Water  Weakening  of  Chalk  –  insight  from  lab  experiments  and  numerical  

modelling        

Aksel  Hiorth  aksel.hiorth@uis.no/ah@iris.no  

25.  April  2016  University  of  Stavanger    

Work  supported  by  

•  Ekofisk  &  Valhall  license  –  BP  Norge  AS  and  the  Valhall  co-­‐venturer;  Amerada  Hess  

Norge  AS,  AND  ConocoPhillips  and  the  Ekofisk  co-­‐venturers,  including  TOTAL,  ENI,  StatoilHydro  and  Petoro  

•  Norwegian  research  council    •  IOR  Centre  of  Norway    (  www.uis.no/ior  )  

Research  Team  •  Rock  mechanics  

–  Merete  V.  Madland  (UiS),  Reidar  I.  Korsnes  (UiS),    Anders  Nermoen,  Kim  Andre  N.  Vorland  (UiS)  MegawaX  MegawaX  (UiS,  now  Statoil)  ,  Ola  KeXl  Siqveland  et  al.    

•  La=ce  Boltzman-­‐  reacAve  flow  modelling    –  Espen  Je[estuen,  Jan  Ludvig,  Janne  Pedersen,  Olav  Aursjø,  Aksel  Hiorth  et  al.  

•  SEM-­‐Sub  micron  –  Mona  Minde  (UiS-­‐IRIS),  Tania  Hildebrand-­‐Habel  (IRIS,  now  at  the  Norgwegian  

Petroleum  department),  Udo  Zimmermann,  Wenxia  Wang  (UiS)  •  Field  Scale  simulaAon  (IORSim)  

–  Jan  Sagen(IFE),  Jarle  Haukås(Schlumberger),  Arild  Lohne(IRIS),  Jan  Nossen(IFE),  Jan  Ludvig  Vinningland(IRIS),  Terje  Sira  (IFE),  Aksel  Hiorth  et  al.    

 

LocaAon  of  the  Ekofisk  Field  

Ekofisk

Recovery  

Ekofisk  compacAon    IniXal:  T=130C  

   σv      =62  MPa              pres=48  MPa  ⇒𝜎↓𝑒𝑓𝑓 ≃14MPa  

 

During  primary  depleXon:     p↓res ≃24MPa⇒𝜎↓𝑒𝑓𝑓 ≃38MPa    

ProducAon  History(*)  

Autumn 2006 57

inelastic deformation and substantial strain. The onset of inelastic behavior occurs at theendcap, a surface in stress space that connects tothe shear-failure line at high shear stresses.However, inelastic compaction alters the chalk,moving the endcap location to the highereffective-stress condition.

As a result of compaction, the subsidencerate in the mid- and late-1980s was about30 cm/yr [1 ft/yr]. The resulting loss of air gapand potential impacts on platform safety becamea major concern. The 6-m increase in platformheight in 1987 was performed to increase the airgap between the lower decks and the expectedmaximum wave height.

In 1980, waterflooding was not initiallyconsidered a viable option in the Ekofisk fieldbecause tests indicated that the chalk was atbest intermediate-wet and at worst oil-wet,reducing the water imbibition that aids water -flood efficiency. Nonetheless, the Ekofiskpartnership felt the potential production gainswarranted a small waterflood pilot, which wasinitiated in 1981.23 The results from the pilotwaterflood suggested good oil displacement andlimited early water breakthrough.

Operator Phillips, now ConocoPhillips, beganstaging a full-field waterflood in 1987. It wasdesigned as a production enhancement mech -anism, with voidage balance achieved in 1994.Despite this, the subsidence rate remainednearly constant as waterflooding continuedunder voidage balancing, reaching a maximumrate of 42 cm/yr [16.5 in./yr] in 1998 (above right).

A new complex of platforms was installed,both to withstand the continuing subsidence andto provide more facilities for an expansion offield activities.24 During the changeover from theold platform complex to the new Ekofisk IIcomplex in late 1998, water injection continuedwhile production was halted for several weeks.During this period, and continuing since then,the subsidence rate decreased dramatically to acurrent rate of 15 cm/yr [5.9 in./yr] (right). Whilea reduction in subsidence rate such as this hadbeen considered by the operator as a possibility,

its magnitude was unexpected, based on the fieldsubsidence history.

The voidage balancing condition achievedduring the mid-1990s should have slowed themechanical compaction, because the effectivestress was no longer increasing. With voidagebalancing, and later repressurization, companyscientists expected the formations to stop

compacting in that time period, and perhapsrebound slightly, but this did not happen.Although creep in the overburden can cause adelayed reaction between compaction andsubsidence, the time delay would not be years, asseen with the subsidence-rate decrease thatfinally began in 1998.

22. Colazas XC and Strehle RW: “Subsidence in theWilmington Oil Field, Long Beach, California, USA,” in Chilingarian GV, Donaldson EC and Yen TF (eds):Subsidence Due to Fluid Withdrawal, Developments inPetroleum Science 41. Amsterdam: Elsevier Science(1995): 285–335.

23. Thomas LK, Dixon TN, Evans CE and Vienot ME: “Ekofisk Waterflood Pilot,” Journal of PetroleumTechnology 39, no. 2 (February 1987): 221–232. Originallypaper SPE 13120, presented at the SPE Annual Technical Conference and Exhibition, Houston,September 16–19, 1984.

24. For more on the Ekofisk platform complex upgrade:“Ekofisk Phase II Looks to the Future,” Journal ofOffshore Technology 5, no. 4 (November 1997): 27–29.

> Ekofisk field production history. The oil rate (green) declined until large-scale water injection (blue)began in the late 1980s. The average reservoir pressure (dashed curve) also decreased until thewater-injection rate increased in 1995. However, the subsidence rate (red) at the hotel, or quarters,platform did not decrease until production was shut in during the transition to the Ekofisk II complexin 1998.

Prod

uctio

n an

d in

ject

ion,

thou

sand

bbl

/d

500

400

700

600

900

800

100

01971 1975 1979 1983 1987 1991 1995 1999 2003 2007

300

200

Subs

iden

ce ra

te, c

m/y

rPr

essu

re, h

undr

ed p

si

50

40

70

60

90

80

10

Average reservoir pressure

Water injection

OilOil

0

30

20

Year

Subsidencerate

> Subsidence and pressures in the Ekofisk field crestal area. Pressure measurements in wells in thecrestal area follow a trend (blue) with a rapid increase in mid-1998 that corresponds closely to theslowing of the subsidence rate (red).

Pres

sure

, psi

7,500

7,000

6,500

6,000

5,500

5,000

4,500

4,000

3,500

3,0001974 1978 1982 1986 1990

Year

Subsidence rate

Pressure

1994 1998 2002 2006

Subs

iden

ce ra

te, c

m/y

r

45

40

35

30

25

20

15

10

5

0

59100schD07R1.qxp:59100schD07R1 11/20/06 10:01 PM Page 57

(*)Doornhof  D.,  KrisXansen  T.  G.,  Nagel  N.,  Pakllo  P.,  Sayers  S.  “CompacXon  and  Subsidence”,  Oilfield  Review  (2006)    

Field  observaAons  of  Water  Weakening(*)  

(*)  Doornhof  D.,  KrisXansen  T.  G.,  Nagel  N.,  Pakllo  P.,  Sayers  S.  “CompacXon  and  Subsidence”,  Oilfield  Review  (2006)    

6yrs  CumulaAve  CompacAon  before  water  front  

2yrs  CumulaAve  CompacAon  aSer  water  front  

CompacAon  in  lab  experiments  

Isotropic  pressure  

L

Stress

Water  injecXon  

0

0

L LL

ε−

=

Strain  

σ↓𝑟   

𝑑𝑃  

σ↓𝑎   

HydrostaXc  tests  1.  Saturate  with  injecXon  

fluid  2.  p=0.8,𝜎↓𝐴 , 𝜎↓𝑟 

=1.3MPa  3.  Heat  to  130C  4.  Raise   𝜎↓𝐴 , 𝜎↓𝑟   to  

~10MPa  5.  Observe  creep  at  const.  

