T
max
of asphaltenes: a parameter for oil maturity assessment
M. Nali *, G. Caccialanza, C. Ghiselli, M.A. Chiaramonte
Eni-Agip Division, Geochemical Department, Via Maritano 26, 20097 San Donato Milanese, Italy
Abstract
A new maturity parameter determined on both oil and bitumen samples, the asphalteneTmax, is proposed and
dis-cussed. This parameter could be very useful to address the maturity of the source rock. The asphalteneTmaxis
mea-sured by programmed Rock-Eval pyrolysis, using a modi®ed temperature program. Some phases of the experimental procedure, such as the asphaltene preparation and the Rock-Eval measurement substratum choice, are crucial in order to achieve reliable data. Laboratory simulations were carried out in order to assess the possible eects of both primary and secondary migration on asphalteneTmaxin the expelled oil: the original value of the asphaltene Tmaxin the
bitu-men is not substantially modi®ed and it is very close to that measured on kerogen. Examples of the determination of asphaltene Tmaxon many samples, collected from dierent areas and with dierent organic matter composition, are
given. Results show thatTmaxvalues from oil asphaltenes are reasonable indicators of source rock maturity.#2000
Elsevier Science Ltd. All rights reserved.
Keywords:Source rock; Kerogen; Bitumen; Oil; Asphaltenes;Tmax; Maturity; Rock-Eval pyrolysis
1. Introduction
Objective assessment of hydrocarbon supply and migration patterns are becoming critical elements in evaluating many exploration and exploitation opportu-nities. Addressing hydrocarbon-supply volumetrics and migration patterns requires systematic analyses of source attributes, source distribution, petroleum poten-tial, level of thermal maturity, source-to-trap transfer eciencies, and correlation of any encountered hydro-carbons (seeps, stains or accumulations) to one another and to source rocks from which they were generated and expelled.
Although oil and gas samples are often readily avail-able for characterization and correlation purposes, per-tinent source rock information is frequently absent because exploratory drilling typically focuses on struc-tural highs and seldom reaches deeply buried, eective basinal source facies. Furthermore, even if the source is reached and sampled, either low maturity or organic facies variation can prevent a reliable oil-source rock correlation. Explorationists are left with three options:
1. make arbitrary assumptions on the subsurface attributes of the petroleum system;
2. forecast these attributes using conceptual and geochemical models constrained by physico-che-mical principles;
3. use the characteristics of any encountered hydro-carbons to infer the possible character, maturity and identity of the potential source rock.
The third approach is referred to as ``geochemical inversion'' (Bissada et al., 1993). In principle, geochem-ical inversion utilizes the same type of analytgeochem-ical proce-dures used in conventional petroleum-to-source correlations. The derived information may include spe-ci®c characteristics of the source rocks such as organic matter input, lithology and maturity.
As already speci®ed, the ``geochemical inversion'' can be carried out using conventional geochemical tools; nevertheless, new parameters, simplifying and speeding up the inferences about the characteristics of the source, are also needed. In this context, a new maturity indi-cator, the asphalteneTmax, has been developed.
Potential source rocks are described in terms of quantity, quality and level of thermal maturity of organic matter (Bordenave et al., 1993a).
0146-6380/00/$ - see front matter#2000 Elsevier Science Ltd. All rights reserved. P I I : S 0 1 4 6 - 6 3 8 0 ( 0 0 ) 0 0 0 6 8 - 1
www.elsevier.nl/locate/orggeochem
* Corresponding author. Fax: +39-02-52056371.
Recognizing the need to describe the thermal maturity of sedimentary organic matter accurately, organic geo-chemists developed various thermal maturity para-meters.
Conventional geochemical methods for assessing source rock maturity include Rock-Eval pyrolysis (Espitalie et al., 1977, 1985), compound class distributions (Tissot et al., 1971; Tissot and Welte, 1984; Hunt, 1996), vitrinite re¯ectance (Ro) (Bostick, 1979), thermal alteration index (TAI) (Staplin, 1969), carbon preference index (CPI) (Bray and Evans, 1961), and biomarker maturity para-meters (Peters and Moldowan, 1993).
