A new methodology for basin temperature modelling has been developed that utilizes large volumes (~10,000 points) of properly indexed and QC'd bottom-hole temperature (BHT) data for an onshore basin or area. This methodology honors the observation that borehole temperatures equilibrate, increasing towards formation temperature with elapsed time since fluid circulation. We thus use the maximum BHTs recorded in a layer (normalized for depth) or cell, rather than a corrected average or regression based model.
Two main models have been developed to construct a present day temperature volume (cube): MaxG and MaxBHT. In the MaxG cube, we first define a depth varying interval geothermal gradient (IGG) function that models the maximum envelope of the BHT cloud for each major lithostratigraphic unit. If there is significant erosion in the basin, then the IGG used is adjusted for the maximum burial conditions. The MaxG cube is constructed by stacking the IGG calculated temperatures for all the units in the basin. In the MaxBHT cube, we use the maximum BHT within each cell to populate the cube provided we have sufficiently dense data. If data are lacking in a cell, we can infill the voids using the MaxG cube values or a moving average.
For both the MaxG and MaxBHT cubes, we can apply a temperature shift related to interval thermal conductivity to more closely approximate formation temperature, if appropriate. Both temperature cubes can be used to identify where favorable gas-to-oil ratios (GOR) exist for shale gas formations. The concept is illustrated with examples from the Delaware Basin.