Wells – Processes – Separating material entering well
Reexamination Certificate
1999-03-29
2001-02-20
Suchfield, George (Department: 3672)
Wells
Processes
Separating material entering well
C166S052000, C166S265000, C166S267000, C166S370000, C405S128350
Reexamination Certificate
active
06189614
ABSTRACT:
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 producing the compressed gas to the surface for processing and/or reinjection and in one aspect relates to a method and downhole system for separating a portion of the gas from a gas-oil stream, compressing the gas, and then producing the compressed gas through the well annulus or by separate flowpath to the surface for processing and/or reinjected into another well.
BACKGROUND
It is well known that many hydrocarbon reservoirs produce extremely large volumes of gas along with crude oil and other liquids. 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 or 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 the producing reservoir is located in a remote area, large volumes of produced gas can present major problems since production may have to 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 usually 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 costs of the gas compressor train which is needed to compress the large volumes of produced gas to the pressures required for injection. As will be understood in this art, significant cost savings can be achieved if the 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 injection of the gas downhole.
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 basically 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. 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 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 is routed through the turbine and acts as the power fluid therefor. 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) adjacent to the wellbore.
Where the separated gas has a use or a market or where there are no formations within the production well for injecting the gas, it is desirable to bring the compressed gas to the surface for further processing or for injection into a separate injection well.
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 flowing both said compressed gas and the remainder of said gas-oil stream to the surface through separate flowpaths in said 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, “gas-oil stream(s)” is intended to include streams which also may include produced water along with the gas and oil.
The system includes a string of tubing positioned within the wellbore wherein the string of tubing, itself, provides the flowpath through which said remainder of said gas-oil stream flows to the surface while the annulus formed between said string of tubing and said wellbore provides the flowpath through which said compressed gas flows to the surface.
Preferably, the means for separating and compressing at least a portion of the gas downhole is a subsurface processing and reinjection compressor (SPARC) downhole which has an auger separator section for separating the gas, a compressor section for compressing the separated gas, and a turbine section for driving the compressor section. The compressed gas is produced to the surface where it may be further processed for sale or use (e.g. additional condensate can be removed from the gas) or it can be reinjected into a separate wellbore for disposal or the like. In some instances, the compressed gas from a plurality of wellbores may be compounded together before the gas is reinjection into a separate wellbore(s).
By separating and compressing at least a portion of the produced gas and then bringing the compressed gas to the surface, several advantages may be realized over the use of a auger separator or a SPARC by themselves. First, the separated gas, which is compressed downhole by the SPARC, does not have to be reinjected directly into a formation which lies adjacent the same wellbore as that from which the stream is produced as is the typically operating procedure proposed in known, prior-art SPARC operations. By bringing the compressed gas to the surface, the compressed gas can now be re-injected into a separate disposal well(s). Further, the compressed gas, once at the surface, is now available of use on site (e.g. fuel, to drive power turbines, etc.) or it be further compressed, if necessary, and pipelined to market. In either event, the compressor horsepower, normally required at the surface, can be significantly reduced.
Also, by bringing the separated gas, which is warmed as it is compressed, to the surface through the well annulus, it flows in parallel to the remainder of the gas-oil stream in the tubing string which, in turn, has been cooled
Brady Jerry L.
Cawvey James L.
Klein John M.
Stevenson Mark D.
Atlantic Richfield Company
Suchfield George
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