Method and relative system for the measurement of the isotope ratio in hydrocarbons

Abstract

Method for measurement of carbon isotope ratio in hydrocarbons obtainable from solid rock samples extracted from subsoil, preferably while oil drilling comprising pre-treatment of rock extracted from subsoil; scrubbing with inert gas of a rock sample taken from said rock; desorption, by heating, of a first gaseous sample containing hydrocarbons contained in pores of said rock sample and pyrolysis of said rock sample, said pyrolysis being suitable for obtaining a second gaseous sample from transformation of organic material of said rock sample; homogenisation and sampling of said first gaseous sample and, subsequently, said second gaseous sample; oxidation of said first gaseous sample and said second gaseous sample, said oxidation being suitable for obtaining carbon dioxide from hydrocarbons contained in said first gaseous sample and said second gaseous sample; separation of said carbon dioxide from other products of oxidation reaction and measurement of carbon isotope ratio in said carbon dioxide.

What is claimed is: 
     
         1 . A method for measurement of a carbon isotope ratio in hydrocarbons obtainable from solid rock samples extracted from subsoil, preferably while oil drilling, wherein said method comprises the following steps:
 pre-treatment of rock extracted from the subsoil;   scrubbing with inert gas of a rock sample (C) taken from the rock previously subjected to said pre-treatment operation;   desorption of a first gaseous sample (S 1 ) containing hydrocarbons contained in pores of said rock samples (C), said desorption being performed by means of heating of said rock sample (C);   homogenisation and sampling of said gaseous sample (S 1 ), said sampling being suitable for obtaining quotas (A 1 ) of said first gaseous sample (S 1 );   oxidation of each of said gaseous quotas (A 1 ) taken from said first gaseous sample (S 1 ), said oxidation ( 4 ) being suitable for obtaining carbon dioxide CO 2  from the hydrocarbons contained in said first gaseous sample (S 1 );   separation of said carbon dioxide CO 2  from other products of the reaction of oxidation, said carbon dioxide CO 2  being obtained from oxidation of each of said gaseous quotas (A 1 ) taken from said first gaseous sample (S 1 ); and   measurement of the carbon isotope ratio in said carbon dioxide CO 2 , said carbon dioxide CO 2  being obtained from oxidation of each of said gaseous quotas (A 1 ) taken from said first gaseous sample (S 1 ).   
     
     
         2 . The method according to  claim 1 , further comprising the steps of:
 scrubbing with inert gas of said rock sample (C) after said rock sample (C) has been subjected to said desorption;   pyrolysis of said rock sample (C), said pyrolysis being suitable for obtaining a second gaseous sample (S 2 ) from transformation of the organic material of said rock sample (C);   homogenisation and sampling of said second gaseous sample (S 2 ), said sampling being suitable for obtaining quotas (A 2 ) of said second gaseous sample (S 2 );   oxidation of each of said gaseous quotas (A 2 ) taken from said second gaseous sample (S 2 ), said oxidation being suitable for obtaining carbon dioxide CO 2  from the hydrocarbons contained in said second gaseous sample (S 2 );   separation of said carbon dioxide CO 2  from other products of the reaction of oxidation, said carbon dioxide CO 2  being obtained from oxidation of each of said gaseous quotas (A 2 ) taken from said second gaseous sample (S 2 ); and   measurement of the carbon isotope ratio in said carbon dioxide CO 2 , said carbon dioxide CO 2  being obtained from the oxidation of each of said gaseous quotas (A 2 ) taken from said second gaseous sample (S 2 ).   
     
     
         3 . The method according to  claim 1 , wherein said step of pre-treatment of the rock extracted from the subsoil comprises the following operations:
 first washing with water of said rock extracted from the subsoil;   first drying of said rock in oven at a temperature of 60-70° C.;   grinding of said rock with known grinding means;   scrubbing of said rock with acid, said scrubbing with acid suitable for removing the carbonate fraction present in said rock;   second washing with water, said second washing with water being suitable for removing said acid;   second drying of said rock at a temperature of 60-70° C.; and   taking of a rock sample (C) from said rock.   
     
