Method for pumping foamed fluids into a well bore or subterranean formation

Abstract

A method for pumping a liquid-gas mixture into a subsurface well includes introducing gas into a liquid at a first pressure to generate a mixture. The mixture is pumped through a first positive displacement pump to a second pressure greater than the first pressure. The mixture at the second pressure is pumped through at least a second positive displacement pump to a third pressure greater than the second pressure. The mixture is moved into the subsurface well at at least the third pressure.

Claims

1. A method for pumping a liquid-gas mixture into a subsurface well, comprising: introducing gas into a liquid flowing at a first pressure to generate a mixture; pumping the mixture through a first positive displacement pump to a second pressure greater than the first pressure; pumping the mixture from the first positive displacement pump to at least one intermediate positive displacement pump, and pumping the mixture from the at least one intermediate positive displacement pump to a second positive displacement pump at a first intermediate pressure greater than the second pressure and less than a third pressure; pumping the mixture at the first intermediate pressure through a second positive displacement pump to the third pressure greater than the first intermediate pressure; moving the mixture into the subsurface well at the third pressure; wherein the first intermediate pressure is sufficient to avoid cavitation at an inlet to either (i) at least a second intermediate positive displacement pump or (ii) the second positive displacement pump; and wherein the first intermediate pressure is proportionately greater, by the fractional gas content of the mixture, than a manufacturer specified minimum suction pressure of either the at least a second intermediate positive displacement pump or the second positive displacement pump.

2. The method of claim 1 wherein the second pressure is related to a fractional amount of gas in the mixture.

3. The method of claim 2 wherein the first positive displacement pump comprises an axial screw pump capable of discharge pressures between 30 psi and 500 pounds per square inch (psi).

4. The method of claim 2 wherein the first positive displacement pump comprises a lobe pump capable of discharge pressures between 30 pounds per square inch (psi) and 500 psi.

5. The method of claim 2 wherein the first positive displacement pump comprises a piston pump capable of discharge pressures between 30 pounds per square inch (psi) and 500 psi.

6. The method of claim 2 wherein the second positive displacement pump comprises a piston pump capable of discharge pressures between 200 pounds per square inch (psi) and 10,000 psi.

7. The method of claim 1 wherein the introducing gas is performed by induction through a Venturi tube disposed in a line connected to an inlet of the first positive displacement pump.

8. The method of claim 1 wherein the introducing gas is performed using gas at atmospheric pressure.

9. The method of claim 1 wherein the introducing gas is performed by injection at a pressure of 0 to 50 pounds per square inch above the first pressure.

10. The method of claim 1 where in the introducing gas is performed using gas compressed above atmospheric pressure.

11. The method of claim 1 further comprising moving the mixture at the first intermediate pressure to the at least a second intermediate positive displacement pump, and pumping the mixture from the at least a second intermediate positive displacement pump at a second intermediate pressure greater than the first intermediate pressure and less than the third pressure.

12. The method of claim 1 wherein the first intermediate pressure is sufficient to avoid cavitation at an inlet to the second positive displacement pump.

13. The method of claim 1 wherein the introducing gas is performed using gas compressed above atmospheric pressure.

14. A method for pumping a liquid-gas mixture into a subsurface well, comprising: introducing gas into a liquid flowing at a first pressure to generate a mixture; pumping the mixture through a first positive displacement pump to a second pressure greater than the first pressure; pumping the mixture at the second pressure through a second positive displacement pump to a third pressure greater than the second pressure wherein the second pressure is proportionately greater, by the fractional gas content of the mixture than a manufacturer specified minimum suction pressure of the second positive displacement pump; and moving the mixture into the subsurface well at the third pressure.

15. The method of claim 14 wherein the second pressure is related to a fractional amount of gas in the mixture.

16. The method of claim 15 wherein the first positive displacement pump comprises an axial screw pump, a lobe pump or a piston pump capable of discharge pressures between 30 psi and 500 pounds per square inch (psi).

17. The method of claim 15 wherein the second positive displacement pump comprises a piston pump capable of discharge pressures between 200 pounds per square inch (psi) and 10,000 psi.

18. The method of claim 14 wherein the introducing gas is performed by induction through a Venturi tube disposed in a line connected to an inlet of the first positive displacement pump.

19. The method of claim 14 wherein the introducing gas is performed using gas at atmospheric pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an example pumping system that may be used in accordance with the present disclosure.

(2) FIG. 2 shows a graph of compressibility with respect to pressure of various liquid-air mixtures.

DETAILED DESCRIPTION

(3) Methods for making and pumping gas-liquid mixtures disclosed herein may use a plurality of positive displacement pumps connected in series (the “series”) in a fluid pumping system, and one or more in-line ports into which gas can be introduced to the liquid fraction of the fluid system while flowing through a pipe into the intake of one of the pumps in the series. An example embodiment of a pumping system that may be used in accordance with the present disclosure is shown in FIG. 1. The gas-liquid mixture (“mixture” for convenience hereafter) may be used, for example to perform various operations on or in a subsurface wellbore 22. The mixture may be pumped into the wellbore 22, may be discharged from a drill bit, mill or other intervention device, shown generally at 24, and then returned to surface for temporary storage in a tank or pit 26 and subsequent processing to remove solids and other contaminants at 28. Cleaned liquid may then be returned to a liquid storage tank 10 for reuse.

(4) In making and pumping the mixture, liquid from the tank 10 may be moved to the inlet of a transfer pump 12. The transfer pump 12 may be any type, including both centrifugal and positive displacement pumps because it is contemplated that the transfer pump 12 will move substantially only liquid and/or liquid/solid mixtures. Additives intended to cause the liquid to have specific properties may be introduced to the liquid at 11, prior to moving the liquid into the transfer pump 12. Such introduction may be by gravity or by pumping using any form of chemical pump. “Additives” as that term is used herein may be in solid (e.g., as particles or powder) form or liquid form, so as to distinguish them from gas to be mixed with the liquid fraction to generate the mixture.

(5) Gas 16, in the form of air or other suitable gas, at atmospheric pressure or compressed to a pressure above atmospheric, may be introduced to the liquid through an injection port or induction port (e.g., Venturi tube) at 14 disposed between the discharge of the transfer pump 12 and an inlet to a first positive displacement pump 18. It will be appreciated that a Venturi device may be used where the gas 16 is at atmospheric pressure or any other pressure below the pressure at the inlet of the first positive displacement pump 18. At this point, all or part of the mixture is generated. The mixture may be conducted to the inlet of the first positive displacement pump 18. Discharge of the mixture from the first positive displacement pump 18 may be conducted to the inlet of a second positive displacement pump 20. The discharge from the second positive displacement pump 20 may be directed into the wellbore 22 as previously explained. In the case that only part of the desired gas amount in the mixture is introduced between the transfer pump 12 and first positive displacement pump 18, the mixture may be conveyed to the inlet of at least one series connected, intermediate positive displacement pump (not shown) with additional gas being introduced into the mixture by an injection or induction port located between the discharge of the first positive displacement pump 18 and the intermediate positive displacement pump. In such cases, the final mixture is ultimately conveyed into the second positive displacement pump 20 (which may be the final positive displacement pump in the series) at an intake sufficient pressure to prevent cavitation or loss of prime. Further intermediate positive displacement pumps may be similarly connected in series between the outlet of the first positive displacement pump 18 and the inlet of the second positive displacement pump 20 to obtain larger gas fractions in the mixture and/or higher discharge pressure to the inlet of the second positive displacement pump.

(6) Positive displacement pumps have been shown to be efficient for moving liquid-gas mixtures because the nature of a positive displacement pump prevents fluid slippage, prevents liquid-gas separation, provides consistent positive discharge pressure, and isolates the intake and discharge line pressures from one another across the pump. There are multiple types of positive displacement pump that may be used in methods according to the present disclosure, including but not limited to piston pumps, plunger pumps, diaphragm pumps, gear pumps, lobe pumps, progressive cavity screw pumps, rotary vane pumps, and cam pumps. It has been determined through testing on gas-liquid mixtures that lobe pumps and progressive cavity screw pumps appear to be most efficient and scalable for use in pumping such mixtures.

