DISSOLVABLE PLUG REMOVAL WITH EROSIVE TOOL

Abstract

Methods of plugging a hydrocarbon well by using degradable plugs are provided. When the plug is no longer needed, a degradation fluid or fluids are pumped downhole under high pressure, typically via jet, such that the degradation fluid provides an erosive force to the degradable plug, thus both speeding its degradation and preventing or minimizing the leaving of solid plug material remnants in the well.

Claims

1) A method of temporarily plugging a hydrocarbon well, comprising: a. providing a section of tubing in a well, said tubing having one or more degradable plug(s) therein, thus providing a plugged section of well; b. performing a downhole activity in said plugged section of well for a period of time; and c. providing one or more degrading fluid(s) downhole to degrade said degradable plug, leaving no solid plug material behind and thereby opening said plugged section of well, wherein said degrading fluid is deployed at a high pressure so as to provide an erosive force to completely remove said plug in 50% of the time required to remove said plug without said high pressure and with just said one or more degrading fluid(s).

2) The method of claim 1, wherein said degradable plug is degradable in less than 48 hours.

3) The method of claim 1, wherein said degradable plug is degradable in less than 24 hours.

4) The method of claim 1, wherein said degradation fluid is applied with a jet.

5) The method of claim 1, wherein said plug is in a side wall of a casing or tubing and said degradation fluid is applied with a jet angled at about 90° to said well.

6) The method of claim 1, said method further comprising providing one or more blocking devices above and below said plugged section before step b), wherein said blocking devices are selected from a plug, a packer, a basket, or combinations thereof.

7) The method of claim 1, wherein said high pressure is at least about 1000 psi and is provided by a jet.

8) The method of claim 1, wherein said high pressure is at least about 1500 psi and is provided by a jet.

9) The method of claim 1, wherein said high pressure is at least about 2000 psi and is provided by a jet.

10) The method of claim 1, wherein said high pressure is at 1500-5000 psi.

11) The method of claim 1, wherein said degradation fluid is selected from an aqueous acid, an aqueous caustic, an aqueous brine, xylene, toluene, chloroform CHCl.sub.3, or other aromatic solvent, dimethylformamide (DMF), dimethylacetamide (DMA), dichloromethane (DCM) CH.sub.2Cl.sub.2, tetrahydrofuran (THF), acetone, hexafluoroisopropanol, or combinations thereof.

12) The method of claim 1, wherein said degradation fluid is combined with an abrasive agent.

13) The method of claim 11, wherein said degradation fluid is combined with an abrasive agent.

14) The method of claim 1, wherein said degradable plug is a threaded plug and wherein said threads are wrapped with a degradable thread tape.

15) The method of claim 14, wherein a first degrading fluid degrades said degradable thread tape and a second degrading fluid degrades said degradable plug.

16) The method of claim 14, wherein a first degrading fluid degrades both said degradable thread tape and said degradable plug.

17) A method of temporarily plugging a hydrocarbon well, comprising: a. providing a section of tubing in a well, said tubing having one or more degradable plug(s) therein, thus providing a plugged section of well; b. performing a downhole activity in said plugged section of well for a period of time; and c. providing one or more degrading fluid(s) downhole to degrade said degradable plug, leaving no solid plug material behind and thereby opening said plugged section of well, wherein said degrading fluid is deployed at a high pressure of 1500 psi so as to provide an erosive force that removes said plug faster than a time required to remove said plug without said high pressure and with just said one or more degrading fluid(s).

18) The method of claim 17, wherein said degradable plug is degradable in less than 24 hours.

19) The method of claim 17, wherein said plug is in a side wall of a casing or tubing and said degradation fluid is applied with a jet angled at about 90° to said well.

20) The method of claim 17, wherein said plug is inline in said well and said degradation fluid is applied with a jet angled at less than +/−10° to said well.

21) The method of claim 17, said method further comprising providing one or more blocking devices above and below said section, wherein said blocking devices are selected from a plug, a packer, a basket, or combinations thereof.

22) The method of claim 17, wherein said degradation fluid is selected from an aqueous acid, an aqueous caustic, an aqueous brine, xylene, toluene, chloroform CHCl.sub.3, or other aromatic solvent, dimethylformamide (DMF), dimethylacetamide (DMA), dichloromethane (DCM) CH.sub.2Cl.sub.2, tetrahydrofuran (THF), acetone, hexafluoroisopropanol, or combinations thereof.

