Abstract

A method for correcting log-derived temperatures in deep wells (3500–6500 m) has been developed by comparing log temperatures from the Gulf of Campeche (Mexican Gulf of Mexico) with DST temperatures in the same wells. The equations developed in this study are modified slightly from those of Waples & Mahadir Ramly (2001), which were calibrated using data from depths <3500 m in Malaysia. The correction depends strongly on time since end of mud circulation (TSC) and, to a much lesser degree, on depth. In this study the true subsurface temperature (Celsius) is given by  
\[T_{true}=T_{surf}+f{\cdot}\left(T_{meas}{-}T_{surf}\right){-}0.001391\left(Z{-}4498\right)\]
where f=1.32866−0.005289TSC, Tsurf is the seafloor or land-surface temperature (°C), Tmeas is the measured log temperature (°C), TSC is in hours and Z is depth below seafloor in metres. If TSC is unknown, it can be estimated from the trend of TSC with depth.
An estimate of the uncertainty in the corrected temperature is obtained from the equation:  
\[{\sigma}=0.10842^{{-}0.029TSC}\]
where σ is the standard deviation of the correction factor f. The uncertainty in the correction factor f can be expressed as ±2σ.
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