DTH Driling Rigs Drill Bit Damage Analysis (Part 2)

Jan. 08, 2022

JK830 All-In-One DTH Automatic Drilling Rig


DTH drilling rigs are mainly based on high-frequency impact crushing methods, 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.


Diving hammer jam

The jamming of falling objects is also caused by unclean drilling tools and surface piping, large particle size adhering to the inner wall (mud block, rock chips, etc.), and other large particle size debris falling into the drill pipe, which causes the upper end of the submersible hammer to be stuck in the backstop valve, causing the backstop valve to be unable to reset quickly, as shown in Figure 5.

Solution measures

(1) Carefully check and clean the drilling tools to ensure that there is no debris on the inner wall of the drilling tools.

(2) Regularly check the sealing and spring reset performance of the backstop valve of the submersible hammer, and replace the wearing parts in time.

(3) Check all parts of the submersible hammer carefully.

(4) Use a special oil injector to ensure normal lubrication of the hammer.

(5) Each time before adding the drill pipe, the slag must be fully drained.

(6) Strictly clean and mark the drill pipe used for cementing, and try not to use this type of drill pipe, but use strict cleaning and inspection measures to ensure smooth construction.


Rock chip backward-absorbing blocking card

The pressure inside and outside the drilling tool is unbalanced, and the rock chips not completely drained from the bottom of the well enter the hammer under the action of the pressure difference between inside and outside, and jam the piston and the spline of the hammerhead or block the exhaust channel.

Solution measures

(1) Check the backstop valve of the submersible hammer carefully before drilling and replacing damaged parts.

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

(3) Strictly implement the operating procedures to prevent the blockage of rock chips by backward suction due to improper operation.

(4) Adopt a reasonable combination of drilling tools, and also borrow the method of adding a floating valve joint at 150-200m of the drilling tools to solve the problem of backward suction of rock chips.

(5) Drain the chips diligently to reduce the residual chips at the bottom of the well.


Mud ring wrapping

Mud ring wrapping is to form a mud ring and wrap the drilling tool by adhering rock powder (chips) to the drilling tool surface or well wall. After the mud ring is formed, the ring space becomes small and the rock chips are not excluded smoothly and continue to gather at the mud ring to form a mud package, which can completely block the borehole in serious cases and cause sticky buried drilling accidents.

Analysis of causes

Stratigraphic factors: micro gushing water and wet strata, micro gushing water in the formation of liquid film on the good wall and make the rock powder wet, the liquid film on the good wall and the rock powder bond with each other to form rock chip group, the rock chip group can not be completely brought out of the wellbore by the air when the mud ring is formed at the good wall and hammerhead, and the phenomenon of mud group adhering and gathering to form a mud ring is especially serious.

Solution measures

(1) Change the drilling process. When drilling in wet formations with a small amount of water seepage, atomized drilling (water injection dilution) is used for chert, dolomite, and other formations. As shown in Figure 9.

(2) Diligent chip removal. Every 0.5~1m drilling, the drilling tool is lifted off the bottom of the well for debris removal.

(3) Increase the air compressor. Increase the air supply and upward return airspeed to enhance the effect of sand removal.

(4) Reasonable configuration of drilling tools. Select a reasonable drill collar and drill pipe.

(5) Short-distance drilling to scratch the good wall. Prevent mud ring formation and thickening of the good wall.


Drill jam, buried drill

Stratigraphic factors: geological structure, dissolution, fractures, and faults generated by the development of joints lead to loose rock, weak cementation, as well as gushing water to absorb water swelling, the disintegration of part of the rock layer, the good wall falling blocks, collapse stuck buried submerged hammer. Technology: High-frequency shock in drilling destroys the overall structure of the rock, high-speed airflow (stripping) destroys the structure of the rock wall, and the circulating medium does not balance the wall protection function and water immersion reduces the structural force of the mud shale, resulting in the falling of the block and the collapse of the buried submersible hammer.


Technical measures

(1) diligent observation.

(2) diligent activity drilling tools.

(3) timely stop drilling processing.

(4) Tug of war to unblock.

(5) Inject foam to relieve the obstruction by strong chip removal.

(6) Short start drilling to explore the good wall.

(7) Foam drilling.

(8) Change the process of wall protection drilling.

(9) Mud injection to protect the wall.

(10) Milling and uncapping.


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