AU2016231635B2 - A method of improving the wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting - Google Patents
A method of improving the wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting Download PDFInfo
- Publication number
- AU2016231635B2 AU2016231635B2 AU2016231635A AU2016231635A AU2016231635B2 AU 2016231635 B2 AU2016231635 B2 AU 2016231635B2 AU 2016231635 A AU2016231635 A AU 2016231635A AU 2016231635 A AU2016231635 A AU 2016231635A AU 2016231635 B2 AU2016231635 B2 AU 2016231635B2
- Authority
- AU
- Australia
- Prior art keywords
- presplitting
- water injection
- high pressure
- pressure water
- borehole
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Ceased
Links
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/20—Displacing by water
Abstract
The present invention provides a method of improving the wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting, which comprises the following steps: the presplitting boreholes with a depth equal to that of the high pressure water injection boreholes are bored with drill rigs at both sides of every existing high pressure water injection borehole at the pre-mined coal seam of the gate entry, and one high pressure water injection borehole and the presplitting boreholes at its both sides form a unit for coal seam weakening and permeability improvement; firstly, one unit for coal seam weakening and permeability improvement is weakened and improved in permeability, then the presplitting device is removed after such weakening and permeability improvement of the said unit and the next unit for coal seam weakening and permeability improvement is weakened and improved in permeability. The carbon dioxide phase transition fracturing technique is utilized, ensuring the uniformity of fissure development, significantly improving the wetted radius of high pressure water injection of the coal seams in China that are difficult to be injected with water, thus changing the properties of the coal seams, minimizing the dust generated from the working face and the risks of the coal and gas outbursts, rockbursts and other disasters.
Description
Α METHOD OF IMPROVING THE WETTED RADIUS OF HIGH PRESSURE WATER
INJECTION OF LOWLY PERMEABLE COAL SEAMS THROUGH SUBLEVEL
PRESPLITTING
FIELD OF THE INVENTION [0001] The present invention relates to a method of improving the water injection radius of coal seams, more specifically to a method of improving the wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting.
BACKGROUND TO THE INVENTION [0002] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
[0003] Compared with the energy consumption structure of most countries around the world, the coal plays a quite important role in China's energy consumption structure, China's raw coal output only in 2012 is up to 3.65 billion tons and the coal consumption accounts for appropriately 70% of total energy consumption. With respect to the existing identified coal resources in China, nearly a half is buried at a level of -1000 m or less and the gross geological reserve is up to about 3 trillion tons. Currently, on the whole, China's coal resource reserve is short, the coal resources in the old mining areas start shrinking gradually, with the development of science and technology and the progress of human society, the demand for energy is more urgent, the depth and difficulty of coal mining also become increasingly prominent and the mines of each country have gradually moved to the deep mining phase. According to the actual situation of China's coal resources, it is predicted by some experts that a lot of coal mines in China will go to the mining depth of 1000-1500m twenty years later. For example, the coal resource reserve of 1000m-deep shafts only in China Shandong Province occupies more than 40% of gross reserve and 21 of 47 over-1 OOOm-deep shafts across China are located in Shandong currently. High ground stress and high gas pressure caused by deep mining plus the generally low permeability of coal seams may lead to rockbursts, coal and gas outbursts and other accidents, seriously restricting the efficient intensive mining and safe production of the mine shafts.
[0004] Coal seam water injection is an important means of preventing and controlling several disasters in the field of coal mines, coal seam water injection can effectively reduce the
-22016231635 15 Nov 2019 amount of dust produced from mining of coal seams, reduce coal seam stress concentration to prevent the occurrence of rockbursts, coal and gas outbursts and other accidents, and increase the thermal conductivity of coal body, thus reducing the coal temperature. When the coal seam is injected with water, the high pressure water penetrates along the fissures and large pores of the coal body, followed by the self movement of water under the physical and chemical effects of the capillary forces and surface phenomena. Coal seam water injection is applied in a number of mining areas across China, but there is a lack of comprehensive and systematic research, resulting in poor effect of coal seam water injection of coal mines in China and a small wetted radius of high pressure water injection, the fundamental reason is that the existing coal bodies in China are relatively soft, low in fissure development and hard to be wetted and water is difficult to penetrate into some lowly permeable coal seams owing to its large surface tension; additionally, the high pressure water force is affected by the coal body stress distribution and coal seam main fissure and cannot control the fissure development direction, and the coal bodies are subject to local stress relaxation but the local coal body stress occurs in a concentrated manner; the uneven distribution of water space leads to abnormal increase of local gas content and pressure, endangering the safety of the working face.
