LEAST-SQUARES OPTIMUM-ORDER REGIONAL GEOTHERMAL GRADIENT DETERMINATION FROM DEEP BOREHOLE TEMPERATURE DATA WITH APPLICATION TO THE WESTERN DESERT OF EGYPT

This paper discusses an approach to determining the least-squares opti mum order of a polynomial fit to temperature-gradient data. The optimu m is reached when two successive least-squares regional maps are suffi ciently similar. This similarity is measured by the correlation factor between the polynomials. The approach was applied to the available de ep bore-hole temperature data in the central part of the Northern West ern Desert of Egypt. The fitting polynomial was found to be of the sec ond degree. Assuming the thermal conductivity to be uniformly 2.2 Wm(- 1)K(-1) for the stratigraphic section in the Western Desert, the heat- flow density ranges between 35 and 70 mW/m(2).