resistor for several minutes and monitoring the increasing voltage. In addition,
resetting the tattletale controller prior to any communication attempt was
necessary. Once several bench tests were satisfactory, the tool was prepared for
deployment.The CBTT was deployed on the fourth core barrel during the initial drilling stages of Hole 1188A. The deviation from the initial plan for CBTT deployments (see "Downhole Measurements" in the "Explanatory Notes" chapter) was necessary because of the difficulties in communicating and initializing the CBTT using a serial line connection with a DB9 communication port (COM1) in the downhole measurements laboratory PC data acquisition system.
One of the tools did not
respond to several communication attempts, and the second tool finally began
responding after several attempts and diagnostic checks were made. The batteries
were revived by connecting a 100-
resistor for several minutes and monitoring the increasing voltage. In addition,
resetting the tattletale controller prior to any communication attempt was
necessary. Once several bench tests were satisfactory, the tool was prepared for
deployment.
After initialization, the tool was placed in a dewar with 320 mL of glycerin that was used as a thermal sink. The purpose of using glycerin was to protect the electronics from excessive temperatures, as they were rated to ~100°C and the downhole conditions were not well known. Shortly after initializing the tool, the external sensor was briefly disconnected for final assembly. After reconnecting the thermocouple and placing the tool in the pressure case, TSF core technicians assisted in placing the tool assembly on top of the core barrel and it was released as soon as the previous core was on deck. The tool was downhole for 3.2 hr, and it recorded data for 2.8 hr (Fig. F137). The discrepancy in time is believed to be similar to the original problems described above.
The temperature vs. time record from Core 193-1188A-4R (28.9-33.6 mbsf) shows profiles for both the internal (Tint) and external (Text) temperature sensors. The time of initialization, a period of ~6 min during which Text was disconnected, a heating period when the tool was at the rig floor, a cooling trend as the core barrel was released from the rig floor, and, finally, the bottom-hole profile, were all recorded (Fig. F137). Text shows an average bottom-hole temperature of 3.9° ± 0.4°C, whereas Tint shows an average temperature of 28.2° ± 0.8°C. These measurements imply either effective cooling of the borehole through pumping an average of 50 strokes per min (spm), which is ~250 gallons per min (gpm), or very cool, shallow subsurface conditions for this area.
The tool was disassembled and cleaned thoroughly after retrieval. Several checks were made to determine the erratic behavior in data recording times and communication. In the meantime, the DSA/CBTT pressure case was deployed in Sites 1189 and 1191 with maximum temperature thermometers to provide an idea of downhole temperature conditions while troubleshooting the CBTT electronics continued. The maximum temperature measurements recorded with the thermometers showed that the conditions were favorable for attempting an LWD hole at Site 1189 (see "Downhole Measurements" in the "Site 1189" chapter). During the deployment of the DSA/CBTT pressure case at the Satanic Mills hydrothermal site (Site 1191), the bit, core barrel, and DSA pressure case were lost at this site (see "Operations Summary" in the "Site 1191" chapter), ending any other potential deployment of the CBTT during Leg 193.
On 21 December 2000, Hole 1188B was reentered and the UHT-MSM temperature probe from the University of Miami was deployed (see "Downhole Measurements" in the "Explanatory Notes" chapter). The bottom of the drill pipe encountered a restriction at 3 mbsf, and the UHT-MSM penetrated to a logging total depth (TD) of 7 mbsf. The tool recorded a maximum temperature of 4.8°C during a 15-min stationary measurement (Fig. F138A).
Following the UHT-MSM deployment, the WSTP was lowered to a depth of 6 mbsf for a 15-min station (Fig. F138B). The maximum recorded temperature was 5.8°C, and a water sample was obtained, although problems with the valve were reported (see "Geochemistry").
