Temperature and heat flow in the Celtic Sea basins

Hydrocarbon exploration wells provide sufficient information to analyse the present-day thermal regime in the Celtic Sea basins. This information cons ists of bottom hole temperatures (BHTs), geophysical well logs, composite l ogs and rock cuttings from the major formations. The BHTs provide numerous but low-quality data which require extensive processing before they provide reliable estimates of formation temperature. Standard corrections (Horner plots) to multiple BHTs can be modified to correct single EHT measurements. A least-squares inversion based on a thermal resistance (Bullard) model fo r conductive heat flow can map many noisy Horner-corrected BHTs into a set of formation temperature estimates with relatively small errors. The averag e geothermal gradient is 32 degrees C km(-1). Laboratory measurements of th e thermal conductivity of rock cuttings taken from representative formation s in selected wells give matrix conductivities at room temperature. These s ample measurements are combined with information about formation porosity a nd temperature to give in situ thermal conductivities for each formation in each well. These are then used with formation temperature gradients from t he BHT analysis to estimate heat flow. The heat flow obtained for the Celti c Sea basins varies between 59 and 81 mW m(-2). The highest values appear t o be where sediments are thickest.