Introduction to Jars and Accelerators

8/10/2019 Introduction to Jars and Accelerators

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Introduction to Jars and

accelerators

Rev: 1.0 24/11/14


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Table of contents

INTRODUCTION TO JARS AND ACCELERATORS................................................... ...........

Table of contents................................................................................................................. ...........

JARS AND ACCELERATORS........................................................................................... ...........

Introduction........................................................................................................................ ...........

General Comments on the Use of Jars............................................................................... ...........Forces Required to Fire Jars............................................................................................... ...........

Jar Descriptions.................................................................................................................. .........

Handling of mall Drilling ! Fishing Jars "Daile#$............................................................ .........

%ccelerator Description...................................................................................................... .........

Jar and %ccelerator &ositioning.......................................................................................... .........

APPENDICES....................................................................................................................... ...........

%ppendi' () Houston *ngineering specifications.............................................................. ...........

%ppendi' +) Griffith specifications.................................................................................... ...........


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Jars and acceleratorsIntroduction

Definition

Jarring is the process of transferring strain energy ( drill pipe stretch ) in thedrillstring to kinetic energy by releasing the detent in the Jar at a given overpullvalue.

Detent . Is a device (as a catch, dog, or spring-operated ball) for positioning andholding one mechanical part in relation to another so that the device can bereleased by force applied to one of the parts.Types

There are three basic types of jar, mechanical hydraulic and hydro-mechanical.Mechanical and hydraulic jars will be discussed within thisn document.

ydraulic jars use a hydraulic fluid to delay the firing of the jar until the driller canapply the appropriate load to the string to give a high impact. The time delay isprovided by hydraulic fluid being forced through a small port or series of jets.

ydraulic jar firing delay is dependent upon the combination of load and time.


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www.kingdomdrilling.co.uk ref JA01

Barrel Lower Connector

Upper Packing Body

JayStem

WashpipeSpringStem

Polished Stem

Upper Connector Lower Packing BodyJay Rollers Torque Spring

Figure 1: Mechanical jar

Splineandrel

Up!n"il

Connector #ousing

BottomConnector #ammer

Upper Pressure

PistonPressure#ousing

BalancePiston

$own!n"il

Lower Pressure

Piston

Washandrel

Spline#ousing

%lowandrel

Triggering&al"e

PistonStop

Figure 2: Hydraulic jar
http://www.kingdomdrilling.co.uk/http://www.kingdomdrilling.co.uk/


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eneral !o""ents on the #se of Jars$Jars are fre!uently returned to the workshops marked "failed# andsubse!uently test successfully. The main reason for this appears to be theinability to fire the jars, often in the down direction. $stimating the forcere!uired to fire jars, when the user is under pressure due to the stuck pipesituation, is not always performed correctly. This chapter gives some insightinto how jars operate and how to choose the correct surface forces to fire the

jars. There are a number of reasons a jar might fail to fire% Incorrect weight applied to fire jar - one or more assumptions in calculation

incorrect. &ump open force e'ceeds compression force at jar ( no down jar action ).

*tuck above the jar.

Jar mechanism failed.

Jar not cocked. +rag too high to allow sufficient force to be applied at the jar to fire it

(usually mechanical jars ). ell path is such that compression cannot be applied to the jar. ( no down

jar action ).

J i fi i b b f l f


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Forces (e)uired to Fire Jars 0ll jars have a firing force envelope for each direction they fire in. 0 dualacting jar (one that can fire up and down ) will have both an up jar forceenvelope and a down jar force envelope.

The firing force envelope consists of two forces, one to cock the jar inpreparation for firing, the second to fire the jar. 0 dual acting jar will thereforehave two force envelopes, one for up jarring and one for down jarring.

The jar envelope forces can be considered at the jar or at the surface. The jar firing force envelope at the jar is known.

Jar Firing Force *n+elo%e

It is the job of the rig team to estimate 2 observe the surface instruments inorder to choose the surface firing force envelopes.

The forces that must be applied to the jar to cock and fire it when it is lying ona test bench are described by the jar force envelopes ( i.e. forces at the Jar ).

In the e'ample above% To cock the jar to fire up, a compression force ofappro'imately 3k lbs is re!uired. This is to overcome internal friction. 4nce

cocked the jar will fire once the force atthe jar reaches 56k lbs.