On 25 November 2000,
drilling operations for the first ODP deployment of the LWD RAB tool began soon
after the lithium batteries arrived from Rabaul, New Britain (PNG). The
batteries did not arrive in Guam before our departure on 14 November 2000,
consequently, they were shipped to Rabaul where they were transported to the JOIDES
Resolution on a helicopter. Upon arrival, they were promptly tested and
revived with a 150-
resistor for several minutes prior to assembling the RAB. After the batteries
were installed, the tool was initialized and the Anadrill engineer began the
assembly of the 9.875-in RAB BHA (see "Downhole Measurements"
in the "Explanatory
Notes" chapter) with the assistance of the rig floor crew. Once the
RAB was within several meters of the seafloor, the VIT camera was lowered and a
suitable location was found for beginning drilling operations in Hole 1188B.
Spudding was delayed by ~1.5 hr because drilling engineers were servicing and
calibrating the AHC system that had not been operational until this time.
Drilling began with a very
high penetration rate (
40
m/hr) in the upper 8 mbsf. At 13 mbsf, a hard formation was encountered as it
stalled the top drive and required ~100,000 klb of overpull to get free. Two
more difficult-to-drill zones were encountered at 27 and 64 mbsf. The
penetration rate slowed down to ~2 m/hr at 68 mbsf, and finally at 72 mbsf, the
LWD operations were terminated. The decision to stop 3 m short of the original
target depth was based on our previous experiences in Holes 1188A and 1189A (see
"Site 1188" and "Site 1189," both in "Operations
Summary" in the "Leg
193 Summary" chapter) as well as the significant decrease in
penetration rates toward the bottom of the hole.
A FFF was deployed after LWD operations were finished and before pulling out of the hole with the intent of reentering with the ADCB and deepening the hole (see "First Return to Site 1188" in "Operations Summary" in the "Leg 193 Summary" chapter). After retrieving the RAB, we noticed that the tool was in good condition with only a few scratches and slight wear on the resistivity buttons.
Sepiolite mud was used to
flush drill cuttings out of the hole. The mud weight was determined to be 8.9
pounds per gallon (ppg), and mud resistivity was determined to be 0.183 m
using the Schlumberger mud resistivity meter. These parameters, along with the
bit size, were used for applying environmental corrections to the data.
The RAB tool in memory mode records data as a function of time. At the surface during deployment, time and depth data were recorded with the depth from Geolograph. The time-depth file was corrected for heave as explained in "Downhole Measurements" in the "Explanatory Notes" chapter. The corrected surface time-depth file was then used to match the recorded downhole time file with the surface depth data, thus generating a depth file for the RAB data.
The RAB tool provides electrical images of the borehole wall with three different levels of investigation (deep, medium, and shallow), as well as individual log curves of electrical resistivity at the same three depths of investigation and of natural radioactivity. The RAB tool records the total gamma radiation but not its spectrum. Therefore, the contribution of the main radioactive elements, such as potassium, thorium, and uranium, cannot be individually separated from the total spectrum measurements. The log curves of electrical resistivity and gamma ray are displayed together with the ROP and bit rotation in Figure F139.
At the beginning of the LWD operations, the optimal ROP was determined to be 20-27 m/hr based on a sampling interval of 20 s. However, in the upper 32 m, the ROP was high and erratic. These data may provide an estimate of formation hardness or fracture zones because the resistance of the rocks to drilling fluctuated and made conditions difficult to maintain a constant penetration rate.
The quality of the electrical images of Hole 1188B are greatly influenced by artifacts causing stripes in the images, especially in the top and bottom intervals. There are several possible explanations that will require additional processing and a detailed look at the raw data and drilling parameters. First, errors during the time-depth conversion and filtering techniques applied to the time-depth file for removing the effects of vertical motion of the bit might be potential reasons for these problems. Second, the sea state was relatively calm (~ 0.5-m heave) during LWD operations, but the active heave compensator was used. Although the Geolograph should correct for the motion of the drawworks, the operation of the active heave compensator may also have contributed to the problems since the weight on bit is not accurately known and the system was being calibrated minutes prior to spudding the hole. Third, a problem with the RAB time-frame file was found when the memory data were downloaded at the end of the run. The RAB tool acquisition time was 28.5 hr from the time of initializing to the time of download, and the RAB time frame file had recorded over 95 hr of data.
