Wells – Processes – Separating material entering well
Reexamination Certificate
1999-07-13
2001-07-17
Neuder, William (Department: 3672)
Wells
Processes
Separating material entering well
C166S105500, C166S306000, C166S369000
Reexamination Certificate
active
06260619
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to separating and compressing a portion of the gas from the oil-gas stream produced from a subterranean zone and reinjecting the compressed gas downhole without producing the compressed gas to the surface and in one aspect relates to a method and downhole or subsurface system for separating a portion of the gas from a gas-oil production stream, passing the remainder of the production stream through a turbine to drive a compressor which, in turn, compresses the separated gas, and then injecting the compressed gas into a downhole formation while allowing substantial amounts of condensate to be recovered to the surface along with the remaining production stream.
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. The system is designed to maintain as much pressure on the separated gas as possible and thereby inject as much gas as possible in the downhole formation. While this system may separate and reinject up to about half of the gas in the production stream, it recovers very little of the desirable condensate that is present in the re-injected gas.
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.
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, now U.S. Pat. No. 6,035,934. In this downhole separation system, the entire production stream is first flowed through the turbine to drive same 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. While this system recovers a significant amount of the desirable condensate in the production stream, substantially less gas from the production stream is likely to be injected downhole.
Accordingly, it is desirable to separate a significant amount of the gas from the production stream while at the same time being able to recover to the surface a significant portion of the condensates from the re-injected gas.
SUMMARY OF THE INVENTION
The present invention provides a method and system for producing a mixed gas-oil stream to the surface from a subterranean zone through a wellbore wherein at least a portion of said gas is separated from said mixed gas-oil stream downhole and is compressed to increase the pressure of the separated gas before the compressed gas is re-injected into a formation adjacent the wellbore. As will be understood in the art, the production stream will normally also include some water which will be produced with the oil and as used herein, “mixed gas-oil stream(s)” is intended to include streams which also may include produced water along with the gas and oil.
In the present invention, the mixed gas-oil stream flows upward through a string of production tubing and through a downhole separator such as an auger which causes the fluids to rotate with the heavier liquid components moving outward toward the
Brady Jerry L.
Cawvey James L.
Klein John M.
Petullo Steven P.
Stevenson Mark D.
Atlantic Richfield Company
Faulconer Drude
Neuder William
Walker Zakiya
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