#DATA ANALYSIS METHODS FOR SURVEYS HOW TO#

if coarse reworked rock material was not removed before the analysis, the results would be wrong, i.e. Regarding liquid hydrocarbons, tests showed that if the whole sample was analysed, i.e. Adsorbed gas GC gave very good results, giving a picture of what gases had seeped through the sediment over geologic time. Not surprisingly, headspace gas GC analysis have been found to give low yields when the samples have been preserved by freezing the samples to – 65 oC or lower temperatures, while occluded gas GC gave good results in showing what was present in the pores of the sample when collected. Various analytical techniques have been tested both for gases and liquid fractions. However, there are significant differences in sampling time, the piston corer requiring over twice as much time as the gravity corer. The conclusion from this is that there is no difference in the quality of the samples from gravity or piston corers. There are no significant differences in the results from the parallel samples. All the samples were analysed both for gaseous and liquid hydrocarbons. Samples were collected at 0.5 m depth intervals over the 4.8 to 5.5 m cores and preserved by canning / freezing to –80 oC. In the second survey, offshore Faeroes, for each of 10 stations, one gravity core and one piston core were collected close together. The conclusion from this is that the only preservation technique that will stop any bacterial activity in surface geochemical samples is freezing at very low temperatures, preferably –65 oC or lower. There was no indication of bacterial activity in samples frozen to –80 oC, but significant bacterial activity in the other aliquots, even for the samples with bactericide and freezing to –20 oC.

The headspace and occluded gases were analysed for molecular composition and carbon isotope composition, with quite revealing results. The first is from the Barents Sea, where samples from 100 cores were quartered and treated to four different combinations of preservation methods, including presence/absence of bactericide, storage at room temperature or freezing to –20 or –80☌. In order to get scientifically reliable answers to these questions, two different surveys have been undertaken.

#DATA ANALYSIS METHODS FOR SURVEYS HOW TO#

In surface geochemical surveys, there has been significant discussion regarding which sampling techniques give the best quality samples, the costs of using one technique compared with others, and how to preserve the samples after collection to ensure that there is no degrading bacterial activity. Sampling, preservation and analysis methods for offshore geochemical surveys, with data from the Barents sea

Data analysis methods for surveys