21-37 of 37 Common Complex Drilling Problems Judgment and Solutions

21. Why does lost circulation occur? How many types of lost circulation are there? How to judge and handle it?
The reason for lost circulation:

• Loose formation, fast drilling speed, poor circulation of mud, excessive pumping.
• Use high density drilling fluid in permeable formations, the pressure lead to leakage in formations.
• Drill through fault zones or fractures in the formation.
• Cave leakage.

There are three types of well leakage:

1. Permeability leakage (with a small amount of leakage).
2. Minor leakage (more in and less out).
3. Serious leakage (with entry but no exit).

Judgment of lost circulation:

• The level in the mud pit decreases.
• The amount of drilling fluid returning from the wellhead decreases, and in severe cases, it can only enter but not exit.
• Sudden increase or lost of drilling speed of drilling tools during tripping in, resulting in a decrease in pump pressure, often leads to lost circulation.

Solutions:

• For permeability leakage, first try to increase the viscosity of drilling fluid, appropriately reduce the density of drilling fluid and pump displacement.
• When there is a serious circulation lost, LCM can be added to the drilling fluid or gel cement can be injected to seal the leak. No matter what method is used to seal the leak, it is necessary to prevent the drill from getting stuck, because if lost circulation, the pressure of the drilling fluid column will decrease, often causing the collapse of the upper soft formation and leading to drill sticking.

22. Why do we need to circulate drilling fluid before pulling out?

• Remove all the rock debris from the well to maintain its cleanliness thoroughly, adjust the property of the drilling fluid, and ensure safe descent to the bottom for the next drilling trip.
• When encountering special operations such as electrical logging, casing running, and pre cementing, it is even more important to fully circulate the drilling fluid to facilitate smooth logging or casing running.
• When drilling into high-pressure oil and gas reservoirs, it is necessary to fully circulate the drilling fluid and adjust the property of the drilling fluid before pulling out to prevent blowouts.

23. Why is drilling fluid filled during the pulling out process? What will happen if not? How can drilling fluid be filled well? What should I do if I can't fill drilling fluid?
During the pulling out process, due to the pulling out of drilling tools and the spraying of some drilling fluid, the level of drilling fluid in the wellbore drops. it is necessary to fill the drilling fluid in a timely manner to balance the formation pressure and ensure downhole safety.
If the drilling fluid is not filled enough, it will cause downhole accidents, and high-pressure oil and gas wells will experience blowouts due to the decrease in drilling fluid column pressure. Loose formations can cause wellbore collapse due to an empty wellbore.
A job responsibility system must be implemented to fill the drilling fluid well, and a dedicated person must inspect it. The drilling fluid should be filled once every three drill pipes or one drill collar, but it must be ensured that the amount of drilling fluid injected is equal to the volume of the drilling tool column. The data of the mud pit liquid level drop should be measured, and the height of the wellhead liquid level should be observed for further implementation. Wells with high-pressure oil, gas, water layers, and without surface casing must be continuously filled with drilling fluid.

24. What is the reason for the sudden backflow and spraying of drilling fluid inside the drill pipe during the drilling process? How should we handle it correctly?
The main reason is:

1. Uneven density of drilling fluid or collapse of wellbore wall.
2. A premonition before a blowout.

Solution: In general, the tripping should be stopped and the drilling fluid should be immediately circulated and the drilling tools should be rotated to ensure that the performance of the inlet and outlet drilling fluids is normal. After stopping the pump, the square kelly should be breakout and the drilling fluid should not return to the drilling tools before pulling out. If oil and gas immersion is severe, well killing should be organized. If drilling fluid circulation is not available, pulling out should be immediately started to prevent wellbore collapse and blockage and try to inject drilling fluid into the well at the same time

25. What is the reason for pipe sticking while pulling out? How to judge and handle it?
The main reason is:

• Well collapse or sand bridging.
• Fishes falling from the wellhead.
• Shrinkage of borehole diameter and bit balling.
• The drill bit enters the keyseat.

The judgment method is:

• The drill string is unable for round trip, limited range of activities, which mostly indicates stuck caused by well collapse or sand bridging.
• Fixed on a stuck point is often caused by junks.
• The drill string can be tripped in but cannot be pulled out well for free stick, mostly due to bit stuck caused by shrinkage of borehole diameter and bit balling.
• Bit stuck often happens at a certain position, which can be rotated or tripped in, often due to keyseating.

