Steam-Assisted Gravity Drainage (“SAGD”) is a commercial thermal Enhanced Oil Recovery (“EOR”) process, using saturated steam injected into a horizontal well 2, where latent heat is used to heat bitumen and lower its viscosity so it drains, by gravity, to an underlaying, parallel, twin horizontal well (i.e. production well 4), completed near the bottom of the reservoir (
Since the process inception in the early 1980's (Butler, R. M., “Thermal Recovery of Oil & Bitumen”, Prentice-Hall, 1991), SAGD has become the dominant, in situ, process to recover bitumen from Alberta's bitumen deposits. Today's SAGD bitumen production, in Alberta, is about 300 K barrels/day (“bbl/d”) (Oil sands Review, (2010)); with installed capacity at about 475 Kbbl/d (ibid). SAGD is now the world's leading thermal EOR process.
After conversion to normal SAGD operations, a steam chamber 10 forms around the injector well 2 and producter well 4 where the void space is occupied by steam 6.
Produced fluids are near saturated steam temperature, so it is only the latent heat of steam that contributes to the process, in the reservoir. But, some of the sensible heat may be capture from surface heat exchangers (a greater fraction at higher temperatures), so a useful rule-of-thumb, for net heat contribution of steam, is 1000 BTU/lb. for the Pressure (“P”) and Temperature (“T”) range of most SAGD projects as best seen in
The operational performance of SAGD may be characterized by measurement of the following parameters—saturated steam P and T in the steam chamber (
During the SAGD process, the SAGD operator has two choices to make—the sub-cool target T difference and the operating pressure P in the reservoir. A typical sub-cool target T difference of about 10° C. to 30° C. is meant to ensure no live steam breaks through to the production well. Process pressure and temperature are linked as best seen in
If these musts are not attained or other limitations are experienced, SAGD may be impaired, as follows:
Lastly, there is a natural hydraulic limit that restricts well lengths and/or well diameters and can override pressure targets for SAGD operations.
Steam-Assisted Gravity Drainage with Oxygen (“SAGDOX”) is an improved thermal EOR process where steam and oxygen are both injected into a bitumen reservoir. As best seen in
The early versions of SAGDOX provide only for oxygen to steam ratios in the range of 0.05 to 1.00. There is a need to extend the oxygen to steam ratio beyond 0.05 to 1.00 and to determine optimal operating conditions in SAGDOX.
According to one aspect, there is provided a process to improve SAGDOX, said process comprising the use of produced-water-to-oil ratio (v/v) (“PWOR”) in determining optimal SAGDOX process parameters.
According to another aspect, there is provided the use of PWOR in controlling thermal EOR, preferably optimizing thermal EOR, more preferably optimizing SAGDOX in hydrocarbon recovery.
According to another aspect, there is provided an improved steam assisted gravity drainage with injected oxygen (“SAGDOX”) process to recover hydrocarbons comprising:
In one embodiment, said improvement comprises extending the oxygen to steam ratios beyond the range of 0.05 to 1.00 (v/v), preferably a steam to oxygen ratio of from about 19 to approaching zero but greater than zero. In a preferred embodiment, the percent oxygen in said oxygen and steam mixture is greater than 50% (v/v).
Preferably, said PWOR target improving said hydrocarbon recovery is from about, 0.5 to 2.0, preferably 1.0. More preferably said PWOR target may be a maximum wherein said amount of oxygen in said process approaches zero but is greater than 0%.
In another embodiment, said improvement comprises using a PWOR to pick an optimal oxygen to steam ratio. In another embodiment, said improvement comprises adjusting pressure and sub-cool targets for optimizing SAGDOX. Preferably, the oxygen to steam ratio is adjusted to attain a target PWOR (Produced Water-to-Oil Ratio). In another embodiment a PWOR target is selected optimizing the oxygen to steam ratio in the SAGDOX process. In one embodiment, said oxygen injected is an oxygen containing gas.
According to one aspect, there is provided a process to recover liquid hydrocarbons from a hydrocarbon reservoir having a top and a bottom, using a substantially horizontal production well wherein:
Preferably the PWOR target is between 0.5 and greater such that said amount of oxygen in said process approaches zero but is greater than zero, more preferably between 0.5 and about 2.0.
Preferably the PWOR target is determined, in the field, by changing PWOR until the cost, preferably opex cost, per bbl. bitumen, is minimized.
Optionally, according to one embodiment, it is not necessary to remove non-condensable combustion gases or inert gas components of the oxygen-containing gas.
Preferably, steam is injected within 10 metres from the horizontal well, more preferably using a parallel, horizontal well, in the same vertical plane as the horizontal production well and from 3 to 8 metres above the well.
In another embodiment, steam is injected into the reservoir using at least one single substantially vertical well, preferably a plurality of substantially vertical wells.
In another embodiment, oxygen, preferably oxygen-containing gas, is injected into the reservoir using at least one single substantially vertical well, preferably a plurality of substantially vertical wells.
