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Geochemical studies of rocks and fluids to give predictive modelling of permeability distribution in a sedimentary basin

Objective

To relate petro-physical characteristics of reservoir rocks to their geochemical history by means of a diagenetic model incorporating both physical and chemical aspects. It is intended to apply the model to predicting petro-physical properties as a function of sedimentary-basin burial and evolution.

The project will use the Paris Basin as the field study area. A sedimentological review study will define which mineral phases will be selected for more detailed petrographical and geochemical analysis. Petrographic descriptions to define the diagenetic history will use optical microscopy (with CL and UV fluorescence), SEM (with CL and EDAX), electron micro-probe and analytical TEM.

The significant, diagenetic minerals or events will be related to the petro-physical properties (porosity and permeability). Having established which mineral phases are key controls, they will be subjected to detailed, quantitative geochemistry of further textural, mineralogical characterization to determine their conditions and timing of formation and source of chemical components.

Mineral phase work will include geochemical, stable isotope (H, C, O, S) and radiogenic isotope analyses (Sr, Ar), fluid inclusion and fission-track studies. Mainly standard techniques will be used, but innovative approaches (e.g. laser sampling of carbonates) will be included. The mineral analyses will be interpreted in terms of compositions of paleo-fluids. Analysis of the composition of present-day fluids will include the isotopic determinations and a comprehensive suite of ionic species (Na, K, Ca, Mg, Li, Fe, Mn, Sr, SiO2, B, Cl, H2S, SO4, HCO3, Br, I, Al), dissolved gases (CO2, N2, O2, H2) and alkanes (up to pentane). Noble gas analysis of selected samples, because of their inert nature and time-dependent production from radioactive elements are seen as key indicators of age and as tracers of provenance of fluids.

Interpretation of data will require two sorts of modelling: thermal and integrated diagenetic. Conversion between age and diagenetic temperature will be handled by thermal history models.

Development of a model which will simultaneously couple all the complex interactions of fluid flux, thermodynamic conditions, chemical reactions, transport of heat and material and their interactive effects on porosity and permeability is seen as an essential analytical tool to interpret and integrate data. The model will be refined and tested by applying it to new data sets and predicting results for future samples and , in particular, permeability variation.

Coordinator

BP Oil International Ltd
Address
1 Finsbury Circus
EC2M 7BA London
United Kingdom

Participants (3)

Bureau de Recherches Géologiques et Minières (BRGM)
France
Address
39-43 Quai André Citroën
75739 Paris
Elf Aquitaine
France
Address
Tour Elf 2 Place De La Coupole
92400 Courbevoie
UNIVERSITE PIERRE ET MARIE CURIE - PARIS VI
France
Address
Place Jussieu 4
75252 Paris