[0001] The present invention relates to improvements in a two stage catalytic hydropyrolysis
process for use on kerogen bearing rock and/or on "heavy oils" which process yields
significant improvements in the yield of bound alkanes. In particular, the two stage
catalytic hydropyrolysis process yields significant improvements in the yield of biological
markers or biomarkers from kerogen-bearing rock or from crude oil typically located
in natural reservoirs.
[0002] Biological markers or "biomarkers" are compounds found in sedimentary organic matter.
Such compounds can be related structurally to their biological precursors. Over geological
time periods, the structural configuration of biomarkers can change, for example via
isomerisation, aromatisation reactions, and cracking: generally, over time biomarker
compounds become more thermodynamically stable.
[0003] The oil industry makes extensive use of biomarker compounds in oil exploration. Biomarker
distribution, such as the distribution of hopanes and steranes, enables the oil industry
to correlate the presence of oils with certain source rocks and to predict the amount
of oil which has been formed therein.
[0004] Conventional procedures for such oil: source rock correlations and maturity assessments
make use of the alkanes and aromatics which are extractable from petroleum source
rocks in common organic solvents, such as dichloromethane (DCM), chloroform and methanol
or mixtures thereof. Such conventional procedures remove only a small proportion of
the total organic matter, typically less than 5% w/w. Also, the distributions of biomarkers
in such solvent extraction samples is not necessarily representative of biomarkers
bound to kerogen.
[0005] It is now known that significant quantities of biomarkers are covalently bound to
the macromolecular (cross-linked) organic matter (kerogen) in petroleum source rock
which are not generally extractable in common solvents and can account for more than
95% of the organic matter.
[0006] It is also known that significant quantities of biomarkers are also covalently bound
to heavy oil fractions (resins and asphaltenes) in petroleum source oils.
[0007] Hydropyrolysis is known in the art of coal processing, for example, GB2007255B teaches
a non-catalytic two-stage hydropyrolysis process.
[0008] Two-stage catalytic hydropyrolysis of coal tars and/or of coal is also known in the
art, for example EP284213 teaches a two-stage catalytic hydropyrolysis process for
the hydrocracking of coal which requires the employment of vigorous operating conditions;
Bolton C. et al (February, 1989) Fuel, Vol. 68, pages 161-167 teaches a two-stage
catalytic hydropyrolysis process for the hydrocracking of coal tars. Bolton et al
teaches the use of vigorous operating conditions such as a high heating rate (300°C/min)
in the first stage and an operating temperature of between 500°-575°C at a hydrogen
pressure of 15 MPa in the second stage.
[0009] In contrast, the improved two stage catalytic hydropyrolysis process of the instant
invention is designed to detect biomarkers such as steranes and hopanes covalently
bound in kerogen bearing rock or heavy oil fractions by hydro-treating source rock/heavy
oils under conditions in which hydrocracking is minimised relative to conventional
two stage catalytic hydropyrolysis processes of the prior art. The two stage catalytic
hydropyrolysis process of the invention provides a more accurate means of assessing
the biomarker content of kerogen bearing rock/heavy oils.
[0010] It has now been found that greater quantities of covalently bound alkanes, such as
hopanes and steranes, can be released from kerogen bearing rock using a two-stage
catalytic hydropyrolysis process of the invention, than by using conventional solvent
extraction procedures. Similarly it has been found that covalently bound alkanes can
be released from heavy oil fractions using the two-stage catalytic process of the
invention.
[0011] The present invention seeks to obviate and/or mitigate the disadvantages associated
with the prior art.
[0012] A two-stage catalytic hydropyrolysis process for recovering biomarkers from a geological
oil-bearing sample, said process comprising the steps of:
[0013] According to a first aspect of the present invention there is provided a two-stage
catalytic hydropyrolysis process wherein in a first stage heating a geological oil-bearing
sample incorporating a dispersed hydrotreating catalyst up to a temperature of from
450°C to 520°C, in the presence of hydrogen at a pressure of from 5 MPa to 15 MPa
so as to release into the vapour phase from said geological oil-bearing sample organic
compound material containing biomarkers; and
in a second stage contacting the material released in the first stage with a hydrotreating
catalyst at a temperature in the range of from 300°C to 350°C in the presence of hydrogen
at a pressure of from 5 MPa to 15 MPa so as to release chemically bonded biomarkers.
[0014] According to a further aspect of the invention there is provided a two-stage catalytic
hydropyrolysis process comprising a first stage of treating a geological oil-bearing
sample comprising from 0.01 to 5% by weight of molybdenum disulphide or a precursor
thereof (ie. loaded sample) with hydrogen at a pressure of from 5 MPa to 15 MPa and
heating the said sample at a heating rate of from 5°C to 20°C min
-1 to a temperature of from 450°C to 520°C, and catalytically releasing chemically bonded
biomarkers from said geological oil-bearing sample in the second stage wherein the
temperature is in the range of from 300°C to 350°C and the hydrogen pressure is substantially
the same as that employed in the first stage.
