SSP Project Summary: 3D Modelling of Heat Flow in Sedimentary Basins

Student

Supervisors

James Iliffe, PGS Tigress Ltd

Jean-Christophe Desplat, EPCC

Hydrocarbons (oil and gas) are produced when sedimentary rocks rich in organic material (source rocks) are heated to high temperatures (60 - 150 C) for long periods of time (millions to tens of millions of years). This process of conversion from primary organic material to hydrocarbons is known as maturation. The accurate assessment, and prediction, of the maturity and maturation history of hydrocarbon source rocks is of key importance to the oil industry when exploring for hydrocarbons in sedimentary basins like the North Sea.

The maturation history of a source rock depends upon its heating history. Temperature increases with depth of burial. In most basins the vertical conduction of heat determines temperature variations and the amount of heat supplied to source rocks. This "layered-earth" assumption for heat transport is used in existing models of solid rock maturation. This assumption is valid for most sedimentary basins.

A number of important oil discoveries have been made during the past five years in the Faeroe-Shetland basin to the west of the British Isles. This area is now the main area of active hydrocarbon exploration in UK waters. The one-dimensional, layered-earth approximations for heat flor is probably inadequate for this basin and may lead to significant errors in determining source rock maturity and the timing of hydrocarbon generation. The reason for this difficulty is a major period of volcanic and igneous activity whcih affected the Faeroe-Shetland basin during the early Tertiary (60-55 million years ago). This igneous activity would have had a major impact on the temperature structure and transport of heat in the sedimentary sucession of the Faeroe-Shetland basin, which includes important source rock horizons. As igneous bodies were emplaced lateral heat conduction is likely to have been extremely important and may have outweighed vertical heat transport locally within the sedimentary succession for several million years, thereby invalidating the 1D vertical model for heat flow.

The project proposed here would concentrate on extending the existing 1-dimensional (vertical) models of heat transport to 3 dimensions, so that the effects of these irregularly shaped additional heat soruces could be determined. This project would be a simle first step to test the importance of 3D heat flow for maturity modelling. If successful it may lead to further research collaboration. Ultimatly, the development of a geologically rigorous 3D heat flow model may be of great importance for source rock maturity modelling and hydrocarbon exploration in the Faeroe-Shetland basin and other sedimentary basins which have been subjected to intense igneous activity.

The principle objective for the student will be to develop a three dimensional model for heat transport. The student could start with a 3 dimensional rock volume with uniform thermal properties into which a three dimensional heat source (representing a volcanic plug, dyke or sill) is intruded. Once this primary model has been developed the student could investigate the effects of making the model more geologically reasonable, for instance by including sedimentary layers, varying the thermal properties of the rocks and altering the timing and amount of heat introduced. The student will also develop visualisation tools to illustrate the effects of 3D heat flow on the rock volume. These tools should be able to illustrate the temperature and heat flow structure of the rock volume at different times and also illustrate the thermal history of individual points, profiles and slices of the rock volumes.

The early Tertiary igneous activity in the Faeroe-Shetland basin took place relatively quickly (within a few million years). It also happened at a time when the main hydrocarbon source rock (the Kimmeridge Clay) had been buried to depths just sufficent for the initiation of hydrocarbon generation. The rapidity of this igneous activity, and the irregular distribution of the new heat sources, may also invalidate an additional assumption of existing maturity models, namely that heat transport can be modelled as a steady-state process. If time is available this key assumption could also be investigated.

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