Peters (1986) described guidelines for evaluating or screening petroleum source rocks using Rock-Eval (programmed temperature) pyrolysis, as did EspitalieÁ et al. (1977, 1984).
During heating, a series of events are observed (Espi-talie et al., 1985). In particular, between 300 and 600C,
hydrocarbons and oxygen containing compounds are expelled from the rock as a consequence of cracking of both kerogen and heavy extractable compounds such as resins and asphaltenes. Hydrocarbons form the S2peak
that corresponds to the present potential of the rock sample for hydrocarbons.
The temperature for which the S2 peak is maximum
(Tmax) was found to vary with the thermal evolution
formerly undergone by the rock sample under analysis (Tissot and EspitalieÂ, 1975; EspitalieÁ et al., 1977). Mature organic matter, that is more condensed, is more dicult to pyrolyze due to higher activation energies, i.e. a higher temperature is required to crack the con-densed structure.Tmaxis inherently linked to the
kinet-ics of the cracking of organic matter. Types I (and II) kerogens are known to have relatively simpler molecular compositions and structures than type III. These simpler structures imply a narrower distribution of cracking activation energies and a smaller temperature range (Tissot and EspitalieÂ, 1975; Pepper and Corvi, 1995).
Tmax variation has been studied for each type of
organic matter as a function of its thermal evolution, taking as a reference its vitrinite re¯ectanceRo. Of par-ticular interest is the determination of the Tmax that
corresponds to the beginning of both the oil and the gas window, for each type of organic matter (Bordenave et al., 1993b).
. For type I, oil genesis generally begins at Roof about 0.7% and aTmaxat 440C. The cracking is
rapid and all the kerogen is completely tran-formed when Ro reaches 1.0%, while the Tmax
remains roughly constant. The threshold of oil generation for oil-prone Type I kerogens is higher than for the other kerogen types; its resistance to thermal degradation may be due to cross-linkage of long, aliphatic chains and a general scarcity of thermally labile heteroatomic bonds.
. For type II, the beginning of the oil genesis occurs at lower maturities (around 0.6% Ro equivalent and Tmax =430-435C). Most of the kerogen is
transformed atRo1%, which corresponds to a
Tmaxof455C. The gas and condensate zones
correspond to a Tmaxrange of 455±470C. In the
case of a type II-S, an organic matter showing a high sulfur and oxygen contents, the oil window begins earlier as the result of the breakage of the weak sulfur and oxygen bonds (Tmax390±420C).
. For type III, hydrocarbons are formed from Ro 0.6 or even 0.7%, at aTmax greater than 435C.
The transition to condensate zone corresponds to
Ro1:3%andTmax=470
C. Thermal
degrada-tion is not yet complete atRo1:6%, which cor-responds to aTmaxhigher than 600C. Dry gas is
produced forTmaxhigher than 540C.
As theTmax is a useful indicator of the thermal
evo-lution/maturity of a source rock, a new parameter has been developed that could be used when suitable source rock samples are not available for a direct measurement. This parameter is the asphaltene Tmax and it is
deter-mined on the asphaltene fraction of either oils or bitu-mens, using the Rock-Eval pyrolysis technique.
The use of asphalteneTmax, as a substitute for
kero-gen Tmax, is made possible and reasonable by the
assumption (Pelet et al., 1986; Behar and Vander-broucke, 1987) that asphaltenes from rock extracts and the corresponding kerogens show a very similar struc-ture and contain the same constituent macromolecular units. A consequence of this compositional similarity is that asphaltenes and kerogen undergo parallel evolution during burial heating.
On the other hand, before using Tmax of the oil
asphaltenes, it was necessary to evaluate the possible eect of primary and secondary migration on this para-meter.
The aim of the present study was to answer the fol-lowing questions:
. Is bitumen asphaltene Tmax comparable to both
source rock and isolated kerogenTmax?
