CN104989317A - Bridge plug for casing fracturing - Google Patents

Bridge plug for casing fracturing Download PDF

Info

Publication number
CN104989317A
CN104989317A CN201510332233.6A CN201510332233A CN104989317A CN 104989317 A CN104989317 A CN 104989317A CN 201510332233 A CN201510332233 A CN 201510332233A CN 104989317 A CN104989317 A CN 104989317A
Authority
CN
China
Prior art keywords
slips
bridging plug
packing element
element type
pole
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.)
Pending
Application number
CN201510332233.6A
Other languages
Chinese (zh)
Inventor
胡相君
桂捷
李旭梅
王效明
邵媛
张安康
张丽娟
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Petrochina Co Ltd
Original Assignee
Petrochina Co Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Petrochina Co Ltd filed Critical Petrochina Co Ltd
Priority to CN201510332233.6A priority Critical patent/CN104989317A/en
Publication of CN104989317A publication Critical patent/CN104989317A/en
Pending legal-status Critical Current

Links

Landscapes

  • Closures For Containers (AREA)

Abstract

The invention relates to a bridge plug for casing fracturing, which comprises a central rod, an upper joint and a lower joint, wherein the upper joint and the lower joint are arranged at the upper end and the lower end of the central rod; a seat ring is arranged between the upper support sleeve and the upper joint, and the upper end and the lower end of the seat ring respectively support against the upper joint and the upper support sleeve; slips are arranged between the lower support sleeve and the lower joint, and anchor flukes are arranged on the slips. The bridge plug for casing fracturing, which is provided with the slips and the locking mechanism, can ensure the reliability of the bridge plug, and can be degraded along with time when certain shaft conditions are reached by adopting degradable materials. The bridge plug for casing fracturing has the characteristics of high pressure bearing capacity, no drilling plug and large drift diameter, and can be used for multi-section transformation of reservoirs of highly deviated wells and horizontal wells and rapid production.

