DTH Drilling Rigs Drill Bit Damage Analysis (Part 1)

DTH driling rigs are mainly based on high frequency impact crushing method, which can often achieve more than 10 times the drilling speed of conventional drilling methods. However, the application is easily affected by the operation process, the complexity of the formation and other factors to produce various accidents.

Hammer head fracture

The location of hammer head fracture mostly occurs at the reducer of the upper end of the hammer head spline. 

The common causes of hammer head fracture are:

(1) poor quality of the hammer head body itself, stress concentration, fatigue resistance, shear strength is low.

(2) The bending and vibration of the drilling tool due to excessive drilling pressure, or the uneven hardness and softness of the ground leading to the unstable work of the hammer head, and the continuous high frequency change of the torque on the hammer head, resulting in fatigue damage and fracture of the hammer head under the action of repeated alternating impact force and alternating shear stress.

Prevention and treatment measures

(1) the use of good quality manufacturers, in order to reduce the quality of the hammer head and the occurrence of accidents in the hole. Hammer head quality strict inspection, strictly prevent damage to the hammer head into the well.

(2) Adjust drilling parameters in advance when entering loose, dissolved fracture zones, broken zones and soft and hard uneven formations.

(3) When the stratigraphic situation is unknown, drill with small drilling pressure first, and then slowly increase the pressure to make the drilling even and smooth, and avoid drilling with large drilling pressure and high speed.

(4) When drilling soft rock formations, lower the drilling pressure to prevent the carbide teeth from eating into the rock too deeply, which will lead to an instant increase in torque on the hammer head.

(5) Use a diving hammer with an anti-release sleeve as much as possible to prevent the hammer head from falling into the well when it breaks.

(6) If the hammer head breaks into the bottom of the well, it should be salvaged in time.

Broken hammer teeth

Most of the hammer head teeth are damaged by abnormal breakage, especially the teeth located at the outermost edge of the hammer head are most likely to break.

The main reasons for the abnormal chipping of hammer head teeth are divided into 3 aspects: stratigraphy, drilling technical parameters and operation methods.

Technical measures

(1) Adjust the technical parameters of drilling in advance.

(2) Test drilling with small drilling pressure.

(3) Small drilling pressure and low speed.

(4) Evenly feed pressure.

(5) Select a suitable hammer head.

Hole hammer clogging

The blockage of falling objects is due to the unclean drilling tools and ground pipeline, the inner wall of the attached materials, especially the rust and tiny debris on the inner wall of the new drill pipe, which fall off to the upper end of the submerged hammer under the action of compressed air and block the air duct, resulting in poor air supply or no air.

Solution measures

(1) Clean the ground air pipeline, especially the gate valve and the elbow of the pipeline, which are difficult to clean.

(2) Thoroughly clean the inner wall of drilling tools in the hole before drilling, so that the inner wall of drilling tools can be cleaned into the well.

Blocking the submersible hammer by rock powder sucking backward

Clogging of the submersible hammer by reverse suction usually occurs when there are more residual chips in the well, especially in the condition of "thick paste", due to improper operation, insertion of "thick paste" when drilling, when the submersible hammer backstop valve is not sealed well, and the pressure difference inside and outside the circulation channel is large, the rock powder at the bottom of the well is sucked back from the submersible hammer fit gap.

Solution measures

(1) carefully check the backstop valve of the submersible hammer before drilling, and replace damaged parts.

(2) carefully check the clearance and sealing performance of the piston and inner (outer) cylinder, piston and air distribution valve are intact, replace damaged parts.

(3) Strictly enforce the operating procedures to avoid blockage of the rock powder due to improper operation.

(4) Use a reasonable combination of drilling tools, and add a floating valve joint at 150-200m of drilling tools to overcome the backward suction of rock powder caused by the pressure difference in the circulation channel.

(5) When the air supply is not smooth, immediately move the drilling tool up and down drastically, and then start drilling immediately for inspection after it is not effective.

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