23) The method of claim 17, wherein said degradation fluid is combined with an abrasive agent.

24) The method of claim 17, wherein said degradable plug is a threaded plug and wherein said threads are wrapped with a degradable thread tape.

25) The method of claim 23, wherein a first degrading fluid degrades said degradable thread tape and a second degrading fluid degrades said degradable plug.

26) The method of claim 23, wherein a first degrading fluid degrades both said degradable thread tape and said degradable plug.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] FIG. 1A Prior art acid tunneling tool. FIG. 1B Enlargement of jet mole or nozzle assembly.

[0070] FIG. 2 Prior art jet drill for making 90° laterals. Here the jet is set to about 90°, but it be set at any desired angle by changing out the deflection shoe which functions to bend the jet hose.

[0071] FIG. 3A well with an inline plug. FIG. 3B Plug being removed with jet tool of FIG. 1, leaving behind the open well in FIG. 3C. The small amount of debris shown in FIG. 3C is merely to indicate where the plug was situated, but it is expected that the plug will be fully degraded leaving no solids discernable by the naked eye.

[0072] FIG. 4A well with a sidewall plug. FIG. 4B Plug being removed with tool having 90° jets, leaving behind the open well in FIG. 4C. The tool is similar to that of FIG. 1, but the jet mole is configured to provide a 90° jet rather than an inline jet.

[0073] FIG. 5A well with a sidewall plug. FIG. 5B Plug being removed with the tool of FIG. 2 having a deflection shoe to turn the jet hose to 90° to reach sidewall plug, leaving behind the open well in FIG. 5C.

DETAILED DESCRIPTION

[0074] Developed herein are methods of temporarily plugging a well, systems of temporarily plugged wells, and tools for use in same. Several degradable plugs are commercially available, including e.g., Halliburton Illusion™ frac plug, Vertechs WIZARD MS™ frac plug, Magnum Oil Fastball™ frac ball, Innovex SWAGE™ frac plug, and Baker Hughes SPECTRE™ frac plug, and the like. In addition, several more are described in the patents referenced herein.

[0075] When the degradable plug is no longer needed, it is removed by its degradation fluid which is provide by jet under high pressure directly at the plug, so as to speed its degradation by at least 50%. Thus, not only is plug removal faster, but the probability of solid remnants is also much reduced.

[0076] If desired, the degradable plug may be combined with degradable thread tape, as described in U.S. Ser. No. 11/053,762. Ideally, both the plug and the tape would degrade under the same degradation fluids, but it is also possible to use two fluids sequentially, if needed. If this is done, it may be preferred to dissolve the tape in advance of the plug, thus improving access to the plug by the degradation fluid.

[0077] FIG. 1A shows one exemplary tool 100 that can be repurposed for use herein, or preferably optimized for this new use. Coiled tubing 99 is connected to the left end of the tool 100. Beginning from the left, shown are the motorhead 101 which is a combination tool that consists of a CT connector, back pressure valve and disconnect. Also seen are first 103, second 105 and third 107 knuckle assemblies which allow the tool to bend under high pressure. This is followed by a short spacer 109 and the jetting mole 113.

[0078] The enlargement in FIG. 1B shows the details of the jetting mole 113 in exploded form, wherein again from the left, we see the nozzle inlet sub 117, O-rings 111a, a short filter 118 which may be optional if abrasives are used, a locator disk 121 for holding the jet nozzles 120, and the jet nozzle O-rings 111b, finally covered by the bull nose 122 which protects the jet nozzles from impact. Here shown are 7 small jet nozzles 120 but of course the number and shape of the nozzles may be varied depending on the plugs to be eroded. In addition, the nozzles can be placed at any angle, though herein shown they are inline with the well. In addition, the number and length of the knuckle subassemblies 103, 105, 107 may vary and this will change the angles for which the tool is capable.

[0079] FIG. 2 provides a cross-section of a reservoir and well 200. Tool 203 that allows a 90° jet to be applied to a plug in the sidewall, such as frac plugs and the like. Here we see the well casing 201, the coiled tubing 203 connected to the tool 200. The tool is held in the center of the casing with centralizers 217, and a deflection shoe 215 bends the jet pipe 213 to an angle of 90° or any other desired angle, allowing the jet to drill laterally. The jet mole 219 and nozzle details are omitted herein, but as above, nozzles can vary and are typically optimized for the use. Although this tool is for jet drilling, similar design principles can be used to optimize a tool for plug erosion. Different layers of limestone 205, oil sands 207, shale 209 and near well damage 211 are also shown, but not relevant to the tool 203.

[0080] The tool designs of FIG. 1 and FIG. 2 may be combined, such that the tool contains one or more knuckle subassemblies as well as a deflection shoe, thus allowing the tool use in deviated or deformed wells, yet still provided for a precise angle of deflection at the plug.

[0081] The cross section of well and reservoir 300 in FIG. 3 shows the method of the invention in a simplified schematic form, wherein tools such as those in FIG. 1 are repurposed for use in the method. Shown in FIG. 3A is well with casing 301 and an inline plug 302. FIG. 3B shows the tool 100 deployed by coiled tubing 99 or otherwise to erode the plug 302 by a jetting degradation fluid at high pressure towards the plug 302, and FIG. 3C shows the plug is completely removed (a small amount of debris is shown to indicate where the plug was, but typically there will be no remnants).

[0082] The cross section of well and reservoir 400 in FIG. 4 shows another embodiment of the invention in a simplified schematic form. A side jetting tool 405 is repurposed for use in the method. Shown in FIG. 4A is well with casing 401 and a sidewall plug 402. FIG. 4B shows the tool 405 set to erode the plug 402 by a jetting degradation fluid at high pressure towards it, and FIG. 4C shows the plug is completely removed.

[0083] The cross section of well and reservoir 500 in FIG. 5A-C is similar, showing well 501 with lateral well 503 having plug 505. FIG. 5B shows the repurposed tool 213 of FIG. 2 with jetting mole or head 219 reaching down the lateral well to erode plug 505. In FIG. 5C the plug has been removed.

Proof of Concept Testing

[0084] The objective of this test was to demonstrate proof of concept, using a commercially available tool (StimTunnel tool by Baker Hughes—developed for use in jetting away limestone) would be able to erode dissolvable plugs as a method to clean out wells post-stimulation.

[0085] The testing consisted of 4 different styles of degradable ball plugs from 4 separate vendors. These plugs were the Innovex's dissolvable frac ball, Yellow Jacket M1 Frac plug, Steel Haus's ReacXion complete plug, and Kureha Degradable Plug (KDP).

[0086] All plugs are dissolvable in aqueous solution and were set in 7′ joints of 5½″, 23 ppf casing. The plugs were not exposed to elevated temperatures, fluids, or differential pressure. Each casing joint was installed in the test fixture and the StimTunnel BHA was placed in the casing on top of the plug. The 2.75″ OD version of the StimTunnel was used for the Innovex frac balls and the 2.50″ OD version was used for the rest.

[0087] TEST 1 GENERAL: The first round of tests was performed on all 4 plug types and consisted of simply jetting with fresh water with the StimTunnel tool. The tool was run pressed onto the face of the plug with a nominal amount of force while the balls were on seat. At periodic intervals pumping was stopped and the plug face was inspected. During the last 45-60 min the ball (or what was left of it) was removed and the tool pumped on the plug body only.

[0088] TEST 1A: Innovex This test consisted of 192 min of pumping, 161 min of which was done with ball on seat and 31 min was done after the ball was removed. The ball was difficult to keep on seat, and so the plug leaked for the entire duration of the test. In this test the casing between shutdowns was also rotated. The pump rate varied anywhere between 95 gpm to 105 gpm and pressures from 4400-4500 psi. Pumping and inspection occurred 5 times in this test.

[0089] Moderate erosion was seen on the plug and ball while the ball was partially in place. A much higher amount of erosion was seen once the ball was removed. The design of the top of the plug caused the StimTunnel tool to center on the plug. The jets appeared to be able to erode the length of the plug, but due to the smaller plug ID and the 0° angle of the jets, the tool would not have been able to pass through the cored out plug. If acid sweeps were used, it would be likely the plug would have lost integrity and started to break apart with a combination of erosion and dissolution.

[0090] TEST 1B: Yellow Jacket The test consisted of 163 min of pumping, 118 min of which was done with the ball on seat and 45 min with the ball removed. The ball was epoxied on to the seat by the vendor and thus held fluid for 73 min. The pump rate varied anywhere between 95 gpm to 105 gpm and pressures from 4400-4500 psi. Pumping and inspection occurred 3 times in this test.

[0091] Slight erosion was seen on the plug and ball while the ball was in place. Moderate erosion was seen once the ball was removed. Due to the geometry of this plug, the StimTunnel remained on the low side of the casing and did not self-center on the plug. One of the seven jets was able to work on the plug body, ˜2″ below the ball seat. It appeared that fluid breakthrough occurred when that jet cut the plug body and found a path into the setting mechanism. If acid sweeps were used, it would be likely the lock ring would have been attacked from below, allowing the plug to collapse.