stress  6.  Pass  fluid  through  core    

Chalk  strength  depends  on  pore  fluid  

0

5

10

15

20

0 5 10 15 20

Average effective stress, p' (MPa)

Gen

eral

ized

she

ar s

tres

s, q

(MP

a)

W ater

Methanol

Oil & Glycol

"Dry" chalk

Glycol and water are fully m iscible fluids

σ↓𝑟   

σ↓𝑎   

𝑞= 𝜎↓𝑎 − 𝜎↓𝑟 (→0  hydrostatic)  

𝑝↑′ = 1/3 (𝜎↓𝑎 + 2𝜎↓𝑟 )− 𝑝↓𝑝 (→𝜎↓𝑣 − 𝑝↓𝑝 ℎ𝑦𝑑𝑟𝑜𝑠𝑡𝑎𝑡𝑖𝑐  )  R.  Risnes  “Deforma)on  and  Yield  in  High  Porosity  Outcrop  Chalk”,  Vol.  26,  No.  1-­‐2,  pp.  53-­‐57,  2001  

HydrostaXc  test  

Why  are  the  cores  weaker  in  water?  •  The  principal  mechanism  causing  the  water  

weakening  effect  is  apparently  related  to  the  added  pressure  on  the  grains  caused  by  a[racXon  of  water  molecules  to  the  chalk  surface.  The  adsorpXon  pressure  acts  like  an  increase  in  pore  pressure,  and  thus  decreasing  the  cohesion  of  the  chalk  R.  Risnes,  M.  Madland  et  al.  J.  Pet.  Sci  Eng  (2005)  Water  weakening  of  chalk—  Mechanical  effects  of  water–glycol  mixtures  

AdsorpAon  pressure  &  surface  tension  •  Pore  collapse  à  creaXng  new  surfaces  

A. Røyne, J. Bisschop, D. Dysthe, “Experimental investigation of surface energy and subcritical crack growth in calcite”, J. Geophys. Res. 116 (2011)  

⇒𝑌𝑖𝑒𝑙𝑑  ~ 𝛾↓𝑐𝑐   

(𝑌𝑖𝑒𝑙𝑑↓𝑑𝑟𝑦 /𝑌𝑖𝑒𝑙𝑑↓𝑤𝑒𝑡  )= 18𝑀𝑃𝑎/10𝑀𝑃𝑎 =1.8  

(𝛾↓𝑑𝑟𝑦 /𝛾↓𝑤𝑒𝑡  )= 0.32𝐽/ 𝑚↑2 /0.15𝐽/ 𝑚↑2  =2.1  

ExplanaAon  for  field  water  weakening?    

0

5

10

15

20

0 5 10 15 20

Average effective stress, p' (MPa)

Gen

eral

ized

she

ar s

tres

s, q

(MP

a)

W ater

Methanol

Oil & Glycol

"Dry" chalk

Glycol and water are fully m iscible fluids

0

2

4

6

8

10

12

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4

Axial  stress  [MPa

]

Axial  strain  [%]

L15,  NaCl  unaged  20C

L27,  NaCl  unaged  20C

L39,  NaCl  unaged  130C

L38,  NaCl  unaged  130C

L20,  NaCl  aged  20C

L22,  NaCl  aged  20C

L14,  NaCl  aged  130C

L33,  NaCl  aged  130C

Seawater  weakens  at  high  T  

0

2

4

6

8

10

12

0,0 0,5 1,0 1,5 2,0 2,5 3,0

Axial  stress  [MPa

]

Axial  strain  [%]

L19,  SSW  unaged  20C

L25,  SSW  unaged  20C

L34,  SSW  unaged  130C

L35,  SSW  unaged  130C

L31,  SSW  aged  20C

L32,  SSW  aged  20C

L6,  SSW  aged  130C

L13,  SSW  aged  130C

~25%  reducXon  in  Yield  

 and  weaker  than  NaCl  

Seawater  affects  creep  

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

0,0 5,0 10,0 15,0 20,0 25,0

Seawater  

DW  

PV  

Axial  Strain  (%

)  

What  can  we  learn  from  geochemical  modelling?  

•  HKF  EOS(*)  makes  it  possible  to  predict  logK,  Gibbs  free  energy,  Enthalpy,  heat  capacity  …  at  high  P  &  T  

•  Seawater  in  equilibrium  with  calcite  @  25C  and  130C    

(*)Johnson  et  al.  SUPCRT92:  A  soxware  package  for  calculaXng  the  standard  molal  thermodynamic  properXes  of  minerals,  gases,  aqueous  species,  and  reacXons  from  1  to  5000  bar  and  0  to  1000  C,  Comp.  Geo.  Sci.,  1992  

Seawater  chemistry  

Ion Molality

Na+ 0.48

Mg2+ 0.054

Ca2+ 0.010

K+ 0.010

Cl- 0.56

SO42- 0.028

HCO3- 0.0024

CO32- 0.00027 4

4

4

4

4

4

4

4

4

4

4

4

,

,

,

,

24

04

24

204

244

244

CaSO

SOCaCaSO

MgSO

SOMgMgSO

KSO

SOKKSO

NaSO

SONaNaSO

aaa

KSOCaCaSO

aaa

KSOMgMgSO

aaa

KSOKKSO

aaa

KSONaNaSO

=+→

=+→

=+→

=+→

−+

−+

−+−

−+−

Sulphate  species,  similar    equaXons  for  other  species  

Result,  25˚C  and  1  bar  Ion Molality

(Total) Free Ion (percent)

Me-SO4 Pair (percent)

Me-HCO3 Pair (percent)

Me-CO3 Pair (percent)

Na+ 0.48 99 1 0.04 0.006 Mg2+ 0.054 86 13 0.6 0.4 Ca2+ 0.010 90 9 0.6 0.1 K+ 0.010 98 12 - -

Ion Molality (Total)

Free Ion (percent)

Ca-anion Pair (percent)

Mg-anion Pair (percent)

Na-anion Pair (percent)

K-anion Pair (percent)

SO42- 0.028 52 3 26 19 0.6

HCO3- 0.0024 76 3 14 8 -

CO32- 0.00027 9 7 72 12 -

Cl- 0.56 100 - - - -

Result,  130˚C  and  8  bar  Ion Molality

(Total) Free Ion (percent) Me-SO4

Pair (percent)

Me-HCO3 Pair (percent)

Me-CO3 Pair (percent)

Me-Cl Pair (percent)

Na+ 0.45 86 2.6 0 0 11.4 Mg2+ 0.045 72 23 0.03 0.02 5 Ca2+ 0.011551 82 15 0.02 0.07 3 K+ 0.01 99.96 0.04 - - -

Ion Molality  (Total) Free  Ion  

(percent) Ca-­‐anion  Pair  

(percent) Mg-­‐anion  

Pair  (percent)

Na-­‐anion  Pair  

(percent)

K-­‐anion  Pair  

(percent)

SO42-­‐ 0.024 0.7 7 43 49 0.002

HCO3-­‐ 5.13E-­‐05 69.6 5 25 0 -­‐

CO32-­‐ 1.73E-­‐05 5 47 48 0 -­‐

Cl-­‐ 0.525 90 0.08 0.4 9 -­‐

Mg,  SO4  in  seawater  alter  mineralogy  in  core    Mineral SSW

Q/K SSW wo/SO42-

Q/K SSW wo/SO42-,Mg2+

Q/K SSW wo/Mg2+ Q/K

Dolomite CaMg(CO3)2

2.16 2.2 - -

Dolomite(ordered) CaMg(CO3)2

2.17 2.2 - -

Dolomite(disord.) CaMg(CO3)2

1.18 1.22 - -

Huntite CaMg3(CO3)4

1.98 2.09 - -

Brucite Mg(OH)2

1.37 1.41 - -

Magnesite MgCO3

1 1.04 - -

Anhydrite CaSO4

0.22 - - 0.35

Calcite CaCO3

0 0 0 0

”A  Chemical  Model  for  the  seawater-­‐CO2-­‐carbonate  system-­‐aqueous  and  surface  chemistry”,    Hiorth,  Cathles  et  al.  SCA,  Abu  Dhabi,  2008  

Flow  through  models  

M4

M4

M3

M2

M1 Seawater Effluent

0 1 20 2

Seawater  flooding  dissolves  calcite  and  precipitate  Mg-­‐carbonates  &  CaSO4  

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 2 4 6 8 10 12

Con

cent

ratio

n [m

ol/L

]

Time [days]

CaCl

MgSO4SO4

MgCaCl

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0 0.01 0.02 0.03 0.04 0.05 0.06Distance[m]

wt_calcitewt_dolomite

wt_anhydrite

-0.008

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

0.01

0 0.01 0.02 0.03 0.04 0.05 0.06Distance[m]

dpor_totdpor_calcite

dpor_dolomitedpor_anhydrite

0.08%/PV dissolve & 0.07%/PV precipitates 0.01%/PV net change

Hiorth,  A.,  Je[estuen,  E.,  Cathles  L.  M.,  Madland  M.  “PrecipitaXon,  dissoluXon,  and  ion  exchange  processes  coupled  with  a  lakce  Boltzmann  advecXon  diffusion  solver”  GCA,  104  (2013)    

Hypothesis:  InjecAon  water  induces  chemical  alteraAon  and  affects  Yield  and  Creep  

•  CalculaXons:  If  Mg  and  SO4  is  removed  from  seawater  à  no(very  li[le)  chemical  alteraXon  

•  0.219M  MgCl2  flooding  à  ~0.07  wt%  alteraXon  per  PV  à  100/0.07=  1429  PV  replace  all  calcite  w  Mg-­‐carbonates  

Seawater  (Io=0.657)  

0.219M  MgCl2  (Io=0.657)  

0.219M  Na2SO4  (Io=0.657)  

Dolomite,  hunXte,  magnesite  ,  …  precipitaXon  

Some  dissoluXon  of  calcite  (comparable  with  NaCl  brine)  

MgCl2  flooding  of  Liege  chalk  @130  

Flood  sequence:  –  0.657  M  NaCl  brine        1-­‐7  days  –  0.219  M  MgCl2          7-­‐58  days  –  DisXlled  water  (DW)        58-­‐65  days  –  0.219  M  MgCl2          65-­‐1072  days  

1-­‐3PV  /day  à  ~1880PV  

Data:  Nermoen,  A.  ,  Korsnes,  R.  I.,  Hiorth,  A.  ,Madland  M.  V.        “Porosity  and  permeability  development  in  compacXng  chalks  during  flooding  of  nonequilibrium  brines:  Insights  from  long-­‐term  experiment”      J.  Geo.  Res.  Solid  Earth  ,  120  (2015)    Pore  Scale  Modelling:  Pedersen,  J.,  Je[estuen  E.,  Madland,  M.  V.,  Hildebrand-­‐Habel,  Korsnes,  R.,  Vinningland  J.  L.,  Hiorth  A.  “A  dissoluXon  model  that  accounts  for  coverage  of  mineral  surfaces  by  precipitaXon  in  core  floods”  Adw.  Wat.  Res.  87  (2016)  

Mg  loss  and  Ca  gain  during  flooding  

Mg2+  

Cl-­‐  

Ca2+  

•  Modelling  highlight  (Pedersen  et  al.):  

•  Literature  dissoluXon  rates  too  high  –  only  match  first  week  

•  Explained  by  dynamic  reacXve  surface  area  

•  Precipitated  minerals  partly  covers  primary  minerals  

𝜑(𝑡)= 𝜑↓𝜀 (𝑡)+ 𝜑↓𝑐 (𝑡)  

𝑘↓𝐶𝐾 (𝑡)= 𝜑(𝑡)↑3 /2𝜏(1−𝜙(𝑡))↑2 𝑆(𝑡)↑2    

10%  deformaAon    

Perm  

Strain  

compacAon  =  dissoluAon  

compacAon  

and  permeability  =  f(φ,  diss.)  

