Wells – With eduction pump or plunger – Having liquid-gas separator
Reexamination Certificate
1999-09-10
2001-09-04
Neuder, William (Department: 3672)
Wells
With eduction pump or plunger
Having liquid-gas separator
C166S265000
Reexamination Certificate
active
06283204
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to separating, compressing, and reinjecting a portion of the gas from the oil-gas stream produced from a subterranean zone and in one aspect relates to a method and subsurface system for separating a portion of the gas from a gas-oil production stream, passing the separated gas through a downhole turbine-compressor unit to compress and reinject the separated gas into a downhole formation wherein particulate material (e.g. sand) is also separated from the production stream and is by-passed around the turbine to prevent damage thereto.
2. Background
It is well known that many hydrocarbon reservoirs produce extremely large volumes of gas along with crude oil and other formation fluids, e.g. water. In producing fields such as these, it is not unusual to experience gas-to-oil ratios (GOR) as high as 25,000 standard cubic feet per barrel (scf/bbl.) or greater. As a result, large volumes of gas must be separated out of the liquids before the liquids are transported to storage for further processing or use. Where the production sites are near or convenient to large markets, this gas is considered a valuable asset when demands for gas are high. However, when demands are low or when a producing reservoir is located in a remote area, large volumes of produced gas can present major problems since production may have to be shut-in or at least drastically reduced if the produced gas can not be timely and properly disposed of.
In areas where substantial volumes of the produced gas can not be marketed or otherwise utilized, it is common to “reinject” the gas into a suitable, subterranean formation. For example, it is well known to inject the gas back into a “gas cap” zone which often overlies a production zone of a reservoir to maintain the pressure within the reservoir and thereby increase the ultimate liquid recovery therefrom. In other applications, the gas may be injected into a producing formation through an injection well to drive the hydrocarbons ahead of the gas towards a production well. Still further, the produced gas may be injected and “stored” in an appropriate, subterranean permeable formation from which it can be recovered later when the situation dictates.
To reinject the gas, large and expensive separation and compression surface facilities must be built at or near the production site. A major economic consideration in such facilities is the relatively high cost of the gas compressor train which is needed to compress and raise the large volumes of produced gas to the pressures required for reinjection. As will be understood in this art, significant cost savings can be achieved if these gas compressor requirements can be down-sized or eliminated altogether. To achieve this, however, it is necessary to either raise the pressure of the gas at the surface by some means other than mechanical compression or else reduce the pressure required at the surface for reinjection of the gas downhole or reduce the volume of gas actually produced to the surface.
Various methods and systems have been proposed for reducing some of the separating/handling steps normally required at the surface to process and/or re-inject at least a portion of the produced gas. These methods all basically involve separating at least a portion of the produced gas from the production stream downhole and then handling the separated gas and the remainder of the production stream separately from each other.
For example, one such method involves the positioning of an “auger” separator downhole within a production wellbore for separating a portion of the gas from the production stream as the stream flows upward through the wellbore; see U.S. Pat. No. 5,431,228, issued Jul. 11, 1998. Both the remainder of the production stream and the separated gas are flowed to the surface through separate flowpaths where each is individually handled. While this downhole separation of gas reduces the amount of separation which would otherwise be required at the surface, the gas which is separated downhole still requires substantially the same amount of compressor horsepower at the surface to process/reinject the gas as that which would be required if all of the gas in the production stream had been separated at the surface.
Another system involving the downhole separation of gas from a production stream is fully disclosed and claimed in U.S. Pat. No. 5,794,697, issued Aug. 18, 1998 wherein a subsurface processing and reinjection compressor (SPARC) is positioned downhole in the wellbore. The SPARC includes an auger separator which first separates at least a portion of the gas from the production stream (i.e. approximately half) and then compresses the separated gas by passing it through a compressor which, in turn, is driven by a turbine.
The remainder of the production stream (i.e. approximately the other half of the gas and the liquids) is routed through the turbine to act as the power fluid for driving the turbine. The compressed gas is not produced to the surface but instead is injected directly from the compressor into a second formation (e.g. gas cap) within the production wellbore. Since the remainder of the production stream is likely to also contain solid particulate material (e.g. produced sand), it can seriously erode the vanes of the turbine as it flows therethrough thereby substantially shortening the operational life of the SPARC.
Another system utilizing a SPARC, positioned downhole within a production well, is disclosed in co-pending and commonly-assigned, U.S. patent application Ser. No. 09/282,056, filed Mar. 29, 1999. In this system, the SPARC separates and compresses a portion of the gas in the production stream basically in the same manner as described above, but instead of re-injecting the compressed gas, both the compressed gas and the remainder of the production stream are produced to the surface through separate flowpaths. Again, substantially all of any solid particulates in the production stream has to pass through the turbine thereby causing possible erosion within the turbine.
Still another similar system is disclosed in co-pending and commonly-assigned, U.S. patent application Ser. No. 09/028,624, filed Feb. 24, 1998. In this downhole separation system, the entire production stream is first flowed through the turbine to drive the turbine before the stream is flowed through an auger separator which, in turn, is positioned above the turbine. A portion of the gas in the production is then separated by the auger and is passed through a compressor which, in turn, is driven by the turbine. The compressed gas is then injected into a formation adjacent the wellbore. Since the entire production stream flows through the turbine, this system is exposed to the same erosion problems as those discussed above.
As can be seen from the above, it is desirable to separate out as much as possible of the solid particulate material from the production stream before the stream is passed through the downhole turbine of a SPARC or like system in order to alleviate erosion of the turbine vanes. One such system is disclosed and claimed in co-pending and commonly-assigned, U.S. patent application Ser. No. 09/088,499, filed Jun. 1, 1998. A spiral groove or passageway is formed in the inner wall of the housing in which the auger separator is mounted. When the production stream flows through the auger separator, liquids are spun outwardly towards the inner wall of the housing.
The heavier portion of the liquids which contain most of any particulate material in the production stream collects in and flows through the spiral passageway which, in turn, empties into a by-pass passageway formed in the housing of the turbine whereby the portion of the stream containing the particulate material does not pass through the turbine. The present invention is directed to a similar system but has a different means for bypassing the turbine with the particulate-laden portion of the production stream.
SUMMARY OF THE INVENTION
The present invention provides a subsurface system for producing a mi
Brady Jerry L.
Cawvey James L.
Klein John M.
Stevenson Mark D.
Atlantic Richfield Company
Faulconer Drude
Neuder William
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