Wenzel Downhole Tools Ltd

Wenzel Downhole Hydraulic/Mechanical Drilling Jar (HMJ)

   Download PDF  |  Hydraulic / Mechanical Drilling Jar

The Wenzel Jar operates with a simple up and down motion and is insensitive to right or left hand torque. It is most commonly run as a hydraulic over mechanical, but can be run as a straight mechanical, by omitting the valve, or as a straight hydraulic by omitting the latch. When run as a hydraulic / mechanical or straight mechanical, it is run in the latched position, this eliminates unexpected jarring and prolongs seal life.


Mechanical Tripping Mechanism

The normal setting for the mechanical latch is the down jarring load being 50% of the up jarring load. This tripping ratio, along with the tripping load, can easily be altered to suit customer requirements.


Operation


Jarring Up (Heavy Jarring)

A pull of at least equal to the mechanical latch trip setting must be taken to trip the latch, at this point the hydraulic delay takes over. The jar can be fired at this pull or the pull increased up to the maximum allowable. The jarring cycle is repeated by closing the jar to where the latch resets.


Down Jarring

To jar down, the jar is simply put in compression until the preset latch tripping load is reached, at which point the jar will jar down. Picking up on the jar resets it for another cycle.


Straight Mechanical

When run as a straight mechanical jar, a load in either tension or compression equal to the preset latch trip setting will cause the tool to jar.


Straight hydraulic

When run as a straight hydraulic jar, its operation is similar to existing hydraulic jars. From a closed position the jar will have a 6.5" free stroke, then the valve will seat causing the hydraulic delay, then the 6" free jar stroke. 


Pump Open

Since the jar is basically an unbalanced slip joint, the pressure drop across the bit, while maintaining circulation will have an extended force on the jar. If circulation is maintained while jarring, this extending force will reduce the pull required to jar up and increase the load required to jar down. The extending force is obtained by multiplying the pressure drop across the bit times the cross sectional area of the mandrel. These cross sectional areas are as follows:

 

Jar Nominal OD in. (mm)
Mandrel Area sq. in. (mm2)
3.12 (79)
4.0 (2,581)
3.50 (89)
6.0 (3,871)
3.75 (95)
6.0 (3,871)
4.75 (121)
11.8 (7,613)
5.25 (133)
11.8 (7,606)
6.25 (159)
19.6 (12,664)
6.50 (165)
19.6 (12,664)
6.62 (168)
21.7 (13,968)
6.75 (171)
23.8 (15,323)
8.00 (203)
30.7 (19,806)
9.00 (229)
41.3 (26,645)
9.00 (229)
38.5 (24,826)
9.50 (241)
41.3 (26,632)

 Example:
6.25" jar 1000 p.s.i. pressure drop. across the bit Mandrel area = 19.6 in2 x 1000 psi = 19,600 lbs.


Weight Below Jar

This weight must be subtracted from the up latch trip setting and added to the down latch trip setting for determining the up and down latch trip setting while in the hole.

Example:

  • Pull at surface to trip the latch
  • 6.25" jar
  • Tripping load 100,000 lbs. up - 50,000 down
  • 19.6 sq. in. mandrel area
  • 250,000 lbs. string weight
  • 30,000 lbs. below jar
     

Up (without circulation) 

To determine the pull at surface or indicator reading to trip the latch, add the latch tripping load to the total string weight and subtract the weight below the jar. Therefore, 250,000 lbs. string weight plus 100,000 lbs. tripping load, minus 30,000 lbs. weight below jar equals 320,000 lbs. pull at surface to trip the latch.


Down (without circulation)

To trip the latch down it is necessary to put the jar in compression the amount the latch is set to tip at, so it is necessary to slack off from the total string weight, the weight below the jar plus the tripping load. Therefore, the string will have to be slacked off to 250,000 lbs. minus (50,000 + 30,000) = 170,000 lbs. to trip the latch down.


Up (while circulating with 1000 p.s.i. pressured drop across the bit)

Extending force from pressure drop across the bit = 19.6 x 1000 = 19,600 lbs. Therefore 250,000 lbs. string weight plus 100,000 lbs. tripping load = 350,000 lbs. 30,000 lbs. weight below jar plus 19,600 lbs hydraulic extending force = 49,600 lbs. 350,000 lbs. minus 49,600 lbs. = 300,400 lbs. pull at surface or indicator reading to trip the latch up.


Down (while circulating with 1000 p.s.i. pressured drop across the bit)

Extending force = 19,600 lbs. Therefore the string will have to be slacked off to 250,000 lbs. minus (50,000 lbs. plus 30,000 lbs. plus 19,600 lbs.) = 150,500 lbs. to trip the latch down.
 

Design Features

  1. The unique design of the Wenzel Jar allows the spline drive along with all working parts to be housed in one sealed oil chamber, eliminating the need for ports which can fill with cuttings, restricting the down jar stroke. This makes it ideal for air drilling.
  2. The collet or tripping mechanism is designed to run in the cocked or latched position, causing the inner mandrel and outer housing to act as an integral part, thereby virtually eliminating seal wear or inner tool wear during normal drilling. This allows the length of the tool runs to be extended.
  3. Being designed to run in the latched position eliminates the need to extend or open the jar before running in the hole, as is required with some hydraulic jars. Unexpected jarring while tripping in or out of the hole is also eliminated, as can happen with conventional hydraulic jars. The possibility of the jar tripping in the hole due to drill collar weight below the jar, and tool extension due to pressure drop across the bit, is virtually eliminated.
  4. The tool joints can be torqued to the same torques as the drill collars.
  5. Standard seals in the tool are effective to 250 degrees fahrenheit and the tool can be dressed with seals effective to 400 degrees fahrenheit.
  6. The tool can be run in tension, at the neutral point, or in compression, within the preset latch settings.
  7. Only one carbide seal area is exposed to the drilling fluid and at this area a secondary seal is incorporated which is lubricated on both sides and is never exposed to the drilling fluid unless the first or primary seal fails.
  8. The unique design of the Wenzel Jar allows the spline drive along with all working parts to be housed in one sealed oil chamber, eliminating the need for ports which can fill with cuttings, restricting the down jar stroke. This makes it ideal for air drilling. 

 

 
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