Abstract:
A system and method to inject a combined hydrocarbon-based liquid stream and a liquid carbon dioxide stream into a subterranean formation via a well using a single high-pressure pump.

Description:
RELATED INVENTION 
       [0001]    This invention is entitled to and hereby claims the benefit of the filing date of Provisional Patent Application Serial No. 60/766,815 filed Feb. 13, 2006 by Randal L. Decker entitled “Liquid CO 2  Emulsion Pumping System.” 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an efficient injection system for injecting a combined aqueous or hydrocarbon-based liquid stream and a liquid carbon dioxide stream via a well into a subterranean formation. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the use of liquid carbon dioxide for injection with various liquid well treating materials, it has been necessary in the past to use two high-pressure pumps; one for the injection of an aqueous or hydrocarbon-based liquid stream and one for the liquid carbon dioxide stream to achieve the required injection and mixing pressures. 
         [0004]    These high-pressure pumps, which are large pumps, are typically mounted on heavy duty trucks for movement to a well area. These pumps are typically massive, positive displacement pumps having one or multiple plungers and are used to increase the pressure of injection streams to a pressure suitable for injection into a well up to and at or exceeding fracturing conditions as required. The use of these pumps is expensive since they are subject to a substantial per diem charge as a result of the high cost of the pumps and because such pumps have relatively high maintenance costs. 
         [0005]    Accordingly, a more efficient and economical way to inject a stream of liquid carbon dioxide and a liquid stream of aqueous or hydrocarbon-based liquid treating solution into a well at a suitable pressure has been sought. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention comprises a system for efficient injection of a combined aqueous or hydrocarbon-based liquid stream and a liquid carbon dioxide stream into a well penetrating a subterranean formation; the system consisting essentially of: a liquid booster pump in fluid communication with a source of an aqueous or hydrocarbon-based liquid and effective to increase a pressure in a liquid stream of the aqueous or hydrocarbon-based liquid to a first selected pressure; a liquid carbon dioxide booster pump in fluid communication with a source of liquid carbon dioxide and effective to increase a pressure in a stream of liquid carbon dioxide to a second selected pressure; and, a high-pressure pump in fluid communication with the liquid booster pump and the liquid carbon dioxide booster pump and adapted to receive and combine the liquid stream of aqueous or hydrocarbon-based liquid and the stream of liquid carbon dioxide and increase a pressure of the combined stream to a pressure suitable for injection into the well. 
         [0007]    The invention further comprises a method for injection of a combined aqueous or hydrocarbon-based liquid stream and a liquid carbon dioxide stream into a well penetrating a subterranean formation, the method consisting essentially of: increasing the pressure of the aqueous or hydrocarbon-based liquid stream to 550 psia, up to 650 psia, in a liquid booster pump; increasing the pressure of a stream of liquid carbon dioxide to about 550 psia, up to 650, psia in a liquid carbon dioxide booster pump; and, passing the liquid carbon dioxide stream and the aqueous or hydrocarbon-based liquid stream to a high-pressure pump wherein the streams are combined and wherein the pressure of the combined streams is increased to a pressure sufficient to inject the combined streams into the well. 
         [0008]    The invention further comprises a method for injection of a combined aqueous or hydrocarbon-based liquid stream and a liquid carbon dioxide stream into a subterranean formation via a well by passing the combined aqueous or hydrocarbon-based liquid stream and the liquid carbon dioxide stream to a high-pressure pump where the liquid streams are combined and wherein the pressure of the combined streams is increased to a pressure greater than 650 psia. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]      FIG. 1  is a schematic diagram of a prior art system for injecting a mixture of a treating solution and carbon dioxide; and, 
           [0010]      FIG. 2  shows a schematic diagram of an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0011]    In the discussion of the Figures and embodiments, various features such as pumps, valves and the like necessary to achieve the flows required and discussed have not been shown for simplicity since such features are considered to be well known to those skilled in the art. 
         [0012]    A prior art system  10  is shown in  FIG. 1 . 
         [0013]    In  FIG. 1  a hydrochloric acid solution source is shown as an HCL transport  12  and a water source is shown as a water transport  16 . These transports are typically large tanker trucks or the like which can be moved to a well site for treatment of the well. Typically these are trucks which discharge their cargos at a pressure from atmospheric pressure, to a booster pump (not shown) that increases the liquid pressure to about 50-150 psia as shown with water and acid solution being passed through lines  14  and  18  to a high-pressure pump  20 . The high-pressure pump  20  increases the pressure of the streams to a pressure sufficient for discharge into a well  24  via a line  22 . 
         [0014]    Liquid carbon dioxide is typically delivered by trucks, shown as CO 2  transports  26  and is typically supplied at about 250-300 psia pressure. The carbon dioxide is typically passed to a liquid carbon dioxide booster pump  32  through one of lines  28  and  30 . Booster pump  32  increases the pressure of the liquid carbon dioxide stream by about 50 to about 75 psia and passes it to a high-pressure pump  36  which increases the pressure of the carbon dioxide stream and discharges the liquid carbon dioxide stream through a line  38  to well  24 . The streams are mixed in well  24  as they pass downwardly through the well. 
         [0015]    In  FIG. 2  a schematic diagram of an embodiment  100  of the present invention is shown wherein an aqueous hydrochloric acid liquid is stored at atmospheric pressure. The liquid carbon dioxide is stored at 250-300 psia. In this embodiment, liquid carbon dioxide is stored in a vessel  124  and is produced through a line  126  and passed through a vapor separator  136  and then through a line  138  to a CO 2  booster pump  140  where it is compressed to a pressure from about 550 psia, up to about 600 psia. The stream compressed in booster pump  140  is passed through a line  142  and then through a line  116  to a high-pressure pump  118 . The high-pressure pump then increases the pressure in this stream along with the aqueous acidic liquid stream for injection through a line  120  to a well  122 . 
