Method for the estimation of kerogen maturity by X-ray photoelectron spectroscopy
Method to estimate the kerogen maturity of a rock containing organic material by X-ray photoelectron spectroscopy (XPS). Significant changes in the XPS spectrum due to changes in C hybridization, particularly sp 2 hybridization, allow to quantify kerogen maturity by comparison with an already known sample.
1. A method to estimate the kerogen maturity of a rock containing organic material, wherein said method comprises the steps of:
a) providing a sample of the rock containing organic material to be analyzed and characterized;
b) obtaining a C1s spectrum of the rock sample by X-ray photoelectron spectroscopy;
c) calculating a parameter P C-C defined by equation (1)
P
C
-
C
=
A
Csp
2
A
TOC
xps
(
1
)
where
A Csp 2 is the peak area of the region of the spectrum obtained in b) corresponding to carbon in a sp 2 hybridization state,
A TOC xps is the peak area of the region of the spectrum obtained in b) corresponding to total organic carbon; and
d) determining the kerogen maturity of the rock containing organic material by comparing the value of P C-C to a reference value corresponding to a known kerogen maturity.
2. The method according to claim 1 , wherein said rock containing organic material is a sedimentary rock.
3. The method according to claim 2 , wherein said sedimentary rock is a shale.
4. The method according to claim 1 , wherein the sample of the rock containing organic material to be analyzed and characterized is selected from a core, a cutting or an outcrop sample.
5. The method according to claim 1 , where the area of the sample analyzed in step b) of obtaining a C1s spectrum of the rock sample by X-ray photoelectron spectroscopy is of about 1 mm 2 .
6. The method according to claim 1 , where step a) of providing a sample of the rock containing organic material to be analyzed and characterized further includes conditioning the sample.
7. The method according to claim 6 , wherein the conditioning of the sample takes place inside the X-ray photoelectron spectroscopy equipment used in step b).
8. The method according to claim 7 , wherein the conditioning of the sample comprises sputtering with argon.
9. The method according to claim 6 , wherein conditioning the sample does not include extraction, dissolution or grinding operations.