Geo Pressures

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GEOPRESSURES

y : T a h e r G o m a a y : T a h e r G o m a a S o n a t r a c h D E S Q S o n a t r a c h D E S Q

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Formation of Geopressures

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 The various geologica The various geological and mechanicall and mechanical

variables conspire to pore pressure, which variables conspire to pore pressure, which is higher or lower than

is higher or lower than the normalthe normal pressure.

pressure.

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 The fundamental dier The fundamental dierence betweenence between

normal and abnormal pressure rock, is normal and abnormal pressure rock, is

that in abnormal pressures zone the pore that in abnormal pressures zone the pore uid is no longer communicate 100% with uid is no longer communicate 100% with the water table t

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Formation of Geopressures

 _{"nce the uid column has been broken, the pore pressure act}

in # dierent wa$s

 _{1& 't can be perfectl$ sealed like a balloon.}  (& 't ma$ leak slowl$ like a punctured tire.

 _{#& 't can leak )uickl$ and does not hold pressure}

for a long time.

 _{The criteria that determine the e*cienc$ of the seal or cap}

rock are

 _{1& +ermeabilit$}  (& Thickness

 _{#& agnitude of dierential pressure}

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Measurements of formation pressure

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The evaluation of formation pressure

is essential for well planning, it is

important to know the formation

pressure so the mud densit$ is

optimized.



/ploration and production database

can provide detailed information

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Measurements of formation pressure

 Information from Seismic, Wireline logs,

FEMWD, FEL, direct methods of formation pressure measurements (DST, RFT and

LOT and production testing can !e used"

 Direct relation !et#een petroleum

geolog$ and drilling engineering can gi%e

accurate ESTIMATION of formation

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Measurements of formation pressure

 _{2 if available is ver$ important, 3amma ra$,}

4esistivit$, 5eutron +orosit$ and formation 2ensit$ can help in estimating pore pressure.

 _{6econdar$ e)uipment such as ud 2ensit$ sensor}

'n 7 "ut!, ud Temperature sensor 'n 7 "ut!, ud low sensor and +it 8olume sensors provide useful information for pore pressure estimation.

 2rilling parameters such as 4"+, formation gas

background gas, trip gas, connection gas,9etc! and the shape and size of shale cuttings provide good information for pore pressure estimation.

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Formation Pressure – Mud Density

relationship

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HYDROS!"# PRESSURE #!$#U$!"ON

 The &$drostatic 'ressure calculation can !e

dri%en from the follo#ing euation) P = 0.0519 * MW * DEPTH Where

'* &$drostatic pressure in 'SI MW* Mud Weight in ppg

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HYDROS!"# PRESSURE #!$#U$!"ON

 The con%ersion factor ("-./ is dri%en

from)

There are 0"12 gallon in one cu!ic ft" There are .11 suare inches in one suare ft"

L!3gal 4 0"12 gal3ft5 4 .3.11 ft63in *0"123.11 psi3ft3l!3gal

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HYDROS!"# PRESSURE #!$#U$!"ON

 _{The same euation can !e changed for S7 units)}

K Pa = Density (kg/m3) * D (meter) * 0.0098

Where)

"/2 is the constant for S7 units

The euation can !e modified to)

'ressure (psi *"-./4MW (S742"514Depth (meter45"62.

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Effe%ti&e #ir%ulatin' Density (E#D)

 Effecti%e circulating densit$ is a measure of

the mud #eight under circulation and pressure, it is dri%en from the euation)

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Pore Pressure E&aluation e%hni*ues

 Man$ methods are used to determine the

pore pressure, such as)

.87eoph$sical measurement #hich can !e su!di%ided to)

4 Seismic methods 4 7ra%it$ methods 4 Magnetic methods 68 Drilling 'arameter)

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Pore Pressure E&aluation e%hni*ues

 _{Mud Density / Gas ut Mud !e"ati#ns$i%&}

 _{Differential pressure is the difference !et#een E9D and Formation} :alance 7radient and is calculated from the euation)

 _{Su!stituting E9D for W gi%es the Differential 'ressure #hile} drilling, it is desira!le to al#a$s ;eep it as a positi%e %alue"

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Pore Pressure E&aluation e%hni*ues



E<ample to the last euation, a hole

is drilled at 6 ft, #ith mud

densit$ of /" and the formation

!alance gradient is 2"= ppg" Thus)

 _{(9.0*2000*0.0$19)%(8.&*2000*0.0$19)= 43 psi}



For the same hole !ut at .- ft

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Pore Pressure E&aluation e%hni*ues

 From the pre%ious e<ample #e can

conclude that gas cut mud #ill !e more critical in shallo# depths than deep

depths"

 This is due to the fact that the deeper the

hole the greater the differential pressure, the lo#er the gas influ< that might influ< from the formation"

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G!S #U MUD

 7as cut mud is the reduction of mud #eight

due to gas influ<, it can !e determined from the euation)

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G!S #U MUD

 >n e<ample for the last euation)

d* 2"-? R* 2- ft3hr O* "6-Sg* "0

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G!S #U MUD

 _{To calculate the same amount of gas at surface, #e use}

the euation)

 _{Where 7%a is the gas flo# at surface}

7% is the gas flo# at stud$ point ' is the pressure at stud$ point

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G!S #U MUD

 _{W. * 7as 9ut Mud Densit$}

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Hole +eha&ior



When a condition of near !alance

occur, the #ell formation pressure

#ill !e held !$ E9D and not the

mud #eight"



If permea!ilit$ e<ists, there might

!e fluid influ< ;ic;"



If permea!ilit$ is lo#, the !orehole

#ill suffer from connection gas, trip

gas

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Hole +eha&ior



The parameters that indicate near

!alance situation are)

.8 E<istence of pressured ca%ing"

68 Drag #hile tripping and connection"

58 9onnection gas and trip gas

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Drilla,ility

The rate at #hich the formation can !e drilled depend on man$ factor

such as) o Force applied" o Rotar$ speed" o Tooth efficienc$" o Differential pressure" o Drilling &$draulics"

o Matri< strength of formation" o Formation compaction

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