Solution:

• No matter what kind of stuck, first connect the kelly to circulate and wash the well, adjust the drilling fluid property, move the drilling tools, analyze the situation, and formulate measures.
• In case of wellbore collapse and sand bridge stuck, in addition to high displacement circulating well cleaning, a bumper sub or drilling jar (super fishing jar) can be used for free stick.
• Pipe stuck caused by wellhead fishes can be resolved by rotating or lowering the drilling tool.
• Shrinkage of borehole diameter and bit balling should be cleaned with high displacement circulation, pull out and ream down for free stick.

26. What should be done if there is a sudden blowout during pulling out?
Follow the "Ten Quick Actions" for processing. The "Ten Quick Actions" refer to:

1. Sound the alarm quickly.
2. Turn on the BOP gate quickly.
3. Connect the back pressure valve quickly.
4. Close the stripper head quickly.
5. Get off the monkey board quickly.
6. Turn on the searchlight and turn off the derrick light quickly.
7. Drive the third car and stop the first car quickly.
8. The cooling water in the exhaust pipe of the doghouse is quickly, and the preparation for blocking the air filter is quickly.
9. Pump on for circulation and kill well quickly.
10. The whole team gathers and goes to work quickly.

27. What is the reason for mud flowing from the wellhead during pulling out? How to handle it?
The reason is:

• Bit balling
•  Warning of blowout.
• The wellhead has been filled with drilling fluid, but the pump has not stopped, or mud has been continuously filled.

Solution: Immediately connect the square drill pipe for circular ream down, rinse the drill bit, and adjust the property of the drilling fluid. If it is a warning of a blowout, the drilling should be stopped immediately, and square kelly should be connected for cyclic weighting.

28. What is a keyseating? How to handle it?
In well sections with frequent alternation of soft and hard formations, due to the drastic changes in wellbore inclination and orientation, a "dog leg" is formed. During long-term pulling out, the keyseat is pulled out of the wellbore wall, and the drilling tool can be stuck. The phenomenon of keyseating is:

• The middle part of drilling tool encounters stuck, and its position is fixed during the pulling process.
• The drilling tool can be lowered and rotated but cannot be pulled out.
• Eccentrically worn of drilling tools.

Solutions: In case of keyseating, the drilling tool should not be lifted and the drilling fluid should be circulated through a square kelly. The drilling tool should be rotated in different directions to pull up. If it still cannot be pulled out, it should be gently pulled, slowly rotated back ream as well. If the keyseating is serious, efforts should be made to damage it.

29. What is differential pressure sticking? What is the reason? How to handle it?
The presence of filter cake on the wellbore is the inherent cause of differential pressure sticking during drilling, as most drilling fluids are two-phase fluids of solid and liquid, or three-phase fluids of solid, liquid, and gas, in which solid particles adsorb onto the wellbore to form filter cake.
There are three reasons for the formation of filter cake:
The first is adsorption, where solid particles in drilling fluid adsorb onto the surface of rocks, both sandstone and mudstone exhibit this characteristic.
The second is sedimentation. During the flow of drilling fluid, the velocity near the wellbore is almost zero, and the solid particles in the drilling fluid deposit on the wellbore. The diameter of the shale section is much larger than that of the sandstone section, and sedimentation is more significant, so the shale section is prone to forming thick filter cakes.
The third is filtration, which accelerates the deposition of solid particles in drilling fluid on the surface of permeable rock layers.
After the occurrence of differential pressure sticking, the following measures can be taken to deal with it:

• Large displacement circulation well cleaning, treatment of drilling fluid performance, and effective purification of drilling fluid.
• Under safe conditions, move the drilling tools according to the operating procedures.
• Measure the stuck points, apply oil, acid, and soak in alkaline water (according to the geological conditions).
• Explosion loosening, milling inversion, and filling well side drilling.

