Absolute Salt Dynamics from Excess Maturity and Thermal Anomalies

THOMSEN, RENE O., Aarhus Universitet, Arhus, Denmark, IAN LERCHE, University of South Carolina, Columbia, SC, and JOHN A. KORSTGARD, Aarhus Universitet, Arhus, Denmark,

In the Danish North Sea area hydrocarbon occurrences are often related to salt structures. Assessment of the dynamic evolution of salt structures and possible related hydrocarbon traps is therefore important in order to predict the potential of a given structure. A new method for assessing the time of onset of diapirism and salt flow-speed from inversion of thermal indicators and temperature anomalies is developed and demonstrated. From vitrinite reflectance measurements from the Danish North Sea well, Lulu-1, drilled on top of a salt structure, the excess maturity is determined caused by the focusing of heat due to the higher thermal conductivity of salt. Down-hole temperature measurements give the present day thermal anomaly, which is directly related to the size of the salt diapir. The method is based on calculation of the thermal anomaly and excess maturity surrounding a rising salt diapir. For a given salt speed, sedimentary time-temperature-integrals are calculated and converted to synthetic vitrinite reflectance values. The synthetic vitrinite reflectance values are then compared with the observed values at given depths, and the speed of salt rise adjusted until consistency of predicted and observed values is obtained. The method can easily be tailored to thermal indicators other than vitrinite reflectance thereby enhancing the resolution of the thermal history and constraining both the onset of salt rise as well as the salt speed. The results of the method compare favorably to an assessment of the dynamical evolution of the salt diapir as interpreted from seis ic.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)