Electrical resistivities
range from 0.2 m
for the shallow button (RBS) to 6.4 m
for the ring measurement (RRING). These values tend to be
low for volcanic rocks with rhyolite and dacite compositions. Young
water-bearing volcanic rocks typically have values between 10 and 200 m
(Keller, 1966). The relatively low resistivity values may indicate a formation
with either a high degree of alteration, exhibiting a significant amount of
fracturing, or having high porosity. Gamma-ray values range from 1 to 56 gAPI
with an average value of 21 gAPI. Both the average resistivity and gamma-ray log
curves from the RAB were used for characterizing the lithostratigraphy of Hole
1188B. Figure F140
shows deep resistivity and gamma-ray curves, the logging units identified from
the logs, and the core lithostratigraphic units found in the upper 75 m of
neighboring Hole 1188A.
Eleven logging units were identified from five different relationships found in the electrical resistivity and gamma-ray measurements (Fig. F140). These relationships are high gamma ray-high resistivity, high gamma ray-low resistivity, low gamma ray-low resistivity, transitional responses, and unclear relations that are labeled unclassified.
Based on log responses and core observations, the high gamma-ray and high resistivity values of logging Units 2, 5, and 8 may reflect less fractured and/or less altered sections of rhyodacite lava flows. In many cases, this is supported by a decreasing ROP (Fig. F139) in logging units with high resistivity, which may be indicative of harder layers. Logging units characterized by low resistivities are interpreted to represent altered or fractured layers (logging Units 3, 7, and 9). The presence of both seawater or conductive clay minerals causes the resistivity to decrease. The higher gamma-ray values of logging Unit 9 may be explained by the presence of K- or U-bearing minerals as seen in the wireline logs from Holes 1188F, 1189B, and 1189C. Logging Unit 7 shows a sharp decrease in resistivity and low gamma-ray values that may represent a fractured zone, but it may also correspond to a high-porosity zone with abundant vesicles.
Logging Units 1, 4, 6, and 11 are interpreted as transitional layers. Logging Unit 1 represents the transition between a softer seafloor cover, also characterized by a high-penetration rate, and the harder layers of logging Unit 2. Logging Units 4 and 6 are interpreted as transitions in alteration and fracturing from a more massive logging Unit 5. Logging Unit 11 is a transitional layer at the bottom of the hole, where the rock properties or style of alteration seem to be changing.
Logging Unit 10 does not show a clear correlation between resistivity and gamma-ray measurements. The upper part of this unit is characterized by high resistivities that decrease with depth and the highest gamma-ray values of the entire upper 65 m, where the drop in resistivity occurs. This logging unit seems to represent a transition between a massive upper part of a flow to considerable alteration toward its base. The gamma-ray response in Hole 1188B suggests the presence of K- or U-rich minerals in logging Unit 10 (~52-60 mbsf). This is consistent with core observations from Hole 1188A, suggesting higher clay concentrations in lithostratigraphic Units 6 and 7 at a similar depth (50-68 mbsf). The XRD mineralogical analyses and core observations also suggest the presence of illite and/or chlorite, which generally have high potassium and thorium contents (see "Hydrothermal Alteration").
Variations within the 11 logging units were subdivided into 31 logging subunits (Fig. F140). These subdivisions are based on the same relationships used to describe the 11 logging units described above. In these subdivisions, two more relationships were recognized, low gamma ray-high resistivity and low gamma ray-intermediate resistivity. The logging subunits represent small-scale variations of the log responses within the logging units (e.g., the thin layers of low resistivity identified in logging Subunits 2B and 2D). Interpretation of the additional logging data relationships awaits postcruise research.