     
         4 . The Method according to  claim 2 , wherein said scrubbing with inert gas has a time duration comprised between 30 and 60 seconds. 
     
     
         5 . The Method according to  claim 1 , wherein said reaction of oxidation takes place 100%, said reaction of oxidation generating, among the reaction products, carbon dioxide CO 2 , the isotope ratio of said carbon dioxide CO 2  being identical to the isotope ratio of the reacting hydrocarbons. 
     
     
         6 . The method according to  claim 1 , wherein said desorption is performed by means of a heating of said rock sample (C) up to a temperature of 300° C., said temperature being maintained for about 5 minutes. 
     
     
         7 . The method according to  claim 2 , wherein said pyrolysis is performed by means of a heating of said rock sample (C) up to a temperature of 650° C., said temperature being maintained for about 5 minutes. 
     
     
         8 . The Method according to  claim 1 , wherein said oxidation takes place at a temperature comprised between 500° C. and 900° C. 
     
     
         9 . The Method according to  claim 1 , wherein said inert gas is nitrogen N 2 . 
     
     
         10 . The Method according to  claim 1 , wherein said inert gas is helium He. 
     
     
         11 . A System for measurement of carbon isotope ratio in hydrocarbons obtainable from solid rock samples extracted from subsoil, preferably while oil drilling, characterised in that said system comprises:
 an oven, said oven being suitable for heating a solid rock sample (C) so as to cause desorption of the gases (S 1 ) present in pores of said rock sample (C), and said oven being suitable for heating a rock sample (C) so as to cause pyrolysis of said rock sample (C), said pyrolysis generating gases (S 2 ) from transformation of organic material of said sample (C);   a first solenoid valve suitable for regulating flow of an inert gas inside said oven;   a second solenoid valve suitable for regulating pressure inside said oven;   a sampling valve, said valve being suitable for sampling gases (S 1 , S 2 ) coming from said oven, said gases being produced by desorption and by pyrolysis of said rock sample (C);   an oxidator wherein gases (S 1 , S 2 ) coming from said oven, said gases being produced by desorption and by pyrolysis of said rock sample (C), undergo a reaction of oxidation, said reaction of oxidation being suitable for producing carbon dioxide CO 2  when said gases (S 1 , S 2 ) come from said oven, said gases being produced by desorption and by pyrolysis of said rock sample (C), are hydrocarbons;   a chromatography column suitable for separating said carbon dioxide CO 2  from other products of said oxidation reaction; and   a laser isotope analyser suitable for measuring carbon isotope ratio in said carbon dioxide CO 2  in output from said chromatography column.   
     
     
         12 . The System according to  claim 11 , wherein said sampling valve is a six-way rotary valve, said sampling valve being switchable between a first state of commutation and a second state of commutation. 
     
     
         13 . The System according to  claim 12 , wherein two ways of said sampling valve are connected in such a way as to form a sampling cell. 
     
     
         14 . The System according to  claim 13 , wherein said first state of commutation of said sampling valve is suitable for transferring gases (S 1 , S 2 ) contained in said oven in said sampling cell, said gases being produced by desorption and by pyrolysis of said rock sample (C). 
     
     
         15 . The System according  claim 14 , wherein said second state of commutation of said sampling valve is suitable for transferring gases (S 1 , S 2 ) contained in said sampling cell to said oxidator, said gases being produced by desorption and by pyrolysis of said rock sample (C). 
     
     
         16 . The System according to  claim 15 , comprising a third solenoid valve, suitable for regulating pressure in said sampling cell. 
     
     
         17 . The System according to  claim 11 , comprising a fourth solenoid valve, suitable for regulating flow of oxygen in said oxidator. 
     
     
         18 . The System according to  claim 11 , wherein said oxidator contains in its interior a catalyst such as for example: copper chromite, copper oxide or hopcalite.