         [0016]    The aqueous acid liquid is stored in storage  102  and passed via a line  108  to a liquid booster pump  110  where its pressure is increased to a pressure of about 600 psia and then combined via a line  112  with the stream from line  142  and fed to a high-pressure pump  118  via line  116 . Liquid booster pump  110  also is in fluid communication with a recycle loop comprising a line  112  and a line  114  so that the output from liquid booster pump  110  can be recycled if desired in whole or in part for pressure and flow volume control. 
         [0017]    Vapor separator  136  operates to remove accumulated vapor that has been formed by the absorption of heat as the liquid carbon dioxide has been moved from storage  124  via line  126 . The vapor is vented to the atmosphere from the top of separator  136 , thereby preventing the booster pump  140  and high-pressure pump  118  from cavitating. In the event that the liquid CO 2  rate must be reduced to pump  118 , a portion of the stream in line  142  can be diverted through a line  144  and can be re-cycled through vapor separator  136  which will remove accumulated vapor and aid in controlling a liquid CO 2  pump  140  rate and pressure from pump  140  to high-pressure pump  118 . The stream is then passed through a line  146  back to line  142 . This enables the operation of vapor separator  136  to separate vapor from the liquid carbon dioxide as required. As indicated, it is contemplated that the vapor separator will contain only relatively small volumes of carbon dioxide vapor at any given time since substantial amounts of carbon dioxide liquid are passing through these vessels. 
         [0018]    This embodiment allows the liquid carbon dioxide to be in storage at 250-300 psia and allows for the aqueous hydrochloric acid to be in storage at atmospheric pressure. According to the present invention, the liquid treating fluid and the carbon dioxide are supplied to a single high-pressure pump at a pressure of about 550 psia, up to 650 psia, and at preferably about 600 psia. In the past it has been considered necessary to have a high-pressure pump for each of the liquid treating solution and the liquid carbon dioxide. 
         [0019]    According to the present invention only a single high-pressure pump is used. This results in a substantial increase in the process efficiency since better emulsification is achieved. It also results in a substantial reduction of expense in that only one high-pressure pump is required to be maintained and operated on site. The resulting emulsions are formed in the high-pressure pump and the emulsion is pumped into the well at a pressure great than 650 psia. 
         [0020]    While the invention has been discussed above by reference to aqueous hydrochloric acid as a treating solution, it should be understood that the acid solution may contain methanol and other additives. While the presence of methanol is optional it is desirable in many instances that the methanol be present in an amount from about 5 to about 25 weight percent in the treating liquid. Further the invention can be used to inject not only aqueous acid but organic solvents, scale inhibitors, corrosion inhibitors and the like into the well. The only real limitation on the use of the treating liquid is that it be liquid when mixed the liquid carbon dioxide. 
         [0021]    As well known to those skilled in the art, whatever arrangement is used to provide the liquid carbon dioxide to the high-pressure pump at the desired pressure must maintain the liquid carbon dioxide under suitable temperature and pressure conditions to maintain it in a liquid state. Such conditions are well known to those skilled in the art. 
         [0022]    While the embodiments shown are preferred, it is considered necessary for the practice of the present invention that the carbon dioxide be delivered in a liquid form at a pressure from about 550 psia, up to 650 psia, to the high-pressure pump along with the aqueous solution which must be delivered at the same or a comparable pressure and at a temperature which does not result in vaporization of the liquid carbon dioxide. These streams may be introduced in mixture or alone into the high-pressure pump. In either event the resulting emulsion is readily pumped by the high-pressure pump into the well as shown, for instance in  FIG. 2 , via line  120  into well  122 . 
         [0023]    As mentioned previously, the high-pressure pumps are typically large, positive displacement pumps having from 1 to 5 or more plungers which are relatively high maintenance and high expense pumps for use because of their ability to generate the extreme pressures used in fracturing operations and the like. These positive displacement pumps are suitable as the high-pressure pump in the present invention. 
         [0024]    Multi-stage centrifugal pumps may be used for similar applications but are not typically used or preferred for fracturing operations. They are suitable for use as the high-pressure pump in the present invention so long as they are capable of mixing the aqueous solution and the liquid carbon dioxide and injecting the resulting mixture into a well at a pressure greater than about 650 psia. 
         [0025]    While typical and preferred operating conditions for the invention have been described above, the aqueous liquid solution could be passed to the high-pressure pump at a higher or lower pressure and the higher-pressure pump is capable of compressing the mixture to pressures much higher than 650 psia. The liquid booster pumps and the feed pumps, if used, may be centrifugal pumps, multi-stage centrifugal pumps and the like as required to achieve the desired pressure increases. The operation of such pumps is much less expensive than for the high-pressure pumps and the maintenance requirements for such pumps are much lower. The preferred pressures discussed above may be varied so long as the liquid streams are mixed as liquids and so long as the carbon dioxide is passed to the high pressure pump as a liquid. 
         [0026]    By the present invention, the use of a second high-pressure pump has been omitted and improved mixing and operational efficiency has been achieved in the delivery of the treating liquid/liquid carbon dioxide mixture into the well. 
         [0027]    While the present invention has been described by reference to certain of its preferred embodiments, it is pointed out that the embodiments described are illustrative rather than limiting in nature and that many variations and modifications are possible within the scope of the present invention. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments.