What is Drilling jar?

The drilling jar converts the potential energy inside the stretched drill into kinetic energy. After the shock occurs, this kinetic energy transmits a power wave to the stuck drill, which unjams the drill.

There are three types of drilling jars: Mechanical drilling jars, Hydraulic drilling jars, and Hydraulic Mechanical integrated drilling jars.

Introduction to the driling jar

 2 .Mechanical Drilling jar

Mechanical jars operate using a series of springs, pins, and release mechanisms. The hydraulic jar controls the shape of the liquid to achieve the jar. The hydraulic mechanical integrated jar combines the above two designs to jar.

The mechanical jar jolts upward if the tension reaches a pre-selected value, and downward if the compression force reaches a pre-selected value. The jar will only operate within the set limit value, which should normally be away from the force on the jar during drilling. During normal drilling, the position of the mechanical jar is either neutral (not stressed) or stretched, but in either case should not be in a downward excitation state, as this may unnecessarily damage the underlying drill tool and bit.

The release mechanism of the mechanical jar can be set on the surface or downhole, depending on the design of the mechanical jar. There are two main designs for mechanical jars. One is the torsion principle of the spring. The mechanical jar is delivered to the well site with both upfired and downfired loads. Their excitation force is achieved by applying a torque variable of 10-15% to the downhole tool, with left turn torque decreasing and right turn torque increasing. Daily L.I uses this principle. The other design is composed of a slotted extension sleeve, a connector and an auxiliary spring. The load required to activate the downhole jar can be reduced by increasing the mud flow. ANADRILL’s EQ mechanical jar is based on this principle, which will be described later.

 3 .Hydraulic Drilling jar

The hydraulic jar consists of two pistons separated by a valve. When a tensile or compressive force is applied to the excited hydraulic jar, the liquid in one piston is compressed and flows to the other piston under great flow resistance. The speed of the liquid flow can control the time required for the tool to stimulate, the stretching or compression force is large, the time required for excitation is short, otherwise the time required for excitation is long. The distance traveled is called a stroke. When the stroke reaches a certain position, the compressed liquid will be suddenly released through the bypass valve, and the door will rush to the second piston with the flowing liquid, so that the pressure between the two pistons immediately reaches balance. The greater the force on the jar, the greater the compressive force on the liquid in the piston, the shorter the excitation time, and the greater the force generated by the excitation. This is how the Anadrill Hydraquaker jar works.

Hydraulic jar excitation conditions do not require a pre-set excitation threshold. When to excite, how much force is generated by excitation, etc., depends on the amplitude of stretching or compression. When excited upward, the excited force is proportional to the pulling force. The greater the pull, the greater the force of the excitation.

Therefore, one advantage of hydraulic jars is that they have a continuously variable jar force within their limits, and another advantage is that they have a larger bore than mechanical jars for 6-1/2 “tools.

When the hydraulic jar is in the firing position again, it will fire again if there is enough time for it to complete the stroke. This gives hydraulic jars a unique advantage when operating in inclined or horizontal Wells at high angles, where the driller may not be able to apply sufficient tension or compression force to the mechanical jar because the drill pipe may be subject to significant friction. The hydraulic jar, on the other hand, will eventually excite even under minimal tensile or compressive force. Of course, this is also a disadvantage of it, it can accidentally trigger and lead to fish accidents, especially in straight Wells.

Frequent excitation of the hydraulic jar will cause the liquid to overheat, which reduces the viscosity of the liquid, shortens its stroke time, and causes the hydraulic jar to advance excitation without the desired tensile force. As a result, the jarring force is reduced.

One of the main advantages of mechanical jars is that they are only activated after the force applied has reached a pre-set threshold. They are more noise-resistant and work longer than hydraulic jars.

Junnie Liu

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Email: landrill@landrilltools.com