Petroleum Engineering 406
Lesson 3
Well Control
Read
• Well Control Manual
– Chapter 7-8
• Homework 2 Due Jan. 30, 2001
Content
•
•
•
•
•
Equivalent Mud Weights - EMW
Casing Seat Tests
Kick Tolerance
Differences in Kick Types
Reaction of Gas in the Wellbore
Equivalent Mud Weight
• EMW - the total pressure exerted at a given
depth expressed in ppg equivalent
• EMW = Surf. Press./(0.052*TVDint)+MW
– or
• EMW = Total Press. /(0.052*TVDint)
Equivalent Mud Weight
• Examples:
– KWM
– ECD - Equivalent Circulating Density
• ECD = Ann. Fric./(0.052*TVD)+OWM
– Frac gradient
– Pore pressure, etc
Casing Seat Tests
• We test casing seats to:
– Determine max pressure that formation can
withstand
– Determine if we have a good cement job
Casing Seat Tests
• LOT - Leak-Off Test
– Measure the fracture
pressure at casing seat
– or, Maximum pressure
the formation can
withstand prior to
fracture
EMW 
LeakOff Pr essure
 MW
.052 * TVDshoe
Fracture Initiation
P
r
e
s
s
u
r
e
Leak-Off
Fracture Extension
Casing Test
Volume pumped
Casing Seat Tests
• PIT - Pressure Integrity Test (FIT)
– Determine if the casing seat can withstand a
pre-determined pressure
• Test Pressure = (EMW-MW)*0.052*TVDcasing seat
Kick Tolerance
• Maximum Casing Pressure - MCP
• Maximum Allowable Annular Surface
Pressure - MAASP, MASP
• Maximum Casing pressure that the
formation can withstand prior to fracture
• = (EMW-MW)*0.052*TVDcasing seat
Kick Tolerance
• Maximum ppg kick - Maximum mud
weight increase on a kick prior to formation
fracture
• =(EMW-MW)*TVDshoe/TVDwell
• Assumes zero pit gain
Kick Tolerance
• Maximum Kick Volume
Kick Types
• Gas Kicks
– Rapid expansion as gas circulated through
choke
– Mud gas separators and flare lines used
– Gas migration problems
– Higher SICP than others
Kick Types
• Gas Kicks, cont.
–
–
–
–
Barite settling in OB mud
Solubility of gas masks kick indicators
Flammability of gas
Slugging of gas at choke
Kick Types
• Oil Kicks
– Flammable but not as explosive as gas
– Density greater than gas-lower SICP
– Very little expansion as kick reaches surface
– But, there is almost always some gas present
Kick Types
• Water kicks
– not flammable
– very little expansion
– lower SICP than gas or oil
– But, there is still usually some gas present.
Kick Types
• Prediction kick types
– Density of gas =1-2 ppg
– Density of oil = 6-8 ppg
– Density of salt water =8.6-9.0 ppg

SICP  SIDPP 
KickDensit y  MW 
0.052  height
PitGain, bbl
height 
Ann.Cap, bbl / ft
Drillers Method
• Pressure at Top of Kick-Px
  VB  PB  TX  Z X  MW  0.052   
    

TB  Z B
  v x 
 
vB
B  PB  PFB 
 D  x   0.052  MW
vX
B  B
Px   
2  4
2
1/ 2
Drillers Method
• Surface Casing Pressure - CP
– CP=Px-0.052*MW*x
• Pressure at casing seat - Pseat
–
–
–
–
Pseat=CP+0.052*MW*Dseat
where the bubble is below the casing seat
Pseat=PB-0.052*MW*(D-Dseat)
where the bubble is above the casing seat
Wait & Weight Method
• Pressure at Top of Kick-Px
B1  B   VB  PB  TX  Z X  MW1  0.052   
Px        

2  4   v x 
TB  Z B
 
v
B1  PB  PFB  B  D'0.052  MW1  MW   D  x   0.052  MW1
vX
2
1
1/ 2
Wait & Weight Method
• Surface Casing Pressure - CP
– CP=Px-0.052*MW*x
• Pressure at casing seat - Pseat
–
–
–
–
–
Pseat=CP+0.052*MW*Dseat
where the bubble is below the casing seat
Pseat=PB-(0.052*MW*D’)
-[0.052*MW1*(D-D’-DSEAT)]
where the bubble is above the casing seat
Nomenclature
Examples
Surface Casing Pressure
Ann. Press @ Various Depths
Reaction of Gas in a Wellbore
• Boyle’s Law
• PV/ZT = nR
– PV=constant
• Charles’ Law
– V/T=constant
• Avagadro’s Law
– PV=nRT
• Real Gas Law
– PV=ZnRT
• P1*V1 = P2*V2
Z1*T1 Z2*T2
• V2 = P1*V1*Z2*T2
P2*Z1*T1
Reaction of Gas in a Wellbore
• Circulating gas from wellbore
• Given:
–
–
–
–
–
–
Depth
=16,000’
BHT
=300oF
BHP
=12480 psi
MW
=15.0 ppg
Surf. Temp =140oF
Drilled up 1 cu.ft. of gas
Reaction of Gas in Wellbore
Reaction of Gas in Wellbore
Gas Migration
Gas Migration
MASP