Case02 Two layers with kerogen 'B' and two layers with kerogen 'F'
Contents
The present case is a variation of the base case data with the first two layers in the column model containing kerogen 'B' and the fourth and fifth layers containing kerogen 'F', with a non-kerogen layer sandwiched in between the kerogen layers. This example demonstrates the different kerogen types interacting in the same example. Where specific hydrocarbon maturation data are not defined, default parameters and settings are applied (default parameters are described in the reference manual Hydrocarbon maturation). In the context of this example, the default settings include:
•Thickness of the kerogen generative layer is the full formation layer.
•Porosity is updated due to hydrocarbon expulsion.
•A factor of 0.5 from the porosity change from hydrocarbon expulsion contributes to the reduced strength of the material.
It is recommended to undertake the base case Case00 beforehand. The data is identical to the base data with the addition of data relevant to hydrocarbon maturation. Only these additional data will be described here. The data file for the project is in : Kin_001\Case02\Data:
Hydrocarbon Maturation Data Definition
The data structures relevant to the definition of hydrocarbon maturation are:
•Group_data (only if pre-existing sediment contains kerogen) •History_point to output hydrocarbon kinetics state variables •Sedimentation_data (only required to be defined for deposition layers containing kerogen)
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Hydrocarbon maturation data is defined by Hydrocarbon_kinetics and Kerogen_kinetics.
Hydrocarbon_kinetics •Defines the assignment and processing data associated with hydrocarbon kinetics, e.g. vitrinite maturation, oil -> gas cracking and hydrocarbon expulsion.
Kerogen_kinetics •Defines the assignment and processing data associated with kerogen kinetics property name "kerogen1" for kerogen 'B' and "kerogen2" for kerogen 'F'. •Depending on the kerogen organofacies type defined, different default parameters are defined for transformation index (TI), hydrocarbon index (HI), gas concentration ratio G and weight fraction of carbon W.
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History Section Line Data •The additional data to output in the history section line data is the hydrocarbon kinetics state variable for the kinetics transformation ratio "K_KTR".
History Point Data •History point data sets 1 and 2 are defined for the four layers which contain kerogen, i.e. layers 1, 2, 4 and 5. The history point data set ID is incremented with each pair of definition in the stages. •The additional data to output is a list of 13 hydrocarbon kinetics state variables. This is only added to the second set of history point data defined in each of the four kerogen layer stages 1, 2, 4 and 5.
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•The additional data to include in the sedimentation data for the three deposition layers 2, 4 and 5 is the assignment of the applicable kerogen property set. In this example, the first deposition layer is defined with the same kerogen type as in the pre-existing layer, i.e. kerogen kinetics property set "kerogen1" with organofacies type 'B' and the fourth and fifth deposition layers are defined with kerogen kinetics property set "kerogen2" with organofacies type 'F'.
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The result files for the project are in directory: Kin_001\Case02\Results. Results of the high definition history files for the output variables including the hydrocarbon kinetic state variables have been processed into the excel file 00_Kin_001_Case02_Results.xlsx. Some of the graphical plots are presented here. Comparison plots are presented against the base case with no kerogen (Case00).
The figure below of the evolution of Kinetic KTR (Kerogen Transformation Ratio) clearly shows the kerogen transformation in layers 1 and 2 which has kerogen 'B' and layers 4 and 5 which has kerogen 'F'. Observed in the plot of Kinetic KTR are the beginnings of kerogen transformation at the base of the column at time 52.5Ma which has a temperature of 115°C and in layer 4 at time 90Ma which has a temperature of 167°C. This correlates to the known threshold temperature for oil expulsion for kerogen 'B' which occurs at 110°C and at 160°C for kerogen 'F' (Pepper and Corvi (1995b)).
The figures below show history plots at a point on the base of the column for hydrocarbon generation, retention and expulsion profiles for kerogen 'B'. These are overlaid against the reference Pepper and Corvi (1995b) results which shows excellent correlation. Also shown in the expulsion plot is the threshold temperature for oil expulsion for kerogen 'B' which occurs at 110°C.
