College of Engineering

Petroleum department

Forth stage

by:

Haider Shabaan

Abstract

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Reservoir Management-Calculate RW and water saturation-

In this report , the work depend on interactive petrophysics program(IP) .

we calculated RW in different methods :- SP, formation temp ,picket plot

and RWa and choose which one is accurate to use in calculation . And then

calculate water saturation depend on different types of porosity and

different methods of measurement .

Introduction:-

First we rely on final geological report of Dujaila-2 because we must

know the formation that we have and where are the region of oil and

area of cavitation before starting work on( IP) and compare the results

that we get it from( IP) with the fgr report to make sure the precision

inaction

The most common technique for calculating Sw is the use of resistivity

logs with a model (empirical or theoretical) that relates Sw to Rt, Rw,

and porosity. As mentioned previously, a large number of Rt/Sw

models have been published. The models are applied at every data

point in the reservoir where deep resistivity, porosity, and shale-

volume estimates, if required, are available. The evaluation of all other

necessary parameters (constant or variable Rw values, a, m, n, QV, Vsh,

R0 = F • Rw, etc.) has been discussed previously. Several commercial

software packages are available that perform these S w calculations for

a variety of log models..

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Well information

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Theoretical part

A- SW

Water saturation

Water saturation can be defined as the amount of pore volume that

occupied by the formation water.

Techniques for calculating water saturation

Sw in wellbores can be determined by the following primary methods:

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Sw calculations from resistivity well logs by application of a model

relating Sw to porosity, connate-water resistivity, and various rock

electrical properties.

Sw determination from well log data

Sw calculations from laboratory capillary pressure/saturation

(Pc/Sw) measurements by application of a model relating Swto

various rock and fluid properties and height above the free-water

level.

Sw calculations using oil-based mud (OBM)-core-plug Dean-Stark

water-volume determinations.

Combinations of these methods.

1.archie's equation

Archie developed his famous equation to calculate Sw , from well log

parameters, the water saturation (Sw) of the uninvaded zone in a

formation next to a borehole. The Archie equation for clean formation

can be expressed as follows:

where:

Sw = water saturation of the uninvaded zone

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n = saturation exponent, which varies from 1.8 to 4.0 but normally

is 2.0

Rw = formation water resistivity at formation temperature

=Φ  porosity

m = cementation exponent, which varies from 1.7 to 3.0 but

normally is 2.0

Rt = true resistivity of the formation, corrected for invasion,

borehole, thin bed, and other effects.

a = 1 ( for carbonate formation)

a =0.62 ( for sandstone )

2. Sw =2√Ro/Rt

In water bearing zone

Where:

Ro = the resistivity of the fully saturated rock

3. Quick look method

A . Rwa method

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Rwa or Rw apparent is used to estimate the value of Rw, the resistivity

of the waters filling the pores of a reservoir rock.  Rwa is derived from

the most basic concepts of well log analysis, the formation resistivity

factor, F and water saturation Sw.

Sw=√Rwa/Rw

Where :

Rwa = Rt/F

B . Rxo/Rt method

The Rxo/Rt quicklook method can be used to identify hydrocarbon-

bearing formations and to indicate hydrocarbon movability

(producibility). When Sw/Sxo is 1 in a permeable zone, the zone will

produce water or be nonproductive regardless of water saturation. A

value Sw/Sxo significantly less than 1 indicates that the zone is

permeable and contains some hydrocarbons, and that the

hydrocarbons have been flushed (moved) by invasion. Thus, the zone

contains producible hydrocarbon.

Sw=10∆ SP/−1.6 K

4. Cross Plot method

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A . pickett plot

Procedure:

1. Plot points of matching porosity and true resistivity (Rt ) on log-

log paper.

2. Plot Rw point on the Rt scale.

3. Determine m using the table of values.

4. Plot the 100% Sw line.

5. Plot the lines representing lower values of Sw 

B . Hingle plot

„ One can determine water saturation directly from the plot,

without … knowing Rw, or … having to calculate porosity. „ In

addition, the plot will predict matrix values of sonic or density, so

porosity can be more confidently calculated. „ But, one has to

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assume values for a, m, n, „ And special paper must be used, which

depends on the assumed value of m.

6.Ratio method

When no porosity data is available, saturation can be obtained

by comparing the shallow and deep resistivity logs. This

formula is not shale corrected..

Sw =[(Rxo/Rt )/(Rmf /Rw )]^5/8

B- RW

There are six ways to calculate formation water resistivity

1. Archie’s Equation

If water zone is present .

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Where:

Rw: formation water resistivity

Ro: formation resistivity when (100%) saturation of water

F: formation resistivity factor

*Formation resistivity factor is depend on type of rock and porosity.

2. Rwa Approach (apparent formation water resistivity).

We choose the lowest value of the curve of (Rwa) and we consider it the

value of (Rw).

Requirements:

1.Rw is constant.

2.lithology is constant.

3.A water zone exists and is identifiable.