In the upper 39 m of the hole, there is a positive correlation between the electrical resistivity and gamma ray (Fig. F140). Most of the rocks in this interval are characterized by high resistivity and gamma-ray values or low resistivity and gamma-ray values. One exception is logging Subunit 3A, which shows low resistivity and high gamma-ray values. This log response may be indicative of a layer rich in conductive K- or U-bearing minerals. Two factors may explain the predominantly positive correlation between resistivity and gamma ray above 39 mbsf. Alteration (i.e., bleaching) may lead to a decrease in radioactive elements; thus, gamma-ray values will be low in an altered zone. However, a predominance of seawater in fractures and voids may also cause the same effect. Lithologic units from the equivalent section of Hole 1188A show that in the upper 39 m, rocks tend to vary from relatively fresh to strongly bleached (see "Hydrothermal Alteration"). Unfortunately, because of the poor core recovery, only a few physical properties, petrological, and geochemical analyses exist from this section, and the contribution of the radioactive elements to the gamma-ray radiation is not known.
Below 39 mbsf, a correlation between resistivity and the gamma-ray logs is not as clear, especially in logging Unit 10 (Fig. F140). Most of the logging units below this depth exhibit an opposite trend to the one observed above 39 mbsf (i.e., many units are either characterized by high resistivity and low gamma-ray values or vice versa). The highest gamma-ray values are recorded in logging Unit 10, but there is no apparent correlation with resistivity measurements. The correlation between electrical resistivity and gamma-ray measurements exhibits a relatively linear trend for most of the logging units, with the exception of logging Unit 10 (Fig. F141).
Figure F142 shows the image of the deep resistivity between 44.5 and 65.5 mbsf after different steps of image processing. For the raw data image, the electrical resistivity values were distributed into 18 classes, each with a different color. An equalized histogram method was used for enhancement of the other two images. This method optimizes the use of a given number of colors (N) in a given interval of the image by determining the color thresholds (N - 1) that will partition the data values into (N) equal populations? in this particular case. The processing module BorNor, which is part of the GeoQuest Geoframe software package, was used for providing two types of image normalization for the Leg 193 RAB data—static and dynamic. Static normalization is a computation where a window covering the entire depth interval is specified. In contrast, dynamic normalization requires a separate set of computations repeated at regularly spaced positions over the specified depth interval. This method uses a sliding window of relatively short length, which for this case was the default value of 0.6 m. The successive windows have an overlap of 75%, and color thresholds are interpolated between the windows so that a continuous movement of the normalization is simulated.
The raw data image gives an overview of the section but the least amount of detail. Static normalization allows for better interpretation than the raw data image as contrast is enhanced and details are highlighted. The dynamically normalized image shows the most detail and fine features. However, it is only suitable for interpretation on a small scale. As the color thresholds are computed in a sliding window, the same color at two widely separated depth points does not necessarily have the same resistivity. With increasing levels of processing, the problems outlined previously in the data quality are magnified. The raw image data show problems only locally, the statically normalized image shows more problematic sections, and the dynamically processed image shows the greatest effects of data degradation. Not much information was gained from the dynamic image after shipboard processing, and further work is needed before the image is suitable for structural analyses.
The static image may be
suitable for correlation with the results of the formation evaluation. The
light-colored (highly resistive) layers between 50 and 54 mbsf (Fig. F142)
correlate with the upper, highly resistive zone of logging Unit 10. In Figure F143,
the depth interval between 18.7 and 32 mbsf is shown as two-dimensional and
three-dimensional image representations. The light-colored features correspond
to the high resistivity layers of logging Units 3, 4, and 5. Although the
resistivities for the entire logged section tend to be low, the high resistivity
contrast and patchy nature of this subvertical feature may imply higher
concentrations of anhydrite, as the reported resistivity values for this calcium
sulfate are in the range of 10,000 m
or higher (Serra, 1972a, 1972b; Rider, 1996). The low resistivity and gamma-ray
values found in logging Subunits 3B and 3D also appear as darker colors or
conductive features in Figure F143.
