- Circulate casing and condition mud. a minimum of 150 % of the casing contents must be circulated. Carry out circulation test to assess displacement rates, carefully monitor for losses.
- Drop first bottom plug (optional) and pump preflush. if a problem occurs which cannot be fixed in less than 20 minutes, the preflush must be circulated out.
- Drop second bottom plug. Pre-mix and re-circulate slurry until gradient is within safe tolerance.
- Mix and pump cement. if a problem occurs before the programmed volume of cement has been pumped, determine the course of action to be taken using the following:
Case 1
Length of cement column is enough to satisfy all objectives of the cementation.
Continue with next step in process.
case 2
Length of cement column is insufficient to satisfy all objectives of the cementation.
There is enough time available to circulate the slurry out.
Circulate the slurry out, solve problem and start again.
case 3
Length of cement column is insufficient to satisfy all objectives of the cementation.
The length of time available is insufficient to circulate the slurry out.
Continue with next step in process.
- Drop the top plug.
- Pump the postflush.
- Displace at pre-determined rate using the rig pumps or cement unit. during displacement, monitor the pressure. If pressure is low, continue displacing with the rig pumps but monitor the returns closely to ensure there are no losses. if the pressure is increasing then this is an indication of premature setting of the cement, and the displacement must be completed using the cement unit.
- Record the pressure differential immediately prior to bump in order to facilitate estimation of TOC. shortly before bumping the plug, reduce rate to 2 bbls/min
- Bump bottom plug. if the plug does not bump, pump a maximum of 1/2 the volume of the shoetrack, monitor for plug bump. if the plug still does not bump stop displacement and woc.
Notes: In the case of failure of the plug to bump the following considerations shall be taken into account:
a. Are displacement pressures continuing to increase?
b. Are there positive indications of top plug release?
c. Are there any indications of circulating system malfunctions which may lead to a decreased pump efficiency from that ascertained during the drilling phase ?
- Pressure test casing for 15 minutes. Refer to drilling programme for casing test pressures.
- Release pressure and check for backflow. If backflow is observed, close the surface line to the cementing head and wait until the surface cement samples have set. do not pump any volume of mud back, on backflow, as there is the possibility of pumping mud contaminated cement around the shoe.