(7) Introducing low-pressure gas into the liquid while the liquid is flowing through a pipe between two pumps (e.g., the transfer pump 12 and the first positive displacement pump 18) prevents the gas from escaping to atmosphere while being homogenized with the liquid within the pipe, within an in-line mixer, and/or shear mixing by the subsequent pump. Additionally, each positive displacement pump in the series increases the line pressure incrementally and further compresses the gas bubbles within the mixture, thereby causing the fluid system to pump more in the manner of a single-phase (liquid only) fluid. With increasing pressure, the degree of gas compression (size of the gas bubbles) within a mixture follows an exponential decline curve. The size of the gas bubbles gets significantly smaller rapidly when the mixture is initially compressed from ambient pressure, but the smaller the gas bubbles become, the more they resist further compression. The foregoing is illustrated graphically for various density mixtures and pressures in FIG. 2. Tests on various gas-liquid mixtures indicated, for example, that a 4.8 lb/gallon liquid-gas mixture that is 57% by weight fresh water with chemical additives and 43% by weight atmospheric air will compress (reduce in volume) 31% from its uncompressed volume at 50 psi but will compress only 35% by volume from its uncompressed volume at 100 psi. In contrast, a mixture with less gas (6.5% by weight) such as the 7.8 lb/gallon mixture shown in the graph in FIG. 2 only compresses 3.5% by volume between 1 psi and 100 psi. Thus, by in-pipe mixing the liquid and gas and “pre-compressing” liquid-gas mixtures that are greater than 20% by weight gas to a sufficient line pressure as they are conveyed to the final pump in the series (e.g., the second positive displacement pump 20 in FIG. 1) results in the final pump in the series being able to convey the final liquid-gas mixture into a wellbore at high pressure substantially without pump slippage or cavitation at the intake of the final pump or any other pump in the series. The necessary degree of pre-compression of the mixture, and therefore the necessary discharge line pressure of the first positive displacement pump 18, or otherwise second to the last positive displacement pump in the series where intermediate pumps are used, is inversely related to final fluid density (required pre-compression increases as the fluid density decreases). To calculate the minimum intake pressure (suction head) required at the inlet of the last positive displacement pump in the series (e.g., the second positive displacement pump 20), the pump manufacturer's minimum recommended intake pressure should be divided by the fraction by weight of the mixture that is liquid, and the resultant value is the minimum intake pressure necessary to prevent cavitation or loss of prime. Line pressures greater than the minimum as calculated by the method described herein are not detrimental so long as the line pressure is less than the manufacturer's maximum recommended intake pressure, which is typically the point at which the pump may be mechanically damaged. In one example, if the manufacturer's recommended minimum intake pressure to the first positive displacement pump 18 is 40 psi and the mixture is comprised of 57% liquid and 43% gas, then the minimum intake pressure necessary to pump the mixture is 70 psi (40 psi/0.57). Using the test mixtures in FIG. 2 for reference, the 4.8 lb/gal mixture would be compressed to 67% of its ambient pressure volume at 70 psi thereby enabling it to be pumped by the second positive displacement pump 20 as the final pump in the series.

(8) If the pressure drop between the first positive displacement pump 18 and the second positive displacement pump 20 resulting from pressure losses in the surface equipment there between such pipe length, manifolds, valves, tees, elbows, additional incremental gas introduction ports, or combinations thereof is such that the intake pressure of the second positive displacement 20 pump is below the manufacturer's recommended minimum intake pressure divided by the fractional gas content of the mixture, one or more sequential, intermediate positive displacement pumps can be inserted there between to boost the intake pressure to the sufficient pressure to prevent cavitation of the final pump in the series, e.g., the second positive displacement pump 20.

(9) An efficient method of introducing in gas into the mixture into the fluid system is by a Venturi tube or plurality of Venturi tubes between two or more of the pumps in the series; although, tests have also been successfully conducted by using positive pressure (compressed gas) and exceeding the flowing line pressure (between two of the positive displacement pumps) by 0-50 psi, preferably 0-10 psi, to introduce the gas at low working pressures either directly into the flow pipe or though the induction port of a Venturi tube (Venturi-assisted compressed gas injection). Thus, the gas phase of the mixture can be successfully introduced either by induction (e.g. Venturi tube), by injection (compressed gas), or by combination of induction and compression.

