Abstract: A model for predicting of Pore Pressure Response Based On Constant

Plastic Index ( CPI ) Method.

Wan Ismail Wan Yusoff . Associate Professor Universiti Teknologi Petronas , Bandar Seri Iskandar , Tronoh , Perak .

Abdull Halim Abdul . Lecture Universiti Teknologi Petronas , Bandar Seri Iskandar , Tronoh , Perak . Email

halim.abdul@petronas.com.my

Historically pore pressure evaluation was based on empirical relationship between Seismic Cone Penetration Test (SCPT) and Cone Penetration

Test (CPT ) methods . Dissipation of excess pore pressure during SCPT and CPT testing in saturated soil and over - consolidated fine – grained

soils provide data curve that cannot be interpreted using published theoretical solution. The available solutions are based on modified Constant

Plastic Index (CPI) on integrated PAD- Mod soft - ware on depth versus pore pressure either cavity - tensile expansion or strain – path

methods , which have been analyzed for very soft to lightly consolidated cohesive soils . The Modification of Constant Plastic Index (CPI)

method is an approach based on volume matrix change on the consolidation theory. The objective behind the Modification of CPI method is to

predict pore pressure, and validate it with the Cone Penetration Test (CPT). The modification of CPI method is derived based on the ultimate

soil settlement , for soils classified according to initial void ratio – porosity , final void ratio- porosity and thickness of the soil layers .

The different types of response from modified CPI are discussed, and classified using cyclic stress formation and the individual specific gravity.

The change of the surface and base of the stratum that occurs as the degree of consolidation builds up and the development of pervious

and impervious base of the layers .In the absence of other external forces, the consolidation is caused by the weight of the soils, which in itself

varies as deposition and the degree of settlement proceeded . The drainage length changes as the deposit builds up and compressed. The linear

and non-linear soil was integrated by the relationship between an exponential stress - void ratio and the parabolic permeability – void ratio curve.

The external vertical compression force was applied on lightly consolidated soil layers and integrate with Stratum Index factor (SIF) and

Void Ratio Function (VRF) for soils being deposition . The Modified CPI method confirms well with the prediction of pore pressure in

ranges from 0.2 to 0.3 MPa , This method can be used in estimating pore pressure as well as the operational ceiling pore pressure margin ,

where the coefficient of consolidation (CF) amounted 0.1067 m2/year for shallow depths.

The CPI in saturated and unsaturated soil will ensure prediction of pore pressure with supported from validation of CPT works . Moreover the

CPI method could provide porosity and thermal conductivity data useful for integrated oil and gas projects .

Keywords: Constant Plastic Index, Void Ratio Function and Stratum Index factors

Introduction

This study focuses on the Modified of Constant Plastic

Index’s (CPI) ( Jamliolkowski 1995), (Hardin Bland 1978) )

method on Soft Ground Soil (SGS) ( (Robert Kirk Bowden ,1988) ,

Wong , Roslan , Faizal (2007 )), as it is observed in a cohesive

soil and presented in shallow well reservoirs . SGS is a mixture

of fragmented organic and massive erosion materials formed in

wetlands and river mouths . The SGS is also partially or totally

decomposed remain of alluvium soil and dead plants which have

accumulated under water for ten to thousands of years. It is

generally found in thick layers in limited areas, and has shown low

shear strength and high compressive deformation which often

result in hinders when drilling works under taken on the deposit.

CPI method is described as the volume matrix change of

consolidation (Teamrat A . Ghezzehei and Dani Or 2001) using

rheological soil properties which varies approximately up to 50m

in depth (to collect undisturbed soil sample) that overlies the

original soft layer in the coastal area figure 1.1 which composed

of soft marine clay with high water content ( Huat , 2004) and

high compressibility (A. Crumley (2006)) . On the other hand,

Constant Plastic Index (CPI) is an analogous term for

consolidation soil containing plastic or liquid limit matter.

Most of the soft grounds illustrate in Figure 1 are found on the

costal lowlands and form a corridor parceling the coastal. Soft

ground in the lowland lies between the stretches of river mouth

courses at ground level tolerance of 2m from the original ground

level .