[0015] A "geological oil-bearing sample" can be a kerogen bearing rock sample or a "heavy
oils fraction" of the type which may be found in underground natural oil reservoirs
in geologically interesting areas for oil exploration. A "loaded sample" comprises
a kerogen bearing rock or heavy oils fraction loaded with a suitable catalyst and
mixed with inert mixing agent or inert adsorbent agent as appropriate.
[0016] We have found that organic materials bound to geological oil-bearing samples can
be released by means of hydropyrolysis (i.e. pyrolysis in the presence of hydrogen)
and a suitable hydrotreating catalyst which selectively promotes breaking of C-O and
C-S bonds without significant breaking of C-C bonds. In order to maximize the effect
of the catalyst it should be dispersed throughout the sample. Conveniently this is
effected by impregnation of the sample with a suitable catalyst - such as molybdenum
disulphide or a precursor thereof.
[0017] In the first stage of the process of the invention there is released into the vapour
phase, a certain amount of biomarkers, together with other organic materials, some
of which comprise biomarkers still covalently bound to other entities such as aromatic
moieties. It will be appreciated that the various different organic materials are
released by the hydropyrolysis process at different temperatures. In order to maximise
preservation of the stereochemistry of those biomarkers which tend to be released
at lower temperatures in the first stage, it is preferred that the temperature of
the sample be increased at a relatively slow controlled rate, desirably from 5°C to
20°C min
-1, so that the released biomarkers can be removed to the second stage as soon as practicable
after release thereof and before being exposed to unnecessarily high temperature,
thereby minimizing degradation of their stereochemical identity.
[0018] Conveniently the organic materials released into the vapour phase are transported
from the first stage to the second stage by means of entrainment in a hydrogen gas
flow. In general this should be at a rate sufficient to remove the released organic
materials from the first stage before significant degradation thereof due to continual
exposure to the first stage reaction conditions, for example, within not more than
2 seconds.
[0019] In the second stage, those biomarkers still covalently bound to aromatic moieties
via C-O and C-S bonds may be substantially released, thereby considerably increasing
the overall yield of biomarkers from the sample. We have found that the amount released
in this way is dependant on the residence time in the second stage in contact with
the hydrotreating catalyst, which is conveniently used in a supported form, up to
a given level which can be simply and readily determined by trial and error. It will
be appreciated that measurement of the actual contact or residence time can be quite
complex to determine and will depend on various factors such as void volume, flow
passage dimensions and configuration etc.- where the second stage is (most conveniently)
carried out by means of passing a flow of organic materials released from the first
stage in a vapour phase, entrained in a hydrogen gas flow through or over a supported
catalyst. Given that in such a system the flow rate generally corresponds to that
used for the first stage, the contact or residence time for the second stage may conveniently
be controlled by varying the length of the supported catalyst zone in the second stage.
Thus in order to maximise the biomarker yield the length may be progressively increased
until no further increase in biomarker yield is obtained. In general substantially
complete biomarker release can be achieved using a notional contact or residence time
(based simply on volumetric flow rate from the inlet to the outlet of the catalyst
zone) of at least 1 second, preferably at least 2 seconds, eg. at least 5 seconds.
[0020] Accordingly there is provided a two-stage catalytic hydropyrolysis process comprising
a first stage of treating a kerogen bearing rock impregnated with from 0.01 to 5%
by weight of molybdenum disulphide or a precursor thereof (ie. loaded sample) with
hydrogen at a pressure of from 5 MPa to 15 MPa and heating the said rock at a heating
rate of from 5°C to 20°C min
-1 to a temperature of from 450°C to 520°C, and catalytically releasing chemically bonded
biomarkers from the said rock in a second stage wherein the temperature is in the
range of from 300°C to 350°C and the hydrogen pressure is substantially the same as
that employed in the first stage. Preferably, the amount of molybdenum disulphide
or precursor thereof is from 0.01 to 1% by weight and most preferably 1% by weight.
[0021] The process of the invention permits significantly higher yields of aliphatic alkanes
from kerogen-bearing rock with a concomitant decrease in the concentration of aromatic
and polar compounds arising from the removal of oxygen and sulphur during the second
stage. Generally, the concentrations of hopanes and steranes can increase by a factor
up to 500%, generally from 20% to 500%, depending on the hopane and sterane content
of the rock.
[0022] The kerogen-bearing rock starting material is preferably a finely divided (eg. <220µm)
petroleum source rock, such as a type I or a type II kerogen, for example a tertiary
oil shale.