In yet another embodiment, vent gas is removed from the reservoir using at least one single substantially vertical well, preferably a plurality of substantially vertical wells.
In yet another embodiment said steam and oxygen are comingled on the surface and injected into the reservoir using at least one single substantially vertical well, preferably a plurality of substantially vertical wells.
In yet another embodiment, said steam and oxygen are segregated using packers in at least one single substantially vertical well, preferably a plurality of substantially vertical wells, and injected separately into the reservoir.
According to another embodiment, said steam and oxygen are segregated using concentric tubing and packers in said well, preferably with steam in a central tubing surrounded by oxygen in an adjacent annulus, preferably said oxygen being injected at a higher elevation in the reservoir than said steam.
According to another embodiment, said process uses a single substantially vertical well to inject steam and oxygen, wherein the single substantially vertical well is completed within 50 metres from the toe of the horizontal production well.
According to another embodiment, said vent gas is removed using one well, preferably a substantially vertical well. In another embodiment said vent gas is removed using multiple vertical wells.
Preferably said vent gas is removed via a segregated annulus section in the heel rise section of the horizontal well.
In another embodiment, oxygen is injected into said reservoir through a segregated toe section of the horizontal well.
In another embodiment, steam is injected into said reservoir through a segregated toe section of the horizontal well.
In another embodiment, said steam and oxygen are comingled at the surface and injected into the reservoir through a segregated toe section of the horizontal well.
In another embodiment, said oxygen and steam are segregated and simultaneously injected into the reservoir through a segregated toe section of the horizontal well.
In another embodiment, said segregation is accomplished using concentric tubing and packers, with steam in the central tubing surrounded by oxygen in the adjacent annulus.
In another embodiment, said vent gas is removed in a segregated annulus in the heel rise section of the horizontal well.
In another embodiment, said toe of the horizontal well is drilled upwards and completed so the lowest injection orifice (for steam or oxygen-containing gas or both) is higher in elevation than the horizontal plane of the horizontal section of the production well, preferably greater than 2 metres higher in elevation than the horizontal plane of the horizontal section of the production well.
In another embodiment, the horizontal well is drilled substantially parallel to the reservoir bottom, in an up-dip direction in a slanted reservoir, so that the lowest injection orifice is higher in elevation than the highest liquid production well orifice, more preferably more than 2 metres higher in elevation than the highest liquid production orifice.
In another embodiment, the oxygen-containing gas is oxygen, with an oxygen content of 95 to 99.99 (v/v) percent.
In another embodiment, the oxygen-containing gas is air, preferably enriched air, with an oxygen content of 21 to 95 (v/v) percent.
In another embodiment, the process further comprises an extender tube proximate the toe of the production well is used, ensuring that the lowest pressure in the production well is proximate the toe.
When the hydrocarbon liquid is bitumen, preferably the API density is less than 10 and the in situ viscosity is greater than 100,000 cp. When the hydrocarbon liquid is heavy oil, preferably the API density is between 10 and 20 and the in situ viscosity is greater than 1,000 cp.
In one embodiment, the horizontal production well is less than 2.0 m from the bottom of the reservoir at its closest point.
Preferably the PWOR target is determined by changing PWOR until bitumen productivity is maximized.
a depicts a preferred embodiment SAGDOX geometry with a vent gas site proximate the producer well.
a depicts a preferred embodiment toe-to-heel SAGDOX geometry with oxygen and steam injected proximate the toe of the producer well.
b depicts a preferred embodiment single well SAGDOX with an uplifted toe geometry.
a) depicts the side view recovery pattern of THSAGDOX.
The objective of SAGDOX is to reduce reservoir energy injection costs, while maintaining good efficiency and productivity. Oxygen combustion produces in situ heat at a rate of about 480 BTU/SCF oxygen, independent of fuel combusted (
The recovery mechanisms are more complex for SAGDOX than for SAGD. As best seen in
Combustion non-condensable gases are collected and removed by vent gas wells or at segregated vent gas sites (
One of the suggested controls for original SAGDOX was to pick a target steam/oxygen mixture for injection. But, other than a suggested range of 5 to 50% (v/v) of oxygen in the mixture (or an oxygen to steam ratio of from 0.05 to 1.00), there were no guidelines on what or how to pick the best composition. The SAGDOXO (SAGDOX—optimized) process overcomes this deficiency. There are two considerations to picking a target composition—
(1) oxygen is less costly and more efficient than steam. So, oxygen levels should be maximized, based on these criteria, alone.
(2) Steam is very useful in the reservoir recovery process. In addition to providing latent heat to bitumen, it preheats zones for combustion, it is a better heat transfer medium than hot combustion gases, and water from steam, when mixed with produced bitumen, creates emulsions (or mixtures) that are easier to produce than bitumen by itself. There is an optimum level of steam in the reservoir that captures most of these benefits and allows oxygen levels to be increased as much as practical.
The key for the SAGDOXO process is to find an optimal level of steam and/or to identify a measurement related to steam performance that will allow steam level optimization by field adjustments, while maintaining other SAGDOX operation controls discussed herein. There is provided a process to optimize steam levels in SAGDOX, said process comprising selecting a PWOR target, preferably between 0.5 and greater such that the level of oxygen approaches zero but remains greater than zero, more preferably between 0.5 and 2.0, most preferably about 1.0, which minimizes bitumen cost.
In one embodiment, said PWOR target is selected which maximizes bitumen productivity.
PWOR (produced fluids, water-to-oil ratio) is also used as a measure to select the optimal oxygen to steam ratio. PWOR is not very useful for SAGD because it is usually close to SOR and normally, there is no reservoir water source that can affect PWOR and act as a performance measure for the SAGD process. In SAGD, based on field experience, connate water is not produced. For SAGDOX, the steam component behaves like SAGD. But the combustion component vapourizes and produces connate water so that PWOR>SOR. At steady state, PWOR for SAGDOX is a direct measure of steam injected and steam produced per unit bitumen production.
According to one aspect, there is provided an optimized SAGDOX process (SAGDOXO) comprising the following 3 components:
In analyzing the PWOR-target implications and mechanics of the SAGDOXO process, the following assumptions are made:
(1) SAGDOX is broken into 2 component processes—steam EOR operates like SAGD, with heat delivered by steam condensation and hot bitumen drainage by gravity; and combustion EOR heats bitumen, directly and indirectly by oxidation of residual bitumen components.
(2) Steam EOR assumes the following:
As a result of the above process model, we can assess the results and impacts of the process with a focus on PWOR, as follows:
PWOR is evaluated for bitumen saturations of 0.6 to 1.0; percent oxygen, in steam+oxygen mixes, from greater than 0 to less than 100 (v/v) % (preferred range is 5 to 50%); and ETOR (MMBTU/bbl bitumen (“bblB”)) from 1.0 to 2.0 (equivalent to SOR from 3 to 6) for a mature operation.
A PWOR of 1.0 or greater may result in good (SAGDOXO) operation, with maximum oxygen content and good heat transfer and other benefits due to steam (i.e. preferred value for target PWOR). But, each reservoir (or recovery pattern) can be different due to geological or fluid property variations. A SAGDOXO operator can start with a PWOR=1 and adjust PWOR to account for specific reservoir conditions. The operational history of nearby or similar reservoirs may also be used to adjust targets.
There are 2 ways to ‘optimize’ PWOR targets using field results. First, PWOR can be used to minimize bitumen costs, while maintaining ‘reasonable’ bitumen productivity. Second, PWOR can be adjusted to maximize bitumen productivity.
Consider a bitumen reservoir with a typical bitumen saturation of 0.8, our mature SAGDOXO process operates with ETOR=1.0 (equivalent to SOR˜3 for SAGD), and the PWOR target is 1.0 (i.e. the produced fluids are 50% water and 50% bitumen).
The above example can also be used to verify (and specify) the range limitations of SAGDOXO (between 5 and 50 (v/v) % oxygen in the steam+oxygen mixture). Suppose our ETOR=1.0 MMBTU/bblB for a mature project (a SAGD equivalent of SOR of about 3); our initial bitumen saturation ranges from 0.75 to 0.90; and our PWOR target range is 0.75 to 1.50. Then,
Although the above ranges justify the limits for SAGDOX gases (5 to 50 (v/v)) % oxygen in the oxygen+steam mixture, SAGDOXO strategy extends oxygen levels outside the original SAGDOX limits. As the SAGDOXO process matures, ETOR will increase, as heat losses increase, and the SAGDOXO process strategy dictates an increase in oxygen levels. For example, using
(9) A SAGDOX operating strategy for this invention, is to taper the oxygen levels in the steam+oxygen mix, starting at a low oxygen level and eventually, near the end-of-life (
(10)
(11)
(12) The SAGDOXO process, using the PWOR target system, is also useful if the process encounters a lean zone, with low bitumen saturation (<0.6) and high connate water saturation (>0.4). As combustion encounters the lean zone, water is produced and PWOR increases (temporarily). The SAGDOXO remedy is to increase oxygen content of the feed gas (steam+oxygen). This reduces operating costs and maintains PWOR targets. When the zone is breached, the oxygen levels are reduced.
(13)
As many changes therefore may be made to the embodiments of the invention without departing from the scope thereof. It is considered that all matter contained herein be considered illustrative of the invention and not in a limiting sense.
Number | Date | Country | |
---|---|---|---|
61727960 | Nov 2012 | US | |
61647153 | May 2012 | US | |
61666116 | Jun 2012 | US |
Number | Date | Country | |
---|---|---|---|
Parent | 13893902 | May 2013 | US |
Child | 14083106 | US | |
Parent | 13928839 | Jun 2013 | US |
Child | 13893902 | US |