SUMMARY OF THE INVENTION [0005] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
[0006] To this end, the present invention is aimed at providing a method of improving the wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting.
[0007] To solve the above-mentioned technical problems, the present invention comprises a method of improving a wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting, which comprises the following steps:
A At least two presplitting boreholes with a depth equal to that of a high pressure water injection borehole are bored with drill rigs at two sides of the high pressure water injection borehole at a pre-mined coal seam of a gate entry, a distance between the presplitting boreholes and the high pressure water injection borehole is 8-15m and the high pressure water injection borehole and the at least two presplitting boreholes form a unit for coal seam weakening and permeability improvement;
-32016231635 15 Nov 2019
B Firstly, one unit for coal seam weakening and permeability improvement is weakened and improved in permeability, several presplitting devices are end-toend connected via connecting devices and the presplitting devices are connected to an initiation controller and placed into the presplitting boreholes via several interconnected special mounting rods with the positions of the presplitting devices being fixed, a total stress relief section length of the presplitting devices being 50% to 60% of the depth of each presplitting borehole, and the at least two presplitting boreholes are sealed with macromolecular materials and special borehole packers, wherein a borehole sealing length is not less than 40% of the length of each presplitting borehole;
C An initiation delay of each presplitting device as indicated in the initiation controller is adjusted so as to enable the presplitting devices located in the presplitting boreholes to be initiated from inside to outside respectively and ensure that the at least two presplitting boreholes at the two sides of the high pressure water injection borehole is consistent in presplitting time;
D A high pressure water injection string is sent into the high pressure water injection borehole which is then sealed with macromolecular materials and special borehole packers, an outer connection of the water injection string is provided with a T-union and stop valve, wherein one of two connections of the said T-union is provided with a pressure gauge and a flowmeter and connected with a high pressure water injection pump while the other is connected with the high pressure rubber hose and direct to a roadway space; the high pressure water injection pump is started, a water injection pressure is set to 8-18 MPa, and when the water injection pressure drops abruptly and is maintained at a corresponding pressure level without change, the water injection into the high pressure water injection boreholes is stopped, meaning that the weakening and permeability improvement of this unit for coal seam weakening and permeability improvement is completed; and
E The presplitting devices in the at least two presplitting boreholes are removed and the next unit for coal seam weakening and permeability improvement is weakened and improved in permeability, which is repeated until the weakening and permeability improvement of the entire mined coal seam is completed.
wherein a stress relief port of the stress relief section of the said presplitting device is an elongated slotted structure.
wherein the said macromolecular material for borehole sealing is a macromolecular polyurethane material.
-42016231635 15 Nov 2019 [0008] The present invention provides a method of improving the wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting, and for the purpose of solving the low permeability, hard coal, difficulty in water injection and other problems arising from the mining of deep mine shafts across China, the backward presplitting method and carbon dioxide phase transition fracturing technique are used to presplit the deep coal body for permeability improvement and makes it possible to control the fracturing starting position and development direction of the fissures in the presplitting boreholes, ensuring the uniformity of the fissure development. Moreover, owing to the presplitting effect of the presplitting boreholes on the deep coal bodies, the high pressure water can be induced to develop into the deep part of the coal during high pressure water injection, thus avoiding the problem of “dense outside and sparse inside” arising from conventional high pressure water injection, and the present invention is easy to operate and convenient in construction and provides liquid carbon dioxide vaporization which will not generate spark and will displace the gas, so more obvious effects can be achieved if the present invention is applied in the high gas mine shafts.
BRIEF DESCRIPTION OF DRAWINGS [0009] One or more preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
[0010] FIG. 1 illustrates a schematic layout for presplitting and permeability improvement through water injection in the present invention;
[0011] FIG. 2 illustrates a sectional view for presplitting borehole in the present invention;
[0012] FIG. 3 illustrates a schematic view of presplitting effect in the present invention.
DETAILED DESCRIPTION [0013] The present invention provides a method of improving the wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting and is further explained here for further clarity of the objective, technical solution and effect of the present invention. It shall be understood that the specific embodiments as described here are merely used to explain the present invention and are not intended to limit the present invention.