•  Increase  in  specific  surface  area  explains  drop  in  perm  

•  DissoluXon  explains  increase  in  porosity    

•  Measured:  𝝓(𝒕↓𝒇 )≃𝝓(𝟎)∼𝟒𝟎%  

Textural  changes  obvious  

Unflooded  

Axer  1072  days  

Specific  surface  area  increases  !  explains  perm  behavior  

•  𝑘↓𝐶𝐾 (𝑡)= 𝜑(𝑡)↑3 /2𝜏(1−𝜙(𝑡))↑2 𝑆(𝑡)↑2  

•  (𝑘(𝑡↓𝑓 )/𝑘(0) )= 1.05𝑚𝐷/0.15𝑚𝐷 ≃6.7  

•  (𝑆(𝑡↓𝑓 )𝜌(𝑡↓𝑓 )/𝑆(0)𝜌(0) )↑2 = (9.4⋅2.9/3.7⋅2.7 )↑2 ≃7.4  

3.56  m2/g  

3.84  m2/g  

8.85  m2/g  

9.92  m2/g  

𝜌(0)≃2.69g/cm↑3   

𝜌(𝑡)≃2.9g/cm↑3   

Pore  scale  simulaAon  of  alteraAon  

5003  voxels  @  12.5  nm  =  (6.25  μm)3   350  voxels  =  4.4  μm

Currently  working  with  Sandia  NaXonal  Lab  to  obtain  high  resoluXon  of  chalk  

IS  IT  POSSIBLE  TO  CONTROL  PERMEABILITY  BY  CHANGING  THE  CHEMISTRY?    

Adding  Ca  stops  creep  and  perm  decline  

0,00

0,05

0,10

0,15

0,20

0,25

0,30

4,0

4,5

5,0

5,5

6,0

6,5

7,0

7,5

8,0

8,5

60 110 160 210 260

Ion  concen

tration  [m

ol/l]

Axial  creep

 strain  [%

]

Creep  time  [days]

0.219  M  MgCl2  pH=5.80

0.219  M  MgCl2  +  0.130  M    CaCl2  +  NaOH  pH=8.9

0.219  M  MgCl2  +  NaOH  pH=9.02

Calcium  concentration

Original  Ca2+  in  0.219  M  +  0.13  M  CaCl2  +  NaOH

Magnesium  concntration

Original  magnesium  concentration

Ca2+

Mg2+

permeability  

Can  Mg-­‐alteraAon  explain  field  water  weakening?  

•  AlteraXon  propagaXon  is  slow  at  high  T    •  Temperature  gradients  in  field  will  slow  down  kineXcs  

•  What  about  SO4?  

0

2

4

6

8

10

12

0,0 0,5 1,0 1,5 2,0 2,5 3,0

Axial  stress  [MPa

]

Axial  strain  [%]

L14,  NaCl  aged  130C

L33,  NaCl  aged  130C

L4,  MgCl2  aged  130C

L9,  MgCl2  aged  130C

L10,  Na2SO4  aged  130C

L17,    Na2SO4  aged  130C

L6,  SSW  aged  130C

L13,  SSW  aged  130C

SO4  affects  Yield  (Mg  less)  

Liege  chalk,  Porosity  =  40.3  –  41.8%  

Na2SO4  @  130C  

Seawater  @  130C  

Sulphate  adsorbes    

Megawati, M., Hiorth, A., Madland, M.V., (2012), The impact of surface charge on the mechanical behaviour of high-porosity chalk, Rock Mechanics and Rock Engineering-Springer

Increasing adsorption & ionic strength SO

4  

0.219M  Na2S

O4  

Sulphate  adsorpAon  !  neg  surface  charge  •  Surface  complexaXon  model(*)  

à  predict  𝜓  from  adsorpXon  

(*)Hiorth,  A.,  L.  M.  Cathles,  Madland  M.  V.  (2010).  "The  Impact  of  Pore  Water  Chemistry  on    Carbonate  Surface  Charge  and  Oil  We[ability."  Transport  in  Porous  Media  85(1):  1-­‐21.    

