Increase required to balance a kick (lb/gal)
03.08 Wait and weight method
This method is also called the "balance method" and is described below.
The well is shut in and pressure values are observed. The drilling fluid is increased to the weight necessary to kill the well. While keeping constant casing pressure the pumps are slowly brought up to slow circulating rate and when running at the desire rate the drill pipe pressure is the ICP.
The primary objective, while killing the well is to keep constant BHP, but as the heavy drilling fluid fills the drill string the ICP cannot be held constant due to the change in hydrostatic head. In the annulus the gas expands as it rises, so therefore casing pressure cannot be held constant either.
However, the choke can be manipulated in such a way that standpipe pressure can be gradually decreased as the heavy drilling fluid is pumped down the drill string. How much and how often it is decreased can be decided in the following way.
Like the Driller's Method we begin to circulate with a standpipe pressure equal to PSIDPP + PL and when the drill string is full of heavy drilling fluid the pressure will be equal to the new PL with heavy drilling fluid inside the string or FCP. This change in standpipe pressure occurs over a certain period of time that depends on the total number of strokes it takes to pump the drill string full of heavy drilling fluid. (Surface-to-bit).
The easiest way is to represent this graphically. The following graph will show standpipe pressure changes in relation to pump strokes combined with a table that shows the new standpipe pressure for every 100 strokes. See Fig 58
The figures used for the graph and table apply to example in Driller’s Method and W&W Method.
Pressure change per 100 strokes is calculated in the following way:
(ICP – FCP) x 100
∆P/100 strk = ---
Surface to bit strokes
Using the previous example we will get:
(1180 – 692) x 100
∆P/100 strk = --- = 27psi/100 strk 1812
Circulation of the heavy drilling fluid from surface-to-bit can now proceed by regulating the choke after the table, so the bottom-hole pressure will remain constant.
As soon as the drill string is full of heavy drilling fluid (after 1812 strokes) no change will occur of drilling fluid density and drilling fluid column in the drill string, which means that standpipe pressure (692 psi) can be held constant for the rest of circulation.
WELL CONTROL MANUAL
MTC
Fig 58
When killing a kick by the Weight and Wait Method, there are four phases that are described below.
Phase 1. Mix the required kill fluid immediately. When the kill fluid is ready, start pumping and open choke slowly while the pump is brought up to speed holding casing pressure constant at this initial start-up. As the drill string is gradually filled with kill fluid, circulation pressure is regulated with the choke to follow the values of the curve, until the calculated FCP with kill fluid at the bit is reached. (At this stage the drill pipe should be dead).
Phase 2. Continue pumping until the gas is at the choke keeping constant drill pipe pressure.
Phase 3. Continue pumping until all the gas is out. At this stage the annulus will be full of kill fluid, minus the capacity of the drill string which is light drilling fluid.
Phase 4. Continue pumping until the annulus is full of heavy drilling fluid. At this stage the well should be dead.
0
WELL CONTROL MANUAL
MTC
Wait and weight method:
Well Kick Data:
Capacity open hole x drill pipe/HWDP 0.04470 bbl/ft Capacity casing x drill pipe 0.04891 bbl/ft
With the following date given the kill sheet can be filled out and the necessary information be required to kill the well:
Internal strokes from surface to bit: 1812 strokes
Situation Fig 59 shows the start of circulation. The standpipe pressure is equal to PSIDPP plus PL (Reduced Rate Circulation Pressure Loss). The pressure at the casing head Pa is equal to PSICp.
While keeping constant casing pressure the pumps are slowly brought up to slow circulating rate, in this case 30 SPM. When the pumps are running at 30 SPM and pressures have stabilized change to ICP and then keep DP pressure on schedule.
ICP = SIDPP + PL
530 psi + 650 psi = 1180 psi
Shoe pressure = Phshoe + SICP
WELL CONTROL MANUAL
MTC
7189 psi + 700 psi = 7889 psi
MAASP = Max Shoe Pressure - Phshoe
8678 psi - 7189 psi = 1489 psi
Fig 59 Fig 60
Situation Fig 60 shows kill fluid fills the drill string while gas is circulated a way up the annulus.
Drill Pipe Pressure is kept on schedule while gas is being pumped up through the open hole section and the top of the gas bubble reach the shoe. The gas is expanding allowing the pressure inside bubble to decrease.
Drill Pipe Pressure is kept on schedule with 27 psi drop per 100 strokes pumped.
DP P = ICP - (470 x 27) 1053 psi
100
Casing pressure increasing due to the expanding gas is displacing drilling fluid.
CSG P = BHP - (Phmud + Phgas) 775 psi
Shoe pressure is increasing with same value as the casing pressure and reach max. value when gas reaches the shoe.
Shoe P = Phshoe + Csg P 7964 psi
MAASP remains constant due to no change in Ph inside the casing.
MAASP = Max Shoe Pressure - Phshoe 1489 psi
Situation Fig 61 shows kill fluid fills the drill string while gas is circulated inside the casing.
The gas is expanding allowing the pressure inside bubble to decrease.
PA
PDP
DRILL STRING ANNULUS
BHP GAS
Shoe OMW
OMW
PA
PDP
DRILL STRING ANNULUS
GAS
BHP
Shoe OMW
OMWKMW
WELL CONTROL MANUAL
MTC
Drill Pipe Pressure is kept on schedule with 27 psi drop per 100 strokes pumped.