-52016231635 15 Nov 2019 [0014] The present invention provides a method of improving the wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting, as shown in FIGs. 1,2 & 3, and comprises the following steps:
A: The presplitting boreholes 1 with a depth equal to that of the high pressure water injection boreholes 2 are bored with drill rigs at both sides of every existing high pressure water injection borehole 2 at the pre-mined coal seam of the gate entry, the distance between the presplitting borehole 1 and the high pressure water injection borehole 2 is 8-15m and one high pressure water injection borehole 2 and the presplitting boreholes 1 at its both sides form a unit for coal seam weakening and permeability improvement;
B: Firstly, one unit for coal seam weakening and permeability improvement is weakened and improved in permeability, several presplitting devices 4 are endto-end connected via the connecting devices 3 and these presplitting devices 4 are connected to an initiation controller 7 and placed into the corresponding presplitting boreholes 1 via several interconnected special mounting rods with the position of these presplitting devices 4 being fixed, the total stress relief section length of these presplitting devices 4 is 50% to 60% of the depth of a presplitting borehole, and the presplitting boreholes 1 are sealed with macromolecular materials 5 and special borehole packers 6, wherein the borehole sealing length is not less than 40% of the length of a presplitting borehole 1;
C: The initiation delay of each presplitting device 4 as indicated in the initiation controller 7 is adjusted so as to enable the presplitting devices 4 located in the presplitting boreholes 1 to be initiated from inside to outside respectively and ensure that the presplitting boreholes 1 at both sides of the high pressure water injection borehole 2 is consistent in presplitting time;
D: A high pressure water injection string is sent into the high pressure water injection borehole 2 which is then sealed with macromolecular materials, the outer connection of the water injection string is provided with a T-union and stop valve, wherein one of two connections of the said T-union is provided with pressure gauge and flowmeter and connected with a high pressure water injection pump while the other is connected with the high pressure rubber hose and direct to the roadway space; the high pressure water injection pump is started, the water injection pressure is set to 8-18MPa, and when the water injection pressure drops abruptly and is maintained at a corresponding pressure level without change, the water injection into the high pressure water injection
-62016231635 15 Nov 2019 boreholes 2 is stopped, meaning that the weakening and permeability improvement of this unit for coal seam weakening and permeability improvement is completed; and
E: The presplitting devices 4 in the corresponding presplitting boreholes 1 are removed and the next unit for coal seam weakening and permeability improvement is weakened and improved in permeability, which is repeated until the weakening and permeability improvement of the entire mined coal seam is completed;
Furthermore, the stress relief port of the stress relief section of the said presplitting device 4 is an elongated slotted structure; and the said macromolecular material for borehole sealing 5 is a macromolecular polyurethane material.
[0015] The carbon dioxide phase transition fracturing technique is used to presplit the deep coal bodies for permeability improvement and the application of the backward presplitting method makes it possible to control the fracturing starting position and development direction of the fissure in the presplitting boreholes, ensuring the uniformity of the fissure development. In addition, owing to the presplitting effect of the presplitting boreholes on the deep coal bodies, the high pressure water can be induced to develop into the deep part of the coal body during high pressure water injection, thus avoiding the problem of “dense outside and sparse inside” arising from conventional high pressure water injection, and the present invention is easy to operate and convenient in construction and its liquid carbon dioxide vaporization will not generate spark and will displace the gas, so more obvious effects can be achieved if the present invention is applied in the high gas mine shafts.
[0016] Of course, the descriptions above are only preferred embodiments of the present invention which is not limited to the exemplified embodiments as described above and it shall be noted that any equivalent alternative mode or obvious variant made by the technicians of this field under the guidance of the Specification shall be included in the substantial scope of the Specification and shall be protected by the present invention.
[0017] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.
