Excerpts from the recorded temperature data are displayed in Figure 9 as temperature profiles
and temperature gradients for successive points in time after the cementing of the wells. As a
result of the thermal disturbance due to the drilling process, a continuous process of
equilibration of the wellbore temperature to the temperature of the surrounding formation can
be observed during the 21-month logging period between January 2002 and September 2003.
The disturbed temperature profiles exhibit specific patterns, which are related to the
mobilization of latent heat during the decomposition of gas hydrate, as a result of the drilling
and completion of the wells. These patterns were used as indicators for the location of the
base of the gas hydrate occurrences (Henninges et al., 2004). A sinusoidal signature in the
temperature-depth gradient marks the transition zone between the gas-hydrate-bearing and
non gas-hydrate-bearing strata. This “pseudo-discontinuity” of the temperature gradient and
the related temperature step both gradually decrease over time as the thermal disturbance
dissipates.