Drilling abnormal or accident

Drilling abnormal or accident

1.Mud Gain

2.Mud loss

3.Pipe washed out

4.Bit worn out

5.percussion drill

6.Bit balling-up

7.Stuck

8.Bore hole collapse

9.Lost bit nozzle

10.Broken drilling string

1.Mud Gain

Phenomenon：

  PVT increase，accompanied with the change of  mud properties such as 

     density, conductivity, and viscosity, sometimes gas data increase.

     cause：

      formation pressure >  pressure of mud column，formation fluid run into hole,

      gas cut, oil cut and water cut.

      Lead to well blowout.

 

2.Mud loss

Mud loss (circulation loss)

phenomenon：

  pit volume decrease, a few to more than 10 cubic meters every hour, even to no return. If the loss velocity is high, SPP decrease.

cause：

  Natural Geological Conditions：For example, poor consolidated or unconsolidated,  and high permeability sandstone or conglomerate; It is easy to loss mud when drilling into fissure, fault or crushed zone caused by tectonism, solution cavity or fissure of carbonate formation.

  Improper Mud Properties：high density, high viscosity and high GEL，be  difficulty to cuttings deposit，lead to high pressure of mud cylinder.

  Improper Drilling Activities：trip in too fast or start pump and SPM increase suddenly，lead to surge.

Lead to formation contamination ，bore hole collapse or stuck. It is often seen that well blow out after mud loss.

   

3.Pipe washed out

Pipe washed out

phenomenon：

  other parameters（such as mud properties, WOB，FLOW IN）no change, SPP decrease slowly.

cause：

  wear and tear of drilling string, at least, one hole come into being on drilling string at least. Some mud take a short way since the hole and run into annular.

Dangerous result：

  bit balling up, even lead to stuck，or drilling string broken.

4.Bit worn out

Phenomenon： 

    WOB and RPM no change, drilling velocity become slow, TORQUE increase and  fluctuates in vast scale, cuttings become smaller. Sometimes see scrap iron.PDC, Tri-cone

          cause：bit life end（bit teeth worn severely; If it is tri-cone bit，sometimes cone movable.)

          Dangerous result：lose cone，lose bit   jet.

 

5.percussion drill

        percussion drill (Drilling string not well braked)

                Phenomenon:

                      suddenly, WOH decrease,  WOB increase， and   BLHT  decrease. At the                            same time,  instant ROP   increase drastically.

                                 Example 

                              Dangerous result：damage bit and drilling string, some time get stuck.

 6.Bit balling-up

                       henomenon: 

                                suddenly, WOH decrease,  WOB increase， and   BLHT decrease. 

                                At the same time,  instant ROP   increase drastically.

                                Example

                                   Dangerous result：damage bit and drilling string, some time get stuck.

  

7.Stuck

     

     Phenomenon: 

•               when drilling string is still in the hole for some time, with no circulation, it is possible  to get sticy stuck. Drilling string can’t move, can’t turn;  can start circulation, SPP no change.

        Cause: the hole azimuth change and there is inclination or  drilling  directional    hole. Drilling string lie on the wall because of gravity and has big interface with wall. In permeable formation, much mud loss; mud cake thick and loose, and has high stick force. Long time still in the hole, drilling string will be pressed on the wall because of pressure difference between mud cylinder and formation.

            Solution: properly move drilling string up and down suddenly, force turn, or pump in diesel oil for unfreezing. If no success in unfreezing, back off and mill. 

             

        Stuck – because of cuttings deposit  

    

    phenomenon：get overpull when moving drilling string up, can’t turn. Start pump, SPP increase, even choke the pump and difficult to start circulation.

               cause：（1）Low mud viscosity and small mud shear force, during fast drilling， stop pump since something happen. It is possible to get stuck because of cuttings deposit.

              （2） Low mud viscosity and small mud shear force, much mud loss, low mud salinity, seriously wash out, or did not fill in the mud in time when trip out, mud loss , blow out. All these things will lead to stuck because of  bore hole collapse.（3）Irregular hole diameter, stop pump suddenly,  it is possible to get cuttings bridge stuck in the place of big hole.

            Solution：try to start circulation, properly improve mud viscosity and shear force. Increase FLOW IN slowly. If no success in starting circulation, back off and mill.

          Key-seating sticking

     

    Phenomenon:

       fixed stuck point, often happen when tripping out, can start circulation, SPP normal, drilling string can trip in and can’t trip out.

             cause：bad hole quality.

             solution：move drilling string up with light overpull and back reaming with low RPM, use jars to unfreeze. If no success in unfreezing, back off and mill.

      tight hole sticking

     

     phenomenon：difficulty to move drilling string up, and easy to move down; difficulty to turn when moving up and possible to turn when moving down. Start circulation, SPP increase little, stuck point fixed when trip in and trip out. After the drilling tools POOH, there is mud cake on the tie-in.  Example

              cause：Underground, for high temperature, plastic deformation happen to the rock salt,  lead to tight hole. High dilatability clay stone or shale meet water and swell to form tight hole.

              solution：if  it is rock salt leads to tight hole stuck, water flushing can be used; if clay stone or shale dilatability lead to tight hole sticking, can move drilling string and ream to unfreezing the sticking.

  

         Bit balling up sticking

      Phenomenon:  

              the bit turns unsteadily on the bottom of hole, accompany

              with bit bouncing, ROP slow, can move down or ream down. It is difficulty to move up and back ream, with abnormal circulation, SPP increase, even choke the pump.

              Cause: （1）high mud viscosity, big shear force, high content of  solid phrase, low flow in, drill into soft formation, bit is easy to balling up. trip out to tight hole and it is easy to get stuck. （2） Since drilling string penetrated, short circuit of  circulation; pump efficiency decrease or drill with no pump in. Bit balling up sticking is easy to happen.

              Solution: start circulation，move down and turn drilling string, properly decrease mud viscosity, shear force, and flush the bit with high flow in.

8.Bore hole collapse

Phenomenon:

          mud density, shear force, viscosity, sand content increase, SPP unstable, sometimes choke the pump, torque increase. Cuttings return to surface become more, and intermix, even include much cavings.

          mud properties unstable, change very soon. There is mud blow out from inside drilling string  when tripping in or tripping out.  

         Cause:

          geological cause：there is abnormal pressure in the shale formation. When drilling into shale formation, the pressure of mud cylinder is less than pore pressure. The fluid in the shale run into the bore hole, accompany with flaking, cavings and collapse.

         Drilling techonics：the washing of mud; high surge or swab lead to instant pressure unbalance; did not fill the mud when trip out, serious mud loss, well blow out, lead to bore hole collapse.

         Geophysical cause：clay stone’s and shale’s hydration.

 

9.Lost bit nozzle

      Phenomenon:

                        flow in no change, SPP decrease suddenly, drilling velocity become slow.

 

1. 10.Broken drilling string

   Phenomenon:

          when drilling, WOH, SPP, TORQUE decrease suddenly；when tripping,     WOH decrease suddenly.