30. What should be paid attention to when releasing stuck by oil spotting?

• Repeatedly verifying the stuck point, calculating the oil consumption or the formula ratio of the pipe-freeing agent, increasing the amount of oil used in deep well appropriately, and the ratio of diesel or kerosene to crude oil is generally 1:3.
• Ground pipelines and rotary hoses should be prevented from being punctured when the pressure is too high, which can cause crude oil to flow back. To prevent accidents of crude oil spillage, the drilling tool should be connected to the back pressure valve before oiling.
• Generally, cement trucks and hydraulic fracturing trucks are used for oiling, and a backup truck should be available. When oiling, it is important to observe changes in pump pressure to determine if the drilling tools are functioning properly.
• When oiling, it is necessary to increase the displacement appropriately to prevent crude oil from entering the tank. After oiling, it should be replaced regularly.
• After winter oiling, it is necessary to prevent pipeline freezing.
• Pay attention to fire prevention and prepare for firefighting.
• During the oil spotting process, do not leave the brake crank to prevent cable drilling or drilling string not well braked.
• If oiling in high-pressure layers, it is necessary to increase the drilling fluid in advance to prevent blowouts after oiling.
• During the spotting process, when replacing the oil, pay attention to changes in pump pressure. If the pump pressure suddenly increases, consider circulating the drilling fluid in a timely manner to prevent blockage of the bit nozzle.

31. How to move the drilling tool correctly after drill pipe sticking? What should be checked before moving drilling tools? What should be paid attention to when moving drilling tools?

• When drill pipe sticking occurs, pay attention to the movement of the drilling tool. According to the operating procedures, move it up and down significantly within the safe load, and sometimes rotate the drilling tool in conjunction. The activity range must pass through the stuck point position to prevent the upper drilling tool from getting stuck again. During activities, they cannot be fixed on the same tonnage to prevent fatigue and breakage of drilling tools. The position of the stuck point should be calculated correctly.
• Before moving the drilling tool, carefully check whether the weight gauge is sensitive, whether the dead and live lines are firmly fixed, whether the arrangement of the drill lines on the drum is neat, check the situation of drill lines, whether the hoisting system is intact, whether the drilling rig is firmly fixed, whether the air system is intact, and whether the switch is flexible and easy to use. After several movements, a comprehensive inspection should be carried out once.
• Pay attention to the changes in the weight indicator and the elongation of the drilling tools during the activity. Always pay attention to the location of the stuck point, and all non-duty personnel must leave the derrick floor to ensure safety. During activities, special attention should be paid to unexpected situations such as drill line jumping or tongue opening of the hook. After oiling, it is necessary to prevent the drilling tools from free stick and the brake crank from not being held by anyone, which may cause cable drilling. When moving drilling tools, be careful not to reverse rotation severely.

32. What are the reasons for cable drilling? How to prevent it?
The main reasons for cable drilling are leaving the post, improper operation, equipment failure and damage, and drilling tool damage.

1. The driller leaves the post, the brake crank is unattended. As long as the drilling tool is working underground, the brake crank needs to be guarded by a dedicated person at all times.
2. Improper operation. Mainly the brake crank operator, but there are also issues with the wellhead driller and the rig operator. The main reason is:
   • During the round trip, there was a serious stuck, and the elevator was opened.
   • Double elevator pulling out but only with one elevator link, which cause the breaking of the drilling tool.
   • The operating procedures is not strictly followed to apply the auxiliary brake when pulling out, the lowering speed was fast, and the braking was too late.
3. Drilling tool damage: Drilling tools are punctured, slipped, or broken underground, causing cable drilling.
4. Mechanical equipment damage or malfunction, including:

• The brake band rim is broken.
• The equalizer bar is broken.
• The brake band adjustment screw is broken or thread slipping.
• The equalizer bar pin is detached.
• Brake crank broken.
• Severe wear of brake band pads or overlapping of broken brake band pads.
• The live line head of the drill line slips or is cut off at the inlet of the drum.
• Too many broken wires in the drill line, causing it to break during the crane operation.
• The dead line clamp is loose and the dead line slips off;
• Air circuit switch failure or freezing in winter

How to prevent:

• Seriously follow the operating procedures and strictly prohibit illegal operations.
• When on duty, one should concentrate their energy and not slack off in their thinking.
• Wellhead tools should be checked regularly to maintain flexibility and usability. When using drill pipes of two or more specifications, it is important to replace the wellhead tools in a timely manner.

33. How to handle malignant cable drilling correctly?
After malignant cable drilling, the cause should be immediately identified and dealt with promptly.

