Drilling Fluids losses - LCM in Non Reservoir Section

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If lost circulation is expected, the following recommendations should be followed:

  • Nozzles of minimum 18/32in shall be used. As a rule-of-thumb, bit nozzles must be three times larger than the largest particle size of LCM, in order to reduce the possibility of blocking. If smaller nozzles are necessary a circulating sub shall be incorporated into the string.
  • Sufficient stocks of mud chemicals, LCM (fine, medium) and whole mud shall be maintained on site to cope with anticipated losses when drilling potential loss circulation zones.
  • LCM particles sizes to be established if LWD/MWD in hole.
  • A contingency LCM pill shall be mixed. Use the formulation applicable to the application and rate of loss, as detailed in the following section.
  • Historically (offshore) when drilling 17 ½”/16” hole with water/viscous pills there is no requirement for LCM to be added to drilling fluid.

Procedure to follow:

1. IF ost circulation occurs, in the first instance THEN, reduce the mud gradient as far as possible. If this doesn’t work continue with step 2.

2. DETERMINE the rate of loss.

3. ATTEMPT to identify the loss zone.

4. CHOOSE LCM formulation from those listed below and MIX a pill of volume 25-50 bbl, taking the following into account:

IF...

THEN...

bit nozzles are smaller than 14/32in

LCM particle size shall not exceed one third of the bit nozzle size. The formulations shall be adjusted accordingly

a circulating sub is included in the string (if needed)

it should be opened to permit application of normal LCM formulations.

there is an MWD tool in the string

coarse LCM shall not be used. Use maximum size as advised by the MWD representative.

Notes:

In non-reservoir sections, use formulations listed below as appropriate to the rate of loss.

In reservoir sections Rig Supervisor shall be contacted for permission to use acid soluble LCM. Only formulations listed    as appropriate for use in reservoirs shall be used.

5. DISPLACE pill at a rate of 200 gal/min and SPOT pill across the previously identified loss zone (75% across loss zone and 25% above it).

6. REPEAT spotting of LCM if not cured at the first attempt.

7. In the event that LCM pills prove ineffective, and there is a long section of hole still to be drilled, then LCM may be added to the active system at a concentration of 2 lbs/bbl. If severe losses continue CONTACT Rig Supervisor and PUMP a specialised pill as directed.

Note: LCM may be added to the active system at a concentration of 2 lbs/bbl before reaching the expected weak zone from experience and data from offset wells.

Formulation and Mixing Procedure for LCM Pills Offshore

Slight losses 1-10 bbl/hr

Micafine       3-5lb/bbl

Mica med      3-5lb/bbl      50 bbls LCM pill

Losses > 10-20 bbls/hr

25-40ppb ultra seal XP

15-40ppb  ultra seal C    50 bbl LCM pill

Losses > 20 bbl/hr

Kwikseal*     40ppb ultra seal XP

40ppb ultra seal C        50-100 bbl LCM pill

*This material is useful in an emergency, as it contains a similar range of particle types to the pill formulation detailed above for ‘slight losses’.

Formulation & Mixing Procedure for LCM Pills-Onshore

Slight Losses

6-10 ppb CaCO3 fine added to the mud

OR 10-15 ppb Ultra seal fine

Major Losses

CaCO3 fine (20ppb), medium (15ppb) and coarse (10ppb) ~ 45 ppb Viscous

pills 50-100 bbls.

Mixing LCM Pills

The amount of LCM that can be added to a mud depends very much on the mud properties. High gels and YP will help keep the material in suspension. Since LCM is generally of low gradient, excess material tends to float on top if too much is added.  The following procedure may prove useful for mixing LCM pills and avoiding the problem of flotation.

1. ENSURE the pill has enough viscosity to keep the low gradient material in suspension before addition of LCM. ADD appropriate viscosifier if required.

2. ADD the material in stages e g. 5, 10, 15, 20 etc. ppb.

3. STOP after desired concentration has been reached, or when it is observed that the material cannot be held in suspension

4. If a higher LCM content is desired, LEAVE the pill to soak for a period of time and then TRY ADDING more material.

Recommended Stocks of  LCM Offshore

The following materials of LCM shall be maintained on site at all times

KWIKSEAL                      Ultraseal  XP 

Mica (fine)                         Ultraseal C

Mica (medium)                  Ca2CO3 Fine/Med/Coarse

Mica (coarse)

CMC-HV (to viscosify pills before addition of LCM)

In addition, sufficient LCM materials shall be on board to be able to mix 300bbls of LCM mud at 50ppb.

 

347 - Loses - decision chart

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