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Drill String Tools
Formation Temperature Measurements
Two types of ODP tools are routinely available for measuring temperatures in sediment and in open hole: the WSTP mentioned before and miniature instruments deployed within special APC cutting shoes. These tools are normally used separately to obtain single measurements of temperature at discrete depths during a sequence of coring a hole through sediments. In addition, they can be configured together for simultaneous use without coring. Either tool or the combination can be washed and pushed through soft sediments or run into open hole, to measure temperatures at multiple depths during a single lowering.
The first generation APC temperature recorders were developed bt R. Von Herzen and colleagues during the last several years of the Deep Sea Drilling Program (DSDP); ODP purchased 10 new instruments designed and built by Adara, a Canadian geotechnical firm. Like its predecessor, the new device monitors the temperature of a single sensor within the APC cutting shoe. The tool contains its own microprocessor, which is programmed to cycle through a series of sleeping and sampling periods. On penetration, the coring shoe must be held in the sediments for 10-15 minutes to obtain enough data to allow extrapolation beyond the thermal distrubance of insertion to in situ temperature. The APC tool is relatively easy to operate, and with sufficient personel can be run on successive cores in an APC hole. The tool is limited to depths where the force required is within safe limits (usually less than 80k-100k lbs). The pullout force is generally greater when the APC temperature tool is run, compared to when an ordinary APC shoe is run, because leaving the core barrel in the bottom for several minutes for the temperature measurement allows sediments to become packed in around the barrel. In practice, this pullout limit is often reached within the upper 100-150 m of sediment below the seafloor.
In contrast, the WSTP has been run to depths greater than 400 mbsf, but it may require several hours per run on the coring line between cores. The WSTP data logger contains no microprocessor, and instead continuously samples at a fixed time interval the resistance of one or more thermistors mounted in a cylindrical probe. Adara is currently developing a new data logger similar in function to the APC tool, containing its own microprocessor. The WSTP is attached to the front end of a special core barrel, which functions as a pressure case for the electronics, batteries, data logger, and hydrolics, and is lowered down the drill string and pushed into the sediments. Again, the probe must be held in place for 10-15 minutes to obtain enough data to allow extrapolation to in situ temperature.
WSTP Temperature Measurements
See also ODP Technical Note 10
APC/Adara Temperature Tool
The APC tool is run with two battery packs, each of which contains seven ordinary "camera" batteries. A diode has been added to allow the instruments to draw power from both batteries, which helps increase overall battery life and reduces the chances of running out of power during a station. In contrast to the WSTP, data storage in the APC tool recorder is nonvolitile, meaning that previously collected data are retained in memory even if power is lost during a station. The APC tools are calibrated over a temperature range of -20 to 100°C and will operate at temperatures up to 125°C.
See also ODP Technical Note 10
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