Procedure:

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3. Resistivity – Porosity Crossplots

a.Picket Plot

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b. Hingle Plot

4. SP log method:

5. Direct measurement of representative (water sample.(laboratory))

6. Chemical analysis of water sample. (laboratory)

Another models of water saturation

1-Poupon-Leveaux (Indonesia) model

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The Indonesia model was developed by field observation in

Indonesia rather than by laboratory experimental measurement

support. [9] It remains useful because it is based on readily available

standard log-analysis parameters and gives reasonably reliable

results. The formula was empirically modeled with field data in water-

bearing shaly sands, but the detailed functionality for hydrocarbon-

bearing sands is unsupported, except by common sense and long-

standing use. Sw results from the formula are comparatively easy to

calculate and, because it is not a quadratic equation, it gives results

that are always greater than zero. Several of the other quadratic and

iterative-solution models can calculate unreasonable

negative Sw results.

....................(5)

....................(6)

The Indonesia model,  and other similar models, are often used

when field-specific SCAL rock electrical-properties data are

unavailable but are also sometimes used where the SCAL exponents

do not measure the full range of shale volumes. Although it was

initially modeled on the basis of Indonesian data, the Indonesia

model can be applied everywhere. The inputs are the effective

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porosity, ϕe, shale volume and resistivity (Vsh and Rsh), and water and

deep resistivities (Rw and Rt). The Sw output is usually taken to be the

water saturation of the effective porosity, but it has been recently

suggested that the output is likely to estimate Swt.[7]Many other log-

based shaly-sand models have been proposed[23] but, for brevity, are

not discussed here.

2- Waxman-Smits-Thomas and dual-water models

Swt, the water saturation of the total porosity, is calculated at each

reservoir data point by iterative solution of the complex

multiparameter Waxman-Smits-Thomas (WST) and dual-water (DW)

equations (Eqs. 7 and 8). For brevity, the details of the solution

methods are not presented here. The WST and DW models are total-

porosity/Sw system models.

The WST model is based on laboratory measurements of resistivity,

porosity, and saturation of real rocks.  Qv is the cation-exchange

capacity (CEC) per unit PV.

....................(7)

where Swt = water saturation of the total porosity as shown

schematically in Fig. 1,

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 B = specific cation conductance in (1/ohm•m)/(meq/mL), and QV =

CEC in meq/mL of total PV. The exponents m* and n* apply to the

total PV

Fig. 1 – Total, effective, and core porosities and their associated water saturations in shaly sands (after Woodhouse and Warner).

3-The DW model

 is also based on the WST data. It uses clay-bound-water

conductivity instead of WST’s BQv factor (see Eqs. 7 and 8) and an

alternative shale-volume descriptor, Swb, the saturation of physically

bound water in the total PV (see Fig. 1). [1][14] When Vsh is zero, Swb is

zero; and when Vsh is 100% BV, Swb and Swt are also 100% PV.

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....................(8)

where Rwb = resistivity of clay-bound water   in the shales,

and Rwf = resistivity of free formation water   in the shale-free

water zones. Because of the different model assumptions, DW

exponents mo and no must always be smaller than the WST

exponents[24] and may be values similar to "clean" sand exponents.

Where the WST and DW models have been properly applied, the

hydrocarbon pore volume (VHCP) results should be equal.

All Swt calculations from the WST and DW methods must be checked

to ensure that they are greater than Swb. After this check, they are

used with ϕt to obtain the VHCP. For the DW model, when the outputs

require conversion to effective porosity, ϕe, and effective water

saturation, Swe, the properties are converted with Eqs. 9 and 10,

respectively.

....................(9)

And   ....................(10)

Porosity and Water Saturation Parameters :

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Result

1-SW by use Density and Neutron devices:

2-SW by use Density-Neutron and sonic devices:

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3-SW by use ND, Sonic, Neutron and Density devices:

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4-SW depend on ND porosity by Archie, Dual Water,

Indonesian methods

5-SW depend on ND porosity by Juhasz, ,

simandoux ,Mod Indonesian methods

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6-RW from formation temp. , SP

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7- RW from formation Picket Plot at fully water zone

only

8- The zone that taken RW picket plot in water bearing

zone

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Discussion:

1-the reading of Vsh from sp, Gr and cross plot are not converge.

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2- the value of m and rw we should corrected because the values of sw

become greater than 100 ./. if we not corrected ,the value of m and rw we

can corrected from peck plot,Tf,sp if the value converge that will be right.

3- we shuold calculate the sw from several methods and then compare its.

4- we must use the shlumberger chart to corect the porosity because its

effect in the value of sw in calculation.

5-The effective porosity is always less than the total porosity because it

equal the total porosity minus the (porosity of shale*volume of shale).

6-must be compute PHIE and SW for each way

(NeuDen ,Neutron ,Density,Sonic) and then compare between them .

7-Different (m) values affect the water saturation dramatically and lead to

completely unreliable petrophysical interpretation ,while differebt in (a) or

(n) values does not affect the water saturation as much as (m) .

8-The evaluation of all other necessary parameters (constant or variable

Rw values, a, m, n, QV, Vsh, R0 = F • Rw, etc.)

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