Wells – Processes – Separating material entering well
Reexamination Certificate
1999-10-29
2001-04-03
Tsay, Frank S. (Department: 3672)
Wells
Processes
Separating material entering well
C166S305100, C166S105500
Reexamination Certificate
active
06209641
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to a method and apparatus for producing through a wellbore while simultaneously injecting gas into a subterranean formation through the same wellbore and in one aspect relates to a method and apparatus for injecting gas into a formation wherein the gas is mixed with a carrier fluid at the surface which, in turn, is flowed down a well where at least a portion of the gas is separated and injected into the formation while fluids are being produced through the wellbore.
2. 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 for further processing. 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, the produced gas can present major problems since production may have to shut-in or at least drastically reduced if the 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 later be recovered 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 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.
Recently, several techniques have been proposed for disposing of at least a part of the produced gas by separating the gas at the surface and then injecting it through the production wellbore into a subterranean formation. For example, in co-pending and commonly assigned U.S. patent application Ser. No. 09/072,657, filed May 5, 1998 a method and apparatus are disclosed wherein gas, which has been separated from a production stream, is mixed with a with a carrier liquid (e.g. brine) to form a dense mixture which, in turn, is flowed downward in a wellbore of an injection well. The mixture flows through a downhole separator in the wellbore to thereby separate at least a portion of the gas from the mixture. The separated gas is then injected into a formation adjacent the wellbore while the carrier liquid and any unseparated gas is returned to the surface. By mixing the gas with a carrier liquid, the need for expensive gas compressors at the surface is eliminated. However, this method requires a dedicated injection well.
Another similar method for disposing of produced gas is disclosed in co-pending and commonly assigned U.S. patent application Ser. No. 09/073,215, filed May 5, 1998 wherein a common wellbore is used for both producing an oil and gas stream and for re-injecting at least a portion of the produced gas. The production stream passes through a separator as it is being produced to the surface to thereby separate at least a portion of the gas from the production stream which, in turn, is then flowed to the surface. After a production cycle, the well is shut-in and the separated gas is the flowed down the same wellbore to be injected into an formation different from the production formation.
The gas is first mixed with a carrier fluid, e.g. brine, at the surface to form a dense mixture which, in turn, is flowed through the downhole separator in the wellbore wherein a portion of the gas is separated from the mixture. The separated gas is then injected into the formation with remainder of the mixture being returned to the surface. Again, by using this method, no gas compressors are needed at the surface but the production well must be shut-in during the injection of the gas.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for producing an oil and gas production stream from a first subterranean zone through a wellbore while simultaneously injecting gas into a second subterranean zone through the same wellbore. The injected gas can be that from the production stream or may be from a separate source. Basically, the production stream is produced to the surface where gas is separated therefrom. Gas from the production stream and/or gas from a separate source is then mixed with a carrier fluid at the surface to form a carrier fluid-gas mixture which, in turn, is flowed back down the wellbore and a downhole separator to separate at least a portion of the gas from the carrier liquid-gas mixture. This separated gas is then injected into the second subterranean zone while the carrier fluid and any unseparated gas is mixed and commingled with the production stream before the combined streams are flowed to the surface.
More specifically, the present invention provides a method and an apparatus for producing an oil and gas stream from a first subterranean zone through a wellbore while simultaneously injecting gas into a second subterranean zone through said wellbore wherein the wellbore has a string of production tubing positioned therein which forms an annulus between the production tubing and the wellbore. An oil and gas stream is produced to said surface through the production tubing where it is separated into its gas, oil, and water components. The separated gas is mixed with a carrier fluid (e.g. water, brine, etc.) at the surface to form a carrier fluid-gas mixture which is then flowed down the annulus in the wellbore while the well is still being produced through the tubing string.
As the carrier fluid-gas mixture approaches the bottom of the annulus, it flow through a downhole separator (e.g. an inverted hydrocyclone separator) wherein at least a portion of the gas is separated from the carrier fluid-gas mixture. The separated portion of the gas is then injected into the second subterranean zone which lies adjacent the wellbore. The mixture of the carrier fluid and any unseparated gas is mixed with the production stream at the outlet of the hydrocyclone separator by means of a jet pump or the like to thereby mix and commingle the streams before they are flowed to the surface through the production tubing.
By forming a mixture with a dense, carrier fluid, the gas does not need to be compressed at the surface before it is injected down the wellbore. As will be appreciated, by reducing or eliminating the need for gas compressors, the costs involved in disposing of excess gas through injection are substantially reduced. Further, since the gas can be injected while the well is being produced, the well does have to be shut-in in order to disposed of excess gas.
REFERENCES:
patent: 5431228 (1995-07-01), Weingarten et al.
patent: 5482117 (1996-01-01), Kolpak et al.
patent: 5605193 (1997-02-01), Bearden et al.
patent: 5730871 (1998-03-01), Kennedy et al.
Atlantic Richfield Company
Metrailer Albert C.
Tsay Frank S.
LandOfFree
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