1. Pore pressure

Pore pressure or formation pressure ( Eaton , 1972 ) is defined as

the pressure of fluids within the pores of a reservoir , usually

hydrostatic pressure , or the pressure exerted by a column water

from the formation ‘s depth to sea level . When impermeable

rocks such as shale form as sediment are compacted , their pore

fluids cannot always escape and must then support the total

overlying rock column , leading to anomalously high pressure

Knowledge of formation is a key requirement for optimal

prediction decision in overpressure formation . Pore-pressure

prediction has application in analysis of hydrocarbon migration

and seal capacity , determination of reservoir drive and

connectivity , analysis of drilling hazard and well casing design .

Given the water depths , drill depths and well costs that challenge

operators around the world , pore pressure prediction should be

an integral part of prospect evaluation and well planning . In the

other hand , information on well temperature is important to avoid

some drilling problem such as hydrate formation ( Taylor , 1991)

. It is a common practice to predict pore pressure before drilling. In

a shallow -water environment, sediment loading has been so fast

that pressures in these sediments are above hydrostatic right below

the mud line . The presented of modification of CPI trend , thus

validating the entire approach in the shallow well water . By

curve –fitting pressure data from an analogue well , most of these

trends violate the fundamental bounds of geo – mechanic . The CPI

method approaches the correct sediment strain just below the

mud line nor approaches a limiting strain or upper the mud line

and approaches a limiting tensile appropriate for very soft or at a

very high overburden pressure .

The methods that is going to be used in this project is by

deriving pore pressure and strain parameters such as void ratio

and porosity will be established by using CPI method . The

characteristic of soil region depends on the steady state or critical

state case, where the volume matrix change of soil integrate

the Pore Pressure or each layer, either horizontally or

vertically. The characteristic of strain either primary or

secondary, depends on the volume matrix change ( Dani Or

( 2001) of shallow surface soil (Jamliolkowski M , (1995)) .

However, there are some boundary limits on SCPTU test because

the shear wave factors and density of the layer influencing the

occurrences of the shear modulus vary greatly depending on the

characteristic of the poros media ( Alexandra – Ioana Iliescu

2012) and the proper way of hitting the hammer , frequency

noise cause of traffic or metal material and observed a good

shear wave velocity that a couple of time . The limitation of

the SCPTU test is limited to unsaturated media and limit

pertaining to the characteristics of volume matrix change of the

over consolidation of the shallow well environment , therefore is

a great research for author to modified Constant Plastic Index

and predict Pore Water Pressure in saturated poros media soil .

The summary of the research implemented in achieving the

objective of this study is shown below in Figure 3

Figure 1.1 Map depicting study sites chosen in the present investigation

Methodology

The aim of this project is to modified Constant

Plastic Index method in order to predict pore water

pressure before drilling and to enhance oil recovery

. As well as other researches ( eg Hardin, Blankford

(1989) , Lee Kuantsai (1977) , Jamliolkowski (1995)

were developed soil-strain model , SCPTU method

and predicts soil strain with Seismic Cone

Penetration Test method (SCPTU ) ( described in

Chapter 2 ) , The key objectives of modified of CPI

method in shallow well reservoir is to predicts the

pore pressure due to varies liquid or plastic limit

and activated clay which presented in Tg Bin field

and various location of Peninsular Malaysia

( Figure 2 ) .

• To modify Constant Plastic Index method based on

Consolidation theory.

• To predict pore pressure using Constant Plastic

Index Method

• To validate prediction of pore pressure between

Constant plastic index method and Cone Penetration

Test .

Figure 3 The steps the implementation of research in achieving the problem statements.

Having thus established confidence and critical review in SCPTU

and CPT procedure , author has established four (4) problem

statement accordingly to the limitation of the SCPTU and CPT

test and the statements are shown below .

Statement 1 ) The shear wave velocity ( Vs ) factors and

density of the layer influencing the occurrences of the shear

modulus vary greatly depending on the characteristic of the

saturated poros media ( Alexandra – Ioana Iliescu 2012), Maria

F . Quijada 2009) . Shear wave velocity is a non pragmatic in

saturated soil and the influence of CPI method of the volume

matrix change will integrate the pore pressure on the saturated

soil behaviour .

The soil flow and deformation consolidation process evolve from

molecular or microscopic interaction ( Chenu and Tessier 1995) ,

Collins and McGown , ( 1974) between soil particle. The process

that govern macroscopic soil rheological properties are

determined by arrangement of constituent components of the

nature and magnitude of bonds them ( Vyalov , (1986) .

Statement 2) The limit pertaining to the characteristics of

volume matrix change or wetting band of water table and the

effected of the over consolidation ratio . This statement CPI

method will investigate the volume matrix change , the soil is

classified as normally consolidated to slightly consolidated.

