After being successfully tested to 414 mbsf during Leg 164, a second tool was completed, along with a third spare tip including thermistors, and two additional thermistor strings. This second tool was deployed 45 times during Leg 168 with 100% data recovery. Depths of measurements ranged from about 40 to 575 mbsf, and formation temperatures ranged up to 64°C.
The DVTP proved to be extremely robust. Contact with basement did not damage the tool, nor did using the tool as a "smart" sinker bar for checking hole depths prior to running in CORK sensor strings and gaining a temperature log at the same time.
A program, originally created to reduce marine heat flow probe measurements (which require extrapolation of penetration transients that follow cylindrical decay functions), has been modified to run with a conical decay function matched to the dimensions and thermal properties of the probe tip. This program, dubbed "Conefit," will be described in a paper being prepared as part of the Leg 168 SR (Grigel, Villinger, Fisher, and Davis). Also, a general description of the tool, its operation, and its data (Davis, Villinger, Macdonald, Meldrum, and Grigel) is being prepared for the Leg 168 IR volume.
Initially, a problem was encountered with the dimensions of the spacer subs for use in the XCB core-barrel assembly, causing too little of the tool to be extended below the bit after the tool was landed (something like only 6 inches). This explains the partial penetrations observed during Leg 164 and early in Leg 168 (with only the tip thermistor correctly registering formation temperature). The problem of partial penetration did not completely disappear after the space-out was revised. It is suspected that a problem still remains with attaining reliable latch-in (with the tool properly extended by 1.1 m beyond the bit, with a full 10 k lbs load limit). Partial penetrations usually gave reliable formation temperatures at the tip thermistor, but agreement between the extrapolation of the lower and upper thermistors (separated by only 10 cm) was rare. A careful investigation of this problem may also help to explain some of the problematic data from the WSTP tool.
Future development of the DVTP may involve adding pressure capabilities to the tool. This will help tremendously when using the tool in "logging" mode, and, although it may be too optimistic, it is hoped to be able to recover formation pressures at a level of accuracy sufficient to make some advances in understanding the distribution of pressures in accretionary prisms and near décollement faults.
(See Downhole Measurements Laboratory and Downhole Measurements Panel (DMP).)
[ Contents of the Semiannual Report, No. 2, June-November 1996 |
| Program Updates | New Initiatives | Project Summaries | Laboratory Working Groups |
| Panel Recommendations | Appendixes |
| Semiannual Report, No. 1, December-May 1996 ]