[0023] It is preferred if the sample is dried, for example at 50°C for 24hrs, and/or that
free biomarkers, that is, those biomarkers not chemically bonded to the rock are removed
prior to hydropyrolysis.
[0024] The removal of the free biomarkers may be effected, for example, by soxhlet extraction
with a suitable solvent such as DCM. Rock samples may be refluxed with pyridine after
soxhlet extraction with organic solvent to remove free biomarkers that are clathrated
within the organic matrix of the rock. Further means of removing biomarkers from petroleum
source rocks are as outlined by A.S. Mackenzie, Applications of Biological Markers
in Petroleum Geochemistry. In Advances in Petroleum Geochemistry Vol. I, Eds. J. Brooks
and D. Welte, Academic (1984) pp 115-214.
[0025] Once the kerogen-bearing rock starting material has been solvent extracted, catalyst
impregnation of the material may be carried out as described, for example, in Love
G.D. Org. Geochem. (1995), Volume 23, pages 981-986; Love G.D. et al Energy Fuels
(1996), Volume 10, pages 149157. In outline, catalyst impregnation of the solvent-extracted
shale can be performed with suitable aqueous/organic solvent solutions, of a suitable
precursor catalyst, for example, aqueous/methanol solutions of ammonium dioxydithiomolybdate
[(NH
4)
2MoO
2S
2], to provide a nominal molybdenum loading of lwt% of sample. Suitable precursor catalysts
suitable for hydropyrolysis are those which reductively decompose upon heating below
250°C, yielding catalytically active oxysulphide molybdenum species with a phase corresponding
to that of molybdenum disulphide (MoS
2), being obtained at about 400°C. Other suitable dispersed catalysts include those
selected from group VIII transition metals and mixed sulphides of molybdenum with
cobalt, nickel and iron.
[0026] Briefly, vacuum-dried catalyst precursor loaded samples of kerogen bearing rock can
be mixed with a suitable inert mixing agent such as sand, or silica and the like,
or, if the sample is a heavy oils fraction sample, such a sample may be mixed with
a suitable inert adsorbent agent such as silica/sand, alumina or active carbon and
the like prior to loading in the first stage of a two stage fixed bed hydropyrolysis
apparatus, such as the one depicted in Figure 1. Such hydropyrolysis apparatuses or
rigs are known in the art (Bolton et al supra). The samples, generally from about
1 to about 2 grams in weight are mixed with mixing agent in a suitable weight for
weight mixing ratio, such as 1:5 w/w, in a first zone, for example, a top zone of
an Incoloy/stainless steel reactor tube which is then heated resistively from ambient
temperature to a desired temperature lying in the range 450°C to 520°C under selected
conditions of heating rate and hydrogen pressure. A suitable heating rate can be from
5°C to 20°C min
-1 and at a hydrogen pressure of from 5 MPa to 15 MPa. In a preferment, the heating
rate can be from 5°C min
-1 to 15°C min
-1 and the hydrogen pressure is from 10 - 15 MPa. A hydrogen sweep gas flow rate of
up to 10 dm
3 min
-1, generally from 5 to 10 dm
3 min
-1 measured at ambient temperature and pressure has been found to remove products from
the reactor quickly.
[0027] The second stage of the catalytic hydropyrolysis process should generally operate
under a similar pressure as the first stage, however, the temperature of the second
stage is generally controlled independently from the temperature of the first stage.
For the second stage there is used a so-called hydrotreating catalyst ie. A catalyst
used for selectively breaking C-O and C-S bonds and not C-C bonds. Conveniently there
is used a supported hydrotreating catalyst which may be placed in a second zone, typically
a lower zone of the reactor tube. A suitable supported hydrotreating catalyst is γ-alumina
supported Ni/Mo catalyst (eg. Criterion 424, Shell), which is held at a suitable temperature
in the range of from 300°-350°C. The amount of catalyst used is not critical to the
invention, however, the yields of desired aliphatics may increase with the provision
of more catalyst. Supported catalysts may include catalysts such as γ-alumina supported
Co/Mo, Mo in combination with either nickel or Mo on other supports which include
silica, titania and carbons. It is to be understood that commercial catalysts suitable
for hydrocracking (for example nickel/tungsten (Ni/W) supported on γ-alumina) are
not suitable for use in the second stage since they induce hydrocracking of the carbon-carbon
bonds of biomarkers.
