Downhole logging tools

The TAP (High Resolution Temperature / Acceleration / Pressure) tool was designed at LDEO to acquire borehole temperature, tool acceleration and hydrostatic pressure data. It is the successor to the Lamont Temperature Tool (TLT), which was used in the early part of ODP.

The TAP tool is fastened to the bottom of the Triple Combo; because it is a memory tool, the stored data are dumped to the third party DAS (Data Acquisition System) upon the tool's return to the rig floor.

Fast and slow response thermistors are mounted near the bottom of the tool to detect borehole fluid temperatures at two different rates. The thinner, fast-response is able to detect small abrupt changes in temperature, the thicker, slow-response thermistor is used to estimate temperature gradient and thermal regimes more accurately. One pressure transducer is included to turn the tool on and off at specified depths when used in memory mode. Typically data acquisition is programmed to begin 100 m above the sea floor.

A 3-axis accelerometer is also included to measure tool movement downhole. These data are expected to be instrumental in analyzing the effects of heave on a deployed tool string, which will lead to the fine tuning of the WHC (wireline heave compensator).

Geothermics
The recording of temperature provides an insight into the thermal regime of the formation surrounding the borehole. The vertical heat flow is estimated from the vertical temperature gradient combined with the measurements of the thermal conductivity from logs or core samples.

Hydrogeology
Crust at mid-ocean ridge crests must be permeable to a considerable depth to allow for the efficient removal of heat by hydrothermal systems. Temperature logs in such an environment can clearly differentiate between the advective (hydrothermal) and conductive heat transfer regimes.

Drilling and circulation operations considerably disturb the temperature distribution inside the borehole thus preventing equilibrated temperature conditions. The amount of time elapsed between the end of drilling fluid circulation and the beginning of logging operations is not long enough to allow the borehole to recover thermally. Therefore the data recorded is not representative of the thermal equilibrium of that environment. In addition, the thermistors may become fouled with sediment from the drilled formation which reduces the sensitivity and accuracy of the recorded temperature data.

Log Presentation

Temperature data acquired by the fast and slow thermistors may be presented with resistivity, density and porosity log data, or simply alone. For an example of temperature profile, click here.

Because it is a memory tool, the TAP needs to be initialized approximately 1/2 hour prior to rig up of the Triple Combo tool string. Once initialized, the TAP tool should be placed on the deck outside of the DHML to be picked up by the roughnecks. The logger then must connect it to the bottom of the Triple Combo using a pin and rotating ring assembly. When the Triple Combo is retrieved to the rig floor, the Logging Staff Scientist must remove the TAP tool, wash it off and download the data on the onboard computer.

Stuck/lost tool information