Lecture 3 [Compatibility Mode]

5/28/2018 Lecture 3 [Compatibility Mode]

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Lecture 3


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reservoirs

ro uc on rom wo-p ase reservo rs

Production from as wells


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Field Production

i. Solution gas drive

a. pressure inside reservoir relieved when well

punctures and gas trapped in oil forms bubbles

b. Bubbles grow, exert pressure push oil to well and up-

ii. Gas cap drive

. ,

gas cap expand

b. Expanding gas pushes oil into well (40%)

iii. Water drive scenario

a. Water layer press against oil layer

b. Water pushes oil towards surface and replace it

within the pores of the reservoir rock

c. Highest recovery: up to 75%


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The diffusivity

equation describes the

pressure profile in ann n e-ac ng, ra a

reservoir, with a

and constant viscosityfluid (Undersaturated

oil or water)


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Transient flow is defined as a flow regime where/when the

reached any boundaries of the reservoir. During transient flow,

the develo in ressure funnel is small relative to the reservoirsize. Therefore, the reservoir acts like an infinitively large

reservoir from transient pressure analysis point of view.


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Forx


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Ori in of the Conce t of Skin Effect


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Zone of Altered Permeabilit


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drAq =ohk =

= ee

rp

kh2w

e

oor

rB )ln(2.141

hkwwf rpBq wfR

w

e

oo

o

o pp

r

rB

q

=

5.0)ln(2.141 Steady State

wfR

w

eoo

o

o pp

rrB

q

=

75.0)ln(2.141 Pseudo Steady State


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-


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-

13AOF


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- -

Pseudosteady-state flow is defined as a flow regime where

the ressure at an oint in the reservoir declines at the same

constant rate over time. This flow condition has propagated to

all no-flow boundaries. A no-flow boundary can be a sealingfault, pinch-out of pay zone, or boundaries of drainage areas of

production wells. )( ppkh wf=

]

472.0

[ln2.141 sr

r

Bw

e

+


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Pseudo-Steady-State Flow

The flow time required for the PSS period begins can be expressed

as

The flow time required for the pressure funnel to reach the

circularboundary can be expressed as


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Production from

Inflow Performance Relationship e o ow ng equa ons are va or n ersa ura e o

reservoirs, or reservoir portions where the pressure is above the

bubble-point pressure. These equations define the productivity- -point pressure.

=

75.0)ln(2.141 eoo

o

rB

hkj

wr


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Usin the well and reservoir data as below construct

transient IPR curves for 1, 6, and 24 months. Assume

zero skin effect.


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Assume that the initial reservoir pressure of the well described

in Example 2 is also the constant pressure of the outer

boundary in steady state condition. Draw IPR curves for skine ec s equa o , , , an respec ve y. se a ra nage

radius of 2980 ft.


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For this exercises, calculate the IPR curves for zero skin effect

but for average reservoir pressure in increment of 500 psi from

the initial 5651 to 3500 psi.


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Production from Undersaturated oil reservoirs

Production from two-phase reservoirs


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Two- hase Reservoirs

The linear IPR model is valid for pressure values as low asu e-po nt pressure. e ow t e u e-po nt pressure, t e

solution gas escapes from the oil and become free gas. The free

gas occupies some portion of pore space, which reduces flow.permeability.

1 1

kr kr

o g

S Sg =1-S0 1

Oil viscosity increases as its solution gas content drops.


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-

The combination of the relative permeability effect and the viscosity

effect results in lower oil production rate at a given bottom-hole

pressure. This makes the IPR curve deviating from the linear trend

below bubble- oint ressure.

The lower the pressure, the larger the deviation. If the reservoir

,

phase flow exists in the whole reservoir domain and the reservoir isreferred as a two-phase reservoir.


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-

4500.0

3000.0

3500.0

.

llhe

ad

2000.0

2500.0

sureatW

(psi)

1000.0

1500.0

Pwf:Pre

0.0

500.0

Rate (bpd )

Rate, Skin = 3.0 Rate Skin = 0 Rate Skin = -2

Rate Skin = 2 Rate Skin = 4 Rate Skin = 6


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Fetkovich Equation Jones-Blount-Glaze Equation


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Vogel Relationship

2

=0 8.02.01ppq wfwf

Apparent

Absolute O en Flow

wfp Potential

maxoq

q


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Vo el Exam le

pwf is 2/3 of pave The reservoir is two-phase (below bubble

point, saturated) What fraction of the maximum possible oil

production rate does the well produce with?

Answer: the well already produces half of themaximum possible (though we use only 1/3

of the maximum available drawdown.)

( ) ( ) 5.067.08.067.02.01 2 =q

max


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Vogel IPR

2

0

= ppq wfwf

max ppqo

-1

.

One phase AOF

pwf pJqo

=max

p wo p ase :

p

J

q o max =

q1 1.8

.

max,o


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( )

n

wfRo ppCq

22 =


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AOF

pJqo =maxOne phase AOF:

Two phase AOF for Vogel:

Jini=

.pq no

2

max =Two phase AOF for Fetkovich:


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3500.0

)

2500.0

3000.0

ure(PSI

Straight Line Above BP Smooth

transition

2000.0

HP

ress pb

1000.0

1500.0

lowing

500.0

Pwf:

0.0

0.0 200.0 400.0 600.0 800.0 1000.0 1200.0


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A


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Reservoir deliverabilit declines with time. Durin

transient flow period in single-phase reservoirs, this

decline is because the radius of the ressure funnelover which the pressure drawdown (pi - pwf ) acts,

increases with time i.e. the overall ressure radient

in the reservoir drops with time. - ,

depletes, reservoir deliverability drops due to reduced

viscosity.


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Production from Undersaturated oil reservoirs

Production from two-phase reservoirs


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Pseudo-Steady State

Non-Darcy Flow


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-


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bottomhole pressure for the well described as

.

state period, there is no skin effect and

re= t


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calculate the exponents in IPR equations.

eren e vera y es s can e

categorized into

Tests that use all stabilized data

stabilized data


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The main method is Flow-After-Flow tests

The test consists of a series of flow rates (often 4)

The test is performed by producing the well at a series of stabilized flow

pressure. In addition a stabilized shut-in bottomhole pressure is required for

the analysis.


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required to obtain stabilized data for low-

.

It means that two pressure readings within 15

minutes agree to within 0,1 psi

approximated as


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Lecture 3 [Compatibility Mode]

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