[0028] According to yet a further aspect of the present invention there is provided a two-stage
catalytic hydropyrolysis process for recovering biomarkers from a geological kerogen
bearing rock sample, said process comprising the steps of:
in a first stage heating a geological kerogen bearing rock sample incorporating
a dispersed hydrotreating catalyst up to a temperature of from 450°C to 520°C, in
the presence of hydrogen at a pressure of from 5 MPa to 15 MPa so as to release into
the vapour phase from said kerogen bearing rock sample organic compound material containing
biomarkers; and
in a second stage contacting the material released in the first stage with a hydrotreating
catalyst at a temperature in the range of from 300°C to 350°C in the presence of hydrogen
at a pressure of from 5 MPa to 15 MPa so as to release chemically bonded biomarkers.
[0029] Accordingly there is provided a method of detecting biomarkers in a geological oil-bearing
sample comprising:
(i) treating a geological oil-bearing sample in contact with a first catalyst with
hydrogen at a pressure of from 5 MPa to 15 MPa and at a temperature of from 450°C
to 520°C; followed by
(ii) catalytically releasing biomarkers from the said rock in the presence of a second
catalyst at a temperature in the range of from 300°C to 350°C at a hydrogen pressure
substantially the same as that employed in (i); and
(iii) detecting biomarkers.
[0030] Accordingly, there is provided a method of detecting biomarkers in kerogen-bearing
rock which comprises:
(i) treating a kerogen bearing rock impregnated with a first catalyst with hydrogen
at a pressure of from 5 MPa to 15 MPa and at a temperature of from 450°C to 520°C;
followed by
(ii) catalytically releasing biomarkers from the said rock in the presence of a second
catalyst at a temperature in the range of from 300°C to 350°C at a hydrogen pressure
substantially the same as that employed in (i); and
(iii)detecting biomarkers.
[0031] The first catalyst can be any suitable catalyst as described above for the first
stage of the two-stage catalytic hydropyrolysis process.
[0032] The second catalyst can be any suitable supported catalyst as described above for
the second stage of the two-stage catalytic hydropyrolysis process.
[0033] The biomarkers obtained may be detected using conventional means known in the art
for example, as described by W.F. Seifert and J.M. Moldowan, Applications of Steranes,
Terpanes and Monoaromatics to the Maturation, Migration and Source of Crude Oils,
Geochim. Cosmochim. Acta., 1978, 42, 77-95; and A.S. Mackenzie supra.
[0034] In gernal the reaction products of the second stage are collected with the aid of
a suitable organic solvent such as, for example, toluene, chloroform, carbon tetrachloride
etc, or most conveniently dichloromethane (DCM). The collected reaction products may
analysed by any suitable method known in the art. In general the reaction products
are fractionated, and individual components then identified on the basis of there
different physical characteristics such as elution rate, molecular weight (conveneintly
using mass spectrometry), etc.
[0035] In yet a further aspect of the invention there is provided the use of a first catalyst
comprising 0.01 to 5% by weight, preferably 0.01 to 1.4% by weight, more preferably
0.8 to 1.2% by weight and most preferably 1% by weight of molybdenum disulphide or
a precursor thereof and a second supported catalyst selected from the group γ-alumina
supported Ni/Co, γ-alumina supported Co/Mo, or Mo in combination with either Ni or
Mo on other suitable supports such as silica, titania and carbons, in a two-stage
catalytic hydropyrolysis process or in a method for detecting biomarkers, in a geological
oil-bearing sample such as a kerogen bearing rock sample or a heavy oils fraction.
[0036] The invention will now be illustrated with reference to the following figures and
tables:
Figure 1. Schematic representation of a conventional hydropyrolysis apparatus generally
designated 5.
Figure 2. Yields and Compositions of DCM-solubles obtained from Normal Pyrolysis (N
2), single-stage hydropyrolysis and two-stage hydropyrolysis of Göynük Oil Shale.
Figure 3: Single ion chromatogram for m/z of 191 showing the distribution of hopanes
released by two-stage hydropyrolysis from the Loufika crude oil asphaltenes. The assignments
for the labelled peaks are listed in Table 2.
[0037] The invention will now be described by way of examples only.
[0038] Table 1: Comparison of the yields*, µg (g TOC solvent-extracted shale)
-1, of selected biomarker compoinds obtained from normal pyrolysis (N
2 environment), single-stage catalytic hydropyrolysis and two-stage cataytic hydropyrolysis
of solvent-extracted Göynük oil shale.
[0039] Table 2: Compound assignments for the labelled peaks indicated in Figure 3.
Example 1
[0040] A tertiary oil shale (Göynük, Northwest Turkey) classified as a type I kerogen on
the basis of hydrogen/carbon and oxygen/carbon atomic ratios was used. This type I
kerogen organics rich sample yields appreciable amounts of immature biomarker species,
in particular the 17β(H), 21β(H) hopanes, when subjected to hydropyrolysis as demonstrated
by Love G.D. et al Org. Geochem. (1995), Volume 23, pages 981-986; Love G.D. et al
Energy Fuels (1996), Volume 10, pages 149-157) on single stage hydropyrolysis. Briefly,
the sample (20g) was ground to less than 220µm and dried in a vacuum oven at 50°C
for 24 hours. Samples were routinely refluxed with pyridine after DCM soxhlet extraction
to remove free biomarkers which are clathrated within the organic matrix of the sample.