Claims (3)
1. A method of improving a wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting, which comprises the following steps:
(a) at least two presplitting boreholes with a depth equal to that of a high pressure water injection borehole are bored with drill rigs at two sides of the high pressure water injection borehole at a pre-mined coal seam of a gate entry, a distance between the presplitting boreholes and the high pressure water injection borehole is 8-15m and the high pressure water injection borehole and the at least two presplitting boreholes form a unit for coal seam weakening and permeability improvement;
(b) firstly, one unit for coal seam weakening and permeability improvement is weakened and improved in permeability, several presplitting devices are end-to-end connected via connecting devices and the presplitting devices are connected to an initiation controller and placed into the presplitting boreholes via several interconnected special mounting rods with the positions of the presplitting devices being fixed, a total stress relief section length of the presplitting devices being 50% to 60% of the depth of each presplitting borehole, and the at least two presplitting boreholes are sealed with macromolecular materials and special borehole packers, wherein a borehole sealing length is not less than 40% of the length of each presplitting borehole;
(c) an initiation delay of each presplitting device as indicated in the initiation controller is adjusted so as to enable the presplitting devices located in the presplitting boreholes to be initiated from inside to outside respectively and ensure that the at least two presplitting boreholes at the two sides of the high pressure water injection borehole is consistent in presplitting time;
(d) a high pressure water injection string is sent into the high pressure water injection borehole which is then sealed with macromolecular materials and special borehole packers, an outer connection of the water injection string is provided with a T-union and stop valve, wherein one of two connections of the said T-union is provided with a pressure gauge and a flowmeter and connected with a high pressure water injection pump while the other is connected with the high pressure rubber hose and direct to a roadway space; the high pressure water injection pump is started, a water injection pressure is set to 8-18 MPa, and when the water injection pressure drops abruptly and is maintained at a corresponding pressure level without change, the water injection into the high pressure water injection boreholes is stopped, meaning that the weakening and permeability improvement of this unit for coal seam weakening and permeability improvement is completed; and (e) the presplitting devices in the at least two presplitting boreholes are removed and the next unit for coal seam weakening and permeability improvement is weakened and
2016231635 15 Nov 2019
-8improved in permeability, which is repeated until the weakening and permeability improvement of the entire mined coal seam is completed.
2. A method according to claim 1, wherein a stress relief port of the stress relief section of the said presplitting device is an elongated slotted structure.
3. A method according to claim 1, wherein the said macromolecular material for borehole sealing is a macromolecular polyurethane material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201510665655.5A CN105370256B (en) | 2015-10-15 | 2015-10-15 | A method of segmentation presplitting improves low air permeability coal seam high pressure water injection radius of wetted bulb |
| CN201510665655.5 | 2015-10-15 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| AU2016231635A1 AU2016231635A1 (en) | 2017-05-04 |
| AU2016231635B2 true AU2016231635B2 (en) | 2019-12-05 |
Family
ID=55372814
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| AU2016231635A Ceased AU2016231635B2 (en) | 2015-10-15 | 2016-09-23 | A method of improving the wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting |
Country Status (2)
| Country | Link |
|---|---|
| CN (1) | CN105370256B (en) |
| AU (1) | AU2016231635B2 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107989611A (en) * | 2017-11-30 | 2018-05-04 | 中铁广州建设有限公司 | Loading method for the fracturing hole internal solid carbon dioxide of non-explosive excavation rock |
| CN110593843B (en) * | 2019-09-24 | 2021-12-10 | 河南理工大学 | Wireless carbon dioxide gas phase fracturing control method |
| CN110646583B (en) * | 2019-10-09 | 2022-02-22 | 中煤科工集团重庆研究院有限公司 | Method and device for coal seam water injection similar simulation test |
| CN112709573B (en) * | 2019-10-24 | 2023-08-11 | 西安闪光能源科技有限公司 | Method for preventing and controlling rock burst of hard coal face based on controllable shock wave presplitting |
| CN112709530A (en) * | 2021-01-05 | 2021-04-27 | 窑街煤电集团有限公司 | Long-short hole crossed coal seam water injection method |
| CN114033346B (en) * | 2021-10-26 | 2023-02-28 | 中国地质大学（武汉） | Deep geothermal exploitation method based on carbon dioxide medium |