DP P = ICP - (620 x 27) 1013 psi
100
Casing pressure increasing due to the expanding gas is displacing drilling fluid.
CSG P = BHP - (Phmud + Phgas) 785 psi
Fig 61 Fig 62
Shoe pressure is decreasing while gas moves from below the shoe until all gas inside the casing.
Shoe P = BHP - Phopen hole 7718 psi
MAASP start increasing from the first gas enters the casing due to change in Ph inside the casing.
MAASP = Max Shoe Pressure - Phshoe 1685 psi
Situation Fig 62 shows kill fluid has filled the drill string.
The gas is expanding allowing the pressure inside bubble to decrease.
Drill Pipe Pressure is kept on schedule with 27 psi drop per 100 strokes pumped and reach FCP when kill fluid at bit.
DP P = ICP - (1812 x 27) 692 psi
100
Casing pressure increasing due to the expanding gas is displacing drilling fluid.
CSG P = BHP - (Phmud + Phgas) 1050 psi
PA PDP
DRILL STRING ANNULUS GAS
BHP
Shoe OMW
OMWKMW
PA PDP
DRILL STRING ANNULUS
GAS
BHP
Shoe OMW
KMW
OMW
WELL CONTROL MANUAL
MTC
Shoe pressure constant due to no change in Phopen hole
Shoe P = BHP - Phopen hole 7718 psi
MAASP increasing with the same value as the Csg P due to change in Ph inside the casing.
MAASP = Max Shoe Pressure - Phshoe 1950 psi
Situation Fig 63 shows kill fluid has displaced the top of the gas to the choke.
The gas is expanding allowing the pressure inside bubble to decrease.
Drill Pipe Pressure constant at FCP after kill fluid reach the bit.
DP P = FCP 692 psi Casing pressure increasing due to the expanding gas is displacing drilling fluid, but slower
due to kill fluid is displacing original mud.
CSG P = BHP - (Phmud + Phgas + Phkill mud) 1278 psi
Shoe pressure remains constant after kill fluid enter casing due to no change in Phopen hole.
Shoe P = BHP - Phopen hole 7641 psi
MAASP increasing with the same value as the Csg P due to change in Ph inside the casing.
MAASP = Max Shoe Pressure - Phshoe 2178 psi
Fig 63 Fig 64
Situation Fig 64 shows kill fluid has displaced all the gas out of the well bore.
Drill Pipe Pressure constant at FCP after kill fluid reaches the bit.
DP P = FCP 692 psi
PA PDP
DRILL STRING ANNULUS
GAS
BHP
Shoe
KMW
OMW
KMW
PA PDP
DRILL STRING ANNULUS
BHP
Shoe
KMW
OMW
KMW
WELL CONTROL MANUAL
MTC
Casing pressure decreasing while gas is displaced out of the well bore.
CSG P = BHP - (Phmud + Phkill mud) 180 psi
Shoe pressure remains constant after kill fluid enter casing due to no change in Phopen hole.
Shoe P = BHP - Phopen hole 7641 psi
MAASP decreasing while gas is displaced out of the well bore.
MAASP = Max Shoe Pressure - Phshoe 1204 psi
Situation Fig 65 shows kill fluid has displaced the remaining original drilling fluid out of the wellbore.
Drill Pipe Pressure constant at FCP after kill fluid reaches the bit.
DP P = FCP 692 psi Casing pressure decreasing to 0 psi while kill fluid displaces original mud out of the well
bore.
CSG P = BHP - Phkill mud 0 psi
Shoe pressure remains constant after kill fluid enter casing due to no change in Phopen hole.
Shoe P = BHP - Phopen hole 7641 psi
MAASP decreasing while kill fluid displace original mud out of the well bore.
MAASP = Max Shoe Pressure - Phshoe 1027 psi
Fig 65
Fig 66 shows the pressure relationships between drill pipe and casing.
PA
PDP
DRILL STRING ANNULUS
BHP
Shoe
KMW KMW
WELL CONTROL MANUAL
MTC
Drill Pipe pressure:
Drill Pipe Pressure decreasing from ICP to FCP while kill fluid fills the drill string.
Drill Pipe Pressure constant at FCP the remaining circulating time.
Casing pressure:
Casing pressure constantly increases until gas reach the choke.
Casing pressure decreases rapidly while gas is displaced from the well bore.
Casing pressure decreases to 0 psi while original mud is displaced with kill fluid.
Shoe pressure:
Increase while gas is moving up in the open hole section.
Decrease while gas enters the casing.
Constant until kill fluid reaches the bit.
Decrease while kill fluid is moving up the open hole section.
Constant after open hole has been displaced to kill fluid.
MAASP pressure:
Constant while gas is moving up in the open hole section.
Increase rapidly while gas enters the casing.
Increase until gas reaches the choke.
Decrease rapidly while gas is displaced from the well bore.
Decrease while original mud is displaced with kill fluid.
Fig 66 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500
0 1000 2000 3000 4000 5000 6000 7000 8000
STROKES
PRESSURE
DRILL PIPE PRESSURE CASING PRESSURE
WELL CONTROL MANUAL
MTC
Annular pressure will fall to 0 PSI as soon as heavy drilling fluid appears at the choke.
When this is observed the well should be dead. A flow check can now be made.
If no flow is observed the blow-out preventer can be opened, and the drilling fluid can be circulated and conditioned as necessary, a trip margin can be added if it was not added to the kill drilling fluid at the start of the operation. Tripping or drilling can now take place again.