[0041] Catalyst impregnation of the solvent-extracted shale was performed as described by
Love G.D. et al Org. Geochem. (1995), Volume 23, pages 981-986, with aqueous/methanol
solutions of the catalyst precursor ammonium dioxydithiomolydbate [NH
4)
2MoO
2S
2] (Love. G.D et al Energy and Fuels (1996) Vol. 10 pp 149-157), to give a molybdenum
loading of 1 wt% sample. Vacuum-dried catalyst loaded samples (1g) are mixed with
sand (5g) in a weight ratio of from 1:5 w/w in the top zone of a reactor tube 22 as
shown in Figure 1, which was heated resistively to 520°C under a heating rate of 5°C
min
-1 and a pressure of 15 MPa. A hydrogen sweep gas flow rate of 5 dm
3 min
-1 measured at ambient temperature and pressure, ensured that products were removed
quickly from the reactor in each of the experiments. Thus, in the first stage, heating
rate was held at 5°C/min at a hydrogen pressure of 15 MPa with the hydrogen entering
the tube 22 at point 15. The apparatus 5 further comprises:
Control thermocouple 10;
Electrical connectors 20;
Sample 25;
First Catalyst bed 30;
Second Catalyst bed 35;
Multiple furnace 45;
Wire wool plug 50;
Control thermocouple 55;
Dry ice cooled trap 60
[0042] The second stage of the catalytic hydropyrolysis process was operated under the same
hydrogen pressure as the first stage, but the temperature was varied independently
(ie. first stage temperature 520°C; second stage temperature 350°C) . The second stage
is conducted in the portion of apparatus 5 designated as region 40. Supported catalyst
35, γ-alumina supported Ni/Mo catalyst Criterion 424 (available from Shell) (lg),
was placed in the lower zone 40 of the reactor tube. The second stage zone 40 of the
reactor tube was held at a temperature of 350°C.
[0043] The products from the first and second stages were removed from the apparatus 5 at
point 65 for gas collection and measurement where the products were separated and
analysed by well established procedures in organic chemistry (G.D. Love, C.E. Snape,
A.D. Carr and R.C. Houghton, The Release of Covalently-bound Biomarker Hydrocarbons
via Pyrolysis at High Hydrogen Pressure (Hydropyrolysis), Organic Geochem., 1995,
23(10), 981-986; G.D. Love, C.E. Snape and A.D. Carr, Changes in Molecular Biomarker
and Bulk Carbon Skeletal Parameters of Vitrinite Concentrates as a Function of Rank,
Energy & Fuels, 1996, 10, 149-157; G.D. Love, A. McAulay and C.E. Snape and A.N. Bishop,
Effect of Process Variables in Catalytic Hydropyrolysis on the Release of Covalently-bound
Aliphatic Hydrocarbons from Sedimentary Organic Matter, Energy & Fuels, 1997, 11,
522-531). The dried DCM-soluble products were then separated by open-column silica
gel adsorption chromatography into alkanes, aromatics and polars by eluting successively
with n-hexane, n-hexane-toluene (1:1 v/v) and DCM/methanol (1:1 v/v). The fraction
yields were determined by transferring concentrated solutions of the fractions into
pre-weighed vials and evaporating the residual solvent off under a stream of nitrogen.
[0044] Gas chromatography - Mass spectrometry (GC-MS) analysis of the aliphatics was performed
using a Hewlett-Packard 5890 GC split/splitless injector (280°C) linked to a Hewlett-Packard
5972 MSD with the single ions monitored including
m/z 191 (triterpanes), 217 (steranes) and 231 (methylsteranes). A sterane standard, 5β(H)-cholane,
(Chiron Ltd. Trondheim, Norway) was added to the alkane fractions prior to GC-MS analysis,
allowing the concentrations of hopanes and steranes to be estimated (Love G.D. et
al Energy Fuels (1996) supra).
Results are shown in Figure 2 and Table 1 herein.
Discussion
[0045] Figure 2 and Table 1 compare the overall yields of aliphatics, aromatics and polars
and the yields of selected hopanes and steranes, respectively obtained by
(i) using normal pyrolysis under nitrogen in the fixed-bed reactor G.D. Love et al
Organic Geochem., 1995, 23(10), 981-986.
(ii) using single-stage catalytic hydropyrolysis Love G.D. et al Organic Geochem (1995)
Vol. 23(10) pp 981-986. and
(iii) using two-stage catalytic hydropyrolysis of solvent extracted Göynük oil shale
in accordance with Example 1.
