Patent Grant
8689865
None.
The present invention relates generally to a process for recovering heavy oil from a reservoir. In particular, the invention provides for utilizing microwaves to heat H2O which interacts with the heavy oil in the reservoir to lower the viscosity of the heavy oil.
Heavy oil is naturally formed oil with very high viscosity but often contains impurities such as sulfur. While conventional light oil has viscosities ranging from about 0.5 centipoise (cP) to about 100 cP, heavy oil has a viscosity that ranges from 100 cP to over 1,000,000 cP. Heavy oil reserves are estimated to equal about fifteen percent of the total remaining oil resources in the world. In the United States alone, heavy oil resources are estimated at about 30.5 billion barrels and heavy oil production accounts for a substantial portion of domestic oil production. For example, in California alone, heavy oil production accounts for over sixty percent of the states total oil production. With reserves of conventional light oil becoming more difficult to find, improved methods of heavy oil extractions have become more important. Unfortunately, heavy oil is typically expensive to extract and recovery is much slower and less complete than for lighter oil reserves. Therefore, there is a compelling need to develop a more efficient and effective means for extracting heavy oil.
Viscous oil that is too deep to be mined from the surface may be heated with hot fluids or steam to reduce the viscosity sufficiently for recovery by production wells. One thermal method, known as steam assisted gravity drainage (SAGD), provides for steam injection and oil production to be carried out through separate wellbores. The optimal configuration is an injector well which is substantially parallel to and situated above a producer well, which lies horizontally near the bottom of the formation. Thermal communication between the two wells is established and, as oil is mobilized and produced, a steam chamber or chest develops. Oil at the surface of the enlarging chest is constantly mobilized by contact with steam and drains under the influence of gravity.
One factor that can limit the economic production of the viscous oil using SAGD is the heterogeneous nature of the reservoir. The applicability of SAGD is often limited by impermeable layers that act as barriers to vertical flow. The impermeable layers effectively compartmentalize the reservoir into thin sub-reservoirs, less than 15 meters in length at its minimum. These thin layers cannot be economically developed with gravity drainage processes because of the thickness requirement for the reservoir. In one embodiment the method utilizes hydraulic methods to fracture the impermeable layers and establish vertical communication between the isolated sub-reservoirs and allow a gravity drainage process to work.
There are several patents on the improvements to SAGD operation. U.S. Pat. No. 6,814,141 describes applying vibrational energy in a well fracture to improve SAGD operation. U.S. Pat. No. 5,899,274 teaches addition of solvents to improve oil recovery. U.S. Pat. No. 6,544,411 describes decreasing the viscosity of crude oil using ultrasonic source. U.S. Pat. No. 7,091,460 claims in situ, dielectric heating using variable radio frequency waves.
In a recent patent publication (U.S. Patent Publication 20070289736/US-A1, filed May 25, 2007), it is disclosed to extract hydrocarbons from a target formation, such as a petroleum reservoir, heavy oil, and tar sands by utilizing microwave energy to fracture the containment rock and for liquification or vitalization of the hydrocarbons.
In another recent patent publication (US Patent Publication 20070131591/US-A1, filed Dec. 14, 2006), it is disclosed that lighter hydrocarbons can be produced from heavier carbon-base materials by subjecting the heavier materials to microwave radiations in the range of about 4 GHz to about 18 GHz. This publication also discloses extracting hydrocarbons from a reservoir where a probe capable of generating microwaves is inserted into the oil wells and the microwaves are used to crack the hydrocarbons with the cracked hydrocarbon thus produced being recovered at the surface.
Despite these disclosures, it is unlikely that direct microwave cracking or heating of hydrocarbons would be practical or efficient. It is known that microwave energy is absorbed by a polar molecule with a dipole moment and bypasses the molecules that lack dipole moment. The absorption of the microwave energy by the polar molecule causes excitation of the polar molecule thereby transforming the microwave energy into heat energy (known as the coupling effect). Accordingly, when a molecule with a dipole moment is exposed to microwave energy it gets selectively heated in the presence of non-polar molecules. Generally, heavy oils comprise non-polar hydrocarbon molecules; accordingly, hydrocarbons would not get excited in the presence of microwaves.
Additionally, while the patent publication above claims to break the hydrocarbon molecules, the energy of microwave photons is very low relative to the energy required to cleave a hydrocarbon molecule. Thus, when hydrocarbons are exposed to microwave energy, it will not affect the structure of a hydrocarbon molecule. (See, for example, “Microwave Synthesis”, CEM Publication, 2002 by Brittany Hayes).
