Integration of a Crustal Stretching Model into the Workflow of Basal Heat Flow Calibration

Thomas Fuchs¹, Christian Zwach², Armin Kauerauf¹, Thomas Hantschel¹, and Jakob Skogseid^2
1IES, Integrated Exploration Systems, Ritterstr. 23, 52072 Aachen, Germany
² Hydro Oil and Energy, Global Exploration, Drammensveien 264, N-0240 Oslo, Norway

The basal heat flow is the most important quantity determining the thermal evolution within a sedimentary basin. Commonly, it is calculated by inversion from vitrinite reflectance and temperature data for a basin model. Unfortunately, this procedure does only cover the younger geologic history of the earth. However, heat flow can be estimated through knowledge of stretching time and factors in rift basins for paleo times. If the type of rifting and its timing is known, it is possible to calculate the stretching factors by inversion of subsidence from the basin model. Heat flow calibration can thus be subdivided into two parts. Firstly, an overall heat flow is calculated by crustal modeling and secondly it is calibrated against well data. An integrated workflow with a consistent and efficient employment of these steps is demonstrated for a case study. The details are given by the following specifications:

A discontinuous, pure shear stretching model which contains two different stretching factors for crust and mantle is used. Heat produced in the crust by radioactivity is taken into account. The stretching factors are fitted to the tectonic subsidence of the basin model, which is extracted by stratigraphic backstripping. According to the ductile nature of the mantle the resulting stretching factor maps are smoothed afterwards. Finally, heat flow maps through time are created from the stretching model. The quality of the fit can be quantified.

In order to achieve calibrated heat flow maps it is necessary to adapt the heat flow so that the model matches vitrinite reflectance and temperature data. Small areas of interest around the wells, which are big enough to include lateral temperature effects, can be modeled fast with varying heat flow in full 3D. The heat flow can accurately be determined with an inversion based on interpolated model runs. In the regions between the wells the heat flow is interpolated. A significant shortcut of the workflow can be achieved by simulating all areas of interest together in one model.

We demonstrate the new integrated workflow on an exploration case study and show the advantages of application of a crustal stretching model.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands