METHOD OF CREATING AND FINISHING PERFORATIONS IN A HYDROCARBON WELL

Abstract

A method of creating and finishing perforations in a hydrocarbon well having a well wall that includes causing a high velocity jet of a material to shoot into the well wall, thereby creating a perforation in the well wall. The method further includes introducing a gas blast into the perforation, for a blast time duration, the gas blast creating an increasing pressure at the perforation until a maximum pressure is reached; and allowing the pressure of the gas blast to undergo a period of rapid decline to a level of less than 50% of the maximum pressure.

Claims

1. A method of creating and finishing perforations in a hydrocarbon well having a well wall, the method comprising: shooting a high velocity jet of metal particles into the well wall, thereby creating a perforation in the well wall; pushing a gas blast into the perforation, for a blast time duration, the gas blast creating an increasing pressure at the perforation, until a maximum is reached, the pressure of the gas then undergoing a period of rapid decline to a level of less than 50% of the maximum pressure; wherein the period of rapid decline takes less than one-sixth of the blast time duration, and wherein the time pattern of speed and pressure of the gas blast results in a higher maximum pressure at the perforation than would have happened had the maximum pressure been reached midway through the gas blast, thereby resulting in localized fracturing, emanating from the perforation, which permits a greater flow of hydrocarbons into the perforation and from the perforation into the well.

2. The method of claim 1, wherein the period of rapid decline takes less than one-tenth of the blast time duration.

3. The method of claim 1, wherein the gas blast flows at an increasing speed, as the pressure increases.

4. A method of creating and finishing perforations in a hydrocarbon well having a well wall, the method comprising: operating a perforation assembly to cause a high velocity jet of a material to shoot into the well wall, thereby creating a perforation in the well wall, the perforation assembly further comprising: a tube having a tube wall; a plurality of shaped charges disposed within the tube and adapted to shoot the high velocity jet through the tube wall and into the well wall; a propellant also disposed within the tube, the propellant having a surface area; and a detonating cord operable to ignite the shaped charges and the propellant, wherein the propellant is configured to undergo a combustion until it is substantially consumed by the combustion, and wherein the propellant initially combusts slowly enough that the combustion of the propellant does not interfere with functioning of an at least one of any of the plurality of shaped charges; introducing a gas blast into the perforation for a blast time duration, the gas blast eventually reaching a maximum pressure; and allowing a pressure of the gas blast to undergo a period of rapid decline to a level of less than 50% of the maximum pressure, wherein the period of rapid decline takes less than one-sixth of the blast time duration.

5. The method of claim 4, wherein the propellant further comprises pieces of propellant packed together in a group, the group being interposed between two shaped charges of the plurality of shaped charges.

6. The method of claim 5, wherein an at least one of the pieces of propellant is configured with a set of through-holes, thereby causing the surface area of each respective piece of propellant to increase during the combustion.

7. The method of claim 6, wherein the set of through-holes comprises seven through-holes.

8. The method of claim 4, wherein the propellant combusts over a period of greater than 10 milliseconds and less than 100 milliseconds.

9. The method of claim 4, wherein the assembly comprises an another propellant that does not combust at an increasing rate after being ignited.

10. A method of perforating a well wall, comprising: providing a perforation creating-and-finishing assembly for use in a well having a well wall, and including: a tube having a tube wall; a plurality of shaped charges positioned within the tube; a propellant also positioned within the tube, the propellant having a surface area and being configured so as to combust at an increasing rate until substantially consumed; and a detonator disposed within the tube; lowering the assembly into the well to a predetermined position; and operating the assembly to ignite the detonator, thereby igniting the plurality of shaped charges and the propellant, the plurality of shaped charges shooting a high velocity jet of metal particles through the tube wall and into the well wall, thereby creating a perforation.

11. The method of claim 10, wherein the propellant combusts at an increasing rate until the propellant is substantially consumed.

