1-10 of 37 Common Complex Drilling Problems Judgment and Solutions

1.   What is the reason for hitting an obstruction? How to handle it?
Commonly reasons:
1)    After drilling, the well collapsed.
2)    Poor drilling fluid property, high fluid loss, thick mud cake, and formation expansion lead to a reduction in wellbore diameter.
3)    Last time, the diameter of the drill bit was severely worn down, causing obstruction when a new drill bit was running in.
4)    Failure to circulate drilling fluid properly before drilling, resulting in inability to drill down to the bottom.
5)    Changes in drilling tool structure. If a larger drilling tool is replaced, or a large-diameter centralizer is added, or the type of drill bit is changed, it is also easy to encounter tight.
Solution (including preventive measures): The drilling fluid must be thoroughly circulated before pulling out of hole, and the performance of the drilling fluid must be treated properly. During pulling out process, drilling fluid must be injected according to regulations. It is necessary to carefully check the type and size of the drill bit before running in. Ream down all the stuck points and stripping operation is forbidden. If the size of the drilling tool changes, the lowering speed should be controlled during drilling, and the operating procedures should be strictly followed to prevent obstruction and pipe sticking.

2.   Why is it sometimes necessary to circulate mud during running in?
1)    the drilling fluid has not been circulated well for a long time underground before the last run, to prevent the pump from not being turned on due to the deterioration of drilling fluid performance.
2)    Collapse phenomenon in underground strata (already founded)
3)    The performance of drilling fluid deteriorates and is invaded by saltwater, gypsum, etc.
4)    There is a slight leakage underground.
5)    The underground situation is complex, and the pump often cannot be turned on.
6)    When there are complex deep or ultra deep wells, as well as high-pressure oil and gas reservoirs, the drilling fluid should be processed in sections. If the drilling fluid is not circulated halfway, it will cause resistance during running in, and the pump may not be turned on after running in, or the pump pressure may be too high and cause leakage in the formation.
7)    Circulating drilling fluid midway can circulate the sediment and sand cut by the drilling tool during running in.

3.   What is the reason for the pump cannot be turned on after running in? How to handle it?
1)    A large number of drilling tools were replaced during this running in, and the nozzle inside the drilling tools was not clean, which blocked the nozzle of the drill bit.
2)    Something fell inside the drilling tool during running in, such as threaded oil brushes, gloves, cotton yarn, etc.
3)    During the running in process, due to the collapse of the wellbore wall, drilling fluid was severely returned, and bit cuttings were carried into the drilling tool, blocking the nozzle of the drill bit.
4)    Ground pipelines or drilling tools freeze in winter.
5)    The wellbore mud cake is thick, bit balling, and the drilling fluid cannot return. If there is a permeable layer in the lower part, it is easy to leak the formation.
Solution: If the pump cannot be turned on, first eliminate surface factors, and then deal with underground blockages. The drilling tool should be moved a long distance, and the pump should be slowly turned on with a small displacement. If there is no effect, the pulling out should be started immediately to prevent downhole deterioration and pipe sticking.

4.   How should the drilling fluid be properly handled if the swivel or rotary hose is damaged during drilling and cannot circulate?
If the swivel leaks mud or the hose is damaged during drilling, when repairing, the first step should be to lift the 100-200 meters drilling tool to a safe section of the well. A dedicated person should move the drilling tool while organizing manpower for repair or replacement. If the underground situation is complex, the drilling tool should be lifted into the intermediate casing string. If the technical casing is not lowered, all drilling tools should be lifted. It is not allowed to connect the square drill rod and place the drilling tool in the well to repair the faucet or replace the fluid hose to prevent pipe sticking.

5.    What is the reason for the decrease or even non-return of drilling fluid from the wellhead during drilling? How to handle it?
First, check the ground pipeline. If the ground pipeline is normal, then check the ground manifold and mud pump in sequence. If the ground is normal, it is judged as underground leakage.
The reasons are as follows:
1)    There is a permeable leakage layer or formation fracture underground.
2)    There are limestone melting caves.
3)    The collapse of the well caused temporary non return of drilling fluid.
Solutions:
a)    Permeability leakage can be reduced appropriately by lower the density of drilling fluid.
b)    You should immediately start pulling out operation for serious leakage and measures should be taken to seal the leak.
c)    If it is a well collapse, the performance of the drilling fluid should be handled well, the drilling tools should be moved extensively, the hole should be slowly drilled, and the rock debris should be circulated to prevent pipe sticking.

