Fig. 8

Temperature-Depth plot showing reported geothermal gradients of petroleum exploration wells in Fang basin sediments and an inset figure showing the only available temperature logs of geothermal wells in crystalline rocks. Large plot: Solid lines connect measurement points (solid dots) of Barr et al. (1979) from wells which are located in oil fields shown in Figs.2, 3 (detailed locations were not published). Dashed lines are gradients in wells (locations in Figs. 2, 3) published by Thienprasert and Raksaskulwong (1984), which we extrapolate upward to an assumed surface temperature of 26 °C. (Because these authors did not publish temperatures, we attempt to reconstruct a profile using their published gradients.) Drill-stem test temperature of 66.5 °C at 1240 m in well FA-HM-50-03 is from Giao et al. (2011). Bottomhole temperature of well IF-12(27) is an unpublished log considered low because it was probably logged shortly after drilling. Selected temperatures of producing geothermal wells shown by symbols on upper right margin (symbols placed at depths of producing fractures) (see Table 1). Inset plot: Temperature logs of geothermal wells (locations shown in Fig. 23 and in Table 1) made 1–150 days after drilling (from Wanakasem and Takabut (1986)) and detail of profiles from wells in sedimentary rocks duplicating those shown in upper left of large plot. Temperature inversions in the geothermal wells are discussed in text