( Malgorzata Jastrzebska 2010) analysis the influence of

overconsolidation ( OCR) on shear modulus . The ranges of over

consolidation > 1 , void ratio ranges between 0.6 to 1 and

moisture content ranges 25 to 37 percent .

Statement 3) During SCPTU testing , some errors was observed

that a couple of time show shear velocities that out of range

because the wrong way hitting the hammer , not at right

depth .This statement will be avoid where CPI method no need to

use on site as a mechanical tools . ( Alexandra – Ioana Iliescu

( 2012))

( 4 ) CPT is a non pragmatic studies for saturated soil because

soils pore pressure behind cone tip become negative and in some

instance rise to cavitation of measuring system ( Powell et al

( 1988)) . If cavitation occurs , the measurement system become

desaturated and sluggish respone , giving negative pore pressure

Based on four (4) problems statement author has a great research

to Modified Constant Plastic Index based on consolidation

theory .

The Modified Constant Plastic Index Method

CPI method is modified from the work of Jamliolkowski

( 1995 ) and Alexandra – Ioana Ilescu (2012) , and is essentially

a modified version of shear modulus ( Hardin (1989) of the shear

plane . In this CPI method , the layer is divided into a m equal

segments (mesh) , and finite differences are used to approximate

the derivatives at each node .In the next time level , the boundary

is moved into a new position within the first segment and

derivatives in the node adjacent to the boundary are approximated

by fix boundary formula for unequally spaced points . At the end

of each time step the node positions are readjusted to be equally

spaced before moving forward to the next time increment , and the

functional values at the new nodes are interpolated from the old

nodal values by fitting schematic below . The procedure in Figure

15 is show how to apply the analyses form of the over

consolidation ratio ( OCR) process, to determine the variation of

excess pore water pressure with time and depth ( Das, B.M.

(1987)).

The value lightly over consolidation ratio ( OCR ) = 1.85 – 0.007

( Pre consolidation pressure ) – 0.255 ( void ratio/void ratio for

liquid ) express as equation

OCR = 1.85 -0.007Po – 0.255(e/eL)

Where P0 is Pre consolidation pressure , e is void ratio and eL is

void ratio at liquid limit

And OCR at Tg Bin fields is amounted ( 0 -4 ) and moisture

content ( 30 -120) % , the soil is classified as lightly consolidated

to slightly consolidated. The degree of under consolidation and

shear modulus (Go) is greater with increase depth (Peter R. Holler.

1992), (Katarzyma , 2008)

Testing Method

Testing method is concerned with the large strain consolidation

theory ( Lee Kuantsai , (1979)). Analytical solutions are thus

limited to two type of analysis deposition namely surface vertical

stresses in Figure 2 and cycling stresses loading in Figure 4

The differential strain of the soil layer surface vertical stress is

calculated by calculating the strain of the individual sub-layers and

adding them, in doing this it is assumed that the voids ratio and the

effective stress are constant throughout the sub-layer and equal to

their values at the centre of the sub-layer as equation .

Cohesive Soils Behaviour under Cyclic stresses cycle .

Cyclic stresses is a monotonic trajectory process for primary loading

and normal consolidation of the litho - facies. The process starts with

unloading and beginning the upper bound of the first loop cycle .

The next cycles stresses is the second identifier of repeatable load in

each cycle . The impression that within the focus of cyclic process is

a conditions of water drainage prevented and the over consolidation

soil resulting from pore pressure accumulation . And the beginning of

each consecutive cycles in Figure 4 is homogeneous soil

( a) shear strain =0

0 is a function

and is strain amplitude and x is mechanical loss angle

( Dealy , 1982) , described shortly by the frequency of

loading

Figure 4 Cyclic stresses diagram ( Adapted from Horn and Baungarti ( 1999) )

Figure 4 Cyclic stress formation methodology

Workflow

Below is described the flow chart of the project and the Figure 20 and Figure 21 shows the main steps and details workflow of the analysis

respectively .

1.4 Scope of Works

The main focus of this study to modify Constant plastic Index

and to predict pore pressure for drilling and to enhance oil

recovery . The Modified of Constant Plastic Index (CPI) is

based on boundary transfer and consolidation of soil layer .

Expected outcomes of the Research

The expected outcomes of the research are mostly on the

Prediction of Pore Water Pressure based on the modified of

Constant Plastic Index (CPI). The modification of CPI method

are integrated model to understanding the void ratio distribution

, continuity , and extension of the reservoir shallow well

environment . Petroleum system modeling using PETROMOD 1

D Schlumberger software is the principal aim of this research .

As such, a systematic shallow well environment distribution

category is deterministic Approach Based on CPI method To

Estimating Pore Pressure Operational Ceiling Enhance Oil

Recovery ( EOR) project pore pressure margin in reducing

coefficient of consolidation ( CF ) uncertainly of shallow depths .

Literature review

The Cone Penetration Test ( CPTU) ( Bouhon, 2010) is an

geotechnical onshore site investigation which is often used

along with SCPTU ( Alexxandra- Ioana Iliescu 2012) )result to

provide with reliable information about soil stratigraphy

interpretation . Hybrid is in-situ geotechnical test ( Paul W.

Mayne ( 2000 )) is collection data by combining two or more

likely tools as SCPTU offer a versatile approach technique. A

bender elements offer a small electro – mechanical transducer

(Bajda M . Lech M 2004) ) which either bend as an applied

voltage as they bend into a single sounding system .

A Bender Element And Seismic Cone Penetration Test

(SCPTU )Test Method

Seismic Cone Penetration Test ( SCPTU ) method ( Alexandra –

Ioana Iliescu ( 2012) is an geotechnical onshore methods which

are represented by combination of standard geotechnical tests

with geophysical module ( shear wave velocity measurement )

( Hardin , Blankford (1989) .

A bender elements was used both in

laboratory( Katarzynaarkowska - Lech 2008) in the field ,

beside seismic cone and seismic flat dilatometer , include cross

hole , vertical seismic profiling ( VSP ) and down hole test in

the classical geophysical version and as well as SCPTU method

( Schnaid F (2005)) .

Laboratory test are represented by resonant column as bender

element , torsion shear and triaxial test with local strain

measurement and bender elements . ( Viggiani G 1995). The

combination of SCPTU Test method from calculation on

field( Jamiolkowski 1995 ) , the initial shear modulus ( impulse

hammer , cross - hole ,geophone and seismic cone or Dilatometer )

and laboratory Test ( undisturbed sample , resonant column ,

Torsion shear , Bender elements , Triaxial strain ) ( Katarzyna

arkowska = Lech 2008) ) is a good correlation to estimating the

initial shear modulus wave due to density of sand layer in

shallow well environment .

Shear modulus G0 at very small strain (initial shear modulus)

( ( Kawaguchi ,et al 2001) ) is widely considered to be a

fundamental soil stiffness property. It is important in practical geo

– mechanic solutions, especially in earthquake engineering and the

prediction of soil structure interaction.

Hardin & Black 1989) was identified major factors which

contribute to the actual value of the shear modulus such as vertical

effective stress, void ratio, over consolidation ratio ( OCR ) , soil

fabric, temperature and degree of saturation. It is known that the

initial shear modulus of soil at induced strain levels (less than

0.0001%) is possible to obtain from shear wave velocity according

to the following equation:

where:

G0 –shearmodulus,

ρ-bulkdensity,

Vs – velocity of shear waves for linear, elastic and isotropic

medium.

The techniques which are represented by combination of standard

geotechnical tests with geophysical module (shear wave velocity

measurement) have been used both in the laboratory and in the

field. Representation of such hybrid (field/lab) method is shown in

Figure 4. Field techniques, besides seismic cone and seismic flat

dilatometer, include crosshole and downhole tests in the classical

Equation 1

geophysical version and as well as SCPTU Test . The represented

by resonant column, torsional shear and triaxial tests with local

strain measurement and bender elements. Such configurations

diminish disadvantages of each group of tests and considerable

enhances optimization of data collection ( Viggiani G , 1995 ) .

Hardin & Blanford (1989) suggested calculation of the initial

shear modulus from Equation 1. Originally this formula was

proposed for sands but it also applies to clayey soils:

Equation 2

where:

Sij – non-dimensional material constant reflecting the soil’s fabric,

F(e)–voidratiofunction,

OCR–overconsolidationratio,

k – empirical function dependent on the plasticity index of the

clay, k=0 when PI<40 and k=1 when PI>40; pr – references stress,

pr=1 kPa; ni, nj – empirical stress exponents.

Jamiolkowski et al. evaluated the constants for a number of clays

using a void ratio function as follows:

Equation 3

where:

x = -1.3 for clays [ Jamliolkowski ] and assuming that ni≈nj they

showed that k=0.