[0092] Test 1C: Steel Haus. The test consisted of 160 min of pumping, 121 min of which was done with ball on seat and 39 min was pumped with the ball removed. The ball was epoxied on to the seat but only held fluid for 10 min. The pump rate varied anywhere between 95 gpm to 105 gpm and pressures from 4400-4500 psi. Pumping and inspection occurred 3 times in this test.

[0093] Moderate erosion was seen on the plug and ball while the ball was in place. Very little erosion was seen after the ball was removed: the 2.50″ OD nozzle centered into the 2.50″ ball seat, causing almost all the rate to be directed through the center nozzle leaving little erosive force on the other 6 nozzles. However, while the ball was in place, the BHA was off-center and worked on the sealing element of the plug. The top of the element was ˜1″ below the ball seat and the jet appeared to erode ˜0.5″ of element and cut through the retaining ring. It appeared that fluid breakthrough occurred when that jet cut the plug body and found a path into the setting mechanism. If acid sweeps were used, it would likely have attacked the element and then the slips, causing the plug to unseat.

[0094] Test 1D— Kureha The test consisted of 157 min of pumping, 78 min of which was done with ball on seat and 79 min with the ball removed. The ball was left loose on the seat and held fluid for 2 min. The pump rate varied anywhere between 95 gpm to 105 gpm and pressures from 4400-4500 psi. Pumping and inspection occurred 2 times in this test.

[0095] Moderate erosion was seen on the plug and slight erosion on the ball while the ball was in place. Significant erosion was seen after the ball was removed. At ˜15″ this was the longest of all the plugs tested; while the erosion was probably the deepest of all the tests the nozzle would have to penetrate greater than ˜7″ to begin working on the sealing elements. Most of this plug is made of plastic that is not affected by acid or chlorides but degrades mostly by temperature.

[0096] The second round of tests were performed on 3 of the 4 plugs (the long Kureha plug was excluded from this test). In this test, silica flour (200 mesh) was mixed into a 20 # gel (160 lbs silica per 20 bbl tub) at 0.2 ppg. The StimTunnel tool was then placed ˜1 inch above the plug face with the ball on seat. Twenty-one barrels of the abrasive solution was then pumped over an 8-9 min period.

[0097] Test 2A: Innovex The test consisted of 8 min of pumping a solids-laden fluid consisting of a 0.2 ppg silica flour in a 20 # gel. The ball did not stay on seat, and so the plug leaked for the entire duration of the test. The pump rate varied anywhere between 95 gpm to 105 gpm and pressures from 4400-4500 psi.

[0098] Significant erosion was seen on the plug and the ball. However, the same issue in Test 2 was noted as observed in Test 1 with the nozzle wanting to bore a hole through the plug without attacking the slips or sealing element, indicating the value of nozzle optimization for the plug at issue.

[0099] Test 2B: Yellow Jacket The test consisted of 16 min of pumping a solids-laden fluid consisting of a 0.2 ppg silica flour in a 20 # gel. This test was pumped in 2 stages of 21 bbl each. The ball was epoxied on seat, and initially held fluid. Approximately 5 min into the pumping the plug began leaking. The pump rate varied anywhere between 95 gpm to 105 gpm and pressures from 4400-4500 psi.

[0100] Significant erosion was seen on the plug and the ball. However, the same issue was noted with the nozzle wanting to bore a hole through the plug without attacking the slips or sealing element.

[0101] Test 2C: Steel Haus The test consisted of 8 min of pumping, a solids-laden fluid consisting of a 0.2 ppg silica flour in a 20 # gel. The ball was epoxied in place and initially held fluid. The plug began leaking 2 minutes into the test. The pump rate varied anywhere between 95 gpm to 105 gpm and pressures from 4400-4500 psi.

[0102] Significant erosion was seen on the plug and the ball. However, the same issue was noted with the nozzle wanting to bore a hole through the plug without attacking the slips or sealing element.

[0103] Overall, the testing showed that the plugs are sensitive to erosion, and are predicted to speed degradation significantly, although head-to-head testing still needs to be done. The results also indicate that further testing is warranted with optimized nozzles, plus and minus acid, and plugs that have been exposed to typical downhole corrosive conditions.