. Is oil asphaltene Tmax representative of bitumen
asphalteneTmax, even if the oil asphaltenes have
undergone both primary and secondary migra-tion? In other words, does asphaltene fractiona-tion during explusion and migrafractiona-tion aect the
Tmaxvalue?
2. Experimental
points, such as the asphaltene precipitation and the Rock-Eval pyrolysis conditions, are described and dis-cussed.
Additional laboratory experiments have been also performed in order to determine, if any, the possible eects of primary and secondary migration on Tmax
measured on asphaltenes obtained from oil samples.
2.1. Asphaltene precipitation
Source rock extract (bitumen), reduced to a volume of 1 ml, is added to ann-pentane containing vial, at room temperature. Then-pentane/bitumen ratio is around 40/ 1 (vol./wt.). The resulting slurry is stirred for 5 min and, then, left to stand for 30 min.
Asphaltenes are recovered by vacuum ®ltration on a Te¯on ®lter (porosity=0.5mm).
After washing thoroughly withn-pentane in order to remove adsorbed and/or coprecipitated material, asphaltenes are dried at 150
C for 2 h.
The same procedure is used when asphaltenes are precipitated from an oil sample. In this case, the starting material is constituted by an oil solution in CH2Cl2.
2.2. Rock-eval pyrolysis conditions
All the experiments were performed using a Rock-Eval II Plus instrument, with a temperature program from 180 to 550C at a heating rate of 10C/min. The
temperature program has been modi®ed from the stan-dard conditions (250±550C, 25C/min), in order to
reduce, by a better peak separation, the interferences derived from possible asphaltene contaminants (for example waxy materials). As the Tmax varies with the
analytical conditions, using the modi®ed procedure one obtains the Tmax values 18±20C lower than the one
measured using the standard conditions. For this reason also a dierent maturity interpretation scheme applies to 10
C/min heating rate than 25
C/min, for example, a
Tmaxof 417C (10C/min heating rate) corresponds to a
value of 435
C using standard condition; indicating onset of oil window.
The Rock-Eval pyrolysis is carried out on 100 mg of source rock, after washing with organic solvent (CHCl3). For both isolated kerogen and asphaltene
pyrolysis, 100 mg of CaCO3 were added in order to
simulate the mineral matrix eect (Espitalie et al., 1980, 1984). The way of adding the sample powder to CaCO3
was investigated on an asphaltene sample. The asphal-tenes were added to CaCO3as (1) a solution at the top
of the vial, (2) dispersed, (3) at the bottom of the sample vial, and (4) as a sandwich (50 mg of CaCO3
+asphal-tenes+50 mg of CaCO3).
The correlation betweenTmaxand sample weight was
previously investigated (EspitalieÁ et al., 1985; Peters, 1986). The ®rst asphaltene sample, used in this experi-ment, was precipitated from the oil generated from a source rock sample (Northern Italy 1) during a hydro-pyrolysis treatment (340
C for 24 h); the other was pre-cipitated directly from the oil (Northern Italy 4) generated by the source rock itself.
2.3. Primary migration (expulsion) eect on asphaltene
Tmax
Eight grams of a limestone source rock sample (Northern Italy 1) were ground (75mm) and extracted with chloroform (CHCl3). From the source rock
pow-der, 16 tablets were obtained (7 ton/cm2for 20 s). The
tablets were kept in a reactor, placed in a gas chroma-tographic oven at a temperature of 340
C for 24 h in an inert atmosphere (helium). After cooling, a careful and mild washing with methylene chloride (CH2Cl2) was
carried out recovering the expelled hydrocarbons (exp. HC). Then, the tablets were ground and extracted with CHCl3. Thus, the unexpelled hydrocarbons (unexp. HC)
Then maltenes (soluble fraction in n-pentane) were fractionated using liquid chromatography. Asphaltene
Tmaxwere measured as already described.