12. The method of claim 10, wherein the propellant combusts, for a propellant combustion period, at a rate that increases to a maximum and then drops from the maximum to a zero rate of combustion, for a combustion cessation period, when all of the propellant has been consumed, and wherein the combustion cessation period is less than one-tenth of the propellant combustion period.

13. The method of claim 12, the propellant comprises a set of through-holes which increase in diameter as combustion progresses, thereby increasing the rate of combustion.

14. The method of claim 13, wherein the set of through holes comprises seven through-holes.

15. The method of claim 12, wherein the propellant is interposed between an at least two of the plurality of shaped charges.

16. The method of claim 16, wherein the propellant comprises seven pieces of propellant packed in a group, the group being interposed between two shaped charges.

17. The method of claim 11, wherein the assembly further comprises an at least one additional piece of propellant that does not combust at an increasing rate after being ignited.

18. The method of claim 11, wherein the rate of combustion of the propellant also increases with greater pressure, thereby causing the combustion rate to increase at a greater than linear rate as the propellant combusts and gas thereby released creates a higher pressure.

19. A method of creating and finishing perforations in a hydrocarbon well having a well wall, the method comprising: causing a high velocity jet of a material to shoot into the well wall, thereby creating a perforation in the well wall; introducing a gas blast into the perforation, for a blast time duration, the gas blast creating an increasing pressure at the perforation until a maximum pressure is reached; and allowing the pressure of the gas blast to undergo a period of rapid decline to a level of less than 50% of the maximum pressure, wherein the period of rapid decline takes less than one-sixth of the blast time duration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] A full understanding of embodiments disclosed herein is obtained from the detailed description of the disclosure presented herein below, and the accompanying drawings, which are given by way of illustration only and are not intended to be limitative of the present embodiments, and wherein:

[0019] FIG. 1 is a sectional view 5 of a portion of a hydrocarbon well having a perforation creating and finishing device, shown in a side view for ease of description.

[0020] FIG. 2 shows the environment and device of FIG. 1, during detonation of the device.

[0021] FIG. 3 shows the environment and device of FIG. 1, at a further stage of deployment, after a perforation in the well wall has been created.

[0022] FIG. 4 is an expanded sectional detail view of the well wall perforation of FIG. 3, taken along line 4-4 of FIG. 3.

[0023] FIG. 5 shows the environment and device of FIG. 1, at a final stage of deployment, showing the finished perforation.

[0024] FIG. 6 is an expanded sectional detail view of the finished well wall perforation of FIG. 5, taken along line 6-6 of FIG. 5.

[0025] FIG. 7 is an isometric view of a cylindrical carton filled with pieces of propellant.

[0026] FIG. 8 is a graph of combustion rate over time of the propellant in the device of FIGS. 1-3 and 5.

[0027] Exemplary embodiments are illustrated in referenced drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

DETAILED DESCRIPTION

[0028] Referring to FIG. 1, in a preferred method of creating finished perforations in the wall 10 of an oil or gas well, which is made up of steel casing 12, cement 13 and underlying rock 14, a perforating gun 15 is lowered into proximity of a portion of wall 10, to be treated. Perforating gun 15 includes a charge tube 16, which supports a number of shaped charges 18, containers 20 of propellant 38 (FIG. 7) and a detonating cord 22, all encased in a fluid-impermeable sealed steel carrier 24.

[0029] Referring to FIGS. 2 and 3, the detonating cord 22 is ignited, causing the shaped charges 18 to expel particles of metal 26 (FIG. 2shown as an ellipse for ease of presentation) at a high velocity, within ten microseconds. Travelling at approximately 30 mach, the metal particles 26 penetrate through steel carrier 24, creating a carrier perforation 27 (FIG. 3) and into the wall 10, creating a perforation 28 (FIG. 3) through the steel casing 12, and a further perforation 29 (FIG. 3) in the rock 14, thereby facilitating the flow of hydrocarbons into the well.