Additionally assuming isotropic stress condition, G0 is simplified

to:

Equation 4

where:σm – mean effective stress.

Figure 4 Field and laboratory methods for determining shear modulus (Schneider J . A (2005)

Disadvantages during SCPTU down hole survey, CPT and Bender elements are list below .

1 ) SCPTU is disadvantages for more air over and saturated media under and the contact surface is not perfect , and not allow the Vs

wave to be properly measured by the geophone or hydrogeophone . ( Alexandra – Ioana Iliesco 2012) .

2) CPT is a non pragmatic studies for saturated soil because soils pore pressure behind cone tip become negative and in some instance rise to

cavitation of measuring system ( Powell et al 1988)) . If cavitation occurs , the measurement system become desaturated and sluggish respone ,

giving negative pore pressure

3) Bender element is disadvantages factors , which the most affecting soil stiffness, are vertical effective stress , void ratio and soil over

consolidation is not to be taking into account ( Schnaid F 2005)) .

As a disadvantages of two item , author is agreed to modified Constant Plastic Index method based on Consolidation theory using isotropic

and anisotropic studies .

Shear modulus

Jamaliolkowski (1995) have been described the dynamic shear modulus and stratum behaviour between soil and rock strata .

Dynamic properties have been evaluated extensively for water- saturated and dry soils by (Hardin and Black 1968, 1969, 1989 ).

Stokoe et al, (2004) on the dynamic properties of soils depended on the mean effective stress , pore water pressure , void ratio

function and they proposed a functional relationship between maximum shear modulus Gmax (Hardin , 1968) and mean effective stress

as follows,

Go = ρVs²

Equation 5

Where Vs is seismic velocity and ρ bulk density .

Gmax =625(OCR) k F (e) (Pσ effective stress)½

Equation 6

To applying the Elastic theory on the effectiveness of plasticity model (Kallol Sett (2008), Hardin and Blandford 1968 ) ) the relationship

between maximum shear modulus observed from elastic-plastic relationship as a void ratio function as equation,

F(e)= 1/ 0.3 +0.7e2 (1968)

And

F(e) = 0.3 +0.7e2 ,(1989)

Equation 7

And the device used in measurement of shear wave velocity to estimate the initial shear modulus consolidation cohesive soil ( Katarzyna

Markoska-Lech (2008), and Jamiolkowski et al 2006) evaluated the constants for the number of clays using a void ratio function as follows,

F (e) = ex

Equation 8

Where x = -1.3 constant parameter

e = void ratio

For isotropic stress (Hardin & Blanford , 1989 ) initial shear modulus is simplified to

Go = S F(e) (σm)

Equation 9

Where σm= mean effective stress

Disadvantages of Jamliolkowski ( 1995) is using constant parameter Clay = -1.3 . For this reason , in the thesis author was agreed to

derived varies void ratio function parameter using CPI method

Consolidation Theory

The theory of one dimensional consolidation was first proposed by Terzaghi(1925). and Peack (1936) , who introduced the concept of effective

stress for one dimensional vertical system. The theory was extended to generate dimensional system by Biot (1945).

In Biot’s consolidation theory, a set of pore water pressure changes simultaneously in both vertical and horizontal displacement. Biot’s pore

elastic consolidation theory provided more rigorous and realistic mathematical treatment for analysing the fully coupled hydro – geo - mechanical

phenomena in porous media compared to Terzaghi’s theory. The coupled Biot consolidation theory was extended by Jinsong Huang , D.V

Griffiths and Gordon A. Fenton (2010) and a combination of a random finite-element method was used to investigate the consolidation

behaviour of soil deposits with spatial variable properties in one-dimensional and two dimensional spaces. The theory of Poros Media (Huang

(2005)) on Consolidation, Plastic, Elastic, Isotropic and Anisotropic was classically described by Casagrande, A (1936), Fadun, R.E. (1940), and

Taylor, D.W. (1948).

Effective stress

The idea of effective stress ( Terzaghi , (1936)) and underpinning pore pressure as equation of porous media

Equation 10

Total stress ( ) =Effective stress ( + Pore Pressure)

where is hydrostatic pore pressure .

In most sedimentary basins , the vertical stress is also the overburden stress and the integration of the weight of the overlying sediments

including the water column as well as the air column . This function was suggests that is the mean effective stress rather than the vertical

stress that controls the porosity reduction . The mean effective stress is defined as the different between the mean stress , which is the mean

of the vertical and horizontal principal stress and pore pressure .