2.4. Secondary migration eect on asphalteneTmax
A stainless steel tube (3 m0.8 cm i.d.) was packed with quartzite (75±100mm) and then saturated with salt water (KCl 2%) yielding a pH around 6. An oil sample (West African 1) was pumped at a ¯ow rate of 0.2 ml/h through the tube, collecting the eluted ¯uid (2 ml). The tube was kept at a temperature of 90
C during the entire experiment.
After cooling, the tube was cut into 3 sections (1 m each), and the adsorbed oil was recovered from each section by ¯owing N2(6 atm) through the section itself.
The asphalteneTmaxwas determined on all the samples,
including the starting oil.
The same experiment was carried out using a second oil sample (Northern Italy 2). The West African 1 oil sample (%S 0.06, API
36.5) has characteristics indica-tive of a pre-salt lacustrine source rock (e.g. C25tricyclic/
C26tricyclic terpanes (C25T/C26T) < 1; presence of a low
amount of extended hopanes; terpanessteranes; pre-sence of a high amount of methylsteranes and abpre-sence of C30steranes).
These characteristics are common in West African Lower Cretaceous Lacustrine Sections (Burwood et al., 1990, 1992, 1995). The studied oil was generated by an argillaceous source (as indicated by the presence of diasteranes, C29Ts and C30*; norhopane/hopane < 1;
absence of 30-norhopanes), in a lacustrine (see above), saline (presence of signi®cant amounts of gamma-cerane), sub-oxic environment (Pr/Ph > 1). The algal contribution to the organic matter is signi®cant (C27/ C29 steranes > 1). The sample shows a middle oil window maturity level (sterane isomerization has reached the equilibrium and sterane aromatization value is high).
The Northern Italy 1 oil sample (%S 0.8, API
36.3) was generated by a mixed lithology source (argillaceous/ carbonatic), in a marine sub-oxic environment with a signi®cant continental contribution. From the biological marker maturity parametrs, the oil can be de®ned as early mature.
3. Results and discussion
The asphaltene fraction has been described in terms of a single, representative asphaltene ``molecule'' including, in the correct proportions, all the chemical and elemental constituents known to be present in a given asphaltenic matrix (condensed aromatic rings, short aliphatic chains, naphtenic ring structures, het-eroatoms, etc.). While this approach gives an idea of the
structural complexity of the compounds comprised in the asphaltenic component, it obscures the highly dif-ferentiated chemical nature of the molecules in this complex petroleum fraction. Asphaltenes are a class of materials de®ned by solubility and not a molecular spe-cies or even a homologous set of molecules. They are the most polar and heaviest fraction of petroleum and they are precipitated from either crude oils or bitumens by addition of a large excess of a low-boiling n-alkane (commonlyn-pentane orn-heptane).
The volume of paranic precipitant added per unit volume of oil should always be speci®ed, as the structure and the chemistry of asphaltenes vary dramatically as a function of the sample work-up. Furthermore, the che-mical constituents of asphaltenes from dierent samples are dierent even if the solubility/extraction recipes are identical (Calemma et al., 1995).
In the experimental section an asphaltene precipita-tion procedure is described. This is only one of the pos-sible recipes, but it works quite well when asphaltene
Tmaxis the measured parameter and, as far as the
pre-cipitation conditions are kept constant, the obtained results are reliable and comparable. This procedure works on a routine basis and does not require any fur-ther puri®cation of the asphaltenes. The possible copre-cipitated waxes do not aect theTmaxvalue as, in our
experimental conditions (program temperature: 180± 550
C, 10
C/min), they are thermally desorbed at a lower temperature, giving rise to a peak that is resolved from the asphaltene peak.
Because Tmax varies with the analytical conditions,
our modi®ed procedure produces Tmax values around
18±20
C lower than the one measured using the stan-dard conditions. For this reason also a dierent matur-ity interpretation scheme applies to 10
C/min heating rate than 25C/min. For example a T
max of 417C
(10
C/min heating rate) corresponds to a value of 435
C using standard conditions; aTmaxof 417C in our
pro-cedure indicates onset of oil generation.
