Petroleum Engineering 406

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

Volume pumped

Pressure

Leak-Off

MWTVD

essureLeakOffEMW

shoe

*052.

Pr

Fracture Initiation

Fracture Extension

Casing Test

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

ftbblCapAnn

bblPitGainheight

height

SIDPPSICPMWyKickDensit

/,.

,

052.0

Drillers Method

• Pressure at Top of Kick-Px

MWxDv

vPPB

ZT

MWZTP

v

VBBP

X

BFBB

BB

XXB

x

Bx

052.0

052.0

42

2/12

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

111

2/1

12

11

052.0052.0'

052.0

42

MWxDMWMWDv

vPPB

ZT

MWZTP

v

VBBP

X

BFBB

BB

XXB

x

Bx

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=constant

• Charles’ Law– V/T=constant

• Avagadro’s Law– PV=nRT

• Real Gas Law– PV=ZnRT

• PV/ZT = nR

• 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