Method of quantifying hydrocarbon formation and retention in a mother rock

Abstract

The method according to the invention allows the formation of oil and the retention phenomenon in the mother rock to be modelled. Organic matter characterization experiments are used to establish the molecular model (MM) of the initial sample (E). The thermal cracking reaction of this molecular model is reproduced by dynamic molecular simulation computations with a reactive force field (RMD) and validated by comparison with experimental data. The reaction mechanism obtained (SR) allows to carry out a kinetic study (C) by variation of the temperature parameter. The phase equilibria (PES) of the reaction medium are determined at any time from dynamic simulation. The successive phase equilibrium assessments at various progress stages of the cracking reaction allow following the physicochemical evolution (PC) of the thermal maturation of the organic sample studied. The free hydrocarbons (liquid and gaseous) that are not retained in the solid residue can be quantified throughout numerical modelling of the sample maturation; representing, in the sedimentary basins, the hydrocarbons that are not retained in the organic matrix of the mother rock (Q). This quantity can be used as an indicator or an input value for the retention threshold in basin models.

1 ) A method of quantifying formation and retention of hydrocarbons within a macromolecular chemical system, comprising construction of a molecular model of the system by means of experimental characterizations of a sample of the system, comprising: 
 defining a thermal maturation reaction mechanism for the macromolecular chemical system by subjecting the molecular model to a molecular dynamic simulation associated with a reactive force field; and    quantifying free hydrocarbons formed throughout thermal maturation of the macromolecular system by: 
 a) determining a physicochemical evolution of a molecular mixture defined by the reaction mechanism, by calculating phase equilibria, directly from the molecular dynamic simulation; and  
 b) determining thermal decomposition kinetics of the macromolecular system by kinetic study from the reaction mechanism.  
   
   
   
       2 ) A method as claimed in  claim 1 , wherein the molecular model and the reaction mechanism are validated by comparison of results from the reactive molecular dynamic simulation with experimental measurements of the thermal maturation of the macromolecular chemical system.  
   
   
       3 ) A method as claimed  claim 1 , wherein determination of the phase equilibria is performed by calculating at any time total energy of each molecule subjected to a force field, then by successive assessments in order to quantify the hydrocarbon retention in the macromolecular chemical system.  
   
   
       4 ) A method as claimed in  claim 1 , wherein the kinetic study is carried out by varying temperature of the reaction mechanism.  
   
   
       5 ) A method as claimed in  claim 1 , wherein the macromolecular chemical system represents organic matter of a mother rock of a petroleum reservoir.  
   
   
       6 ) A method of simulating genesis of a sedimentary basin, wherein formation and retention of hydrocarbons within a mother rock containing kerogen are modelled, comprising: 
 defining by means of experimental characterizations a molecular model of the kerogen of the mother rock;    defining a reaction mechanism by subjecting the molecular model to a molecular dynamic simulation associated with a reactive force field;    quantifying evolution of the kerogen to heavy products and hydrocarbons, by carrying out a kinetic study of the thermal decomposition of the kerogen from the reaction mechanism;    quantifying hydrocarbon retention within the mother rock by carrying out assessments on fractions linked to than organic matrix of the mother rock and on free fractions from phase equilibria determined by molecular dynamic simulation; and    using as the input data in a basin simulator amounts of hydrocarbons formed and amounts of hydrocarbons that are not retained in the mother rock, that can be expelled from the mother rock and migrate to a petroleum reservoir.    
   
   
       7 ) A method as claimed  claim 2 , wherein determination of the phase equilibria is performed by calculating at any time total energy of each molecule subjected to a force field, then by successive assessments in order to quantify hydrocarbon retention in the macromolecular chemical system.  
   
   
       8 ) A method as claimed  claim 2 , wherein the kinetic study is carried out by varying temperature of the reaction mechanism.  
   
   
       9 ) A method as claimed  claim 3 , wherein the kinetic study is carried out by varying temperature of the reaction mechanism.  
   
   
       10 ) A method as claimed  claim 7 , wherein the kinetic study is carried out by varying temperature of the reaction mechanism.  
   
   
       11 ) A method as claimed in  claim 2 , wherein the macromolecular chemical system represents organic matter of a mother rock of a petroleum reservoir.  
   
   
       12 ) A method as claimed in  claim 3 , wherein the macromolecular chemical system represents organic matter of a mother rock of a petroleum reservoir.  
   
   
       13 ) A method as claimed in  claim 4 , wherein the macromolecular chemical system represents organic matter of a mother rock of a petroleum reservoir.  
   
   
       14 ) A method as claimed in  claim 7 , wherein the macromolecular chemical system represents the organic matter of a mother rock of a petroleum reservoir.  
   
   
       15 ) A method as claimed in  claim 8 , wherein the macromolecular chemical system represents organic matter of a mother rock of a petroleum reservoir.  
   
   
       16 ) A method as claimed in  claim 9 , wherein the macromolecular chemical system represents organic matter of a mother rock of a petroleum reservoir.  
   
   
       17 ) A method as claimed in  claim 10 , wherein the macromolecular chemical system represents organic matter of a mother rock of a petroleum reservoir.