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doi:10.2204/iodp.proc.322.201.2013

Results

The calculated porosity profiles were compared to the core porosity (Fig. F2). Because of the poor quality of the recovered core (see the “Site C0011” chapter [Expedition 322 Scientists, 2010]), the core-based porosity measurements exhibit a lot of scatter. However, the general trend and concentration of data points can be matched to the LWD resistivity porosities.

For each of the constant and variable thermal gradient results, bit resistivity porosity exhibits a very similar trend to ring resistivity porosity but always at slightly lower values and with less scatter. Considering the difference in vertical resolution of the bit and ring resistivity measurements, the smooth nature of the bit resistivity porosity is most likely caused by the large volume of investigation. Because ring resistivity offers a more focused and better vertical resolution than bit resistivity, the ring resistivity–derived porosity is taken to be the more accurate and reliable of the two resistivity porosity estimates.

In relation to the variation between the porosity calculated from the variable thermal gradients and that calculated from the constant thermal gradients, there is very little difference, most likely due to the very similar data ranges seen in the core data. However, the constant thermal gradient of 91.3°C/km (Temp C1) gives a slightly improved fit to the core data, particularly through the upper section of lithologic Unit I (Fig. F2).

Overall, the most accurate LWD resistivity–based porosity estimate is calculated from ring resistivity, using the fluid resistivity corrected for temperature based on the constant temperature gradient recorded during Expedition 333. Therefore, it is suggested that for further analysis this porosity estimate should be used.

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