When either isolated kerogen or bitumen/oil asphal-teneTmaxwas measured, calcium carbonate was used to
simulate the matrix eect because of its poor retention eects on pyrolysis products.
Each methodology used to add the asphaltene powder to CaCO3 (solution, dispersion, at the bottom of the
sample vial, as a sandwich) gives a dierent Tmaxvalue
(Table 1). The highest value is obtained when asphal-tenes are positioned at the bottom of the sample vials. However, when asphaltenes are added as a solution on the top of CaCO3, the obtainedTmaxvalue is the lowest.
These observations may be explained by invoking the presence of two combined phenomena. On one hand, theTmaxshift could be related to a temperature gradient
bottom of the oven than at the top (EspitalieÁ et al., 1985). On the other hand, it was found (EspitalieÂ, 1985) that it is the heaviest hydrocarbon compound (hetero-polar compound and C20+ hydrocarbons) making up
the peaks S2 and, partly, S1 that are the most easily
retained on mineral matrices and ``coked'' during heat-ing. This retention phenomenon is related to the speci®c surface area of the mineral matter and will have two main eects on the pyrolysis parameters: a decrease in S1and S2peaks and an increase in Tmaxvalue with the
activity of the mineral matrix, minerals such as quartz and carbonates having little eect (EspitaleÂ, 1985). In our opinion, this retention eect is not negligible. In fact, when the correlation between Tmax and sample
weight is investigated (Table 2), the highestTmaxvalue is
obtained when the amount of asphaltenes is the lowest, i.e. when the matrix/sample weight ratio is the highest, regardless of the asphaltene origin. In this case the pos-sible temperature gradient across the Rock-Eval oven (and the crucible) can be considered negligible because asphaltenes have been added to the carbonate in a dis-persed state so their position in the crucible is homo-geneous.
So, the asphaltene dispersion gives the most reliable results when compared to the source rockTmax(Table 3
and Fig. 1) and to the isolated kerogen Tmax (Table 4
and Fig. 1). Furthermore, Tmax determinations have
to be carried out always on the same amount of sample (2±3 mg).
The laboratory experiments, performed to assess the possible eects of both primary and secondary migra-tion on asphalteneTmax, were essential before using oil
asphaltenes as substitutes for bitumen asphaltenes. Laboratory generated HCs, both ``expelled'' and ``unexpelled'' hydrocarbons (exp. HC and unexp. HC), were fractionated into saturates, aromatics, resins and asphaltenes in order to con®rm the dierences in
com-position of exp. HC and unexp. HC (Table. 5). As expected, ``unexpelled'' hydrocarbons are heavier than the ``expelled'' hydrocarbons. The resin content remains almost constant even if the composition of the two samples is quite dierent. A comparison between the asphalteneTmax obtained from ``expelled'' and
``unex-pelled'' hydrocarbons showed that there are no sig-ni®cant dierences in their values (Table 6); suggesting a minimal eect of primary migration, at least in the experimental conditions used to tentatively simulate the expulsion from the source rock.
The possible secondary migration eects on asphal-teneTmaxwere tested on two oil samples (West African
Table 1
Comparison among dierent methodologies used to add bitu-men asphaltenes to CaCO3(West Africa 2 well)a
Methodology Tmax(C)
Solution (at the top of the vial) 426
Dispersion 432
As a sandwich
(50 mg CaCO3+asph.+ 50 mg CaCO3)
436
At the bottom of the vial (100 mg CaCO3+asph.)
442
a T
max values are obtained at 10C/min, which results in Tmaxvalues approximately 18±20C lower than 25C/min as is
commonly used.
Table 2
Sample weight eect on asphalteneTmaxa
Northern Italy 1 hydropyrolysis oil asphaltenes
Sample weight (mg) S2 (mg/g) Tmax(C)
Northern Italy 4 oil asphaltenes
Sample weight (mg) S2 (mg/g) Tmax(C)
max values are obtained at 10C/min, which results in Tmaxvalues approximately 18±20C lower than 25C/min as is
commonly used.
