4. Pressure Control
Table of Content
4.1 Kill Sheets & Related Calculations
Normal Kill Sheet
Pre-recorded Data
Original mud weight (OMW)____________ ppg
Measured depth (MD)__________________ ft
Kill rate pressure (KRP)___ psi @ ___ spm
Kill rate pressure (KRP)___ psi @ ___ spm
Drill String Volume
Drill pipe capacity:
___ bbl/ft × ___ length, ft = ___ bbl
Drill pipe capacity:
___ bbl/ft × ___ length, ft = ___ bbl
Drill collar capacity:
___ bbl/ft × ___ length, ft = ___ bbl
Total drill string volume _________ bbl
Annular Volume
Drill collar/open hole
Capacity ___ bbl/ft × ___ length, ft = ___ bbl
Drill pipe/open hole
Capacity ___ bbl/ft × ___ length, ft = ___ bbl
Drill pipe/casing
Capacity ___ bbl/ft × ___ length, ft = ___ bbl
Total barrels in open hole _______________ bbl
Total annular volume _____________________ bbl
Pump Data
Pump output ___ bbl/stk @ ___ % efficiency
Surface to bit strokes:
Drill string volume ___ bbl ÷ ___ pump output, bbl/stk = ___ stk
Bit to casing shoe strokes:
Open hole volume ___ bbl ÷ ___ pump output, bbl/stk = ___ stk
Bit to surface strokes:
Annulus volume ___ bbl ÷ ___ pump output, bbl/stk = ___ stk
Maximum allowable shut-in casing pressure:
Leak-off test ___ psi, using ppg mud weight @ casing setting depth of ___ TVD
Kick data
SIDPP ______________________ psi
SICP _______________________ psi
Pit gain ___________________ bbl
True vertical depth ________ ft
Calculations
Kill Weight Mud (KWM), ppg = SIDPP, psi ÷ 0.052 ÷ TVD, ft + OMW, ppg
Initial Circulating Pressure (ICP), psi = SIDPP, psi + KRP, psi
Final Circulating Pressure (FCP), psi = KWM, ppg x KRP, psi ÷ OMW, ppg
Psi/stroke, psi/stk = (ICP, psi — FCP, psi) ÷ strokes to bit, stk
Pressure Chart
| Strokes | Pressure | ||
|---|---|---|---|
| 0 | ___ | Initial Circulating Pressure | |
| ___ | ___ | ||
| ___ | ___ | ||
| ___ | ___ | ||
| ___ | ___ | ||
| ___ | ___ | ||
| ___ | ___ | ||
| Strokes to Bit | ___ | ___ | Final Circulating Pressure |
Example: Use the following data and fill out a kill sheet:
Data:
Original mud weight = 9.6 ppg
Measured depth = 10,525 ft
Kill rate pressure @ 50 spm = 1000 psi
Kill rate pressure @ 30 spm = 600 psi
Drill string:
drill pipe 5.0 in. — 19.5 lb/ft capacity = 0.01776 bbl/ft
HWDP 5.0 in. 49.3 lb/ft
capacity = 0.00883 bbl/ft
length = 240 ft
drill collars 8.0 in. OD — 3.0 in. ID
capacity = 0.0087 bbl/ft
length = 360 ft
Annulus:
hole size = 12 1/4 in.
drill collar/open hole capacity = 0.0836 bbl/ft
drill pipe/open hole capacity = 0.1215 bbl/ft
drill pipe/casing capacity= 0.1303 bbl/ft
Mud pump (7 in. x 12 in. triplex @ 95% eff.) = 0.136 bbl/stk
Leak-off test with 9,0 ppg mud = 1130 psi
Casing setting depth = 4000 ft
Shut-in drill pipe pressure = 480 psi
Shut-in casing pressure = 600 psi
Pit volume gain = 35 bbl
True vertical depth = 10,000 ft
Calculation:
Drill string volume:
Drill pipe capacity = 0.01776 bbl/ft × 9925 ft = 176.27 bbl
HWDP capacity = 0.00883 bbl/ft × 240 ft = 2.12 bbl
Drill collar capacity = 0.0087 bbl/ft × 360 ft = 3.13 bbl
Total drill string volume = 181.5 bbl
Annular volume:
Drill collar/open hole = 0.0836 bbl/ft × 360 ft = 30.10 bbl
Drill pipe/open hole = 0.1215 bbl/ft × 6165 ft = 749.05 bbl
Drill pipe/casing = 0.1303 bbl/ft × 4000 ft = 521.20 bbl
Total annular volume = 1300.35 bbl
Strokes to bit: Drill string volume 181.5 bbl ÷ 0.136
bbl/stk
Strokes to bit = 1335 stk
Bit to casing strokes:
Open hole volume = 779.15 bbl ÷ 0.136 bbl/stk
Bit to casing strokes = 5729 stk
Bit to surface strokes:
Annular volume = 1300.35 bbl 0.136 bbl/stk
Bit to surface strokes = 9561 stk
Kill weight mud (KWM) 480 psi ÷ 0.052 ÷ 10,000 ft +
9.6 ppg = 10.5 ppg
Initial circulating pressure (ICP) 480 psi + 1000 psi = 1480
psi
Final circulating pressure (FCP) 10.5 ppg x 1000 psi ÷ 9.6 ppg
= 1094 psi
Pressure Chart
Strokes to bit = 1335 ÷ 10 = 133.5
Therefore, strokes will increase by 133.5 per line:
| Strokes | Pressure | ||
|---|---|---|---|
| 133.5 rounded up | 0 | ___ | Initial Circulating Pressure |
| 133.5 = | 134 | ___ | |
| + 133.5 = | 267 | ___ | |
| + 133.5 = | 401 | ___ | |
| + 133.5 = | 534 | ___ | |
| + 133.5 = | 668 | ___ | |
| + 133.5 = | 801 | ___ | |
| + 133.5 = | 935 | ___ | |
| + 133.5 = | 1068 | ___ | |
| + 133.5 = | 1202 | ___ | |
| + 133.5 = | 1335 | ___ |
Pressure
ICP (1480) psi − FCP (1094) ÷ 10 = 38.6 psi
Therefore, the pressure will decrease by 38.6 psi per line.
| Strokes | Pressure | ||
|---|---|---|---|
| 1480 − 38.6 = | 0 | 1480 | Initial Circulating Pressure |
| − 38.6 = | ___ | 1441 | |
| − 38.6 = | ___ | 1403 | |
| − 38.6 = | ___ | 1364 | |
| − 38.6 = | ___ | 1326 | |
| − 38.6 = | ___ | 1287 | |
| − 38.6 = | ___ | 1248 | |
| − 38.6 = | ___ | 1210 | |
| − 38.6 = | ___ | 1171 | |
| − 38.6 = | ___ | 1133 | |
| − 38.6 = | ___ | 1094 | Final Circulating Pressure |
Trip Margin (TM)
TM = Yield point ÷ 11.7(Dh, in. − Dp, in.)
Example: Yield point = 10 lb/l00 sq ft; Dh = 8.5 in.; Dp = 4.5
in.
TM = 10 ÷ 11.7 (8.5 − 4.5)
TM = 0.2 ppg
Determine Psi/stk
Example: Using the kill sheet just completed, adjust the
pressure chart to read in increments that are easy to read on pressure
gauges. Example: 50 psi:
Initial circulating pressure = 1480 psi
Final circulating pressure = 1094 psi
Strokes to bit = 1335 stk
Psi/stk = (1480 psi − 1094 psi) ÷ 1335 stk
Psi/stk = 0.2891 psi/stk