DEVICE AND METHOD FOR ENHACNING WELL PERFORATING
A perforation enhancement cap for a shaped charge contains a shell and a pack of a solid propellant disposed inside the shell. The shell has a tubular straight section and a rounded cap. The rounded cap has a hole. The propellant pack has a through hole. The straight section, the rounded cap, the hole in the rounded cap, as well as the through hole are disposed about a common longitudinal axis. The through hole has a conical frustum section with its larger base facing the inside of the enhancement cap. The enhancement cap is adapted to receive the shaped charge to-form an enhanced perforation charge assembly for perforation and fracturing the formation.
This application claims the benefit of priority under 35 U.S.C. § 119 to U.S. Provisional Application No. 62/574,118, filed on Oct. 18, 2017, the entire contents of which are hereby incorporated by reference.
FIELD OF TECHNOLOGYThis disclosure relates generally to oil & gas field services, particularly to devices and methods for enhancing well perforation.
BACKGROUNDPerforation is frequently used in oil or gas well completion nowadays. In this context, a borehole is drilled down past the formation desired for oil or gas production (i.e., the pay zone). Casing is installed between the borehole and the formation to separate them from each other. A perforating gun is lowed into the borehole to a desired depth and pay zone. The perforating gun is a tubular device that carries many shaped charges. A shaped charge has a metal case, explosives inside charge cavity, and conical liner. The explosive in the shaped charge is then detonated, the charge produces a jet of metal particles penetrating the casing, cement, and into the surrounding formation. These jets thereby punch many holes on the casing wall and many perforation tunnels in the formation. The formation around the perforation tunnels is crushed and compacted as a result, forming a crush zone in the formation. The permeability of the crush zone may be much less than the initial undamaged formation impeding the flow into from the formation into the wellbore.
U.S. Pat. No. 9,835,014 discloses a perforation assembly having a shaped charge and a case having a fracture explosive which is attached to the open-face of the shaped charge. The fracture explosive case and the shaped charge is coaxially disposed to a common longitudinal axis. The fracture explosive enters the perforation tunnel following the perforation jet and produces ample energy that eliminates the crush zone and creates micro-fractures and induced fractures in the formation around the perforation tunnel. Fractures increases the formation permeability, which results in oil and gas well production enhancement. However, if the design of the assembly with the fracture explosive is improper, the fracture explosive may interfere with the perforating jet so as to reduce the effectiveness of perforation, even causing the failure of perforation. Accordingly, there is a need for a perforation charge assembly that eliminates or reduces the crush zone, creates fractures and increases the permeability after perforation.
SUMMARYIn view of the aforementioned needs, this disclosure provides a perforation enhancement cap, which is designed to be amounted on the open-face of the shaped charge, contains a shell and a pack of a solid propellant disposed inside the shell. The shell has a tubular straight section and a rounded cap. The rounded cap has a hole. The propellant pack has a through hole. The straight section, the rounded cap, the hole in the rounded cap, as well as the through hole are disposed about a common longitudinal axis. The through hole has a conical frustum section with its larger base facing the inside of the enhancement cap. The enhancement cap is adapted to receive the shaped charge to form an enhanced perforation charge assembly.
In some embodiments, the through hole in the propellant pack has a conical frustum section connected with an optional straight section. The opening angle of the conical frustum is in the range of 90° to 150°, for example, 90° to 120° or 120° to 150°.
In other embodiments, the diameter of the straight section equals the diameter of the hole in the rounded cap, and is in the range of 10-40 mm. The length of the straight section is in the range of 0-40 mm.
In still other embodiments, the rounded cap is a spherical cap having an inner diameter of 14-80 mm and a height of 10-40 mm. The tubular straight section has a height in the range of 8-30 mm, an inner diameter in the range of 28-58 mm, and an outer diameter of 30-60 mm.
In further embodiments, the propellant pack has a weight in the range of 6-50 grams, up to 100 grams. Such an enhancement cap can be mounted to the open-face of a shaped charge to form a perforation charge assembly. The corresponding shaped charge has an explosive pack having a weight of 6-80 grams. The perforation charge assembly is installed in a perforation gun.
The propellant contains 30-70 wt % of ammonium perchlorate, 10-30 wt % aluminum powder, 10-15 wt % additive, and 3-5 wt % dioctyl sebacate. The additive contains hydroxyl-terminated polybutadiene (HTPB), for example, it is a mixture of HTPB, N, N′-diphenyl-p-phenylenediamine, and toluene di-isocyanate (TDI) at a weight ratio of (2.85-7):(0.05-0.2):(3-7.8).
This disclosure also provides an enhanced perforation charge assembly for formation perforation, which has a shaped charge and the enhancement cap. The enhanced perforation charge assembly is installed in a perforating gun and lowered into a wellbore. Upon the detonation of the enhanced perforation charge assembly, the perforation jet creates perforation tunnel and carries the propellant into the tunnel. The propellant ignites in the tunnel and creates fractures in the formation. The outer diameter of the perforating gun is 2″-3.5″, 3.5″-5″, or can be above 5″.
Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout the several views. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the present description. Terms used herein are for descriptive purposes only and are not intended to limit the scope of the disclosure. The terms “comprises” and/or “comprising” are used to specify the presence of stated elements, steps, operations, and/or components, but do not preclude the presence or addition of one or more other elements, steps, operations, and/or components. The terms “first,” “second,” and the like may be used to describe various elements, but do not limit the elements. Such terms are only used to distinguish one element from another. These and/or other aspects become apparent and are more readily appreciated by those of ordinary skill in the art from the following description of embodiments of the present disclosure, taken in conjunction with the accompanying drawings. The figures depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
The propellant has a composition of 30-70 wt % of ammonium perchlorate (e.g., 30-40 wt %, 30-50 wt %, or 50-70 wt %), 10-30 wt % aluminum powder (e.g., 10-15 wt %), 10-15 wt % additive, 3-5 wt % dioctyl sebacate, e.g., 1-4 wt %. The additive is hydroxyl-terminated polybutadiene (HTPB). The additive can also be a mixture of HTPB, N, N′-diphenyl-p-phenylenediamine, and toluene di-isocyanate (TDI) at a weight ratio of (2.85-7):(0.05-0.2):(3-7.8).
In the first embodiment of the enhancement cap, the propellant pack weighs about 6-20 grams of the propellant. The straight section of the shell 11 is a straight tube having a height (H) in the range of 10-20 mm, e.g., 10-18 mm or 12-16 mm. The inner diameter of the straight tube (B) is in the range of 25-41 mm (e.g. 28-38 mm or 30-38 mm) while its outer diameter (A) is 30-46 mm (e.g., 32-44 mm or 36-42 mm). In this embodiment, the thickness of the wall of the straight tube is 1 mm. The spherical cap has a round hole in the top of a diameter of 10-18 mm. The radius of the spherical cap (J) is 34-49 mm, e.g., 40-48 mm.
The enhancement cap of the first embodiment, the base radius of the through hole D1 (i.e., the larger base of the conical frustum) of the propellant pack is in the range of 16-35 mm (e.g., 18-30 mm or 20-30 mm) and the diameter of the straight stem D2 is from 10-18 mm (e.g., 12-16 mm), coincide with the hole in the spherical cap. The height of the stem section of the propellant pack is in the range of 1-20 mm, e.g., 1-10 mm or 10-18 mm. The opening angle R1 of the conical frustum in the propellant pack is from 80°-150°, for example, 85°-140°, 100°-130°, 110°-120°. This embodiment of enhancement cap is particularly suitable for a perforating gun having an outer diameter of 2″-3.5″.
In the second embodiment of the enhancement cap, the propellant pack weighs about 15-50 grams of the propellant. The straight section of the shell 11 has a height (H) in the range of 10-30 mm, e.g., 12-28 mm or 18-26 mm. The inner diameter of the straight tube (B) is in the range of 36-48 mm (e.g. 36-46 mm or 40-44 mm) while its outer diameter (A) is 42-58 mm (e.g., 45-55 mm or 50-55 mm). In this embodiment, the thickness of the wall of the straight tube is 1 mm. The spherical cap has a round hole in the top, which has a diameter of 18-30 mm. The radius of the spherical cap (J) is 49-79 mm, e.g., 50-65 mm or 65-75 mm.
Further, the base radius of the through hole D1 (i.e., the diameter of the larger base of the conical frustum) of the propellant pack is in the range of 20-45 mm (e.g., 20-40 mm or 25-35 mm) and the diameter of the straight stem D2 is from 18-30 mm (e.g., 20-28 mm). The height of the stem section of the propellant pack is in the range of 10-40 mm, e.g., 15-35 mm or 18-35 mm. The opening angle R1 of the conical frustum in the propellant pack is from 90°-150°, for example, 90°-140°, 100°-130°, or 110°-120°. This embodiment of enhancement cap is particularly suitable for a perforating gun having an outer diameter of 3.5″-5″.
The enhancement cap 10 can be installed on a shaped charge 20 as shown in
Without being bound by the theory, it is believed that the energy and heat released by the explosive material 23 disintegrates the propellant pack 10. The propellant travels with the jet through the casing into the formation tunnel, where the propellant releases more energy. With the additional boost of energy from the propellant, the metal jet penetrates deeper into the formation. Also, more fractures are created in the compact zone, increasing permeability. Nevertheless, it is noticed that if the enhancement cap is not properly design, the propellant may not ignite at the proper time or proper location, reducing the effectiveness of the enhancement cap. In the extreme, the propellant may explode in the perforating gun, causing the failure of perforation.
In this regard, various designs of the enhancement cap have been tested.
One aspect of this test is to simulate the pressure profile in the perforation tunnel in the formation. For example, if there is only one pressure peak at the positions of sensors 308 and 309, it would mean that the propellant may have ignited outside the perforation tunnel. If instead there are two pressure spikes, it would indicate that the propellant is ignited inside the perforation tunnel in the formation for the first pressure spike is likely caused by the initial metal jet and the second pressure spike is caused by the ignition of the propellant in the perforation tunnel.
EXAMPLE 1
In comparison, the enhancement cap with the propellant pack B was also tested, the results are shown in
As shown in
The performance of enhancement caps A and B were tested by shooting at steel bars. In these experiments, caps A and B were respectively combined with the same type of shaped charge. The enhanced perforation charge assembly was placed on top of a steel bar and detonated, creating a perforation hole in the steel bar.
Table 3 compares the results from the shaped charge with or without the enhancement cap A.
Table 4 compares the results from the shaped charge with or without the enhancement cap B.
The shaped charge without any enhancement cap created perforation tunnels about 169 mm long on average and openings about 11 mm in diameter on average. The shaped charge equipped with the enhancement cap A created perforation tunnels having an average length of 171 mm and an average opening diameter of 12 mm. In comparison, the shaped charge equipped with the enhancement cap B created an average penetration length of 137 mm and an average opening diameter of 11 mm.
It is believed that the perforation tunnel in steel bar was mainly created by the first pressure peak because the second pressure wave does not have sufficient energy to lengthen or enlarge the tunnel in steel. Therefore, the results from the shape charge with cap A is only slightly better than that of the shaped charge alone. However, the penetration by the shaped charge with cap B is about 20% less than by the shaped charge only while the size of the opening in the steel bar was practically the same. The result suggests that the enhancement cap B may have hindered the metal jet, possibly due to a premature detonation that in fact reduced the peak pressure of the metal jet.
These experiments again confirmed that the perforation performance is heavily dependent upon the shape of the propellant cap.
EXAMPLE 3The enhancement cap described in this disclosure has been used on a total of 240,000 charges in over 2,000 vertical oil wells by China Yanchang Petroleum. There was no explosion accident or other safety issues. The average yield of crude oil for those wells was increased by 28.04% by using the enhancement cap.
Total oil output from test wells using the enhancement cap was 4364.16 T while those did not employ enhancement wells have a total output of 1318.51 T for the test period.
It is to be understood that the exemplary embodiments described herein are that for presently preferred embodiments and are not limiting. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments.
Claims
1. A perforation enhancement cap for a shaped charge, comprising:
- a shell and a pack of a solid propellant,
- wherein the shell comprises a tubular straight section with a first end and a second end, and a rounded cap having a hole,
- wherein the rounded cap is connected to the first end of the tubular straight section, the second end of the tubular straight section is adapted to be coupled with a shaped charge,
- wherein the propellant pack resides in a cavity formed by the rounded cap and the tubular straight section, and the propellant pack has a through hole in alignment with the hole in the rounded cap, and
- wherein the tubular straight section, the rounded cap, the hole in the rounded cap, and the through hole are coaxially aligned.
2. The perforation enhancement cap of claim 1, wherein the through hole in the propellant pack has a conical frustum section connected with an optional straight section, wherein an opening angle of the conical frustum is in the range of 90° to 150°.
3. The perforation enhancement cap of claim 2, wherein the opening angle of the conical frustum is in the range of 90° to 120°.
4. The perforation enhancement cap of claim 2, wherein the opening angle of the conical frustum is in the range of 120° to 150°.
5. The perforation enhancement cap of claim 2, wherein the diameter of the optional straight section equals the diameter of the hole in the rounded cap, and is in the range of 10-40 mm.
6. The perforated enhancement cap of claim 2, wherein the through hole is in the propellant pack is in the shape of a conical frustum, wherein the hole facing the rounded cap is the smaller base in the conical frustum.
7. The perforation enhancement cap of claim 1, wherein the rounded cap is a spherical cap having an inner diameter of 14-80 mm and a height of 10-30 mm.
8. The perforation enhancement cap of claim 7, wherein the tubular straight section has a height in the range of 8-30 mm, an inner diameter in the range of 28-58 mm, and an outer diameter of 30-60 mm.
9. The perforation enhancement cap of claim 1, wherein the propellant pack has a weight in the range of 6-50 grams.
10. The perforation enhance cap of claim 2, wherein the propellant pack is in the shape of a conical frustum without a straight section.
11. The perforation enhancement cap of claim 1, wherein the propellant comprises 30-70 wt % of ammonium perchlorate, 10-30 wt % aluminum powder, 10-15 wt % additive, and 3-5 wt % dioctyl sebacate.
12. The perforation enhancement cap of claim 11, wherein the additive comprises hydroxyl-terminated polybutadiene (HTPB).
13. The perforation enhancement cap of claim 12, wherein the additive is a mixture of HTPB, N, N′-diphenyl-p-phenylenediamine, and toluene di-isocyanate (TDI) at a weight ratio of (2.85-7):(0.05-0.2):(3-7.8).
14. An enhanced perforation charge assembly for formation perforation, comprising a shaped charge and the perforation enhancement cap of claim 1 coaxially mounted on a front-face of the shaped charge.
15. The enhanced perforation charge assembly of claim 14, wherein the shaped charge contains an explosive pack having a weight of 6 to 80 grams and the perforation enhancement cap contains a propellant pace having a weight of 6 to 50 grams.
16. A method for formation perforation, comprising:
- lowering a perforating gun into a borehole, wherein the perforating gun comprises the enhanced perforation charge assembly of claim 14; and
- detonating the enhanced shaped charge of claim 14.