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is a very good indicator that the a'ial neutral point is at the jar. It is oftenobserved whilst drilling vertical wells but can be very difficult to observe inhighly deviated, e'tended reach or hori8ontal wells.If this neutral weight indicator is observed it is relatively easy to set surface

jarring forces. The measured weight at which the neutral point is observed isrecorded. The up trip force ( mechanical only ) is added to this value, togetherwith any up drag.

Note: When stuck, any pull on the string results in an increase in drag over and abovethe normal up drag. The full amount of overpull applied at surface ill not reach the

!ar. "n deviated ells this must be compensated for by additional overpull.

If the pumps are running then the pump open force must also be subtractedfrom the firing force and added to the setdown weight used to cock the jars.

Note: The pump open force charts ill be found in the manual for the !ar being used. # copy of the current pump open force charts for the types of !ars covered by

this te$t is included after the description of each !ar type.*imilarly the down trip force ( mechanical only ), the down drag and the pumpopen force are subtracted from the neutral point reading.

If the neutral point at the jars cannot be observed then the calculated neutralweight at the jars must be used.


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Pressure

!rea

Pump Open ForceThe jar pump open force ( also called jarextension force ) is the effect of the differencein surface areas of the jar e'posed topressures on the out side and inside the jar.

hen a differential pressure e'ists betweenthe inside of the jar and the outside of the jarit causes a force that opens the jar.+epending on the jar type the force acts on

the cross-sectional area of the wash pipe, orthe wash pipe and any floating pressuree!ualising piston e'posed to the internal fluidof the jar. The effect on jarring can beconsiderable if for e'ample 7666psi istrapped inside the jar when the string ispacked off below the jar. The pump openforce chart for each type of jar discussed isincluded in these guidelines.The pump open force acts to%

Assist firing the jar u%Assists coc'ing the jar after firingdo&n,%%oses firing the jar do&n

%% 'i h j f fi i %


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As an example we can look at a situation that happened recently in theNorth Sea.

&aving struggled out of the hole pumping and ith indications of pack-offs the string finally packed off. 'arring commenced in a do n ard direction. There ere psi trapped in the string and the pack-off as belo the dual acting hydraulic !ar.The parameters ere as sho n at right -

As can be seen with 2000 psi trapped in the string a 34k lbs pump open forceresulted. Down jarring was attempted six times, each time the measured weightreading of 60k lbs was held for 30 seconds without any indication of the jar firing.

Example Case ' lbs ' lbs9p Trip :orce (at jar) 56 +own Trip :orce (at jar) ;69p /ocking :orce (at jar)


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Jar Descri%tions

Weir ouston

eir ouston ydra-Jars are dual acting hydraulic drilling jars.

These jars fire up and down from a central @cockedA position. The time to fireis dependent upon the pull applied at the jar and the position of the jar in itscycle when the pull is applied. The minimum force at the jar re!uired to strokethe jar up or down is dependent upon the jar#s internal friction. The ma'imumforce that can be applied to the jar is determined by two factors%


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+etails of the jars used in orthern orth *ea cold conditions service(:oinaven &roject).


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Weir ou!ton" Tool #pecification #ummar$

Tool 4+= GA = HA ? GA ? A B HA EA


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!o"en J#rs

1owen hydraulic drilling jars are often rented by companies other than 1owen.1owen do not rent hydraulic drilling jars from 0berdeen. They only sell them.In countries other than the 9 1owen hydraulic drilling jars may be used bysome service and drilling companies.

1owen hydraulic drilling jars are a dual acting combination tool. The hydraulicmechanism is only on the up jar action. The down jar is a friction mechanical

system.

The metering action of the hydraulic mechanism is controlled by ports on aninsert within a piston. This differs from other types which use metering jets.There are no details on the time delay of the 1owen hydraulic mechanism.

3,-* Hydraulic #% Jar . u"% o%en force

36

?6

B6

E6

r c e

4 2 1 0 0 0 5 l b s

=.73D 9& Jar

?D 9p Jar

?.73 - ?.B3D 9p Jar

B.B3D 9p Jar


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3o&en Hydraulic Do&n Jar . u"% ,%en Force

6

76

=6

?6

E6


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Cou$#r % IPE

The /ougar +rilling Jar ( DJ ! ) can be configured in three ways.


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!ougar hydraulic Jar "etering ti"es

200

260

e c o n

d s

5

!ougar hydraulic Jar u"% o%en force

0

20000

70000

80000

90000

100000

120000

0 600 1000 1600 2000 2600 =000 =600Diff %re ss inside to outside jar 4%si5

% u " % o % e n

f o r c e

4 l b s

5 : 6;9

Documents

Introduction to Jars and Accelerators