On 21 December 2000,
wireline logging operations in Hole 1188F began with the deployment of a
high-temperature/pressure telemetry gamma-ray cartridge (HTGC) and dual
induction resistivity (DIT-E) tool string combination with real-time cable head
temperature capabilities (MTEM). The water depth was estimated from pipe
measurements at ~1653 mbrf. The first casing string (13.375 in) was set to a
depth of 58.9 mbsf, and the base of a second casing string (10.75 in) was at
190.4 mbsf (see "Introduction").
The drill pipe was placed at ~185 mbsf. A wiper trip to the bottom of the hole
was done ~12 hr before logging operations began, and 15 bbl of sepiolite mud was
circulated at the end of that hole-cleaning operation. A sepiolite mud weight of
8.9 ppg and a mud resistivity of 0.183 m
were used to apply corrections to the logging data.
The MTEM-HTGC-DIT-E tool string was deployed, but the wireline heave compensator (WHC) was not used because the system would not power up. A problem was found with the limit switch as the piston extended to a maximum position sending a current imbalance (current flowing on the ground line) to the ground fault interrupt (GFI) and causing the GFI to shut the system down. An external power supply was used to manually move the piston to a middle position where the limit switch would not affect the system. The WHC was then used during the second and third tool string deployments.
The second wireline deployment included the MTEM, the hostile environment natural gamma-ray sonde (HNGS), the accelerator porosity sonde (APS), and the hostile environment lithodensity sonde (HLDS). The third tool string combination consisted of the MTEM, the natural gamma-ray tool (NGT), the dipole sonic imager (DSI), and the FMS. During the last two logging runs, heave measurements were recorded with the guideline tensionometer encoder that was installed on the WHC for LWD operations. These records show <1-ft average heave during the second deployment and <1-m average motion for the third run (Fig. F144).
Drilling operations achieved a TD of 386.7 mbsf in Hole 1188F, and all wireline tool deployments reached a logging TD of 356 mbsf. An obstruction was encountered 30 m above the hole's TD, and all attempts to get past this were unsuccessful. Prior to the beginning of the logging operations, a borehole restriction was encountered at 362 mbsf during a wiper trip, and, although this spot is 6 m deeper than the logging TD, the hole problems are probably related.
On 26 December 2000, 5 days after the hole was drilled, the UHT-MSM temperature probe was lowered on the sand line to a depth of 20 m above the seafloor, and then Hole 1188F was reentered. Core barrel sinker bars were placed on top of the tool to add weight, and the UHT-MSM was deployed prior to reentering the hole to minimize the disturbance in the water column by displaced fluids as the tool was descending. The pipe was lowered 8 mbsf, and downlog temperatures were recorded at a sampling rate of 1 s and a logging speed of 250 m/hr until a logging TD was reached at 361 mbsf. The uplog was recorded using the same parameters and logging speed. Following the temperature log, the WSTP was deployed to a depth of 104 mbsf. On 29 December 2000, once again Hole 1188F was reentered and the UHT-MSM probe and WSTP were deployed following the similar procedures. The logging speed for the UHT-MSM was 300 m/hr, and the depth for the WSTP measurement was 207 mbsf.
Caliper measurements show that Hole 1188F is oversized (Fig. F145). The caliper from the HLDS measured 17.26 in throughout the entire logged interval, whereas the FMS calipers measured 15.14 in throughout the same interval. The maximum extension of these calipers is 17.75 and 15.5 in, respectively. The less-than-maximum extension on the FMS caliper lead us to question the accuracy of the borehole measurements. To confirm the accuracy of the borehole measurements, the second tool string was run inside the 10.75-in casing with the HLDS caliper open. The caliper measured 10.39 in, suggesting that the borehole measurements with this caliper (>17 in) were correct.