[0046] It can be seen that the two-stage catalytic hydropyrolysis process of the invention
increases the total alkane yield by about a factor of 2 (Figure 2) with a concomitant
decrease in the concentration of aromatic and polar compounds arising from the removal
of oxygen and sulphur during the second stage. The concentrations of the hopanes and
steranes listed in Table 2 have all increased by factors ranging from 20 to 500%,
with the relative increase being greatest for the C27 aaa-sterane (20R). Analysis
of the hopane distributions indicates that the biologically inherited but thermodynamically
unstable 17β(H), 21β(H) configurations dominate for two stage as well as single stage
hydropyrolysis.
Example 2
Application of two-stage hydropyrolysis to an asphaltene fraction.
Background
[0047] Crude oils are composed of three main fractions: asphaltenes, resins and hydrocarbons.
Asphaltenes and resins are heavy N, S, O-containing molecu les, while the hydrocarbons
are usually of lower molecular mass. Asphaltenes are the fraction of an oil (or bitumen)
precipitated by the addition of an excess of a low molecular mass alkane (usually
n-pentane or n-heptane)
(1). The amounts of asphaltenes in crude oils varies widely from less than 1% in light
oils to more than 20% in heavy oils and bitumens
(2). Resins are the non-hydrocarbon components which are soluble in an excess of low
molecular mass alkane solvent
(1). The origin of crude oil resins/asphaltenes has not been conclusively determined
but there is evidence that they are genetically related to the kerogen of the source
rock, and it has been suggested that they are small parts of the kerogen released
during thermal maturation
(3). Since resins/asphaltenes appear to be resistant to biodegradation, conventional
pyrolysis methods have been applied to generate hydrocarbon biomarker profiles to
provide information on the source and maturity of the resins/asphaltenes an d therefore
on the oils (or bitumens) that contain them
(4-10). These profiles are especially valuable for correlation purposes when the distribution
of free hydrocarbon components of crude oils, which are normally used for correlation
purposes, have been altered beyond recognition by biodegradation.
[0048] As for kerogens, two-stage hydropyrolysis can generate much greater amounts of hydrocarbon
biomarkers from resins/asphaltenes than conventional pyrolysis methods while preserving
their carbon skeletons and stereochemistries intact. This allows a more accurate geochemical
assessment of the source and maturity of biodegraded crude oils as demonstrated for
an aspahaltene fraction from Loufika crude oil (West Africa) below.
Experimental
[0049] Asphaltenes were obtained from a sample of Loufika crude oil (West Africa) by addition
of an excess of n-heptane as described by Jones et al. (1987)
(10). A mass of 43.3 mg asphaltenes was pre-adsorbed on 1g of alumina (Grade I) by dissolving
the asphaltenes in 3 mL of DCM and adding the solution to the alumina which had been
activated at 500°C overnight. The solvent was allowed to evaporate off completely
in a fume-hood at ambient temperature. The pre-adsorbed asphaltenes were then mixed
with 7.00 g of acid-washed sand before being placed in the top half (first-stage pyrolysis
zone) of the reactor 5. This was heated resistively from ambient temperature to 140°C
at 50°C/min and then from 140 to 500°C/min. under high hydrogen pressure (15.0 MPa).
0.61g of pre-sulphided Criterion 424 catalyst was placed in the lower half of the
reactor and this zone 40 was maintained at 320°C for the duration of the experiment.
A hydrogen sweep gas flow rate of 10 dm
3/min, measured at ambient temperature and pressure, ensured that products were quickly
removed from the reactor. The oil was collected in a dry-ice cooled trap 60 and recovered
in DCM/methanol (2:1 v/v) for subsequent fractionation as described in Example 1.
[0050] Gas chromatography-mass spectrometry (GC-MS) of the aliphatic hydrocarbon fraction
was performed on a Fisons 8060 GC linked to a Fisons Trio MS (electron voltage 70
eV; filament current 4.1 A; source current 2000 A; source temperature 200°C; multiplier
voltage 500 V; interface temperature 300°C). Data acquisition was controlled by a
TVM 486 computer (Masslab software) in selected ion mode. Separation was performed
by on-column injection onto a HP-1 fused silica capillary column (0.25 µm film thickness,
30m x 0.25 mm i.d.). Helium was employed as the carrier gas, and a temperature program
of 50 to 175°C at 10°C/min, then from 175 to 225°C at 6°C/min, and, finally, from
225 to 300°C at 4°C/min with a final hold time of 32 minutes, was used.