The consideration of its variation during the flow – coupled – deformation ( Biot , 1945 .Tanahashi H ( 2010) ) , will deform under an external

force field in a time – dependent manner . This time-dependent process is governed by the compressibility of the skeleton – which determines the

amount of deformation that will take place – and permeability of the soil , which determines how fast the pore water can seep out to allow

deformation to take place . The idea is to explains the theory of long term strain behaviour often observed in geo mechanic structures and

provides a basic for an estimation to be made of the rate as well as the magnitude of strain .

Workflow

Below is described the flow chart of the project and the Figure 5 shows the main steps and details workflow of the analysis respectively .

Figure 5 CPI field and Laboratory field set up

The measurement of Constant Plastic Index ( CPI) in soil can be

accomplished using laboratory and field test and these are

illustrated by Figure 5 Test on small laboratory specimen include

oedometer test and special triaxial system with internal strain

measurement . Field test methods include the rotary wash boring ,

Standard Penetration Test ( SPT) , Disturbed and undisturbed

sample ( BS 1377 , BS5930) . The electrical cone penetration

tests ( CPT) is an apparatus used to determine soil parameter by

measurement the soil parameter to penetration at the tip , and the

local side friction resistance . It is consist of a series of

cyclindrical rods with a terminal body , the penetrometer tip , in

which the tip resistance and local side friction sensors are located

. Cone Penetration Test , are performed in order to obtain data on

one or more of the following subjects :

a) To validate pore water pressure versus depth between CPT

method and CPI method .

b) To integrate the depth to firm layers , the location of porosity,

voids and other discontinuities in the soil .

Method of Projection

The projection method was program initiated used (Lee

Kuantsai (1979) ) in Void ratio versus applied pressure curve soil

in Figure 5 . This was quickly extended to encompass the effect

of Constant Plastic Index ( CPI ) and the coordinate –x (applied

pressure to stress body ) and y ( void ratio ) between soil layer .

Figure 5 Void ratio function versus Applied pressure

The focuses on prediction of pore-pressure are on the variations

of litho facies porosity to integrate void ratio function using

modified of Constant plastic index method .The is used to ensure a

constant rate on space coordinate. There are two types of space

and coordinate on large strain ( Lee Kuantsai (1977) , Tanahashi

H . (2010)) .Two type space and coordinate are namely:

• The global space coordinates in boundary moving.

• The local soil material in fixed boundary.

The global space is the coordinate of the soil layer on the fields,

and the number of solid particles is a coordinate at the local

space . The local material is a fixed boundary of the coordinate .

Meanwhile, the global formulation is to realize that the position of

moving boundary of the soil layer in space and changing as

consolidation proceeds. Taking into account the case of infinitely

large strain, the boundary in local system is assumed to be fixed at

some coordinate value and the non-linear and pore-pressure will

be integrated based on the of degree of consolidation and degree

of settlement soil model . The structure of soft soil and

specifically how percent for degree of consolidation ( Sivaran &

Swamme ( 1997) and degree of settlement ( Lee Kuantsai , 1977)

of strain in poorly consolidated , and to minimum pore pressure

during drilling rig is under operation .

General : This study involved modification of CPI method

based on application of consolidation analyses for following cases

:

• Homogeneous Soil Profile .

• Constant loading and constant coefficient of consolidation case

( Cv and .

• Two layer Soil Profile case . Constant loading and constant

coefficient of consolidation case. Constant loading and

constant rate variation of coefficient of consolidation. Constant

rate variability in loading and constant coefficient of

consolidation case

• Multi- Layered Stratified Soil case . Constant loading and

constant coefficient of consolidation case . Constant loading

and constant rate variation of coefficient of consolidation

case . Constant rate variability in loading and constant

coefficient of consolidation case .

The knowledge acquired from the documented and undocumented

sources were put through a series of field studies in order to

translate the knowledge into a form could be used by CPI data .

The field data that were identified into three categories

• Void ratio parameters

• Ultimate settlement properties

• Thickness of soil layer

Result & Conclusion

Implication for CPI method Using PetroMod Image

Modeling lithofacies strata in static Petro Mod Image , is

important stage to modified CPI for integrate the volume matrix

change by introducing facies distribution and void ratio

distribution , such as the heterogeneity of void ratio function as

well . CPI can be considered in term of consolidation factor .

Having an idea about the deposition environment of litho facies

based on facies distribution , continuity compression soil will

reduced CPI and PetroMod image consider linear graph .