The HLDS and FMS calipers
were calibrated at 8 and 12 in before the logging runs because of the 7.25-in
ADCB bit that was used to drill Hole 1188F. However, nonlinear changes may occur
as the maximum aperture is reached; hence, the calipers were checked after
logging operations concluded. On deck, the maximum extension of the HLDS caliper
measured at 17.75 in, a 0.49-in difference with the recorded downhole data, and
the FMS caliper arms measured at 15.5 in, a 0.36-in difference with the borehole
measurements. Therefore, we interpret the diameter of the borehole to be in
excess of 15 in and probably 17
in.
The enlarged diameter of the borehole affects several of the measurements. The FMS produced only several short intervals with high-resolution images, and most of the borehole has intervals where only a range of one to three pads were in direct contact with the borehole walls. In most instances, the neutron porosity data are high and density readings are low with values approaching 1 g/cm3 between 210 and 240 mbsf, which can also be explained by an enlarged borehole.
Electrical resistivity
values measured in Hole 1188F are low throughout the entire logged interval.
Deep resistivity measurements range from 0.4 to 2.3 m,
and the shallow-resistivity log shows variations between 1.0 and 3.4 m
(Fig. F145).
The medium-resistivity log shows isolated spikes with higher resistivity values
that range up to 43 m.
These spikes do not show any correlation with the other logs and are probably
caused by a malfunction of the medium-resistivity receiver. For this reason,
this log was not included in the site report.
Formation natural radioactivity was measured during each run and with three different tools. The HTGC measured total gamma counts, whereas the HNGS and NGT provided spectral measurements. The different gamma-ray tools show good correlation between each other.
All gamma-ray curves show high values ranging up to 558 gAPI for the interval between 197.3 and 208.9 mbsf (Fig. F145). The spectral gamma-ray measurements show a significant increase in uranium within this interval. Uranium values increase up to 64 ppm. Potassium values are also slightly elevated, with values as high as 2.7 wt%. Another interval with increased gamma-ray and uranium values is present between 238.7 and 245.0 mbsf. Gamma-ray values increase to 62 gAPI and uranium values to 5.2 ppm. Besides these anomalies, gamma-ray values are between 2.8 and 80 gAPI. A good correlation between the standard gamma-ray curve and the potassium log indicates that potassium makes a significant contribution to the gamma-ray spectrum. Both the total gamma ray and the potassium values show downward increasing trends between 255 and 275 and between 300 and 338 mbsf.
Neutron porosity values range from 20% to 94% with an average value of 54%. These values are very high when compared to the core porosities measured, which range from 12% to 28% (see "Physical Properties"). These high porosity values may be explained by the enlarged borehole, the overall high fracturing of the rocks as observed in the FMS images, and, to some degree, the presence of hydrous minerals such as clay minerals (see "Downhole Measurements" in the "Explanatory Notes" chapter).
Density measurements show values ranging between 1.1 and 2.7 g/cm3. The average density for the entire logged interval is 2.0 g/cm3. Densities are especially low in the depth interval between 210 and 238 mbsf, where the values decrease to slightly above 1 g/cm3. The low values are indicative of the large diameter of the borehole, where, in many cases, the tool standoff reaches values close to or >1 in. Above 210 mbsf and below 298 mbsf, density values are higher, interrupted only locally by narrow peaks of low values. The photoelectric factor (PEF) values range between 1.4 and 11.7 barn/e-. The highest values correlate with the gamma-ray anomaly between 197.3 and 208.9 mbsf. However, for most of the borehole, the PEF reaches a maximum of 5.0 barn/e-, with an average value of 2.1 barn/e-. Values are low between 210 and 298 mbsf and show a slight increase below 298 mbsf.
Compressional wave velocities range from 2.3 to 5.9 km/s. The mean value is 3.1 km/s. In general, these compressional wave velocities are low for dacite or rhyodacite. This may be a direct effect of the large dimensions of the borehole and the relatively high fracture density of the formation. The depth intervals between 197.3 and 208.9 mbsf and also between 270.5 and 281 mbsf show significant changes in velocity with the largest low-velocity zones of the entire logged interval. The interval between 197.3 and 208.9 mbsf is especially unique because the porosity is low, whereas density, gamma-ray, and photoelectric effect values tend to be high. Postcruise processing and detailed analysis of the shipboard slowness time coherence processing will determine if the low-velocity zone is not a processing artifact. Stoneley and shear wave velocities are also low (Fig. F145). The shear wave velocity profile shows a high of 2.5 km/s at the top of logging Unit 2 that corresponds to highs in both bulk density and PEF. However, for most of the hole, the recorded shear wave velocities are below 2.0 km/s.
Temperature measurements were made during wireline operations on 21 and 22 December 2000, as well as 5 and 7 days later with the UHT-MSM temperature probe. These profiles are displayed in Figure F146. The MTEM located in the cable head was used in every wireline deployment during the 20 to 21 December 2000 logging operations. The profiles show an average steady increase in temperature from inside the 13.375-in casing string starting at 30 mbsf to ~234 mbsf. Temperature lows were recorded inside the 10.75-in casing from 156 to 160 mbsf and from 174 to 183 mbsf. A temperature high was also recorded from 184 to 191 mbsf. The high corresponds to the transition between the logging BHA and the 10.75-in casing. The low from 174 to 183 mbsf corresponds to the tool entering the logging BHA, whereas the low at 156-160 mbsf is well inside the pipe.
The interval from 234 to 289 mbsf shows that all 20 and 21 December 2000 temperature profiles have a decreasing trend followed by increasing temperatures until reaching the logging TD at 357 mbsf. The maximum recorded temperature in these runs was 99.6°C. This temperature was recorded with the second string at the bottom of the hole during the repeat section. The second pass with the FMS showed a maximum temperature of 98.4°C at ~15 m shallower than the previous high-temperature reading.
The temperature profile recorded 5 days later using the UHT-MSM probe shows a much smoother profile than the temperature measurements from the wireline operations, especially because the drill pipe was placed at 20 mbsf. In the upper part of Hole 1188F, temperatures are lower than those obtained with the wireline temperature sensor down to 250 mbsf. However, a sharp increase in temperature is observed starting from 250 mbsf to the bottom of the hole. The maximum recorded temperature is 304°C, which is an increase of 204°C over the previous wireline measurements. There were concerns about the reliability of these measurements, especially after a WSTP measurement at 107 mbsf recorded only 12°C and faulty pressure readings were obtained with the UHT-MSM probe during the previous run. This uncertainty lead to the deployment of the wireline telemetry cartridge that was used during the previous wireline measurements. This tool recorded increases with depth until it failed at ~338 mbsf (Fig. F146), where the temperature readings dropped from 118° to ~20°C. When the tool was back on deck, maximum-temperature thermometers that were placed in the cable head prior to deployment provided measurements >260°C. These measurements and the state of the wireline sensor, which had the electrical leads fused together, confirmed the previous measurements made with the UHT-MSM temperature probe.
Additional temperature measurements were planned for 29 December 2000 to determine the amount of thermal rebound in Hole 1188F and to estimate a suitable depth for obtaining water samples. The UTH-MSM tool recorded temperature and pressure as a function of time. To obtain depth, the internal tool clock was synchronized with rig floor time and the computer in the subsea shop. The computer in the subsea shop was then used to obtain time-depth records of the sand line as the tool was being lowered in the hole. Attempts to match times proved to be a time consuming task because of the different sampling rates between the tool (1 sample/s) and the subsea computer (1 sample every 4 or 5 s). In addition, in many instances the depth files from the subsea shop contained records from previous deployments; hence, depth matching required detailed inspection of several thousand data points before a correlation was possible. This process proved to be too lengthy; therefore, quick depth estimates based on pressure records and previous temperature profiles were made for determining the WSTP depth estimates. After downloading the time-temperature measurements from the UHT-MSM and filtering the time-depth files from the subsea shop, times were matched and the two files were merged to get the temperatures measurements as a function of depth (Fig. F146). The maximum temperature recorded during this deployment was 313°C.
WSTP deployments in Hole 1188F were made to depths of 107 and 207 mbsf. The profiles show maximum temperatures of 12° and 20°C (Fig. F147) that correlate well with the UHT-MSM profiles made shortly before the WSTP measurements. Unfortunately, estimates from previous records failed to provide higher-temperature water samples because the depth of the cold water front seemed to be increasing as a function of time, and estimates using pressure records were 70 m shallower than the desired 60°C temperature range.
Eleven logging units were defined in Hole 1188F (Fig. F145). The topmost unit (logging Unit 1) is characterized by increasing values in potassium, thorium, and uranium concentrations with depth. High values of electrical resistivity and density and low values of neutron porosity suggest a low degree of fracturing (Fig. F145). FMS images show that this unit corresponds to the part of the borehole that was cemented during casing operations (Fig. F148). FMS images also show that the interval below the cemented part corresponds to a highly fractured interval followed by a zone showing breccias composed of high resistivity clasts and horizontal to subhorizontal fractures (Fig. F148). The zone between 202 and 207.5 mbsf is >15.5 in, and no FMS images were acquired; whereas, below this interval one pad shows glimpses of a brecciated zone suggesting that the brecciation is continuous for the entire interval from 196 to ~211 mbsf. This brecciated interval corresponds to the high uranium anomaly in logging Unit 2 (Fig. F145) and may correspond to a zone of predominantly lateral fluid flow or the presence of a low-angle fault. Total gamma-ray values in logging Unit 2 reach 558 gAPI, and uranium values go up to 64 ppm. Potassium and thorium are high, with values reaching 2.7 wt% for potassium and 4.8 ppm for thorium. The PEF is also high in this zone with a maximum value of 11.7 barn/e-.
Very high neutron porosity and low density values characterize logging Unit 3. Log responses in this logging unit are probably strongly influenced by an enlarged borehole as shown in Figure F148. Electrical resistivities, which are less sensitive to variations in the size of the borehole than the neutron porosity and density measurements, show intermediate to high values that correlate with changes in porosity. Gamma-ray values are low, as well as photoelectric factor values.
A decrease in neutron porosity and an increase in density characterize logging Unit 4. Electrical resistivities are at an intermediate level, slightly decreasing downward. The upper part of logging Unit 4 (logging Subunit 4A) corresponds to a second anomaly in the gamma ray and uranium (Fig. F145).
Logging Units 5 and 7 show intermediate to high electrical resistivity, neutron porosity, density, and compressional wave velocity values as well as low gamma-ray values. Partial FMS images of logging Unit 5 show a high degree of brecciation that features a high fracture density predominantly exhibiting horizontal to subhorizontal orientations. Logging Units 5 and 7 are separated by logging Unit 6, which is characterized by low electrical resistivity and sonic velocity values and high neutron porosity values. Partial FMS images show a highly brecciated zone composed of high-resistivity clasts and high fracture density (Fig. F149).
The transition to logging Units 8 to 11 is marked by a slight but sharp increase in the photoelectric factor log at 298 mbsf. Logging Units 8 and 9 are identified by high electrical resistivity and density values and intermediate to high compressional wave velocities. Gamma ray values increase downward in both units. FMS images of this unit show that although there is a high fracture density, there is a small amount of brecciation in this unit (Fig. F150). The difference between these two units is in the neutron porosity, which is lower in logging Unit 9 and confirms the FMS measurements. Logging Unit 10 is a thin unit with slightly lower electrical resistivities than logging Units 8 and 9 and with increased values of the total gamma-ray and potassium log and of the photoelectric factor log. Logging Unit 11 is the lowest logging unit. It shows intermediate to high electrical resistivity, neutron porosity, and density values.