Description

A kind of casing fracturing bridging plug
Technical field
The invention belongs to petroleum-gas fiedl High angle and horizontal well multistage renovation technique field, particularly a kind of casing fracturing bridging plug.
Background technology
The effect of bridging plug is Oil/gas Well sealing, has that working procedure is few, the cycle is short, a card envelope position feature accurately.Cable or tubing string is utilized to be transported to pit shaft precalculated position, the thrust produced by powder burning, hydraulic pressure or mechanical setting tool is in top connection, pulling force acts on center-pole, by upper and lower support set, upper pressure is imposed to cartridge and draw two power, when pulling force reaches certain value, tension force stick ruptures, and setting tool and bridging plug depart from.Locking device now on bridging plug center-pole plays usefulness, and slips fragmentation is also embedded on internal surface of sleeve pipe, and packing element expands and seals, and completes and sets.
Conventional 139.7mm casing fracturing all-metal bridging plug mainly adopts unidirectional dual-grip structure, usual without latus rectum or latus rectum less, there is the features such as good seal performance, resistance to pressure reduction is high, Sealing period is long, supporting capacity is large, replace cement plug, become one of the main downhole tool of pressure break, shutoff operation.But there is problems such as setting, be difficult to that brill removes halfway in Yin Qiyi, is not suitable for high angle hole, horizontal well;
Conventional composite bridge plug mainly adopts unidirectional dual-grip structure, and usual latus rectum is less than 50mm or without latus rectum, except there is all-metal feature, also have fluid passage, can the feature removed of quick drill, extensive use in fractured horizontal well.But need brill to remove after pressing, could normally produce, because the high-strength metal material for slips uses more, brill grinds more difficult, and it is large that chip returns out difficulty, operating cost height and brill grind the problems such as operating risk is large still to be existed.
Therefore, be necessary to provide a kind of novel press-fracturing bridge plug, overcome above-mentioned defect.
Summary of the invention
The object of the present invention is to provide a kind of casing fracturing bridging plug, have grappling reliable, latus rectum is comparatively large, exempts to bore the feature that fluid passage set up fast by plug, can reliably complete bridging plug packing, casing fracturing after pressure, eliminates the cost and construction risk that bore mill operation.
For this reason, the invention provides a kind of casing fracturing bridging plug, comprise center-pole and the top connection and the lower contact that are connected to the upper and lower two ends of center-pole, the middle part of described center-pole is set with columnar long packing element type and short rubber cylinder, the upper and lower side of long packing element type is symmetrically arranged with short rubber cylinder respectively successively, outside the upper and lower of center-pole, cover has upper support set and lower support cover respectively, upper support set and lower support put and are fixed with glue tube base respectively, and the described short rubber cylinder being positioned at long packing element type upper and lower side is installed on glue tube base;
Be provided with seat ring between described upper support set and top connection, described seat ring upper and lower side props up top connection and upper support set respectively;
Be provided with slips between described lower support cover and lower contact, slips is provided with anchor fluke, and slips lower end props up lower contact, and described lower support cover lower end is provided with radially the guide finger of tiltedly inclined 120 °, and the upper surface of slips is the inclined-plane led by guide finger.
Described seat ring inwall is stepped, and ladder is provided with latch segment, and latch segment is enclosed within center-pole, and the upper and lower side of latch segment is undertaken spacing by the step of top connection and seat ring inwall respectively.
Described latch segment is tubular structure, links the mode connect connect between latch segment and center-pole by gingival cyst of mucous gland in the newborn.
Described guide finger has three at least, is distributed on lower support cover lower end in circumference; Described slips is made up of multiple monolithic slips, monolithic slips is provided with 4 anchor flukes.
Joint face between described upper support set, glue tube base, short rubber cylinder, long packing element type and lower support cover is inclined-plane, and these inclined-planes are the inclined-plane of the long packing element type in the middle of deflection.
Described glue tube base material is polytetrafluoroethylene (PTFE), and described short rubber cylinder, long packing element type material are fluorubber, and described anchor fluke material is engineering ceramics.
Except glue tube base, short rubber cylinder, long packing element type and anchor fluke, all degradation material is adopted in described casing fracturing bridging plug.
Beneficial effect of the present invention:
The first, bridging plug of the present invention adopts degradation material, can realize degraded automatically under the specified conditions of down-hole, removes from boring and grinds operation.
The second, bridging plug design single deck tape-recorder watt and latch segment, improve bridging plug reliability.
Three, bridging plug has larger interior latus rectum, does not affect normal production.
Below with reference to accompanying drawing, the present invention is described in further details.
Accompanying drawing explanation
Fig. 1 is structural representation of the present invention.
Description of reference numerals: 1, top connection; 2, latch segment; 3, seat ring; 4, upper support set; 5, glue tube base; 6, short rubber cylinder; 7, long packing element type; 8, lower support cover; 9, guide finger; 10, anchor fluke; 11, slips; 12, lower contact; 13, center-pole.
Detailed description of the invention
Be applicable to the casing fracturing bridging plug of φ 139.7 millimeters of casing cementing completions for one, the present invention is described in further detail.
Embodiment 1:
The present embodiment provides a kind of casing fracturing bridging plug, as shown in Figure 1, comprise center-pole 13 and the top connection 1 and the lower contact 12 that are connected to center-pole about 13 two ends, the middle part of described center-pole 13 is set with columnar long packing element type 7 and short rubber cylinder 6, the upper and lower side of long packing element type 7 is symmetrically arranged with short rubber cylinder 6 respectively successively, outside the upper and lower of center-pole 13, cover has upper support set 4 and lower support cover 8 respectively, upper support set 4 and lower support cover 8 are fixed with glue tube base 5 respectively, and the described short rubber cylinder 6 being positioned at long packing element type 7 upper and lower side is installed on glue tube base 5;
Be provided with seat ring 3 between upper support set 4 and top connection 1, described seat ring 3 upper and lower side props up top connection 1 and upper support set 4 respectively;
Slips 11 is provided with between lower support cover 8 and lower contact 12, slips 11 is provided with anchor fluke 10, slips 11 lower end props up lower contact 12, and described lower support overlaps the guide finger 9 that 8 lower ends are provided with radially tiltedly inclined 120 °, and the upper surface of slips 11 is the inclined-plane led by guide finger 9.
This casing fracturing bridging plug of the present embodiment realizes in the following manner:
First by top connection 1 and central tube 13, this casing fracturing bridging plug of the present embodiment is connected to setting tool lower end, then designs block-up position in lower going-into-well.When setting, setting tool compression sleeve acts in top connection 1, and top connection 1 promotes seat ring 3 downwards, and seat ring 3 promotes upper support set 4, and upper support set 4 moves down compression short rubber cylinder 6 and long packing element type 7; Simultaneously, center-pole 13 is threaded connection and drives lower contact 12 upwards to push away slips 11, and slips 11 upwards pushes support set 8 and compresses short rubber cylinder 6 and long packing element type 7, after shutoff sleeve pipe, slips 11 along guide finger 9 lead along lower support cover 8 continue on move, until anchor fluke 10 is anchored to internal surface of sleeve pipe.When central tube 13 is stressed be greater than the thin-walled weakness maximum pull of design time, bridging plug and setting tool depart from, and complete bridging plug and set and give up.
Embodiment 2:
On the basis of embodiment 1, be also provided with retaining mechanism in the present embodiment, in the present embodiment, seat ring 3 inwall is stepped, ladder is provided with latch segment 2, latch segment 2 is enclosed within center-pole 13, and the upper and lower side of latch segment 2 is undertaken spacing by the step of top connection 1 and seat ring 3 inwall respectively.
Latch segment 2 is tubular structure, links the mode connect connect between latch segment 2 and center-pole 13 by gingival cyst of mucous gland in the newborn.
This retaining mechanism of the present embodiment, gingival cyst of mucous gland in the newborn is adopted to link the mode connect, form pure stress, here gingival cyst of mucous gland in the newborn links the form connecing and adopt positive and negative two gingival cyst of mucous gland in the newborn button snappings, center-pole 13 being reverse gingival cyst of mucous gland in the newborn button, latch segment 2 is forward gingival cyst of mucous gland in the newborn button, makes seat ring 3 and upper support set 4 by downward stress like this, can only move down, prevent from compressing the bounce-back in short rubber cylinder 6 and long packing element type 7 process.
Embodiment 3:
On the basis of embodiment 1 and embodiment 2, in the present embodiment, guide finger 9 has three at least, is distributed on lower support overlaps 8 lower ends in circumference; Described slips 11 is made up of multiple monolithic slips, monolithic slips is provided with 4 anchor flukes 10.
Slips 11 is made up of multiple monolithic slips, such slips 11 lead along guide finger 9 along lower support cover 8 continue on move past in journey, can be broken into single monolithic slips at leisure, 4 anchor flukes 10 on monolithic slips radially move, until anchor fluke 10 is anchored to internal surface of sleeve pipe along with monolithic slips.
Joint face between upper support set 4, glue tube base 5, short rubber cylinder 6, long packing element type 7 and lower support cover 8 is inclined-plane, and these inclined-planes are the inclined-plane of the long packing element type 7 in the middle of deflection.
The end face of this inclined plane shape of the present embodiment is arranged, and can make the short rubber cylinder 6 between support set 4 and lower support cover 8, long packing element type 7 can better by compression, arranges better effects if compared to what only have planar end structure.
Embodiment 4:
Under the prerequisite of above-mentioned several embodiment, as preferred, in the present embodiment, glue tube base 5 material is polytetrafluoroethylene (PTFE), and polytetrafluoroethylene (PTFE) class can be adopted to have high ductility material; Described short rubber cylinder 6, long packing element type 7 material are fluorubber, described anchor fluke 10 material is engineering ceramics, all degradation material is adopted except glue tube base 5, short rubber cylinder 6, long packing element type 7 and anchor fluke 10, its main component is function alloy Al, Ga, strengthen alloy A l, Mg, activated alloy Al, In, Sn, low-temperature alloy Pb, Bi, In, Ga.Under the condition meeting pressure break, ensure the degradable requirement of bridging plug.
In sum, this casing fracturing bridging plug of the present invention, be designed with slips and retaining mechanism, can ensure the reliability of bridging plug, critical piece have employed degradation material, when reaching certain wellbore conditions, can degrade in time.This casing fracturing bridging plug has the advantages that bearing capacity is high, exempt to bore plug, big orifice, can be used for the transformation of high-angle wells and horizontal wells reservoir multistage, goes into operation fast.
More than exemplifying is only illustrate of the present invention, does not form the restriction to protection scope of the present invention, everyly all belongs within protection scope of the present invention with the same or analogous design of the present invention.