Results
[0051] GC-MS analysis of the aliphatic hydrocarbons revealed that discernible biomarker
traces are evident which could be used as a molecular fingerprint for correlation
purposes. The m/z 191 single ion chromatogram showing the distribution of hopane isomer
s produced from two-stage hydropyropyrolysis of the asphaltenes is presented in Figure
3 with compound designation of the labelled peaks being listed in Table 2. The distribution
of hopanes is characteristic of a fairly mature crude oil with the hopane to moretane
ratio being approximately 3.
References
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8. Cassani, F.; Eglinton, G. Chem. Geol. 1986, 56, 167-183.
9. Van Grass, G. Org. Geochem. 1986, 10, 1127-1135. 10. Jones, D.M.; Douglas, A.G.
and Connan, J. Energy & Fuels 1987,1, 468-476.
TABLE 2
Peak |
Compound Name |
Formula |
A |
18α(H), 21β(H)-22,29,30-trisnorhopane (Ts) |
C27H46 |
B |
17αH, 21α(H)-22,29,30-trisnorhopane (Tm) |
C27H46 |
C |
17α(H), 21β(H)-30-norhopane |
C29H50 |
D |
17β(H), 21α(H)-30-normoretane |
C29H50 |
E |
17α(H), 21β(H)-hopane |
C30H52 |
F |
17β(H), 21α(H)-moretane |
C30H52 |
G |
17α(H), 21β(H)-homohopane(22S)
17α(H), 21β(H)-homohopane(22R) |
C31H54
C31H54 |
H |
17α(H), 21β(H)-bishomohopane(22S)
17α(H), 21β(H)-bishomohopane(22R) |
C32H56
C32H56 |
I |
17α(H), 21β(H)-trishomohopane(22S)
17α(H), 21β(H)-trihomohopane(22R) |
C33H58
C33H58 |
1. A two-stage catalytic hydropyrolysis process for recovering biomarkers from a geological
oil-bearing sample, said process comprising the steps of:
in a first stage heating a geological oil-bearing sample incorporating a dispersed
hydrotreating catalyst up to a temperature of from 450°C to 520°C, in the presence
of hydrogen at a pressure of from 5 MPa to 15 MPa so as to release into the vapour
phase from said geological oil-bearing sample organic compound material containing
biomarkers; and
in a second stage contacting the material released in the first stage with a hydrotreating
catalyst at a temperature in the range of from 300°C to 350°C in the presence of hydrogen
at a pressure of from 5 MPa to 15 MPa so as to release chemically bonded biomarkers.
2. The process of claim 1 wherein said sample is heated up at a rate of from 5°C to 20°C
min-1.
3. The process of claim 2 wherein said dispersed hydrotreating catalyst comprises molybdenum
disulphide or a precursor thereof.
4. The process of claim 3 wherein said dispersed hydrotreating catalyst is incorporated
in said sample in an amount of from 0.01 to 5% by weight.
5. The process according to claim 1 wherein the amount of molybdenum disulphide or precursor
thereof is from 0.01 to 1.4% by weight.
6. The process according to claim 2 wherein the amount of molybdenum disulphide or precursor
thereof is 1% by weight.
7. The process according to claim 1 wherein said process additionally includes the preliminary
step of drying said geological oil-bearing sample prior to said process.
8. The process according to claim 4 wherein said drying is conducted at 50°C for 24h.
9. The process according to claim 1 wherein said process additionally contains the step
of removing said free biomarkers from said geological oil-bearing sample prior to
said process.
10. The process according to claim 1 wherein said geological oil bearing sample additionally
comprises an inert adsorbent agent.
11. The process according to claim 7 wherein said inert adsorbent agent is selected from
the group consisting of silica, sand, alumina and active carbon.
12. The process according to claim 1 wherein said precursor catalysts are those which
reductively decompose upon heating below 250°C, yielding catalytically active oxysulphide
molybdenum species with a phase corresponding to that of molybdenum disulphide (MoS2), being obtained at about 400°C.
13. A two-stage catalytic hydropyrolysis process for recovering biomarkers from a geological
kerogen bearing rock sample, said process comprising the steps of:
in a first stage heating a geological kerogen bearing rock sample incorporating
a dispersed hydrotreating catalyst up to a temperature of from 450°C to 520°C, in
the presence of hydrogen at a pressure of from 5 MPa to 15 MPa so as to release into
the vapour phase from said kerogen bearing rock sample organic compound material containing
biomarkers; and
in a second stage contacting the material released in the first stage with a hydrotreating
catalyst at a temperature in the range of from 300°C to 350°C in the presence of hydrogen
at a pressure of from 5 MPa to 15 MPa so as to release chemically bonded biomarkers.
14. The process according to claim 13 wherein the amount of molybdenum disulphide or precursor
thereof is from 0.01 to 1% by weight.