A process of drilling a borehole into a heavy oil formation comprising a frac barrier between a first pay zone and a second pay zone wherein the frac barrier prevents a subterranean steam chamber region to be formed between the first pay zone and the second pay zone. The frac barrier is then heated with a microwave frequency and the frac barrier is fractured to permit the subterranean steam chamber region to be formed within the first pay zone and the second pay zone. H2O is then injected into the subterranean steam chamber region through a first wellbore of a steam assisted gravity drainage operation. Microwaves are introduced into the subterranean steam chamber region at a frequency sufficient to excite the H2O molecules and increase the temperature of at least a portion of the H2O within the region to produce heated H2O. At least a portion of the heavy oil in the region is heated by contact with the heated H2O to produce heated heavy oil. Heated heavy oil is then produced through a second wellbore of the steam assisted gravity drainage operation. Heavy oil is then recovered with the steam assisted gravity drainage operation from the subterranean steam chamber region. A portion of the H2O is injected as steam and the steam contact with at least a portion of the heavy oil in the subterranean steam chamber region so as to heat the portion of the heavy oil and reduce its viscosity so that it flows generally towards the second wellbore.
In an alternate embodiment a process is taught of drilling a borehole into a heavy oil formation comprising a frac barrier between a first pay zone and a second pay zone wherein the minimum distance of at least one pay zone is less than about 15 meters and the frac barrier prevents a subterranean steam chamber to form between the first pay zone and the second pay zone. The heavy oil formation is then perforated and fracturing fluid is injected into the heavy oil formation. The frac barrier is then heated with a microwave frequency. The frac barrier is then fracted with the fracturing fluid to permit a subterranean steam chamber region to be formed within the first pay zone and the second pay zone. H2O is then injected into the subterranean steam chamber region through a first wellbore of a steam assisted gravity drainage operation. Microwaves are introduced into the subterranean steam chamber region at a frequency sufficient to excite the H2O molecules and increase the temperature of at least a portion of the H2O within the region to produce heated H2O. At least a portion of the heavy oil in the region is ten heated by contacting with the heated H2O to produce heated heavy oil. Heated heavy oil is then produced through a second wellbore of the steam assisted gravity drainage operation, thereby recovering the heavy oil with the steam assisted gravity drainage operation from the subterranean steam chamber region. In this embodiment a portion of the H2O is injected as steam and the steam contact with at least a portion of the heavy oil in the subterranean steam chamber region so as to heat the portion of the heavy oil and reduce its viscosity so that it flows generally towards the second wellbore.
A more complete understanding of the present invention and benefits thereof may be acquired by referring to the follow description taken in conjunction with the accompanying drawings in which:
Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.
In this description, the term water is used to refer to H2O in a liquid state and the term steam is used to refer to H2O in a gaseous state.
The present embodiment describes a method of producing heavy oil from a heavy oil formation with steam assisted gravity drainage. The method begins by drilling a borehole into a heavy oil formation comprising a frac barrier between a first pay zone and a second pay zone, wherein the frac barrier prevents a steam chamber to be formed between the first pay zone and the second pay zone. The frac barrier is then heated with a radio frequency. The frac barrier is then fractured to permit a subterranean steam chamber to be formed within the first pay zone and the second pay zone. Water (H2O) is then injected into the subterranean steam chamber region through a first wellbore of a steam assisted gravity drainage operation. Microwaves are introduced into the subterranean steam chamber region at a frequency sufficient to excite the water molecules and increase the temperature of at least a portion of the water within a region to produce heated water. At least a portion of the heavy oil is heated in the region by contact with the heated water to produce heated heavy oil. This is subsequently followed by producing the heated heavy oil through a second wellbore of the steam assisted gravity drainage operation. Heavy oil is then recovered with the steam assisted gravity drainage operation from the subterranean steam chamber region. In this embodiment, a portion of the water is injected as steam and the steam contact with at least a portion of the heavy oil in the subterranean steam chamber region so as to heat the portion of the heavy oil and reduce its viscosity so that it flows generally towards the second wellbore.
In one embodiment the borehole can be either the first wellbore or the second wellbore.
