Chapter 4
Rock Eval Analysis
Introduction
Rock Eval pyrolysis is used to study the source rock potential and type and maturity of kerogen present in the rock. As compared to Elemental analysis study for type and maturity of organic matter of van krevelen, Rock Eval pyrolysis is very fast and inexpensive. The analysis takes only 20 minutes to process the sample and gives data which can be further interpreted for the desired purpose.
Sample Prepration
Working Principle
The Rock Eval (RE) pyrolysis method consists of a programmed temperature heating in an inert environmnet (H2 or N2) of 100 mg of pulverised rock to determine the free hydrocarbons contained in the sample and the hydrocarbon- and oxygen-containing compounds (CO2) that are volatilized…show more content… Heating the sample at 300oC will distills any free hydrocarbon already present in the sample. This is represented by peak P1 (S1) which is obtained by analysing the vapours with a flame ionisation detector (FID).
The temperature of the Rock Eval pyrolyser oven is then programed to increase to 550oC with the rate of increase being 25oC/min. The cracking of the kerogen takes place between 350 to 550oC which yield hydrocarbon until only the nongenerating residual carbon remains.This is represented by the peak P2 (S2).The temperature at which S2 reaches maximum is called Tmax and is depends upon the nature and maturity of kerogen.
Between 300 to 390oC the carboxyl group present in the kerogen breaks off, yeilding CO2 which is trapped and analysed later during the cooling cycle with the help of thermal conductivity detector (TCD).This is represented by peak P3…show more content… The TOC is then determined by adding the residual organic carbon detected to the pyrolyzed organic carbon, which in turn is measured from the hydrocarbon compounds issuing from pyrolysis
Important terms used in Rock Eval pyrolysis Analysis.
S1 (P1): - Free hydrocarbon present in the rock which are generated by heating the rock at 300oC for 3 minutes. It is measured in mg of HC per gram of rock. S1 increases with depth.
S2 (P2): - Hydrocarbon which are produced by thermal cracking of the kerogen by heating the sample at 350 to 550oC. This represents the amount of hydrocarbon that can be produced by the rock if subjected to required pressure and temperature conditions. It is measured in mg of HC per gram of rock.
This may also contain heavy molecular weight hydrocarbon (C24+ ) liberated from the cracking of the bitumens as they were not released during S1 temperature 300oC due to their molecular weight.This may cause multiple S2 peaks and will make Tmax data unreliable. S2 decreases with