CA2242774A1 - Method for upgrading heavy and semi-heavy oils - Google Patents

Description

Method for Up~radin Heavy and Semi-Heavy In investigating extraction of oil or oil precursor matter from coal, oil shales, bitumen and heavy oils with supercritical or near-supercritical water we observed that conjoint use of carbon monoxide can lead to significant upgrading of the precursor material during extraction. Such upgrading manifested itself specifically in the class composition of the recovered organic matter, i.e., higher proportions of aliphatics and correspondingly lowered presence of aromatics and so-called upolar" compounds carrying heteroatoms such as oxygen, nitrogen and/or sulfur.
An example, which relates to extraction of a Fort McMurray (Alberta) high-grade" oil sand,l is shown in the table below:
' In jurisdictions other than Alberta, this resource is commonly referred to as tar sand or bituminous sand.

-2-feed 36 11 37 16 extracted with H20 at 400°C/14.0 M Pa 30 19 39 12 400°C/17.9 MPa 24 24 40 12 400°C/24.5 MPa 28 27 43 2 extracted with H20 + CO~a~ at 400°C/14.0 MPa 74 5 19 2 400°C/17.9 MPa 72 5 21 2 400°C/24.5 Mpa 66 5 27 2 H20/CO mole ratios in these runs were 1.05, 1.3 and 2.2 respectively.
1: aliphatics 2: aromatics 3: polar compounds 4: asphaltenes Recovery of hydrocarbon material, which depended on sweep rates and on the disposition of the test sample in the reactor, ranged between ~80 and 90 wt.% of the bitumen in place.
The evidence at hand permits the conjecture that such compositional shifts --which are associated with concurrent reductions of the average molecular weight of the recovered hydrocarbon material (and therefore lower viscosity) -- accrue from a complex reaction sequence that entails [1] thermally driven homolytic and/or hydrolytic bond scission -- in particular scission of carbon-carbon bonds within the constituent molecules, and consequent formation of short-lived radical species which would, in the absence of modifiers, randomly recombine without substantially changing the molecular weights of the precursors;
[2] some interaction of radical species with H20 to generate alcohols by reactions such as R ~ CH3 + H20 ~ R ~ CH20H . . . . . [1]
and

[3] an in situ shift reaction CO + H20 ~ H2 + C02 . . . . . . . . . . [2]

which generates elemental hydrogen and can thereby (i) stabilize radical species before they can recombine or interact with H20 or (ii) reduce alcohols by, in effect, reversing reaction [1].
These or similar chemical processes make conjoint use of supercritical (or near-supercritical) H20 and CO practical means for recovering fossil hydrocarbons such as heavy oils, bitumens and heavy oil precursors from oil shales. The following examples may serve to illustrate this form of recovery.
1. One procedure, specifically but not exclusively designed for in-situ recovery of heavy oils, entails (a) completing two suitably spaced small diameter boreholes (I and II) vertically into the payzone;
(b) where necessary, enhancing communication between these holes by hydraulic or electrical fracturing of the formation in order to establish suitable communication;
(c) through one hole (I) injecting supercritical (or near-supercritical) H20 into the formation at temperatures in the range of 400-450°C (~ 750-840°~
and pressures between 14 and 21 Mpa (~ 2000-3000 psi);
(d) through the other hole (II) producing the steam with its load of extracted oil;
and (e) at a convenient (surface or downhole) location passing the produced stream through a pressure letdown vessel in which lower pressures and/or lower temperatures cause the oil and coproduced inorganic matter (if any) to fall out, i.e., to spontaneously separate from the steam.
Before processing the separated crude letdown oil (e.g., by secondary hydrogenation or coking) it can then, where necessary, be freed of inorganic matter by filtration or use of an antisolvent. Recovered steam and condensed H20 are then prepared for recycling to the injection hole.
Bitumens and related asphaltics, which from a production standpoint differ from heavy oils only in specific gravities, can be recovered from oil sands (or their equivalents) and processed by substantially the same steps.
1A. Where the permeability of the prospective payzone and/or the effective floor and roof of that zone is low, the objectives of the procedure outlined in #1 can be attained by

-4-(a) completing a directional (substantially horizontal) borehole over an appropriate distance;
(b) fracturing the stata hydraulically;
(c) where necessary, lining the borehole with a perforated casing; and (d) injecting supercritical (or near-supercritical) HZO and CO at 400-450°C while producing from the other end of the borehole.
2. Another example of implementing recovery -- this form being particularly suitable or in-situ extraction of organic matter from very dense envelopes such as oil shales, but not limited to such strata -- involves (a) creating an underground retort by completing a borehole of suitable diameter vertically into the payzone;
(b) fragmenting the formation near the bottom of the hole, e.g., by suitably placed explosive charges;
(c) injecting supercritical (or near-supercritical) H20 and CO at 400-450°C and 14-21 Mpa;
(d) producing the steam with its load of extracted organic matter through an off-take pipe concentrically positioned within the borehole so that the annulus between them can serve as the injection hole; and (e) proceeding as in example #1.
Subsequent coking then allows upgrading of the organic material and concurrent separation from entrained inorganic matter.
An essential feature of the technique illustrated by examples #1, 1A and 2 is (i) the use of near-supercritical steam as 'solvent' and (ii) uninterrupted 'sweeping' of the pay zone during the production cycle by continuous injection of H20 and CO as well as continuous recovery (and processing) of the product stream.
However, fundamental to satisfactory operation of the schemes exemplified in #1, 1A and 2 is recognition that optimum injection temperatures and pressures are site-specific and depend upon the thermal characteristics of the strata from which the hydrocarbon is to be recovered. Our experience to date suggests that optimum temperatures in the pay zone will generally but not always lie between 400 and 425°C and optimum pressures will range from 14 to 17.5 Mpa.

-5-3. An alternative method for recovering fossil hydrocarbon material with supercritical (or near-supercritical) H20 and CO entails processing in a suitably constructed and sized surface reactor. In such an operation, the feed -- mined oil sand, oil shale or coal --would be coarsely crushed before transfer to the pressure vessel, but all other steps correspond to those outlined above.
Our laboratory test on bitumen extraction by supercritical H20 clearly suggests that removal of residual bitumen from, e.g., hot water extraction process tailings, by such extraction in a surface facility holds commercial potential. Major benefits would lie in accelerated settling of ponded tailings and, consepuently, in greatly enhanced capability for recycling process water.
4. A further aspect of conjoint use of H20 and CO at 400-425°C and 14-21 Mpa is accelerated partial upgrading of heavy oils, accomplished in situ (as in examples #1, 1A and 2) or surface reactor operations (as in #3) by entraining a catalyst such as iron oxide in the H20/CO stream. Such catalysts are often available as a "throw-away" product from other processes.
5. In appropriate adapted form, the procedure outlined in #3 could also offer means for rendering toxic or otherwise noxious organic wastes substantially harmless by eliminating heteroatom configurations that endow them with unacceptable characteristics and thereby converting them into hydrocarbons. For that purpose, interaction with H20 and CO would optimally proceed at 450-600°C and >
17.5 Mpa.
SIGNED at Calgary, SIGNED at Calgary, this 11t" day of August, 1998. 11'" day of August, 1998.
105, 11660 - 79 Avenue 1144 Edgemont Road N.W.
Edmonton, Alberta T6G OP7 Calgary, Alberta T3A 2J8

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