Claims (7)

1. a casing fracturing bridging plug, comprise center-pole (13) and be connected to center-pole (13) the up and down top connection (1) at two ends and lower contact (12), it is characterized in that: the middle part of described center-pole (13) is set with columnar long packing element type (7) and short rubber cylinder (6), the upper and lower side of long packing element type (7) is symmetrically arranged with short rubber cylinder (6) respectively successively, outside the upper and lower of center-pole (13), cover has upper support set (4) and lower support cover (8) respectively, upper support set (4) and lower support cover (8) are fixed with glue tube base (5) respectively, the described short rubber cylinder (6) being positioned at long packing element type (7) upper and lower side is installed on glue tube base (5),
Be provided with seat ring (3) between described upper support set (4) and top connection (1), described seat ring (3) upper and lower side props up top connection (1) and upper support set (4) respectively;
Slips (11) is provided with between described lower support cover (8) and lower contact (12), slips (11) is provided with anchor fluke (10), slips (11) lower end props up lower contact (12), described lower support cover (8) lower end is provided with radially the guide finger (9) of tiltedly inclined 120 °, and the upper surface of slips (11) is the inclined-plane led by guide finger (9).
2. casing fracturing bridging plug as claimed in claim 1, it is characterized in that: described seat ring (3) inwall is stepped, ladder is provided with latch segment (2), latch segment (2) is enclosed within center-pole (13), and the upper and lower side of latch segment (2) is undertaken spacing by the step of top connection (1) and seat ring (3) inwall respectively.
3. casing fracturing bridging plug as claimed in claim 2, is characterized in that: described latch segment (2) is tubular structure, links the mode connect connect between latch segment (2) and center-pole (13) by gingival cyst of mucous gland in the newborn.
4. casing fracturing bridging plug as claimed in claim 1 or 2, is characterized in that: described guide finger (9) has three at least, is distributed on lower support cover (8) lower end in circumference; Described slips (11) is made up of multiple monolithic slips, monolithic slips is provided with 4 anchor flukes (10).
5. casing fracturing bridging plug as claimed in claim 4, it is characterized in that: described upper support set (4), glue tube base (5), short rubber cylinder (6), joint face between long packing element type (7) and lower support cover (8) are inclined-plane, and these inclined-planes are the inclined-plane of the long packing element type (7) in the middle of deflection.
6. casing fracturing bridging plug as claimed in claim 1, it is characterized in that: described glue tube base (5) material is polytetrafluoroethylene (PTFE), described short rubber cylinder (6), long packing element type (7) material are fluorubber, and described anchor fluke (10) material is engineering ceramics.
7. the casing fracturing bridging plug as described in claim 1 or 5, is characterized in that: except glue tube base (5), short rubber cylinder (6), long packing element type (7) and anchor fluke (10), all adopt degradation material in described casing fracturing bridging plug.
CN201510332233.6A 2015-06-16 2015-06-16 Bridge plug for casing fracturing Pending CN104989317A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN201510332233.6A CN104989317A (en) 2015-06-16 2015-06-16 Bridge plug for casing fracturing

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN201510332233.6A CN104989317A (en) 2015-06-16 2015-06-16 Bridge plug for casing fracturing

Publications (1)

Publication Number Publication Date
CN104989317A true CN104989317A (en) 2015-10-21

Family

ID=54301186

Family Applications (1)

Application Number Title Priority Date Filing Date
CN201510332233.6A Pending CN104989317A (en) 2015-06-16 2015-06-16 Bridge plug for casing fracturing

Country Status (1)