As shown in
The present embodiment can be used in any situation where a frac barrier prevents the formation of a subterranean steam chamber between two or more pay zones to a bitumen thickness greater than 20 meters. In one embodiment the subterranean steam chamber region extends from the first pay zone into the second pay zone. In an alternate embodiment the minimum distance of at least one pay zone, indicated by x in
The perforation of the well can be done by any conventional method known to one skilled in the art. Typically perforation refers to a hole punched in the casing or liner of an oil well to connect it to the reservoir. In cased hole completions, the well will be drilled down past the section of the formation desired for production and will have casing or a liner run in separating the formation from the well bore. The final stage of the completion will involve running in perforating guns, a string of shaped charges, down to the desired depth and firing them to perforate the casing or liner. A typical perforating gun can carry many dozens of charges.
After the perforation of the well a fracturing fluid can then be injected into the fracture to form a hydraulic fracture. A hydraulic fracture is typically formed by pumping the fracturing fluid into the wellbore at a rate sufficient to increase the pressure downhole to a value in excess of the fracture gradient of the formation rock. The pressure causes the formation to crack, allowing the fracturing fluid to enter and extend the crack further into the formation.
To keep this fracture open after the injection stops, a solid proppant can be added to the fracture fluid. The proppant, which is commonly a sieved round sand, is carried into the fracture. This sand is chosen to be higher in permeability than the surrounding formation, and the propped hydraulic fracture then becomes a high permeability conduit through which the formation fluids can flow to the well.
Different fracturing fluids can be used as long as they have characteristics such as:
Examples of fracturing fluids that can be used include: water to gels, foams, nitrogen, carbon dioxide or air. In addition to the fracturing fluids different additives can be added to enhance the fracturing fluids such as: acid, glutaraldehyde, sodium chloride, n,n-dimethyl formaide, borate salts, polyacrylamide, petroleum distillates, guar gum, citric acid, potassium chloride, ammonium bisulfite, sodium or potassium carbonate, various proppants, ethylene glycol, and/or isopropanol.
Microwave frequency generators are operated to generate microwave frequencies capable of causing maximum excitation of the substances in the frac barrier. In some embodiments the microwave frequency will be not greater than 3000 megahertz and at a resonant frequency of water. Examples of substances present in the frac barrier include: water or salt water used in SAGD operations, asphaltene, heteroatoms and metals. For some embodiments, the microwave frequency generator defines a variable frequency source of a preselected bandwidth sweeping around a central frequency. As opposed to a fixed frequency source, the sweeping by the microwave frequency generator can provide time-averaged uniform heating of the hydrocarbons with proper adjustment of frequency sweep rate and sweep range to encompass absorption frequencies of constituents, such as water and the microwave energy absorbing substance, within the mixture. In some embodiments the microwave frequency will be not greater than 3000 megahertz and/or at a resonant frequency of water. For example, the microwave frequency generator may introduce microwaves with power peaks at a first discrete energy band around 2.45 GHz associated with water and a second discrete energy band spaced from the first discrete energy band and associated with the components with existing dipole moments in the frac barrier.
By heating the frac barrier with a radio frequency the pressure required to fracture the frac barrier is less than what is necessary the fracture the frac barrier prior to heating with the radio frequency. The pressure can be reduced with this method anywhere from 3 psi to 0.05 psi. In alternate embodiments the pressure can be reduced by 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75 or even 2 psi.
In one embodiment the fracturing of the frac barrier permits a steam chamber to be formed within the first pay zone and the second pay zone. By enlarging the space for the subterranean steam chamber the steam to oil ratio is lower than 3.5 when the steam assisted gravity drainage is performed in the subterranean steam chamber.
In one embodiment processes such as cyclic steam stimulation, vapor extraction, J-well steam assisted gravity drainage, in situ combustion, high pressure air injection, expanding solvent steam assisted gravity drainage or cross-steam assisted gravity drainage can be used to produce oil from the heavy oil formation.
