Thermal and organic matter modeling in the fault bend fold and fault propagation fold structural models

Abstract

In Colombia the areas of greatest petroleum exploration interest are characterized by complex structure with folds and thrust faults where it is important to estimate the thermal effects of faults to evaluate organic matter maturity and hydrocarbon generation processes. Except for a software model recently developed by the French Petroleum Institute (Francois Roure personal communication), current and public domain one dimension models do not consider lateral or downward heat flow, which are of normal occurrence in these areas, in addition such models assume instantaneous fault movement contrary to geologic observations. For balanced cross sections with (1) fault bend folds and (2) fault propagation folds we model heat conduction from the basement and organic matter maturity; outputs of the model are temperature and organic matter maturity at each point of the sections at different times while deformation is occurring. Boundary conditions are: absence of lateral heat flow on the lateral border of the sections, constant heat flow at the bottom of the sections, and constant temperature at the surface of the earth. The heat conduction equation applied to the sections was solved by the finite element numerical method with the ANSYS software. The obtained results for different deformation rates are shown and analyzed. Results show lateral variations of temperature and organic matter maturity. Contrary to one dimensional models, the steady state in two dimensions is reached faster, it is cooler and the temperature inversion is shorter. The less deformation rate the less thermal anomaly. At the topographic peaks temperature and maturity are lower than in the valleys. The fault propagation section presents a depth maturity inversion more pronounced than in the fault bend fold model. Depth maturity inversion intensity depends on the ratio between the deformation time Td and the time passed just after deformation ceased Tp: Td /Tp. If this ratio is greater the depth maturity inversion will be greater. This paper shows the possibility to determine the organic matter distribution in a structural section with a known thermal and deformation history.