The realization are important in modified CPI stage to test on

saturated poros media soil and compare due to CPT method for

first 6 meter at Tg Bin fields as different interpretation are

possible in Pet Mod image and uncertainties in hydro static

pressure . In order to understand the litho facies distribution and

heterogeneity , the different result based on CPI method have been

consider .

Void ratio distribution for future development of CPI method is

demonstrated and show by CPI model , theory in consolidation

technique . The CPI method all suggest that unconsolidated soil is

increased due to increased porosity , reduced hydraulic

conductivity and increased hydrostatic pore pressure and CPT

and seismic method unsuitable to fit hydrostatic pore pressure

Figure 6 Output Pore pressure versus depth ( m ).

Validate model

To make the research have a valuable tool for use in prediction

pore water pressure ,it must be tested against current Cone

Penetration Test, due to data collection to check the validity of the

Pore Water pressure using CPI method . To estimate and predict

pore pressure using CPI Method . Several technique are available

including SCPTU test where suitable to unsaturated soil and CPI

method suitable for saturated soil . A starting point for pressure

prediction from CPI method is to build an empirical relationship

between the porosity and void ratio function as is illustrated in

schematic diagram (below ) , pore pressure can be estimated from

modification CPI using degree of settlement and degree of

consolidation. Porosity , void ratio , temperature analysis are

using Petro Mod 1DV 11 Schlumberger software .

Figure 7 Validation depth versus pore pressure between CPI method and Cone Penetration Test Method ( CPI ).

The pore pressure evaluation using CPI method suggests that the

pore pressure generated in these strata is predominantly generated

by disequilibrium compaction . Concerning the CPI equation to

calculate the pore pressure , the is recommended to use the

equation CPI method as a long it is assumed the most of over

pressure is generated by disequilibrium compaction . Figure 8

shows that CPT method that the negative pore ( < 0.1 MPa )

pressure in saturated soil ( ranges 0-6 ) m depth and Figure 115

show CPI method absent pore pressure ranges ( 0.15 to 0.3 )

MPa.

CPI linear graph

Figure 8 Depth (m ) versus pore pressure for CPT 1 and CPT 2.

Abnormal Pressures

Abnormal pressure are found throughout Tg Bin field . It can

happens at 6m in Figure 117 depth and is defined as litho static

pressure that is greater than the hydrostatic pressure of the

formation water occupying the pore space . It also referred to as

overpressure or geo pressure . Subnormal pore pressure or under

pressure 6 m above than the corresponding fluid hydrostatic

pressure at 6m depth . It is encountered less frequently than the

abnormal pressure and can be generated by stratigraphic , tectonic

and geochemical and geothermal history (Figure 121) of an area .

Temperature will increased due to 12 m depth and turn to lower

because the integrating stratigraphic between two layer and the

absent of abnormal pressure between two layer .

It increased in temperature at 12 m depth and lower at the deepest

12 m and observed , appreciably prior to or when entering a high

– pressure zone . Tg Bin reservoir have temperature ranges at ( 20

to 20.5 ) oC pore pressure below 0.2 MPa . This is almost the same

range 1 atm ..

Conclusion

Implication for CPI method Using PetroMod Image

In static Petro Mod Image , lithofacies strata is important stage to

modified CPI for the volume matrix change by introducing facies

distribution and effectively void ratio distribution , such as the

heterogeneity of void ratio function as well CPI can be

considered in term of consolidation factor . Having an idea about

the deposition environment of litho facies based on facies

distribution , continuity compression soil will reduced CPI and

PetroMod image consider linear graph .

CPI

CPT curve & negative

skin friction

The realization are important in modified CPI stage to test on

saturated poros media soil and compare due to CPT method for

first 6 meter at Tg Bin fields as different interpretation are

possible in Pet Mod image and uncertainties in hydro static

pressure . In order to understand the litho facies distribution and

heterogeneity , the different result based on CPI method have been

consider .

Effective Void ratio distribution for future development of CPI

method is demonstrated and show by CPI model , theory in

consolidation technique . The CPI method all suggest that

unconsolidated soil is increased due to increased porosity ,

conductivity and hydrostatic pore pressure

References

[1] Robert Kirk Bowden (1988)

“Compression Behavior and Shear Strength Characteristies of a Natural Silty Clay Sedimented in the Laboratory ”, A thesis submitted to the University of Oxford for Degree of Doctor of Philosophy , Trinity Term, 1988.

