Sifat Fisika Batuan Dan Fluida

SIFAT

FISIKA

BATUAN

dan FLUIDA

1

Sifat Fisik Batuan Reservoir 





Sifat fisik Batuan: 

Porosity



Pore size distribution



Permeability



Formation compressibilit compressibility y

Sifat statis batuan-fluida (interaksi batuan & fluids di dalam pori): 

Wettability & contact angle



Capillary pressure & interf interfacial acial tension



Irreducible & connate water saturation



Residual oil saturation

Sifat Dinamis batuan-fluida (interaksi batuan & fluida): 

Relative Relativ e permeability



Mobility



Saturation Satur ation distribution during immiscible fluid displacement

2

Sifat Fisik Batuan Reservoir 





Sifat fisik Batuan: 

Porosity



Pore size distribution



Permeability



Formation compressibilit compressibility y

Sifat statis batuan-fluida (interaksi batuan & fluids di dalam pori): 

Wettability & contact angle



Capillary pressure & interf interfacial acial tension



Irreducible & connate water saturation



Residual oil saturation

Sifat Dinamis batuan-fluida (interaksi batuan & fluida): 

Relative Relativ e permeability



Mobility



Saturation Satur ation distribution during immiscible fluid displacement

2

Properties of the Rock Material

Porosity or primary porosity - dibentuk bersamaan dgn pengendapan batuan, terkompaksi dan tersemen bersama menjadi matriks

 Original

or secondary porosity - berkembang akibat proses geologi yang terjadi setelah pengendapan

 Induced

 Total

po rosity - total rongga batuan dibagi bulk volume batuan porosity

porosity - ratio rongga yang saling saling berhubungan berhubungan terhadap bulk volume batuan

Effective ctive  Effe

3


Porosity

Porosity   

Void Volume Bulk Volume

Effective Porosity   e 

Total Porosity   T Bulk Volume 

Interconnected Pore Volume Bulk Volume

Total Pore Volume  Bulk Volume

Rock Volume occupiedby solidgrains

 Void volume beween cementedgrains 4


Porosity

Pore Space in Packing of Uniform Spheres



Sandstones  = 1% - 38%  rata-rata = 20%



Limestone & dolomite  rata-rata = 10%

5


Permeability – Persamaan Darcy’s  Persamaan

Darcy’s untuk aliran horizontal linear melalui

media pori Q

dimana: q = volumetric rate (cm3 /sec)

q

k A

p1 p 







k = permeability (darcies) 2

L

μ

A = area (cm2)

p2

A

m = viscosity (cp) L p

Q

k

q μ L Ap1 p2  



p1

p1 = upstream pressure (atm) p2 = downstream pressure (atm) L = length of porous media (cm)





6


Permeability – Persamaan Darcy’s

 Batuan

memiliki permeabilitas satu Darcy akan mengalirkan fluida berviskositas satu centipoise melalui luasan satu cm2 dengan laju alir satu centimeter cubic per detik pada gradient tekanan sebesar satu atmosphere per cm. 

Biasanya 1 Darcy terlalu besar untuk ukuran batuan reservoir, sehingga millidarcy, merupakan satuan yang biasa digunakan

1000 md = 1 D

7

Properties of the Rock Material Permeability – Persamaan Darcy’s

 Persamaa

Darcy’s untuk aliran horisontal / linier :

1.1271x103  k  A  p1  p2  q μ L q = volumetric flow rate of liquid (bbl/day) k = permeability (md) A = flow area (ft2) p1 = upstream pressure (psi) p2 = downstream pressure (psi)

m = fluid viscosity (cp) L = thickness of porous media (ft) 8


Permeability – Persamaan Darcy’s

 Asumsi

persamaan Darcy’s adalah:



Aliran Incompressible flow



Viskositas konstan



Aliran laminar sangat pelan



Aliran Steady state

Ketika menggunakan persamaan Darcy’s, apakah batasab tersebut sepenuhnya dapat terpenuhi untuk mendapatkan permeability menjadi akurat ? 9


Permeabilitas Absolute dan Effective

 Permeabilitas  Sifat

batuan & bukan fluida yang mengair melaluinya, menyebabkan fluida 100% mensaturasi seluruh pori batuan

 Permeabilitas Absolute  Permeabilitas  Permeabilitas

batuan yang di saturasi satu jenis fluida

Effective

 Permeabilitas

batuan bila pada batuan tersebut disaturasi oleh lebih dari satu fluida

 Jumlah

dari permeabilitas effective utk fluida yang berlainan selalu < permeabilitas absolute-nya 10