Table 3
Comparison among source rockTmaxand bitumen asphaltene
Tmax(two dierent methodologies were used to add asphaltenes
to Ca CO3)a
Northern Africa 1 426 426 434
Northern Africa 2 429 427 433
Northern Africa 3 434 430 442
Northern Africa 4 425 423 429
Western Africa 2 432 431 442
Northern Italy 1 398 398 Not determined
Northern Italy 2 415 415 421
Northern Italy 3 434 434 442
a T
max values are obtained at 10C/min, which results in Tmaxvalues approximately 18-20C lower than 25C/min as is
1 and Northern Italy 2). No eect was noted on asphaltene Tmax from the simulated secondary
migra-tion, as the results remained constant for all the samples (Table 7).
We are aware that experimental conditions always dier from the geological conditions.
In the case of secondary migration, the migration scale can be orders of magnitude higher in nature than the few meters used in our experiment.
Generation and primary migration are even more complex phenomena to be simulated in laboratory experiments. Inan et al. (1998) demonstrated that simu-lating primary migration by pyrolysis is very dicult
especially for tight carbonates. Pyrolysis of carbonates is greatly aected by grain-size of the pyrolyzed sample. For this reason, in our experiments we used a limestone source rock sample. Inan et al. (1998) also suggested to pyrolyze coarse grain-size (from few millimeters to cen-timeters) to maintain the original texture, porosity, per-meability, etc.; this was possible in their experiments as Fig. 1. Comparison among source rockTmax, isolated kerogenTmax(dispersed) and bitumen asphalteneTmax(two dierent
meth-odologies were used to add asphaltenes to CaCO3, dispersed and at the bottom of the sample vial).Tmaxvalues are obtained at 10C/
min, which results inTmaxvalues approximately 18-20C lower than 25C/min as is commonly used.
Table 4
Comparison among isolated kerogen Tmax and bitumen
asphaltene Tmax, both added to the mineral matrix (calcium
carbonate) as a dispersiona
Sample Isolated kerogen
Tmax(C)
Asph.Tmax(C)
Northern Africa 2 426 427 Northern Africa 3 428 430 Northern Africa 4 424 423
Western Africa 2 431 431
Northern Italy 1 398 398
Northern Italy 2 414 415
Northern Italy 3 433 434
a T
max values are obtained at 10C/min, which results in Tmaxvalues approximately 18±20C lower than 25C/min as is
commonly used.
Table 5
Liquid chromatography fractionation results of the expulsion laboratory testsa
Sample HCS% HCA% Res.% Asph.%
Exp. HC 11.5 37.3 46.7 4.5
Unexp. HC 4.1 15.1 42.1 38.7
a T
max values are obtained at 10C/min, which results in Tmaxvalues approximately 18±20C lower than 25C/min as is
commonly used.
Table 6
Primary migration (expulsion) eect on asphalteneTmaxa
Sample Asph.Tmax(C)
Exp. HC 414±417
Unexp. HC 415±417
Extracted source rock 419±419
a T
max values are obtained at 10C/min, which results in Tmaxvalues approximately 18±20C lower than 25C/min as is
they used pyrolysis methodologies directly combined to analytical devices (Rock-Eval pyrolysis and pyrolysis± gas chromatography). On the contrary, we performed o-line closed-system pyrolysis with the aim of recover-ing both ``expelled'' and ``unexpelled'' hydrocarbons to compare their asphaltene Tmax. For this reason, we
needed to entrap the ``unexpelled'' hydrocarbons using compressed pellets obtained from crushed rock. More-over, the rock sample was not pulverized to a ®ne pow-der (<62mm) in order to prevent the destruction of the organic and inorganic matrix-relationship (Lewan, 1993).