[2] R.P.Chen , W.H . Zhou. And Y.M . Chen (2009)

“Influences of soil consolidation and pile load on the development of negative skin friction of a pile ”,The Hong Kong Polytechnic University , Hung Hom , Kowloon , Hong Kong , China .

[ 3] Huat (2004) , Vivi Anggraini (2006)

“ Thesis Shear Strength Improvement of Peat Soil Due to the Consolidation ”,Thesis UTM , at Pontian , Johore .

[4] Lee , Kuantsai (1979)

“ An Analytical And Experimental Study Of Large Strain Soil Consolidation”: A Thesis submitted to the University of Oxford for the Degree of Doctor of Philosophy , Trinity Term .

[ 5] Kupchella, C and Hyland , M.C (1986)

“Environmental Science ; Living within the System of Nature “ (Allyn and Bacon, Inc , USA .1986) .

.[6] Zahari Muda (2006) ‘ Work shop Pengurusan Lebukraya Berhad ,

[7] Sivaram, B, Swamme , A . (1977)

“ A Computation Method for Consolidation Coefficient ”, Soil and Foundation , Vol 17 .No2, 48-52

[8] Mesri, G and Godlewski, P.M (1977)

“Time and Stress - Compressibility Interrelationship ”,Journal of Geotechnical Engineering , ASCE , Vol 103 ,No,GTS5, 417-430

[9] Roscoe , K, H. and Burland , J.B (1968) ( critical state case )

“ On the generalized stress-strain behavior of wet clay . ”, Engineering Plasticity , Cambridge University , pp 535-609 .

[ 10] Skempton Taylor , A.W, Bjerrum , L , (1957)

“ A Contribution to Settlement Analysis of Foundations Clay ”, Geotechnique , London , Vol 7, 178 .

“ Fundamentals of Geotechnical Engineering , 3 Edition , Braja M . Das (2008)” pp 223-230.

[11] Hardin , B.O (1978) “The nature of Stress-Strain behavior of Soils ”, Earthquake Engineering and Soil Dynamics , ASCE , Vol 1. Pp 3-99

Hardin , B.O (1969)” Vibration Modulus of Normally Consolidation Clay , “ Journal of the Soil Mechanics and Foundation Division . ASCE , 95(SM6) 1531-1537 .

“ A Computation Method for Consolidation Coefficient ”, Soil and Foundation , Vol 17 .No2, 48-52

[12] Teamrat A .Ghezzehei and Dani Or (2001)

“Rheological Properties Of Wet Soil and Clays under Steady and Oscillatory Stress ”, Soil Sci , Am , J,65:624-637.

[13] T.C.,Kung 1 ,C.Y.Ou 2 (2000)

“Prediction of Surface Settlement Caused by Excavation ”, 1) Department of Civil Engineering , Clemson University , South Carolina , USA 2) Department of Construction Engineering , National Taiwan University of Science and Technology , Taipei .

[ 14] Stokoe , K.H , Hwang et al (2004)

“ Effects of various parameter on the stiffness and Damping of soils to medium strains “ Proc of 1 The International Symp. On Pre – failure deformation characteristic of GEOMATERIAL 2 , 785-816 .

[15] Eaton , Sam Clarke , C.C Hird (2006)

“Optimal Design of Vertical Drain in Soft Ground ”,CIV405 Final Report , Department of Civil and Structural Engineering , University og Sheffield ,2005

.

[16]Tanahashi H . (2010)

“Degree of consolidation and reduction coefficient concerning differential consolidation settlement ”, Department of Civil and Environmental Engineering , University of Delaware,Newark ,Delaware 19716 ESTATS-UNIS .

[17] Tan ,S.A (1993) “ Ultimate Settlement by Hyperbolic Plot for Clays with Vertical Drain ”, J Geotechnical Engineering , Vol 119, No 5 pp 950-956 .

[18]T.Harnpattanapanich, I. Vardoulakis (2005)

“Numerical Laplace – Fourier transform inversion technique for layered soil consolidation problems ; Gibson soil layer ”, International Journal for Numerical and Analytical Methods in Geomechanics, Volume 11, Issue 1, pages 103-112 Jan/Feb 1987

[19] S.L.Chen1 , L.M.Zhang2 , and L.Z . Chen (2005)

“ Consolidation of a Finite Transversely Isotropic Soil Layer on a Rough Impervious Base ”, Journal Engineering , Mechanics , Volume 131 , Issue 12 , pp 1279-1290