Thermal Conductivity Contrast Due to Gas Saturated Pore Space -- Application in Basin Simulation
H. S. Poelchau, C. Zwach, D. H. Welte, and TH. Hantschel
Calibration of thermal histories in basin modeling usually relies on matching temperature and vitrinite reflectance distribution in wells. The four main variables that can be adjusted to improve such a match are heatflow, surface temperature, maximum depth of burial (or eroded overburden), and thermal conductivity of the individual layers of rocks. The last parameter can be used to match the fine structure of the vertical temperature distribution, thermal gradient changes and heat anomalies.
While most commercial simulation packages use thermal conductivity values calculated with water as the pore fluid, we have experimented with using decreased conductivity resulting from high gas saturation in the pore space of specific formations in our modeling. One such case study is the Alberta Deep Basin in western Canada, where a large part of the lower Cretaceous section is thought to be gas saturated, underneath a water-saturated seal. Another case study comes from northwestern Siberia, where the largest gas accumulations on earth have been discovered.
Results show that the thermal effect of gas in pores, as opposed to water, are significant and cannot be neglected in basin basin modeling. Such gas saturations can explain frequently observed sudden increases in vitrinite reflectance gradients or socalled "kinky" reflection profiles. The gas effect can also be used to model heat anomalies in past geologic periods where hypothetical increased heatflow evens cannot be justified.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California