory mode; and 2) the High Temperature Tool (HTT), which could only be deployed in standalone mode and was difficult to use. The MTT is a high accuracy and fast responding instrument that resolves inch-scale temperature variations at typical 900 ft/hr logging speeds.

The MTT uses two temperature sensors: a fast responding thermocouple and a highly accurate RTD (Resistance Temperature Detector). It contains two sensor sondes; one is for use at the end of string (typically memory logging), and the other allows the MTT to operate in the middle of a tool string (typically sending data back via Schlumberger telemetry). The MTT can either store log data in flash memory for later recall or send real-time data to the surface via Schlumberger's telemetry system. To cope with the high ambient temperature, all components except the temperature sensors are contained in a vacuum flask.

The MTT also includes an accelerometer channel to improve data stacking by precisely measuring logging speed and providing better depth corrections. A specialized telemetry system, the Schlumberger-Lamont Telemetry Adapter (SLTA), was developed specifically for the MTT in order to allow the tool to be combined with Schlumberger tools for single logging tool string deployment and to minimize the required rig time necessary to acquire the log.



Helps identify sections of inflow or outflow as fluids move through the sediments and oceanic crust.


Aids in estimating the vertical fluid flow regime and potential geothermal gradients


Determines temperatures ranges and potential fluid flow zones where microbes could thrive.

Gas Hydrates

Constrains the depth range of the gas hydrate stability zone.


Evaluates fluid temperatures to prevent damage to heat sensitive instruments.

Environmental Effects

The MTT response can be affected by borehole size and circulation of fluids during drilling operations. Down flow of colder and denser ocean bottom water after drilling into the borehole can affect the temperature profiles.

Log Presentation

Temperature data (including MTT) from Hole 1256D

MTT data acquired from Hole U1632A, IODP Expedition 327

Tool Specifications

Temperature rating: 621° F (327° C )
Pressure rating: 10,000 psi (6.9 kPa)
Diameter: 3.5 in (8.9 cm)
  Inline Sonde: 1.7 ft (0.5 m)
  Bottom Sonde: 0.9 ft (0.3 m)
  Inline Sonde: 37 lbs (16.8 kg)
  Bottom Sonde: 27 lbs (12.3 kg)
Number of temperature modules: 2
Module spacing: Variable
  RTD: 1/8 in. diameter, 4 wire, Class A
  Thermocouple: 1/32 in. diameter, K thermocouple
  Accelerometer: Surface mounted - ADXL203, U17
Maximum cable length: 30,000 ft (9144 m)
Maximum logging speed: 900 ft/hr (275 m/hr)
Cablehead connection: Schlumberger style
Sample rate  
  RTD: 1 Hz
  Thermocouple: 4 Hz
  Accelerometer: 4 Hz

Measurement Specifications

Measurement range  
  Temperature: -273°C to 327°C
  Acceleration: ±17 m/s² (±1.7g)
Measurement resolution  
  RTD: 0.05°C
  Thermocouple: 0.05°C
  Accelerometer: 0.001 m/s²

Major Outputs

Temperature: WTEP_LDEO (°C)
Acceleration: AZ_LDEO (m/s²)

Deployment Notes

The MTT can be run either at the at bottom of the Schlumberger Triple Combo tool string as a memory only tool, or inline between other Schlumberger tools in real-time mode. If used in inline mode, the SLTA needs to be included and pressure bulkheads at the top and bottom of the MTT need to be part of the tool string to isolate Schlumberger tools from potential pressure leaks.

Stuck/lost tool information