Country Link
CN (1) CN104989317A (en)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106522869A (en) * 2016-12-30 2017-03-22 新疆能新科油气技术有限公司 Shaft cast-plugging device and mounting method thereof
CN106703746A (en) * 2016-12-19 2017-05-24 中国石油集团渤海钻探工程有限公司 Expansion-type degradable bridge plug
CN107869323A (en) * 2016-09-23 2018-04-03 深圳市百勤石油技术有限公司 A kind of solvable bridging plug and its construction technology
CN109415929A (en) * 2016-05-06 2019-03-01 托尔奇公司 Rupture plugs
CN111492120A (en) * 2018-01-29 2020-08-04 株式会社吴羽 Decomposable downhole blanking plug
CN112127834A (en) * 2020-09-15 2020-12-25 张军 Soluble bridge plug
US11661813B2 (en) 2020-05-19 2023-05-30 Schlumberger Technology Corporation Isolation plugs for enhanced geothermal systems
US12091931B2 (en) 2021-02-01 2024-09-17 Schlumberger Technology Corporation Slip system for use in downhole applications

Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4784226A (en) * 1987-05-22 1988-11-15 Arrow Oil Tools, Inc. Drillable bridge plug
GB2448960A (en) * 2007-05-01 2008-11-05 Weatherford Lamb Pressure isolation plug / packer with rollers and ring
CN202181876U (en) * 2011-08-23 2012-04-04 中国石油天然气股份有限公司 Drillable composite bridge plug
CN202596661U (en) * 2012-04-13 2012-12-12 中国石油天然气股份有限公司 High-temperature and high-pressure resistant quick drillable composite bridge plug
CN203081398U (en) * 2012-11-12 2013-07-24 中国石油天然气股份有限公司 Hydraulic setting type small-drift-diameter oil pipe bridge plug
CN203441401U (en) * 2013-08-05 2014-02-19 中国石油天然气股份有限公司 Ceramic slip composite bridge plug
CN203559864U (en) * 2013-11-28 2014-04-23 中国石油天然气股份有限公司 Quick drilling composite bridge plug for fracturing
CN103806864A (en) * 2012-11-12 2014-05-21 中国石油天然气股份有限公司 Hydraulic setting type small-drift-diameter oil pipe bridge plug
CN204113212U (en) * 2014-10-11 2015-01-21 中国石油天然气股份有限公司 Composite bridge plug
CN104612626A (en) * 2015-02-11 2015-05-13 四机赛瓦石油钻采设备有限公司 Bridge plug with large drift diameter
CN104632126A (en) * 2014-12-26 2015-05-20 杰瑞能源服务有限公司 Bridge plug with large drift diameter and setting method of bridge plug
CN204782916U (en) * 2015-06-16 2015-11-18 中国石油天然气股份有限公司 Bridge plug for casing fracturing

Patent Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4784226A (en) * 1987-05-22 1988-11-15 Arrow Oil Tools, Inc. Drillable bridge plug
GB2448960A (en) * 2007-05-01 2008-11-05 Weatherford Lamb Pressure isolation plug / packer with rollers and ring
CN202181876U (en) * 2011-08-23 2012-04-04 中国石油天然气股份有限公司 Drillable composite bridge plug
CN202596661U (en) * 2012-04-13 2012-12-12 中国石油天然气股份有限公司 High-temperature and high-pressure resistant quick drillable composite bridge plug
CN203081398U (en) * 2012-11-12 2013-07-24 中国石油天然气股份有限公司 Hydraulic setting type small-drift-diameter oil pipe bridge plug
CN103806864A (en) * 2012-11-12 2014-05-21 中国石油天然气股份有限公司 Hydraulic setting type small-drift-diameter oil pipe bridge plug
CN203441401U (en) * 2013-08-05 2014-02-19 中国石油天然气股份有限公司 Ceramic slip composite bridge plug
CN203559864U (en) * 2013-11-28 2014-04-23 中国石油天然气股份有限公司 Quick drilling composite bridge plug for fracturing
CN204113212U (en) * 2014-10-11 2015-01-21 中国石油天然气股份有限公司 Composite bridge plug
CN104632126A (en) * 2014-12-26 2015-05-20 杰瑞能源服务有限公司 Bridge plug with large drift diameter and setting method of bridge plug
CN104612626A (en) * 2015-02-11 2015-05-13 四机赛瓦石油钻采设备有限公司 Bridge plug with large drift diameter
CN204782916U (en) * 2015-06-16 2015-11-18 中国石油天然气股份有限公司 Bridge plug for casing fracturing