Static Rock-Fluid Properties

Wettability 

Wettability - kecenderungan satu fluida ter-adesi di permukaan padatan dibandingkan fluida taktercampur lainnya Forces in Equilibrium at Oilwater Interface

Sudut kontak < 90° (water-wet) Sudut kontak > 90° (oil-wet) Sudut kontak = 90° (neutral)

11


Wettability  Pada

umumnya reservoirs, merupakan:

 25%

water-wet

 25%

oil-wet

 50%

intermediate or mixed wettability Sand Grain

Sand Grain

Water

Oil Water

Oil

Oil Wet

Water Wet

 Efficiency

Pendesakan fluida nonwetting mendesak fluida membasahi biasanya lebih kecil dibandingkan fluida wetting terhadap non-wetting 12


Wettability

 Drainage

- apabila fasa non-wetting displaces fasa wetting

 Imbibition –

apabila fasa wetting displaces fasa non-wetting 13


Wettability

 Wettability

dapat diidentifikasi dengan cara:

 Apabila

air produksi memiliki komposisi sama dengan air conat, reservoir bersifat water-wet.

 Apabila

air produksi sama dengan air injeksi, ada dua kemungkinan:  Reservoir

adalah oil-wet.

 Air

injeksi melewati zona porous yang sangat tipis atau fracture, dan karenanya tidak mempunyai kesempatan kontak secara cukup dengan connat water kecuali pada sistem dengan proses water breakthrough yang lama

14


Capillary Pressure

pressure - perbedaan tekanan antar muka dua fluida tidak membasahi pada sistem kapiler (porous)

 Capillary

15


Capillary Pressure

 Hubungan

antara saturasi air, Sw, pada setiap titik di media pori dengan tekanan kapiler-nya didefinisikan sebagai capillary-pressure curve

 Dua

tipe:

curves - memperlihatkan perubahan saturasi fasa nonwetting mendesak fasa wetting

 Drainage

curves - memperlihatkan perubahan saturasi fasa wetting mendesak fasa non-wetting

 Imbibition

16


Capillary Pressure Example of a typical capillary pressure curve and the corresponding vertical fluid distribution in the reservoir



Capillary Pressure Curve menyatakan distribution air di dalam reservoir



Terdapat interval saturation yang secara gradual berubah dari 100% hingga saturasi air konate < 20%

17


Capillary Pressure

 Layer

yang kurang permeabel memiliki zona transisi yang lebih lebar dan Saturasi air konat lebih besar

 Kesalahan

dalam menentukan Tekanan Kapiler dapat menyebabkan estimasi OOIP yang optimistik

 Capillary

pressure curves menyatakan sifat sample & kehatihatian diperlukan ketika scaling up ke skala reservoir

 Untuk

menjamin distribusi saturasi dari data pengukuran tekanan kapiler, saturasi harus dikalibrasi terhadap logs

18


Capillary Pressure

Sw = Swir

5000

h t p e D

Top of OW Transition Zone

OWC 5800 0

100%

Water Saturation, Swc 19

Irreducible & Connate Water Saturation  Irreducible 

Minimum saturation pada capillary pressure curve vertical



Maximum saturation tanpa aliran air

 Connate



water saturation, Swir

water saturation, Swc



Saturasi air asli dalam reservoir – yang dapat lebih besar atau sama dengan Swir



Jika Swc > Swir berarti fasa mobile



Pada beberapa perhitungan reservoir, irreducible & connate water saturations dapat diasumsikan identik

Dipengaruhi oleh wettability batuan - cenderung lebih rendah pada batuan oil-wet dibandingkan pada water-wet rocks 20

Dynamic Rock-Fluid Properties

Relative Permeability

 Relative

permeability - perbandingan permeabilitas effective terhadap

permeabilitas absolute-nya



keff kr  kabs

Persamaan Darcy's, aslinya diformulasikan untuk digunakan pada media pori yang disaturasi hanya dengan satu fluida . . yaitu air