One example of a steam assisted gravity drainage system is as follows. In the steam assisted gravity drainage process, two parallel horizontal oil wells are drilled in the formation, one about 4 to 6 meters above the other. The upper well injects steam, possibly mixed with solvents, and the lower one collects the heated crude oil or bitumen that flows out of the formation, along with any water from the condensation of injected steam. The basis of the process is that the injected steam forms a “subterranean steam chamber” that grows vertically and/or horizontally in the heavy oil formation. The heat from the steam reduces the viscosity of the heavy crude oil or bitumen which allows it to flow down into the lower wellbore. The steam and gases rise because of their low density compared to the heavy crude oil below, ensuring that steam is not produced at the lower production well. The gases released, which include methane, carbon dioxide, and usually some hydrogen sulfide, tend to rise in the subterranean steam chamber, filling the void space left by the oil and, to a certain extent, forming an insulating heat blanket above the steam. Oil and water flow is by a countercurrent, gravity driven drainage into the lower well bore. The condensed water and crude oil or bitumen is recovered to the surface by pumps such as progressive cavity pumps that work well for moving high-viscosity fluids with suspended solids.
The depiction of
In operation, steam generated in boiler 111 is provided into the subterranean steam chamber region 112 through upper wellbore leg 116. The steam heats the heavy oil within zone 117 of the oil-bearing portion 113 of subterranean steam chamber region 112 causing it to become less viscous and, hence, increase its mobility. The heated heavy oil flows downward by gravity and is produced through wellbore leg 114. While
Generally, the wellbore for steam injection, wellbore 116, will be substantially parallel to and situated above the wellbore for production, wellbore 114, which is located horizontally near the bottom of the formation. Pairs of steam injection wellbores and production wellbores will generally be close together and located at a suitable distance to create an effective steam chamber and yet minimizing the preheating time. Typically, the pairs of injection and production wellbores will be from about 3 meters to 7 meters apart and preferably there will be about 5 meters of vertical separation between the injector and producer wellbores. In other embodiments it is possible for the injection and production wellbores be anywhere from 1, 3, 5, 7, 12, 15, 20 even 25 meters of horizontal separation apart. Additionally, in other embodiments it is possible for the injection and production wellbores be anywhere from 1, 3, 5, 7, 12, 15, 20 even 25 meters of vertical separation apart. In this type of SAGD operation, the zone 117 is preheated by steam circulation until the reservoir temperature between the injector and producer wellbore is at a temperature sufficient to drop the viscosity of the heavy oil so that it has sufficient mobility to flow to and be extracted through wellbore 114. Generally, the heavy oil will need to be heated sufficiently to reduce its viscosity to below 3000 cP; however, lower viscosities are better for oil extraction and, thus, it is preferable that the viscosity be below 1500 cP and more preferably below 1000 cP. Preheating zone 117 involves circulating steam inside a liner using a tubing string to the toe of the wellbore. Both the injector and producer would be so equipped. Steam circulation through wellbores 114 and 116 will occur over a period of time, typically about 3 months. During the steam circulation, heat is conducted through the liner wall into the reservoir near the liner. At some point before the circulation period ends, the temperature midway between the injector and producer will reach a temperature wherein the bitumen will become movable typically around 3000 cP or less or from about 80 to 100° C. Once this occurs, the steam circulation rate for wellbore 114 will be gradually reduced while the steam rate for the injector wellbore 116 will be maintained or increased. This imposes a pressure gradient from high, for the area around wellbore 116, to low, for the area around wellbore 114. With the oil viscosity low enough to move and the imposed pressure differential between the injection and production wellbores, steam (usually condensed to hot water) starts to flow from the injector into the producer. As the steam rate is continued to be adjusted downward in wellbore 114 and upward in wellbore 116, the system arrives at steam assisted gravity drainage operation with no steam injection through wellbore 114 and all the steam injection through wellbore 116. Once hydraulic communication is established between the pair of injector and producer wellbores, steam injection in the upper well and liquid production from the lower well can proceed. Due to gravity effects, the steam vapor tends to rise and develop a steam chamber at the top section 119 of zone 117. The process is operated so that the liquid/vapor interface is maintained between the injector and producer wellbores to form a steam trap which prevents live steam from being produced through the lower wellbore.
During operation, steam will come into contact with the heavy oil in zone 117 and, thus, heat the heavy oil and increase its mobility by lessening its viscosity. Heated heavy oil will tend to flow downward by gravity and collect around wellbore 114. Heated heavy oil is produced through wellbore 114 as it collects. Steam contacting the heavy oil will lose heat and tend to condense into water. The water will also tend to flow downward toward wellbore 114. In past SAGD operations, this water would also be produced through wellbore 114. Such produced water would need to be treated to reduce impurities before being reheated in the boiler for subsequent injection. As the process continues operation, zone 117 will expand with heavy oil production occurring from a larger portion of oil-bearing portion 113 of subterranean steam chamber formation 112.