[0030] The movement of the metal particles 26 into the rock creates a perforation 29, having walls 30, which have been seared and made more dense by rock 14 that has been pushed to the side or pushed toward the back of the perforation 29. Consequently, the perforation does not facilitate the flow of oil as much as might be possible. The containers 20 of propellant 38 combust over a period between 10 and 100 milliseconds, far more slowly than the action of the shaped charges 18.

[0031] In one preferred embodiment, the rate of combustion 56 of the propellant 38 increases with greater pressure, causing the combustion rate to increase at a greater than linear rate 48 as some propellant 38 combusts and the gas thereby released creates a higher pressure; however, at least one additional piece 39 of propellant 38 may not combust 5 at an increasing rate after being ignited. Referring to FIGS. 5, 6, 7 and 8, in a few milliseconds, the combustion has spread over the surface areas of the pieces 39 of propellant 38 (FIG. 7), including the interior surface areas, created by a set of seven through-holes 40 in each piece 39 of propellant 38.

[0032] As the through-holes 40 grow in diameter, due to the combustion, the surface area of each through-hole grows, just as the outer diameter of the piece 39 of propellant 38 is reduced over time. In one preferred embodiment, the pieces 39 of propellant 38 are packed together in groups, with each group including seven pieces 39 of propellant 38, and being interposed between two shaped charges.

[0033] Referring to FIG. 8, as the propellant collectively combusts, the combustion rate 48 of propellant 38 reaches a maximum 50 (FIG. 8), directly before the fuel is exhausted, resulting in a high maximum combustion rate 50, followed by a rapid plunge 58 to zero 60. In one preferred embodiment, the rapid decline 58 takes less than one-sixth of the blast time duration. In another preferred embodiment, the rapid decline 58 takes less than one-tenth of the blast time duration. Not only does the combustion rate increase due to through-holes 40, but also because propellant 38 combusts more rapidly under higher pressure.

[0034] As the combustion progresses, a gas 70 is produced, which increases the pressure inside carrier 24 (and very quickly, outside of carrier 24, as well). This increased pressure also causes propellant 38 to combust more rapidly, leading to the nonlinear combustion rate curve 48. In a preferred embodiment, the period during which the combustion rate plunges from the maximum 50 to zero 60 (the combustion cessation period), takes less than one-tenth of the total time period of combustion 56. For 5 each piece 39 of propellant 38 the combustion cessation period is less than one-thirtieth of the period of combustion 56 (for the same piece 39 of propellant 38).

[0035] The hot gas 70, that is the product of the propellant combustion is pushed rapidly and forcefully out of the tubing perforations 26 with increasing speed that is proportional to the increasing pressure caused by the gas blast, and into well wall perforations 28 and 29, which are still fairly well aligned with carrier perforation 27, as the relatively massive perforating gun 16 accelerates and moves relatively slowly. In one preferred method, the pressure created by gas 70 increases until a maximum is reached before declining rapidly. Both the speed and the pressure of the gas 70 act to break apart the rock 14, and create a star pattern of fissures 72 emanating radially from perforation 28, thereby facilitating the flow of oil and gas into the well.

[0036] The through-holes 40 of propellant 38 result in a higher maximum combustion rate and a corresponding higher pressure at perforation 29, than would be otherwise the case. Surprisingly, because of the through-holes 40, the maximum pressure applied to the perforations 29 is high enough to be effective, even though large portions of steel carrier 24 are taken up by shaped charges 18, and thereby not available for stowage of propellant 38.

[0037] The propellant 38 includes its own oxidizer, and so does not need any external source of oxygen to combust. Further, propellant 38 may be either single-based (nitrocellulose), double-based (nitrocellulose and nitroglycerin), or triple-based (nitrocellulose, nitroglycerin, and nitroguanadine). These propellants may be available from BAE Systems, in Radford, Va.

[0038] While a number of exemplary aspects and embodiments have been discussed above, those possessed of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. For example, one or more pieces of propellant that do not include through-holes could be included and combust at a decreasing rate, or that include a single through-hole and combust at a steady rate, could be included. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and subcombinations as are within their true spirit and scope.