Heterogeneity effects in thermal borehole measurements in the Chicxulub impact crater

Abstract

Boreholes drilled in impact structures are especially suited for investigations of the influence of heterogeneities on petrophysical properties and thermal field. In the scientific well Yaxcopoil-1 drilled within the frame of the International Continental Deep Drilling Program (ICDP) and as a part of the Chicxulub Scientific Drilling Project (CSDP) high resolution temperature measurements and a dense petrophysical profile measured on core samples at ∼2.2 m depth intervals were recorded. From the calculated vertical component of the thermal gradient and the thermal conductivity measured on the core samples a mean heat flow density of 70.5 ± 1.9 mW m-2 in the depth interval 400-1400 m was determined. On the basis of a simple purely conductive heterogeneous 2D thermal model the effect of the refraction of heat caused by heterogeneities is demonstrated. A statistical investigation shows that if the scales of the heterogeneities influencing the values of the measured thermal conductivity and the calculated thermal gradient are small compared to the length of the borehole the effect of the heterogeneities on the vertical heat flow density can be interpreted as thermal noise. © 2005 Nanjing Institute of Geophysical Prospecting.