4. Conclusions
The experimental results obtained from the Tmax
determinations on many samples collected from dier-ent areas and containing dierdier-ent organic matter types, demonstrated that the kerogen Tmax values are very
close to those measured on the asphaltenes precipitated from the associated bitumen. In practice, this means that theTmaxof oil asphaltenes could re¯ect the source
rockTmaxat expulsion, provided that primary and
sec-ondary migration processes do not aect signi®cantly this parameter.
Laboratory simulations were carried out in order to assess the possible eect of both primary and secondary migration on asphalteneTmax. Even if the extrapolation
of the measurements should always be considered with the limitation of the laboratory simulations in mind, we think that our experimental conditions could give at least a rough indication concerning the negligible eect of both primary and secondary migration on oil asphalteneTmax.
Consequently, such a parameter can be very useful in predicting the maturity of the source rock, even though not penetrated. This is particularly eective, for exam-ple, in those basins where the source is deeper than the reservoir. At the same time, this parameter can be very useful in basin modeling exercises to calibrate the
expulsion processes through the evaluation of theTmax
of the source during the oil expulsion.
Possible future developments of this methodology could be:
. the use of oil asphaltenes in inferring the source rock kinetic parameters, this application has been initiated by di Primio et al. (1999);
. the extrapolation of the Tmax values to deeper
horizons that were not penetrated to predict the stratigraphical level where the measured values might be reached and where the source rock responsible for the oil occurrences could be loca-ted.
Acknowledgements
The authors thank Mr. Dan Jarvie, Dr. Sedat Inan and an anonymous reviewer for helpful reviews.
References
Behar, F., Vandenbroucke, M., 1987. Chemical modelling of kerogens. Organic Geochemistry 11, 15±24.
Bissada, K.K., Elrod, L.W., Robinson, C.R., Darnell, L.M., Szymczyk, H.M., Trostle, J.L., 1993. Geochemical inversion. A modern approach to inferring source-rock identity from characteristics of accumulated oil and gas. Energy Explora-tion and ExploitaExplora-tion 11, 295±328.
Bordenave, M.L., EspitalieÂ, J., Leplat, P., Oudin, J.L., Van-denbroucke, M., 1993a. Screening tecniques for source rock evaluation. In: Bordenave, M.L. (Ed.), Applied Petroleum Geochemistry. Editions Technip, Paris, pp. 219±224. Bordenave, M.L., EspitalieÂ, J., Leplat, P., Oudin, J.L.,
Van-denbroucke, M., 1993b. Screening tecniques for source rock evaluation. In: Bordenave, M.L. (Ed.), Applied Petroleum Geochemistry. Editions Technip, Paris, pp. 246±250. Bostick, N.H., 1979. Microscopic measurement of the level of
catagenesis of solid organic matter in sedimentary rocks to aid exploration for petroleum and to determine formar bur-ial temperatures. A review. Society of Economic Paleontolo-gists and MineraloPaleontolo-gists Special Publication 26, 17±43. Bray, E.E., Evans, E.D., 1961. Distribution ofn-parans as a
clue to recognition of source beds. Geochimica Cosmochi-mica Acta 22, 2, ±15.
Burwood, R., Cornet, P.J., Jacobs, L., Paulet, J., 1990. Orga-nofacies variation control on hydrocarbon generation: a Lower Congo basin (Angola) case history. Organic Geo-chemistry 16, 325±338.
Burwood, R., Leplat, P., Mycke, B., Paulet, J., 1992. Rifted margin source rock deposition: carbon isotope and bio-marker study of a West African Lower Cretaceous ``lacus-trine'' section. Organic Geochemistry 19, 41±52.
Burwood, R., De Witte, S.M., Mycke, B., Paulet, J., 1995. Petroleum geochemical characterization of the Lower Congo coastal basin Bucomazi formation. In: Katz, B. (Ed.), Table 7
Secondary migration eect on asphalteneTmaxa
Western Africa 1 oil asphalteneTmax(C)
Northern Italy 2 oil asphalteneTmax(C)
Oil 427 423
Fraction 1 428 425
Fraction 2 428 425
Fraction 3 428 423
Eluted oil 427 425
a T
max values are obtained at 10C/min, which results in Tmaxvalues approximately 18±20C lower than 25C/min as is
Petroleum Source Rocks. Spinger Verlag, Berlin Heidelberg, pp. 235±263.
