Interpretation of the geophysical well log from the San Lorenzo Tezonco well and its lithological correlation in the Mexico basin

Abstract

We describe the results obtained from the analysis of the geophysical well log conducted at the San Lorenzo Tezonco (SLT) well, which is located in the eastern part of Mexico City and has 2,008 m in depth. The geophysical well log was conducted in three stages and consisted of temperature, electrical resistivity, natural potential and gamma radiation, although the gamma radiation and natural potential logs malfunctioned during the last stage. The analysis presented here is based mainly on the electrical resistivity and gamma logs; the interpretation is based on channel (cutting) samples and petrologic and stratigraphic descriptions of the SLT well previously published. By analyzing the well log data and correlating them with the lithology reported for nearby shallow wells it was possible to complete the stratigraphy between 120 m and 500 m, which was absent in previous reports due to the lack of channel cuttings. The results show that the geologic materials in the SLT well are considerably more heterogeneous and have differing thicknesses than those previously reported. Among the zones of hydrogeological interest, an aquitard of volcanic origin, with relatively low clay content, is inferred between 750 and 880 m depth from the well log. In addition, the analysis allowed identifying potential water-productive strata. For future exploratory deep wells in the Basin of Mexico, it is suggested to include additional geophysical logs (density and sonic) and to obtain cores, which would allow a quantitative interpretation of petrophysical properties of the subsurface.