02 Review Of Reservoir Rock And Fluid Properties

Well Test Analysis The review of reservoir rock and fluid properties (Oilfield Units) Instructors: Bui Tu An (PVU) Huynh Thanh Tung (Schlumberger) Nguyen Tuan Duong (VSP)

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Reservoir rock properties

 Porosity  Saturation

 Permeability  Pore volume Compressibility  Net Pay Thickness

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Porosity

pore volume  bulk volum e

Porosity is a measure of the capacity of the reservoir rock to store fluids. TALENTS FOR DEVELOPMENT

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Porosity • Symbol - 

• Units

– Equations - fraction – Reports - % (or fraction) • Source

– Logs, cores • Range or Typical Value

– 30%, unconsolidated well-sorted sandstone – 20%, clean, well-sorted consolidated sandstone

– 8%, low permeability reservoir rock – 0.5%, natural fracture porosity TALENTS FOR DEVELOPMENT

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Porosity

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Saturation  Saturation is the fraction of pore volume occupied by a

particular fluid.

oil volume So  pore volume gas volume Sg  pore volume water volu me Sw  pore volume

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Saturation • Units – fraction or %

• Source – logs • Range or Typical Value

– 15 to 25% – connate water saturation in well-sorted, coarse sandstones – 40 to 60% – connate water saturation in poorly sorted, fine-grained, shaly, low-permeability reservoir rock

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Saturation

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Permeability

 Permeability is the measure of capacity

of rock to transmit fluid.

qL k Ap TALENTS FOR DEVELOPMENT

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Permeability • Units: Darcy or millidarcy (D or mD)

• Source: Well tests, core analysis • Range: 0.001 md - 10,000 md

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Pore volume Compressibility  Pore volume compressibility (formation compressibility

or rock compressibility) is the fractional change in porosity due to unit change in pressure

1 V p 1   ln   cf    V p p  p p

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Pore volume Compressibility • Units – psi-1, microsips (1 psip = 10-6 psi-1)

• Source – Lab measurement, correlation, guess

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Net Pay Thickness

The net pay thickness is the total thickness of all productive layers in communication with the well. h = h1 + h2 + h3 Shale h1

Sand

h2

h3

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Net Pay Thickness • Symbol – h

Units – ft

Source – logs

• Range: 5 ft or even less - 1,000 ft or more

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Fluid Properties  Formation Volume Factor  Fluid Compressibility  Viscosity

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Formation Volume Factor  The formation volume factor is the volume of fluid at

reservoir conditions necessary to produce a unit volume of fluid at surface conditions (stock tank).

Vres B Vst  Symbol – Bo, Bg, Bw  Units – res bbl/STB, res bbl/ Mscf  Source – Lab measurements, correlations

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Formation Volume Factor • Range and typical values

– Gas • 0.5 •5

res bbl/Mscf, at 680 psi

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res bbl/Mscf, at 9000 psi

res bbl/Mscf, at 115 psi @MSc. Bui Tu An

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Fluid Compressibility  Compressibility is the fractional change in volume due

to a unit change in pressure.

 ln Vo  1 Vo co    Vo p p  ln Vw  1 Vw cw    Vw p p  ln Vg 1 Vg cg    Vg p p

 

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Fluid Compressibility • Units – psi-1, microsips (1 microsip = 1x10-6 psi-1) • Source – Lab measurements, correlations

Ideal gas – 60x10-6 psi-1, at 9000 psi – 1.5x10-3 psi-1, at 680 psi – 9x10-3 psi-1, at 115 psi TALENTS FOR DEVELOPMENT

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Viscosity  Viscosity is a measure of resistance to flow --

specifically, is defined as the rate of shear strain to the applied shear stress within a fluid.  Symbols: o, g, w v + dv

dy

v F  dv A dy

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Other Properties

 Two other variables used in well test

interpretation are neither rock nor fluid properties:  The total compressibility  The wellbore radius

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Total Compressibility  The total compressibility defined reflects change of

both pore volume and fluid volume with change in pressure.

c t  c f  Soco  Sw c w  Sgcg • Units – psi-1, microsips • Source – Calculated

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Wellbore Radius  Wellbore radius is the size of wellbore. rw

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Wellbore Radius • Symbol

– rw • Units

– feet • Source

– Bit diameter/2

– Caliper log • Range or Typical Value

– 2 to 8 in.

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Exercise 1

List 4 objectives of well testing?

List as many as possible without referring to the notes.

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Exercise 2 Define variables used in well testing  Define, give the units for, and name a common source for each of

the following variables used in well testing. Complete as much of this exercise as possible before referring to the notes. 1. Porosity 2. Saturation 3. Permeability 4. Pore-Volum Compressibility 5. Net sand thickness 6. Formation volume factor 7. Fluide Compressibility 8. Viscosity 9. Total Compressibility 10. Wellbore radius TALENTS FOR DEVELOPMENT

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Exercise 3 Calculate total compressibility for undersaturated oil reservoir (above the bubblepoint) Sw = 17%, oil gravity = 27API, Rso = 530 scf/STB, gas gravity = 0.85, Tf = 185F,

p = 3500 psi, cf = 3.610-6 psi-1 Tsep= 75°F, psep = 115 psia From fluid properties correlations, pb

=

2803 psi

co

=

1.158 x 10-5 psi-1

cw

=

2.277 x 10-5 psi-1

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Exercise 4 Calculate total compressibility for saturated oil reservoir (below the original bubblepoint) Sw = 17%, Sg = 5%, oil gravity = 27API, Rso = 530 scf/STB, gas gravity = 0.85, Tf = 185F,

p = 2000 psi, cf = 3.610-6 psi-1 Tsep = 75°F, psep = 115 psia From fluid properties correlations, pb

=

2803 psi

co

=

1.429 x 10-4 psi-1

cg

=

5.251 x 10-4 psi-1

cw

=

4.995 x 10-6 psi-1

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Exercise 5 Calculate total compressibility for the following Lowpressure, high-permeability gas reservoir Sw = 20%, gas gravity = 0.74, Tf = 125F, p = 125 psi,

cf = 3.610-6 psi-1, cw = 4 x 10-6 psi From fluid properties correlations, cg = 8.144 x 10-3 psi-1 cw = 4x10-6 psi-1

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Exercise 6 Calculate total compressibility for the following high pressure, low permeability gas reservoir Sw = 35%, gas gravity = 0.67, Tf = 270F,

p = 5,000 psi, cf = 2010-6 psi-1

From fluid properties correlations, cg

=

cw =

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1.447 x 10-4 psi-1

3.512 x10-6 psi-1

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