Geo Pressures

GEOPRESSURES

Formation of Geopressures 

 The various geological geological and mechanical variables conspire to pore pressure, which is higher or lower than the normal pressure.

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 The fundamental dierence dierence between normal and abnormal pressure rock, is that in abnormal pressures zone the pore uid is no longer communicate 100% with the water table trapped!. t rapped!.

Formation of Geopressures 

"nce the uid column has been broken, the pore pressure act in # dierent wa$s   

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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  -& Time over which pressure changes have occurred.

Formation of Geopressures

Measurements of formation pressure 

 The evaluation of formation pressure is essential for well planning, it is important to know the formation pressure so the mud densit$ is optimized.

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/ploration and production database can provide detailed information about pore pressure estimation.

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"

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Direct relation !et#een petroleum geolog$ and drilling engineering can gi%e accurate ESTIMATION  of formation pressures"

Measurements of formation pressure 

2 if available is ver$ important, 3amma ra$, 4esistivit$, 5eutron +orosit$ and formation 2ensit$ can help in estimating pore pressure.

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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.

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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.

Formation Pressure – Mud Density relationship

Normal Pressure Profile

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 D* +ertical depth in ft

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 *"-./ psi3ft3l!3gal

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. Pressure (psi) = 1.42 * M (!") * Dept# (meter)

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)

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

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

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)

Pore Pressure E&aluation e%hni*ues 

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

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

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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"

Pore Pressure E&aluation e%hni*ues 

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