Calemma, V., Iwanski, P., Nali, M., Scotti, R., Montanari, L., 1995. Structural characterization of asphaltenes of dierent origins. Energy and Fuels 9, 225±230.
di Primio, R., Hors®eld, B., Guzman-Vega, M. and Jarvie, D., 1999. Bulk kinetics of petroleum asphaltenes: characterisa-tion of source rock stability at time of liquid phase genera-tion.19th International Meeting on Organic Geochemistry, 6± 10 September 1999, Istanbul, Turkey. Book of abstracts, pp. 5±6.
EspitalieÂ, J., 1985. Use ofTmaxas a maturity index for dierent
types of organic matter. Comparison with vitrinite re¯ec-tance. In: Burrus, J. (Ed.), Thermal Modelling in Sedimen-tary Basins. Edition Technip, Paris, pp. 475±496.
EspitalieÂ, J., Laporte, J.L., Madec, M., Marquis, F., Leplat, P., Paulet, J. et al., 1977. Methode rapide de caracterisation des roches meres, de leur potential petrolier et de leur degre d'evo-lution. Revue Institute Francais du Petrol 32, 23±45.
EspitalieÂ, J., Madec, M., Tissot, B., 1980. Role of mineral matrix in kerogen pyrolysis: in¯uence on petroleum genera-tion and migragenera-tion. American Associagenera-tion of Petroleum Geologists Bulletin 64, 59±66.
EspitalieÂ, J., Senga Makadi, K., Trichet, J., 1984. Role of the mineral matrix during kerogen pyrolysis. Organic Geochem-istry 6, 365±382.
EspitalieÂ, J., Deroo, G., Marquis, F., 1985. La pyrolyse Rock-Eval et ses applications.Revue Institute Francais du Petrole, Part I 40, 563-578, Part II 40, 755±784.
Hunt, J.M., 1996. Petroleum Geochemistry and Geology, 2nd Edition. Freeman, New York, 743 p.
Inan, S., Yalcin, M.N., Mann, U., 1998. Expulsion of oil from
petroleum source rocks: inferences from pyrolysis of samples of unconventional grain size. Organic Geochemistry 29, 45± 61.
Lewan, M.D., 1993. Laboratory simulation of petroleum for-mation: hydrous pyrolysis. In: Engel, M.H., Macko, S.A. (Eds.), Organic Geochemistry. Principles and Application. Plenum Press, New York, pp. 419±442.
Pelet, R., Behar, F., Monin, J.M., 1986. Resins and asphaltenes in the generation and migration of petroleum. Organic Geo-chemistry 10, 481±498.
Pepper, A.S., Corvi, P., 1995. Simple kinetic models of petro-leum formation. Part I: oil and gas generation from kerogen. Marine and Petroleum Geology 12, 291±319.
Peters, K.E., 1986. Guidelines for evaluating petroleum source rock using programmed pyrolysis. American Association of Petroleum Geologists Bulletin 70, 318±329.
Peters, K.E., Moldowan, J.M., 1993. Biomarker maturity parameters. In:The Biomarker Guide. Prentice Hall, Engle-wood Clis, New Jersey, pp. 221±251.
Staplin, F.L., 1969. Sedimentary organic matter, organic meta-morphism, and oil and gas occurrence. Canadian Petroleum Geologists Bulletin 17, 47±66.
Tissot, B.P., Califet-Debyser, Y., Deroo, G., Oudin, J.L., 1971. Origin and evolution of hydrocarbons in early Toarcian shales, Paris Basin, France. American Association of Petro-leum Geologists Bulletin 55, 2177±2193.
Tissot, B.P., EspitalieÂ, J., 1975. L'evolution thermique de la matiere organique des sediments: application d'une simula-tion mathematique. Revue Institute Francais du Petrole 30, 743±777.