(10) In uses of methods according to the present disclosure, other chemical additives may be mixed into the liquid fraction of the mixture to convey desired rheological and lubricating properties to the final mixture. These chemical additives may be premixed with the liquid prior to gas introduction, e.g., at 11 in FIG. 1, although successful injecting has been tested wherein the chemical additives are introduced into the flow line upstream of the first gas introduction port (i.e., at 14 in FIG. 1) as well. The chemical additives in the liquid fraction will typically consist of some combination of the following: Friction reducers such as polyacrylamide, partially-hydrolyzed polyacrylamide, polyethylene oxide, AMPS, acrylamide-acrylic acid co-polymers, and others known to those skilled in the art; Gelling agents (viscosifiers) such as xanthan gum, guar gum, wellan gum, alginates, and others known to those skilled in the art; Surfactants; Lubricants; Biocides; Gel Breakers; Oxygen Scavengers; H.sub.2S Scavengers; Dispersants; and Defoamers; specific chemical compositions and combinations of which are well known in the industry and available in the public domain.

(11) The depiction of a pumping system as shown in FIG. 1 is just one illustrative embodiment of systems that may be used in accordance with the present disclosure, and derivatives of the described system, with additional gas injection/induction ports, positive displacement pumps in the series, control valves, by-pass flow lines, pressure relief valves, flow manifolds, automated controls, flow meters, sample ports, in-line sensors, in-line mixers, and the incorporation of other standard equipment necessary to complete a specific operation or procedure are contemplated to be used and are within the scope of the present disclosure.

(12) In one example embodiment of a method according to the present disclosure, 750 pounds (lbs) of xanthan gum powder is mixed and hydrated in 500 barrel (bbl) of fresh water in the tank or reservoir 10. A chemical injection pump (not shown) is used to pump additive 11, in the present embodiment 0.15 gallons/bbl of a non-ionic surfactant. Injection takes place as shown in FIG. 1, whereupon the liquid is moved into a flow line on the suction side of the transfer displacement pump 12, which in this example embodiment is a tri-lobe positive displacement pump. The liquid having additives mixed therein is discharged at 3 bbl/minute at 80 psi by the transfer pump 12 through a manifold of Venturi tubes, i.e., at 14 in FIG. 1, where at 16, 2.7 standard cubic feet per minute (scf/min) of air is induced into the liquid, resulting a liquid-gas mixture (at 1 atmosphere) having a density of 5 pounds per gallon (ppg). The first positive displacement pump 18, which in this example embodiment may be an axial progressive cavity (screw) pump, is connected at its inlet to the outlet of the manifold 14 receives the liquid-gas mixture at 40 psi and discharges the mixture at 80 psi into the suction side of the second positive displacement pump 20. In this embodiment, the second positive displacement pump 20 may be a quintaplex piston pump that will increase the fluid pressure sufficiently to circulate through the wellbore 22 at 3 bbl/min. The fluid that is returned to surface is reconditioned for reuse in the procedure using standard solids control equipment like shaker screens, centrifuge, and settling tanks. This process is continued throughout an operation, for example, of running production tubing into the wellbore 22, circulating the liquid-gas mixture up the annulus 30 (space between pipe 23 in the wellbore 22 and the wellbore wall 25), and cleaning debris out of wellbore 22.

(13) According to the present disclosure, the creation of a liquid-gas mixture using one or more positive displacements connected in series to the inlet side of the final pump (e.g., the second positive displacement pump 20 in FIG. 1) will expand the utility and efficiency of foams, micro-foams, and colloidal gas aphrons in drilling, completions, work-overs, and underground boring operations. It is within the scope of the present disclosure to provide additional positive displacement pumps in series beyond the second positive displacement pump 20 in the event higher pressure is required to intervene in a subsurface well or bore hole.

(14) In light of the principles and example embodiments described and illustrated herein, it will be recognized that the example embodiments can be modified in arrangement and detail without departing from such principles. The foregoing discussion has focused on specific embodiments, but other configurations are also contemplated. In particular, even though expressions such as in “an embodiment,” or the like are used herein, these phrases are meant to generally reference embodiment possibilities, and are not intended to limit the disclosure to particular embodiment configurations. As used herein, these terms may reference the same or different embodiments that are combinable into other embodiments. As a rule, any embodiment referenced herein is freely combinable with any one or more of the other embodiments referenced herein, and any number of features of different embodiments are combinable with one another, unless indicated otherwise. Although only a few examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible within the scope of the described examples. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.