Turning again to
Turning now to
In still another embodiment of the invention, also illustrated in
Microwave generators useful in the invention would be ones suitable for generating microwaves in the desired frequency ranges recited above. Microwave generators and wave guide systems adaptable to the invention are sold by Cober Muegge LLC, Richardson Electronics and CPI International Inc.
Steam to oil ratio is an important factor in SAGD operations and typically the amount of water required will be 2 to 3 times the oil production. Higher steam to oil production ratios require higher water and natural gas costs. The present invention reduces water and natural gas requirements and reduces some of the water handling involving recycling, cooling, and cleaning up the water.
In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as additional embodiments of the present invention.
Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.
This application is a continuation-in-part application which claims benefit under 35 USC §120 to U.S. application Ser. No. 12/239,051 filed Sep. 26, 2008 entitled “PROCESS FOR ENHANCED PRODUCING OF HEAVY OIL USING MICROWAVES,” incorporated herein in their entirety and a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/382,763 filed Sep. 14, 2010 entitled “FRACTURING SHALE AND MUDSTONE LAYERS TO IMPROVE SAGD PERFORMANCE” and U.S. Provisional Application Ser. No. 61/414,744 filed Nov. 17, 2010 entitled “FRACTURING SHALE AND MUDSTONE LAYERS TO IMPROVE SAGD PERFORMANCE” which is incorporated herein in its entirety.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3237690 | Karp et al. | Mar 1966 | A |
| 4094798 | Tate et al. | Jun 1978 | A |
| RE30738 | Bridges et al. | Sep 1981 | E |
| 4457365 | Kasevich et al. | Jul 1984 | A |
| 4485868 | Sresty et al. | Dec 1984 | A |
| 4620593 | Haagensen | Nov 1986 | A |
| 4638863 | Wilson | Jan 1987 | A |
| 4700716 | Kasevich et al. | Oct 1987 | A |
| 4817711 | Jeambey | Apr 1989 | A |
| 4912971 | Jeambey | Apr 1990 | A |
| 5082054 | Kiamanesh | Jan 1992 | A |
| 5109927 | Supernaw et al. | May 1992 | A |
| 5321222 | Bible et al. | Jun 1994 | A |
| 5521360 | Johnson et al. | May 1996 | A |
| 5899274 | Frauenfeld et al. | May 1999 | A |
| 6012520 | Yu et al. | Jan 2000 | A |
| 6544411 | Varadaraj | Apr 2003 | B2 |
| 6814141 | Huh et al. | Nov 2004 | B2 |
| 6929066 | Hill | Aug 2005 | B2 |
| 7073577 | Yu | Jul 2006 | B2 |
| 7091460 | Kinzer | Aug 2006 | B2 |
| 7461693 | Considine et al. | Dec 2008 | B2 |
| 7484561 | Bridges | Feb 2009 | B2 |
| 7677673 | Tranquilla et al. | Mar 2010 | B2 |
| 7975763 | Banerjee et al. | Jul 2011 | B2 |
| 20040040717 | Hill | Mar 2004 | A1 |
| 20050199386 | Kinzer | Sep 2005 | A1 |
| 20070131591 | Pringle | Jun 2007 | A1 |
| 20070289736 | Kearl et al. | Dec 2007 | A1 |
| 20080073079 | Tranquilla et al. | Mar 2008 | A1 |
| 20090071648 | Hagen et al. | Mar 2009 | A1 |
| 20090139716 | Brock et al. | Jun 2009 | A1 |
| 20110186295 | Kaminsky et al. | Aug 2011 | A1 |
| 20120061081 | Sultenfuss et al. | Mar 2012 | A1 |
| Number | Date | Country |
|---|---|---|
| 0896407 | May 1962 | GB |
| 5112004104 | Oct 1976 | JP |
| 2007081493 | Jul 2007 | WO |
| Entry |
|---|
| Deutsch, C.V. and McLennan, J.A., Guide to SAGD (Steam Assisted Gravity Drainage) Reservoir Characterization Using Geostatistics, 2005, Centre for Computational Geostatistics. |
| Number | Date | Country | |
|---|---|---|---|
| 20110259585 A1 | Oct 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61382763 | Sep 2010 | US | |
| 61414744 | Nov 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12239051 | Sep 2008 | US |
| Child | 13154882 | US |
