A method of drilling a geothermal well, the method comprising: running a computer program product comprising computer readable instructions on a computer to cause a processer to: acquire at least two types of geophysical data of a geological structure wherein the geothermal well is located, the geophysical data being measured prior to or during drilling of the geothermal well, and at least one of the geophysical data being electromagnetic data and magnetic data; select one or more forward models in which there is statistical independence between at least two geophysical parameters and statistical dependence between each respective geophysical parameter and a temperature and/or porosity of the geological structure; invert the at least two types of geophysical data to calculate values of the at least two respective geophysical parameters at multiple different points in the geological structure; and invert the at least two geophysical parameters to estimate values of the temperature of the geological structure at corresponding multiple different points in the geological structure; and using the calculated temperature and/or porosity in a decision-making process for the drilling of the geothermal well; characterised in that the at least two geophysical parameters comprise one of magnetic susceptibility or magnetic remanence, and at least one of rock density, seismic velocity, electrical conductivity or electrical resistivity. running a computer program product comprising computer readable instructions on a computer to cause a processer to: acquire at least two types of geophysical data of a geological structure wherein the geothermal well is located, the geophysical data being measured prior to or during drilling of the geothermal well, and at least one of the geophysical data being electromagnetic data and magnetic data; select one or more forward models in which there is statistical independence between at least two geophysical parameters and statistical dependence between each respective geophysical parameter and a temperature and/or porosity of the geological structure; invert the at least two types of geophysical data to calculate values of the at least two respective geophysical parameters at multiple different points in the geological structure; and invert the at least two geophysical parameters to estimate values of the temperature of the geological structure at corresponding multiple different points in the geological structure; and select one or more forward models in which there is statistical independence between at least two geophysical parameters and statistical dependence between each respective geophysical parameter and a temperature and/or porosity of the geological structure; invert the at least two types of geophysical data to calculate values of the at least two respective geophysical parameters at multiple different points in the geological structure; and invert the at least two geophysical parameters to estimate values of the temperature of the geological structure at corresponding multiple different points in the geological structure; and using the calculated temperature and/or porosity in a decision-making process for the drilling of the geothermal well; characterised in that the at least two geophysical parameters comprise one of magnetic susceptibility or magnetic remanence, and at least one of rock density, seismic velocity, electrical conductivity or electrical resistivity.