[0104] We observed that the nozzles that were directly in contact with the plug/ball did the least amount of work. It is hypothesized that the back pressure formed (as there was no escape path for the jetting fluid) caused the flow rate to be diminished at that nozzle and thus be less effective. The addition of water courses on the jetting tool could correct this issue.

[0105] For locations where casing deformation is not an issue, a larger OD nozzle should be effective, e.g., a drift nozzle (a larger OD nozzle, closer to the ID of the casing) can be utilized. This will allow the erosive jets to work along the outside of the plug, attacking the slips and sealing element. The pressure drop across the nozzle may need to be adjusted in certain wells due to high well head pressures.

[0106] In locations where deformation creates restrictions, the nozzle pattern needs to be altered due to use of an undersized BHA. The existing 2.50″ OD StimTunnel tool may not cut a large enough hole to allow drift of the tool itself.

[0107] While the ability to pump acid will probably be the biggest positive for implementing this invention downhole, changes to the geometry of the tool are also expected to be beneficial. Providing a variety of jet moles—each optimized to accommodate a different plug style—allows the same BHA body to be used to erode many different plugs, merely by switching out the jet mole.

[0108] Proposed changes for further testing may include:

[0109] 1) The StimTunnel diameter and overall configuration needs to account for specific plug geometry. For instance, an observation from Test 1C is that the ball seat diameter and the BHA diameter need to be different.

[0110] 2) Changing the face geometry of the nozzle so that the BHA can “move” the ball off seat could be beneficial as the ball appeared to be the biggest hinderance to erosional force. By moving the ball off center, it should allow some erosional action to begin working on the plug body.

[0111] 3) Giving the nozzles some directional paths could allow for more destructive erosion by allowing it to cut across the plug rather than just through the center of it.

[0112] 4) Changing the nozzle exit angle from 0° to 10-20° could allow making ‘cuts’ rather than boring holes through the plug.

[0113] 5) Targeted acid sweeps throughout the erosional process could also be very beneficial.

[0114] 6) Silica flour sweeps greatly increased the rate of erosion, but did not necessarily change tunnel geometry. The StimTunnel nozzles showed some degradation from erosion from the silica flour, but that was not unexpected since the tool was not designed to accommodate abrasives. A toughened tool will be able to accommodate abrasives.

[0115] Speculating about actual well bore conditions, we believe that a partially degraded plug should be considerably weaker, particularly if it has aged significantly in a corrosive environment. Thus, when material is being eroded away the loss of integrity may cause the plug to fall in on itself allowing the jetting action to ‘push’ the debris down hole. This would also continue to increase the surface area and speed along the dissolution process. It is probably not sufficient to simply push a weakened plug body deeper into the hole. The BHA likely needs to be able to cut the weakened body into very small pieces so they can fully degrade and allow the BHA to contact the next plug.

[0116] In the case of a plug that has a lock ring (e.g., Yellow Jacket and Steel Haus), if the erosion attacks the lock ring, the plug should fall apart relatively easily. If the jets can attack the weakened sealing element (Steel Haus), this should accelerate the plug's failure. Thus, this is one of the proposed optimization targets for jet mole optimization.

[0117] The longer the plug, the more difficult erosion will be because the erosion does not happen uniformly across the plug body. The erosion tunnels must attack parts of the plug that will cause plug failure (e.g. lock ring, sealing element, etc.). If these elements are far from the top of the plug, it will take much longer to work through.

[0118] Using abrasives accelerated the erosion process significantly. However, as the plugs will most likely be in a semi-dissolved state when encountered downhole the abrasives may not be very helpful unless the ball is still mostly intact. On the plugs with larger balls, abrasives could be useful in quickly eroding past the ball to begin working on the plug body. With semi-dissolved plugs, application of acid along with erosive force will probably be most effective, but further testing will need to be done to confirm our predictions.

[0119] Our proof of concept testing thus showed a benefit for additional testing to optimize certain features:

[0120] 1) Optimized BHA. We plan to test jets having larger OD, different nozzle patterns, different nozzle angles, and the like. Preliminary design considerations can be tested computationally, using, for example, Computational Fluid Dynamics (CFD) software, and optimized models tested physically, in a manner similar to the tests described herein.

[0121] 2) Realistic Test Conditions. We plan to repeat tests by first heating up the plugs for 24-48 hours to test more realistic degradation conditions. In addition, we will have no jet comparisons to prove the increased speed of degradation.

[0122] 3) Repeat tests with acidic solutions.

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