21


Relative Permeability dz  ko A  dpo = g ρo qo  ds  μo  ds

kro =

ko k

dz  kg A  dpg qg =  ds - ρg g ds  μg  

krg =

kg k

dz  k w A  dpw - ρw g qw =  ds  μw  ds

krw =

kw k

22


Pengaruh Wettability pada Relative Permeability

Examples of relative permeability curves

23

 Kharakteristik

water-oil relative permeability untuk waterwet & oil-wet reservoirs: n 1.0 o i t c a r 0.8 F y t i l i 0.6 b a e m r 0.4 e P e v i t 0.2 a l e R 0

Oil

Water

0

20

40

60

80

100

Water Sat., % PV

Typical water/oil relative permeability characteristics - strongly water-wet rock

n 1.0 o i t c a r 0.8 F n o y i t t i l c a i r 0.6 b F a y e i t l i m r b e 0.4 a P e e m v r e i t P 0.2 a l e e i v R t a l 0 e

R 0

Oil Water 20

40

60

80

100

Water Sat., % PV

Typical water/oil relative permeability characteristics - strongly oil-wet rock

24





Craig “rules of thumb” Water-Wet

Oil-Wet

Connate water saturation

Usually greater than 20 -25%PV

Generally less than 15%PV Frequently less than 10%PV

Saturation at which oil and water relative permeabilities are equal

Greater than 50% water saturation

Less than 50% water saturation

Relative permeability to water Generally less than at maximum water saturation 30% (i.e., floodout)

Greater than 50% and approaches 100%

25





Ini adalah oil-water relative permeability plot untuk "T" Sand di lapangan KB

Menggunakan Craig rules of thumb, apa jenis batuan reservoir



“T” sand ?

26







Swir sample Irreducible core dari water lab: saturation

0.20

Sorw

Residual oil saturation to water

0.48

Swc

Connate (initial) water saturation

0.20

Sgc

Critical gas saturation

0.00

Sorg

Residual oil saturation to gas

0.54

ew

Exponent for k rw equation

1.6

eow

Exponent for k row equation

2.0

eg

Exponent for k rg equation

2.0

eog

Exponent for k rog equation

3.0

krwro

Water relative permeability at residual oil (to water)

0.02

krocw

Oil relative permeability at connate water saturation

0.73

k

Gas relative permeability at residual oil (to gas at connate water

0.3

rgro Calculate krw, krog, krow, and kro for the values of Sw listed in the table in saturation) your manual. This is an oil-water system. 27


Mobility

 Pada

persamaan Darcy’s, mobility sebagai berbanding lurus dengan kecepatan alir fluida dan berbanding terbalik terhadap gradien tekanan kw  Jadi water mobility is: μw ko  dan

oil mobility is:

μo

- ukuran seberapa mudah satu fluida melalui reservoir pada kondisi batuan dan fluida tertentu

 Mobility

28


Distribusi Saturasi Selama Pendesakan Fluida Tak Tercampur



Miscible displacement - apabila dua fluida dapat bercampur secara proporsional dan tak terpisahkan menjadi dua fasa 

Minyak dan Air tidak dapat bercampur, sehingga merupakan fluida tak tercampur.



Immiscible displacement – apabila air mendesak minyak seperti pada water drive atau project injeksi air.



Secara Umum, karena air mendesak minyak, maka akan terjadi distribusi saturasi yang seragam pada suatu daerah diskontinuitas saturasi didepannya setelah pemindahan oleh air. 29


Distribusi Saturasi Selama Pendesakan Fluida Tak Tercampur Schematic of Saturation Profile (After Slider)

 Penampang

bagian water drive reservoir dengan distrbusi saturasi uniform.

 Hubungan

saturasi terhadap jarak distance diperlihatkan pada gambar bawah.

Slider, H. C., “Practical Petroleum Reservoir Engineering 30 Methods”, Petroleum Publishing Corp.


Distribusi Saturasi Selama Pendesakan Fluida Tak Tercampur  Minyak

bergerak kearah sumur produksi dan air masuk dari aquifer atau sumur injeksi, distibusi saturasi akan berubah terhadap : Fluid Displacement Characteristics with Initial Distribution (After Slider)

31


Perhitungan Saturasi Selama Pendesakan

Example oil-water relative permeabilities

 Fraksi

fluida pendesak dibelakang front akan meningkat terhadap jarak

32


Penentuan Kurva Fractional Flow Example of Fraction Flow Curve (After Slider)

 Fraksi

air f w disebut water cut

 Dasar

fractional flow :