6.    What is drilling fluid reverse circulation? What is the reason and how to judge and handle it? 
Incomplete return of drilling fluid from the drill bit nozzle is called drilling fluid reverse circulation, also called cross-over circulation.
1)    Ground high-pressure pipelines and manifolds (gates, flanges, unions, welds) are punctured or gates are reversed.
2)    Downhole drilling tools are punctured, inverted, tripped, and broken.
3)    The safety valve of the drilling pump is punctured.
The phenomenon of short circuit drilling fluid is that the pump pressure drops, the displacement does not decrease, and the rock debris cannot be carried out, causing mud bags on the drill bit, sticking and jumping, slowing down the drilling process, and in severe cases, jamming the drill bit.
Solutions: If the ground is normal, the drilling tool should be immediately run out steadily at low speed, and the breakout of rotary table is strictly forbidden. The drilling tool should be carefully inspected, and serious stuck should be avoided during running out. It is not allowed to pull or brake the drilling tool abruptly, which may cause accidents.

7.    What is the reason for the increase in pump pressure during drilling? How to handle it?
The reasons for the increase in pump pressure during drilling are well collapse, blockage of drilling tool nozzles, 1-2 blockages of drill bit nozzles, and changes in drilling fluid property.
If the well collapses, a large amount of circulating drilling fluid should be used, and the wellbore should be repeatedly ream down to clean the rock debris at the bottom of the hole. Light pressure drilling should be carried out to restore normal operation. If something falls into the drilling tool, the drilling tool should be checked one by one to see if stones and sand, swivel hose rubber blocks, and valve rubber are brought in when connecting a single piece. The valve core should be pressed back to prevent nozzle blockage. If the performance of the drilling fluid changes, drilling should be stopped, the drilling tools should be moved, and the drilling fluid should be treated.

8.    What is the reason for the decrease in hanging load of weight indicator during drilling? How to handle it?
The reason for the decrease in hanging load:
1)    The weight indicator is damaged.
2)    The drilling tool is broken.
3)    Pump pressure drops.
4)    Lost circulation and blowout.
Solution: Firstly, lift the drilling tool to check the pressure transmitter of the weight gauge, hydraulic oil pipeline, whether there is hydraulic oil in the gauge, and whether the parts in the gauge are damaged. Then, recalibrate the weight gauge and hanging weight. If the weight gauge is intact, run out and inspect the drilling tool immediately, determine the solution based on the fracture of the drilling tool.

9.    What causes the reverse rotation of table when the clutch is disengaged during drilling? How to handle it?
1)    Formation collapse, and there are large pieces of rock debris collapsing (such as drilling to fault planes, fracture development zones, formation fracture zones, etc.).
2)    Dry drilling or bit balling.
3)    All drill bits and cones are stuck.
4)    There are fishes underground (or previously fishes are squeezed onto the wellbore and fall back down again).
5)    Drilling string not well braked seriously.
Solution: When handling, first check whether the drill bit is normal. If it is dry drilling, lift the drilling tool and repeatedly ream down to release it. In addition, use light drilling pressure to determine the condition of the drill bit. If the drill is still stuck, immediately lift it up for inspection. Secondly, based on the geological forecast, adjacent well data, and returned rock debris, analyze the location and degree of well collapse, take effective measures, and pay special attention to preventing pipe stuck.

10.    What is the reason for bit jumping during tripping in? How to handle it?
Bit jumping often occurs when the tricone bit is drilling, and the reasons are as follows:
1)    Encountering gravel layers, soft and hard interlayers, heterogeneous formations (such as chert), and limestone formations with cracks and caves.
2)    Well collapse or junks underground.
3)    Serious bit balling.
Solution: Adjust drilling parameters, eliminate drill jumping. If the solution is ineffective, consider the presence of junks underground, check the wear of the drill bit during pulling out, and take effective measures to prevent pipe sticking during the treatment process.