Approaches

 

There are two ways to tackle the past thermal history in orogen-basin settings, the direct and indirect approaches (Fig. 1):

 

  • The first one aims to 'directly' constrain the thermal history of the orogen on bedrocks from the orogen and substratum of the basin. This allows an immediate inspection of thermal history for the first 15-10 kilometres of the crust. Substratum here does not obligatory imply crystalline, volcanics or metamorphics as it can be a sedimentary level that has been fully reset to temperatures higher than the metastable zone = the low-thermochronometer is put back to 0 Ma.

 

  • ‘Indirect’ thermochronology traces cooling records that are no longer present in the orogen since erosion has removed the record of earlier stages. This approach is not detailed here because it has no interest for O&G prospect but indicate that burial/heating was not sufficient to reset one or more thermochronometers.

What I offer

 

I propose you 15 years of expertise in the reconstruction of the thermal history of different basin-orogen systems. All the projects we initiated got granted without any rejection from National Institutions or O&G industry. The determination of Peak Temperature or Raman Spectroscopy analyses on carbonaceous shale is a method we use in combination with low-Temperature thermochronolgy. This approach was applied to study the Atlas-Sahara and Petroleum systems of SW Morocco. It permits to reconstruct thermal paths within the oil (160-60°C) and gas (200-160°C) temperature windows (Fig. 2). Investigating the gas temperature window is brand new and operational for exploration.

 

Thermal reconstructions can be produced from outcrop or well sample, onshore and offshore. The reconstruction of the thermal history from a reservoir, carbonate or shale levels is usually impossible because they do not host apatite nor zircon minerals. However, we can handle this by analysing additional samples and using an approach we developed. This is where stands our intellectual property.

 

Fault gouge dating thanks to Ar/Ar analyses when Illite is present

Chicken or egg?

It is very than important to note that a thermochronological age of 50 Ma does not imply that something happened 50 My ago. For comparison, if you blast a zircon for U/Pb dating without considering that it has 2-3 rims (left), the obtained age is useless because it is a mixed one = it has not got any geological meaning as a sole thermochronological age.

 

The Fission-Track and U-Th-Sm/He ages on zircons of Figure 2 are between 190-170 Ma and related to eruption ages. These Jurassic volcanics are the substratum of an O&G rich Cretaceous basin.

 

On the other hand the Apatite Fission-Track (150 Ma) and U-Th-Sm/He (18 Ma) ages both on apatite are the result of complex paths within their retention/metastable zones and do not indicate that there were changes in the thermal history for these 2 dates (Fig. 2).

 

Additional measurements, inputs are needed such as the geochemistry of the minerals, geological relationships to trace the past thermal history.

Conclusion

 

We developed a novel approach for Oil and Gas exploration that can be used to reconstruct the thermal history from 200 to 45°C (and up to 310°C). The temperature range is large and encompasses the oil and gas temperature windows. It is also free of lithological restriction, it is flexible - we mean that if the information is obliterated it can always be found somewhere else (Fig. 1).