 Metode

Analitis didasarkan pada material balance dari 2 fasa fluida incompressible

 Assumsi

system reservoir homogeneous 33


Penentuan Kurva Fractional Flow  Fractional

flow untuk air mendesak minyak: qw f w  qw  qo

 Sesuai

persamaan, asumsi aliran horizontal & tekanan kapiler diabaikan : f wNO 

1

 kro  μw    1    krw  μo 

 If

gravity effects (densities of the fluids) & non-horizontal flow (dip of the reservoir) are significant: 1 f w 

0.000488kroKA Δγ sina μo q t

 kro  μw    μ k   

1  

34

Penentuan Kurva Fractional Flow 

A water drive reservoir is of such size & shape that water encroachment to first line of producers can be treated as linear flow. The water drive is sufficiently active that fluid flow is steady state. The withdrawal rate from the reservoir averages 2,830 reservoir BPD. Reservoir data are as follows: Item Average formation dip,  Average “width” of reservoir, feet Reservoir thickness, feet 2 Average cross-sectional area, feet Permeability, mD Connate water (irreducible water) saturation, % Reservoir oil specific gravity Reservoir oil viscosity, cps Reservoir water specific gravity Reservoir water viscosity, cps

Symbol 

A K Swc o mo w mw

Value 15.5 8000 30 240,000 108 16 1.01 1.51 1.05 0.83 35

Penentuan Kurva Fractional Flow 

Relative Permeability Data: Sw, % 79 (1 – Sorw ) 75 65 55 45 35 25 16 (Swc)



krw 0.63 0.54 0.37 0.23 0.13 0.06 0.02 0.00

kro 0.00 0.02 0.09 0.23 0.44 0.73 0.94 0.98

Calculate the fractional flow for this reservoir corresponding to the saturations listed above for:  Inclusion of dip and gravity effects  Excluding dip and gravity effects  Use oil viscosity of 8.6 cps & exclude dip/gravity effects 36

Welge Method 1. 2. 3. 4. 5.

Estimate OOIP Plot relative permeability curves Estimate average reservoir dip Calculate & plot fractional flow curve, f w Determine water saturation at breakthrough, S wbt, from fractional flow curve 6. Determine average Sw behind the flood front at time of breakthrough 7. Calculate the slope of the fractional flow curve for each water saturation on the relative permeability table 8. Calculate the pore volumes of cumulative injected water required to obtain each water saturation 9. Calculate the cumulative water injection (BBLS) required to obtain each water saturation 10. Calculate the time needed to obtain each water saturation 11. Calculate oil & water production rates for each water saturation 12. Plot oil & water rate versus time 37 Ch 2 - 37 13. Calculate mobility ratio (favorable or adverse?)

Penentuan Kurva Fractional Flow

1. Estimate OOIP 2. Plot relative permeability curves 3. Estimate average reservoir dip 4. Calculate and plot fractional flow curve, f w 5. Determine water saturation at breakthrough, Swbt., from fractional flow curve 6. Determine average Sw behind the flood front at time of breakthrough 7. Calculate the slope of the fractional flow curve for each water saturation on the relative permeability table 38


8. Calculate the pore volumes of cumulative injected water required to obtain each water saturation 9. Calculate the cumulative water injection (BBLS) required to obtain each water saturation 10. Calculate the time needed to obtain each water saturation 11. Calculate oil and water production rates for each water saturation 12. Plot oil and water rate versus time 13. Calculate mobility ratio (favorable or adverse?)

39



qw



Average saturation behind the flood front is always greater than S w at the front

qo, qw

Key points about fractional flow curves

sw x Same Sbt for all fronts

Sharp front Saturation ahead of the flood front is S wc 40



Sw should be as close to 1 as possible for best sweep efficiency

Fractional Flow Curves

1

Sw behind the front

0.9 

Key points

10.0

w 0.8 f , about fractional flow curves w 0.7 o Sw at breakthrough l F 0.6 l a n 0.5 o i t c 0.4 a r F 0.3

2.0 0.5

w=

0.5

o

w=

10

o

w=

2

0.2 0.1 0 0

0.2

0.4

0.6

0.8

1

Water Saturation, Sw 41



At breakthrough:

 f w   bt  Maximum slopeof f w (tangent)  Sw 

f w  f w  f w  S S   w w    Key points about fractional flow  Sw  Sw  Sw 2

Behind the flood front:

2

curves At the flood front::

1

bt

1

 f w   Sw  Sw  0.0  Sw  bt

42

Sifat Fisika Batuan Dan Fluida

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