• If the drilling tool has not fallen into the well, the first thing is to restore the circulation of drilling fluid, move the drilling tool, and prevent from pipe sticking.
• Conduct a comprehensive inspection of the hoisting system, braking system, and related pneumatic and transmission components, as well as drilling tools and instruments, to eliminate surface issues before addressing downhole problems.
• If the drilling tool has not fallen into the well, it can be slowly pulled out. If the drill is not stuck, the hanging load should be checked, and attention should be paid to checking the drilling tool when pulling out.
• The situation of drilling tools falling into the well will be complicated, especially when the number of drilling tools falling into the well is large, the drilling tools will be lumped into large sections of "Fried Dough Twists", or even into several sections, and the position of the fish top is unknown. At this point, the first step is to trip in and explore the top of the fish, slowly exploring within the possible wellbore section. Do not drill down too much to prevent the top of the fish from being squeezed into the wellbore and increasing the difficulty of treatment. Step two, if the top of the fish can be detected, it should be promptly hooked and fished (if it is a broken fish head, the depth of the top of the fish should be recorded, and the drilling tool should be replaced). When lifting, pay attention to preventing pipe sticking. Step three, if the top of the fish cannot be detected, other methods such as electrical record can be used to locate the top of the fish and then try to fish it.

34. How to use a fishing magnet correctly?

1. Select a suitable fishing magnet based on the diameter of the wellbore, with a maximum outer diameter 10-25mm smaller than the wellbore.
2. Create real samples of junks and test the magnetism of fishing magnet.
3. Determine whether to wear guiding shoes based on the size of the junks. If the O.D. of the junk is larger than the O.D. of the guiding shoe, the guiding shoe should be removed.
4. Measure the dimensions of each part of the shoe, draw a sketch, check the thread, and ensure smooth nozzles.
5. After tripping in, rinse 1-2 meters away from the top of the fish and slowly lower it while rinsing. After rinsing the top of the fish, stop the pump for fishing. Accurately calculate and measure the kelly in, multiple fishing should be carried out in different directions within a circle, with a pressure of 0.5-1 ton, which should not be too large. If the direction of drilling is consistent in all directions, the pulling can be started.
6. If the placement is inconsistent multiple times, it indicates that the junks has not been fished. You can gently turn the table, move it, and then fish it again.
7. If the fish is small, the guiding shoe is long, and the formation is soft, you can start with a small displacement, light pressure, and slow rotation to drill 3-5 meters, and then stop the pump for fishing.
8. Do not turn on the pump too forcefully to prevent the magnet from breaking off.

35. How to use the overshot correctly? What are the precautions?

• Select the appropriate size of overshot and install the appropriate size of slip according to the fish top and wellbore diameter.
• Remove the bowl of the overshot, inspect and maintain the slips, springs, and packer, measure the dimensions, draw a sketch, and tighten the threads.
• Drill down to at least 5 meters above the top of the fish and turn on the pump to circulate the drilling fluid, flushing away the accumulated mud and sand around the top of the fish.
• Accurately calculate and measure the kelly in of fishing and calibrate the weight indicator.
• Turn off the pump and running the fish tool. If the top of the fish is very straight, you can lower it to the top of the slip and pull it out for fishing. If the shoe touches the top of the fish, you can gently turn it or lift the overshot to turn it downwards for fishing.

Precautions:

• The kelly in of fishing must be accurate, and the fish should not be placed too much at the top of the clamp.
• The fish top cannot rotate after entering the slip.
• It is strictly prohibited to breakout by table (the table pin can be closed);
• Use an American style overshot, which should be connected to a drilling jar, hydraulic jar intensifier, etc. If the pipe gets stuck after catching a fish, use the drilling jar to vibrate and free sticking in a timely manner. If it doesn't work, soak it in crude oil. If it still doesn't work, lower the overshot and turn the slip to the right to remove the drill.

36. Why is it necessary to fill mud while running casing?
Filling mud when running casing is to balance the pressure difference inside and outside the casing, achieving the following three purposes:

1. Prevent the back pressure valve from being damaged due to excessive compression.
2. Prevent excessive hollowing out of the casing and damage.
3. Increase the weight of the casing string to facilitate smooth insertion of the casing.

37. What measures should be taken to protect the casing during drilling after installing the technical casing?

• The crown block, table, and wellhead are arranged in a straight line.
• The table and wellhead must be securely fixed.
• Drilling tools should be straight, especially square kelly.
• Rubber hoops should be added to the drill pipes inside the casing.
• When tripping in, the drilling speed should not be too high.
• Pay attention to fill drilling fluid during pulling out and avoid hollow casing too much.
• Optimize drill bits and drilling parameters to improve efficiency and reduce casing wear time.