Case02: Evolution of Hydrocarbon Generation, Retention and Expulsion Profiles with Temperature at History Point Located at Base of Column for Kerogen Type 'B' (Overlaid against Pepper and Corvi (1995b))
The figures below show history plots at a point near the base of layer 4 for hydrocarbon generation, retention and expulsion profiles for kerogen 'F'. These are overlaid against the reference Pepper and Corvi (1995b) results which shows excellent correlation. The "wave" in the plots correspond to the deposition of new sediments. Also shown in the expulsion plot is the threshold temperature for oil expulsion for kerogen 'F' which occurs at 160°C.
Case02: Evolution of Hydrocarbon Generation, Retention and Expulsion Profiles with Temperature at History Point Located at Base of Column for Kerogen Type 'F' (Overlaid against Pepper and Corvi (1995b))
The figures below shows the Kinetic KTR and temperature in the four kerogen layers (kerogen 'B' in layers 1 and 2 and kerogen 'F' in layers 4 and 5) at various times. Of the three plots, the largest range of transformation for kerogen 'F' (KTR 10 - 45%) occurs at t=90Ma with the temperatures in the kerogen layers between 145 - 168°C. This correlates with the plots above which shows the amount of hydrocarbon generation and expulsion for kerogen 'F' is very significant in this temperature range. At t=120Ma, all the kerogen 'B' has been transformed in the first two layers and 88 - 98% have been transformed for kerogen 'F' in layers 4 and 5.
The comparison plot of horizontal and vertical stresses with the no kerogen case shows a general reduction in stresses due to the hydrocarbon kinetics with greatest reduction in the vicinity of the four kerogen layers. Towards the bottom of the column in layer 1, there is a marginal stress increase with corresponding reduction in pore pressure compared against the no kerogen case.
Case 02: Contours of Stress Distribution as a Function of Depth at t=120Ma Plotted against the Reference Base Case with No Kerogen (Case00) shown in Dotted Lines
The comparison plots of porosity with the no kerogen case shows increased porosity change due to hydrocarbon kinetics. As expected, this increase is more evident in the kerogen 'B' layers 1 and 2 and at t=120Ma, the porosity change in the kerogen 'F' layers 4 and 5 start becoming more prominent. The 'delayed' response of the kerogen 'F' layers 4 and 5 is due to the higher threshold temperature required for the kerogen 'F' oil expulsion and being in upper layers, subject to lower temperatures than the kerogen 'B' layers 1 and 2. Kerogen 'F' layers are expected to have less impact on porosity change than kerogen 'B' layers due to the higher amount of inert kerogen in 'F' (88% compared to 54.3% for kerogen 'B', Pepper and Corvi (1995b)).
The comparison plots of pore pressure with the no kerogen case shows an increase in pore pressure due to the expulsion, which is expected. However, at the end of the simulation in layer 1, the pore pressure drops below the no kerogen case with corresponding stress increase shown earlier. In this instance, the reduction in pore pressure due to the higher permeability associated with the porosity increase is less than the overpressure generated from the expulsion. Also at the end of the simulation, some of the overpressure generated at t=75Ma has dissipated.
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[1] Pepper, A.S. and Corvi, P.J. (1995(a)): Simple kinetic models of petroleum formation. Part I: Oil and gas generation from kerogen. Marine and Petroleum Geology. 12(3) 291–319. 1995(a). [2] Pepper, A.S., Dodd, T.A. (1995): Simple kinetic models of petroleum formation. Part II: Oil-gas cracking. Marine and Petroleum Geology. 12(3) 321-340. [3] Pepper, A.S. and Corvi, P.J. (1995(b)): Simple kinetic models of petroleum formation. Part III: Modelling an open system. Marine and Petroleum Geology. 12(4) 417-452.
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