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
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
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