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109415929A (en) * 2016-05-06 2019-03-01 托尔奇公司 Rupture plugs
US11162345B2 (en) 2016-05-06 2021-11-02 Schlumberger Technology Corporation Fracing plug
CN109415929B (en) * 2016-05-06 2022-03-15 斯伦贝谢技术有限公司 Apparatus for forming plugs during hydraulic fracturing of subterranean soil layers
CN107869323A (en) * 2016-09-23 2018-04-03 深圳市百勤石油技术有限公司 A kind of solvable bridging plug and its construction technology
CN106703746A (en) * 2016-12-19 2017-05-24 中国石油集团渤海钻探工程有限公司 Expansion-type degradable bridge plug
CN106703746B (en) * 2016-12-19 2022-06-10 中国石油天然气集团有限公司 Expansion type degradable bridge plug
CN106522869A (en) * 2016-12-30 2017-03-22 新疆能新科油气技术有限公司 Shaft cast-plugging device and mounting method thereof
CN111492120A (en) * 2018-01-29 2020-08-04 株式会社吴羽 Decomposable downhole blanking plug
US11346178B2 (en) 2018-01-29 2022-05-31 Kureha Corporation Degradable downhole plug
US11661813B2 (en) 2020-05-19 2023-05-30 Schlumberger Technology Corporation Isolation plugs for enhanced geothermal systems
CN112127834A (en) * 2020-09-15 2020-12-25 张军 Soluble bridge plug
US12091931B2 (en) 2021-02-01 2024-09-17 Schlumberger Technology Corporation Slip system for use in downhole applications

Similar Documents

Publication Publication Date Title
CN104989317A (en) Bridge plug for casing fracturing
CN202181876U (en) Drillable composite bridge plug
CN101864922B (en) Compression type dual-sealing open hole packer
US3915226A (en) Double collet release mechanism
CN202560158U (en) Drillable Composite Bridge Plug
CN103835677B (en) A kind of horizontal well two-stage sealing bruising salvagable completion system
CN105672942A (en) Degradable drilling-free bridge plug
CN115749677B (en) Small-diameter soluble bridge plug for staged fracturing C-type shale casing variable well
CN204782916U (en) Bridge plug for casing fracturing
CN206830123U (en) A kind of HTHP packer of band elasticity deblocking ratchet and balance bypass
CN103573210A (en) Quick drill composite pipe bridge plug
CN105971537A (en) Fishable bridge plug releasing mechanism and releasing and fishing method thereof
CN101781977A (en) Bidirectional high-pressure detachable bridge plug
CN103835678A (en) Horizontal well inner-pipe-free drilling-plug-free grading cementing well completion method
CN205000943U (en) But anchor tile modus ponens casing packer
CN111425148A (en) Casing pipe column applying toe end sliding sleeve to full-bore sliding sleeve and using method of casing pipe column
CN103195389B (en) A kind of suspension packer for open hole well completion
CN203223203U (en) Hanging packer for open hole completion pipe string
CN207268169U (en) A kind of efficiently speed bores bridge plug
CN201843573U (en) Underground available and drillable ash injection bridge plug
CN201092845Y (en) Hydraulic pressure, double back-off hand type dragable bridge plug
CN116816308A (en) Oil-free pipe paraffin removal lifting device for small-bore shale oil well
CN109899047B (en) Tieback fracturing method and anchoring retrievable tieback fracturing shaft
CN103291235A (en) Tool for sending hydraulic packer into well
CN204163682U (en) Formula blanking plug in oil pipe delivered by snubbing serving steel wire

Legal Events

Date Code Title Description
C06 Publication
PB01 Publication
C10 Entry into substantive examination
SE01 Entry into force of request for substantive examination
RJ01 Rejection of invention patent application after publication
RJ01 Rejection of invention patent application after publication

Application publication date: 20151021