15. The process according to claim 14 wherein the amount of molybdenum disulphide or precursor
thereof is 1% by weight.
16. The process according to claim 13 wherein said kerogen-bearing rock is a petroleum
source rock.
17. The process according to claim 16 wherein said petroleum source rock is finely divided.
18. The process according to claim 17 wherein said petroleum source rock is divided to
less than 200µm.
19. The process according to claim 13 wherein said kerogen-bearing rock is a type I or
type II kerogen bearing rock.
20. The process according to claim 13 wherein said kerogen-bearing rock is a tertiary
oil shale.
21. The process according to claim 13 wherein said process additionally contains the step
of drying said kerogen bearing rock sample prior to said process.
22. The process according to claim 21 wherein said drying is conducted at 50°C for 24h.
23. The process according to claim 13 wherein said process additionally contains the step
of removing said free biomarkers from said kerogen bearing rock sample prior to said
process.
24. The process according to claim 23 wherein removal of the free biomarkers is effected
by soxhlet extraction with a suitable solvent.
25. The process according to claim 24 wherein said solvent is dichloromethane.
26. The process according to claim 24 wherein said kerogen bearing rock sample is refluxed
with pyridine following soxhlet extraction.
27. The process according to claim 26 wherein said reflux with pyridine removes free biomarkers
that are clathrated within an organic matrix of said kerogen bearing rock sample.
28. The process according to claim 13 wherein said catalyst impregnation is performed
with aqueous/organic solvent solutions, of said catalyst precursor.
29. The process according to claim 28 wherein said aqueous/organic solvent solution is
an aqueous/methanol solution of ammonium dioxydithiomolybdate [(NH4)2MoO2S2].
30. The process according to claim 13 wherein said kerogen bearing rock sample additionally
comprises an inert agent.
31. The process according to claim 30 wherein said inert agent is sand or silica.
32. The process according to claim 13 wherein said catalysts precursor is one which reductively
decomposes upon heating below 250°C, yielding catalytically active oxysulphide molybdenum
species with a phase corresponding to that of molybdenum disulphide (MoS2), being obtainable at a temperature of about 400°C.
33. A method of detecting biomarkers in a geological oil-bearing sample comprising the
steps of:
(i) treating a geological oil-bearing sample in contact with a dispersed hydrotreating
catalyst, with hydrogen at a pressure of from 5 MPa to 15 MPa and at a temperature
of from 450°C to 520°C, so as to release into the vapour phase organic material containing
biomarkers;
(ii) Treating said organic material released from said geological oil-bearing sample,
in the presence of a second hydrotreating catalyst at a temperature in the range of
from 300°C to 350°C with hydrogen at a pressure of from 5 MPa to 15 MPa, so as to
release biomarkers from said organic material; and
(iii) analysing material obtained from said process step (ii) for the presence of
said biomarkers.
34. The method according to claim 33 wherein said first catalyst is chosen from the group
consisting of molybdenum disulphide, group VIII transition metals or mixed sulphides
of molybdenum with cobalt, nickel or iron.
35. The method according to claim 33 wherein said second catalyst is selected from the
group consisting of γ-aluminum supported Ni/Co, γ-alumina supported Co/Mo, or Mo in
combination with either Ni or Mo on silica, titania or carbons.
36. A method of detecting biomarkers in kerogen-bearing rock which comprises:
(i) treating a kerogen bearing rock impregnated with a first catalyst with hydrogen
at a pressure of from 5 MPa to 15 MPa and at a temperature of from 450°C to 520°C;
followed by
(ii) catalytically releasing biomarkers from the said rock in the presence of a second
catalyst at a temperature in the range of from 300°C to 350°C at a hydrogen pressure
substantially the same as that employed in (i); and
(iii) detecting biomarkers.
37. The method of claim 36 wherein said step of analysing material obtained form process
step (ii) includes the step of fractionating said material.
38. The method according to claim 36 wherein said first catalyst is chosen from the group
consisting of molybdenum disulphide, group VIII transition metals or mixed sulphides
of molybdenum with cobalt, nickel or iron.
39. The method according to claim 36 wherein said second catalyst is selected from the
group consisting of γ-aluminum supported Ni/Co, γ-alumina supported Co/Mo, or Mo in
combination with either Ni or Mo on silica, titania or carbons.
40. Use of a first catalyst comprising 0.01 to 5% by weight of molybdenum disulphide or
a precursor thereof and a second supported catalyst selected from the group γ-alumina
supported Ni/Co, γ-alumina supported Co/Mo, or Mo in combination with either Ni or
Mo on silica, titania or carbons, in a two-stage catalytic hydropyrolysis process
or in a method for detecting biomarkers, in a geological oil-bearing sample such as
a kerogen bearing rock sample or a heavy oils fraction.