| CN114046148B (en) * | 2021-11-10 | 2023-02-21 | 中国矿业大学 | Liquid CO 2 Method for improving coal seam water injection effect by fracturing and permeability increasing |
| CN114151124B (en) * | 2021-11-30 | 2023-03-24 | 中国矿业大学 | Water injection dust reduction method for intelligent liquid carbon-water circulating injection fracturing and moistening coal seam |
| CN114109382B (en) * | 2021-11-30 | 2023-02-24 | 中国矿业大学 | Coal bed liquid CO 2 Water intelligent circulating filling, cracking, moistening and dust reducing system |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009088294A1 (en) * | 2008-01-07 | 2009-07-16 | Statoilhydro Asa | Assembly and method for production of gas or gas and condensate/oil |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102155254B (en) * | 2011-02-28 | 2013-05-22 | 中国矿业大学 | Method for extracting gas in low air permeability coal layer by pulse fracture anti-reflection |
| CN102359391A (en) * | 2011-09-12 | 2012-02-22 | 张海成 | Coal bed presplitting device |
| CN102635388A (en) * | 2012-02-24 | 2012-08-15 | 煤炭科学研究总院沈阳研究院 | Interaction permeability-increasing method of pre-splitting blasting and hydraulic cracking of coal seam |
| CN102654049B (en) * | 2012-05-28 | 2015-04-29 | 中国矿业大学 | Porous linear control hydraulic fracturing method |
| CN104389529A (en) * | 2014-10-31 | 2015-03-04 | 河南神华能源工程有限公司 | Deep hole gas phase fracturing pipe multi-stage connecting device |
-
2015
- 2015-10-15 CN CN201510665655.5A patent/CN105370256B/en active Active
-
2016
- 2016-09-23 AU AU2016231635A patent/AU2016231635B2/en not_active Ceased
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009088294A1 (en) * | 2008-01-07 | 2009-07-16 | Statoilhydro Asa | Assembly and method for production of gas or gas and condensate/oil |
Also Published As
| Publication number | Publication date |
|---|---|
| AU2016231635A1 (en) | 2017-05-04 |
| CN105370256A (en) | 2016-03-02 |
| CN105370256B (en) | 2018-09-21 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| AU2016231635B2 (en) | A method of improving the wetted radius of high pressure water injection of lowly permeable coal seams through sublevel presplitting | |
| US20200080382A1 (en) | Drill-power-based directional hydraulic fracturing system for downhole quick slotting and method thereof | |
| CN103061785B (en) | Grouting process for borehole casing pressure-proof seepage sealing grouting device for drilling roadway breaking water burst surrounding rock | |
| CN202560157U (en) | Grouting device | |
| CN102678083B (en) | Grouting method and grouting device | |
| CN106884655B (en) | A kind of two-way reinforcement means of gob side entry driving coal column | |
| Huang et al. | Phenomenon of methane driven caused by hydraulic fracturing in methane-bearing coal seams | |
| WO2017049783A1 (en) | Silica sol slow infiltration reinforcing method for argillaceous soft rock | |
| CN103924945A (en) | High-pressure grouting process of water-rich weathering fracture rock formation below thick unconsolidated formation for coal mine | |
| CN103089276B (en) | Deep-shallow hole and high-low pressure coupling grouting technology | |
| WO2015021783A1 (en) | Man-made retaining dam for coal mine underground reservoir, and method for connecting coal pillar dam body, surrounding rock, and same | |
| CN104775787B (en) | Uphole method for sealing on a kind of breaking surrounding rock hydraulic fracturing layer-through drilling | |
| CN104594919A (en) | Soft rock roadway buffering tapered double strong shell support system and construction method thereof | |
| Liu et al. | A proposed method of coal pillar design, goaf filling, and grouting of steeply inclined coal seams under water-filled strata | |
| Li et al. | Trial of small gateroad pillar in top coal caving longwall mining of large mining height | |
| CN105952492A (en) | A method for high-gas coal seam working surface drilling and exploitation gas pre-drainage | |
| CN110566155B (en) | Circulating grouting and hole sealing method for deformation-resistant gas extraction drill hole in mining area | |
| CN104533430B (en) | Release high-pressure water injection device and the construction method thereof of fracture slide type rockburst risk | |
| CN104612644A (en) | Gas phase fracturing and fast gas extraction method for low permeability coal bed | |
| CN108843371B (en) | It is a kind of based on the coal seam subregion Dynamic Water Injection process for adopting release | |
| CN106089174A (en) | The method in hydrofracturing chemically expansible agent filling speedy drivage tunnel | |
| CN104612625A (en) | Hole sealing device for low-permeability coal bed gas-phase fracturing drilling | |
| CN204457782U (en) | Remove the high-pressure water injection device of fracture slide type rockburst risk | |
| CN204492742U (en) | A kind of hole sealing device for the boring of hypotonic coal seam gas phase pressure break | |
| CN113669061B (en) | Device capable of lap joint anti-slip static pre-splitting top plate and use method thereof |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FGA | Letters patent sealed or granted (standard patent) | ||
| MK14 | Patent ceased section 143(a) (annual fees not paid) or expired |