𝜉↓0 ≡ 𝑒↑𝐹𝜓/𝑅𝑇  

Weakening  effect  by  disjoining  pressure  

•  Disjoining  pressure:  

•  Results  from(*)  shows  that  reducXon  in  Yield  follows  formula  obove    

Megawati, M., Hiorth, A., Madland, M.V., (2012), The impact of surface charge on the mechanical behaviour of high-porosity chalk, Rock Mechanics and Rock Engineering-Springer

𝐼≡ 1/2 ∑ 𝑍↓𝑖↑2 𝑚↓𝑖   

Summarize  Water  Weakening  

•  Pore  collapse  due  to    – Lower  cohesion    – Surface  tension  (adsorpXon  pressure)  – Chemical  effects    

•  Textural  changes  (dissoluXon/precipitaXon)  (slow)    (Mg-­‐carbonates)  

•  Surface  charge  (fast)  (SO4-­‐absorpXon)  

physical  

Next  crucial  steps  

•  Can  chemical  water  weakening  explain  Ekofisk  compacXon?  

•  Need  to  Xe  chemical  alteraXon  to  field  data  •  IOR  Center  project  

–  Add  geochemistry  to  reservoir  simulaXon  –  Predict  alteraXon  –  Compare  with  Ekofisk  data  

IORSim(*)-­‐An  add  on  tool  to  ECLIPSE  for  fast  and  accurate  simula=on  of  mul=  phase  geochemical  interac=ons  at  the  field  scale  

 Eclipse  

Reservoir  simulator  

IORSim(*)    

advect  components  

Geo-­‐chemistry  

   

Restart  Files  Sw,  Po,  Pw,  qw  

…  

Oil  Rate  

Water  Rate  SO4  

Mg  

(*)Hiorth,  A.,  Sagen  J.,  Lohne  L.,  Nossen  J.,  VinninglandJ.,  Sira,  T.IEA,  Sapporo,  Japan  (2015)    

INJ  I  

PRD  I  

INJ  III  

INJ  II  

Simulated  “Ekofisk  sector”  

Produced  water  composiAon  

Mg  ions  

Reservoir  pH  

SO4  Model  Constant  Temp  

SO4  Model  Temp  Gradients  

IORSim  Backward  coupling  

Eclipse  Reservoir  simulator  

Files  

IORSim  

Geo-­‐chemistry   Temp  

First  step  use  Ocean  technology  Schlumberger  

Example  –  core  flood  Run  Eclipse  

𝚫𝒕    Stop  Eclipse  process  

Run  IORSim  𝚫𝒕,  calc  X  ,  calc  X  

Update  SATNUM    

Summarize  •  Lab  Water  weakening  can  be  explained  by:  

–  Change  in  surface  energy  (lower  cohesion)  –  Chemical  dissoluXon    –  InteracXon  energy  (disjoining  pressure)  

•  Field  water  weakening:  –  Need  to  couple  flow  and  geochemistry  –  Predict    chemical  alteraXon  speed  &  compacXon  –  Compare  with    field  data  (IOR  Centre)      

IOR  NORWAY  2016      

•  April  26-­‐27  2016  •  For  more  informaXon:  

uis.no/ior  

45

Monitoring  CompacAon.    C-11A CumulativeCompaction Rate

9600

9700

9800

9900

10000

10100

10200

10300

10400

10500

10600

10700

10800

10900

-5 5 15 25 35 45 55 65 75

Cumulative Compaction Rate (cm/year)

Dept

h (ft

)

Jun94-Jan95 Jan95-Jun95 Jun95-Nov95Nov95-Jun96 Jun96-Mar97 Mar97-Jun97Jun97-Feb98 Feb98-Oct98 Oct98-Apr99Apr99-Jan00

•  Results  from  compacXon  monitoring  tool  can  prove  to  be  criXcal  to  understanding  the  nature  of  the  compacXon  phenomenon  

•  The  water  weakening  effect  on  reservoir  compacXon  and  seabed  subsidence  has  been  verified  by  direct  field  measurements  including  reservoir  compacXon,  water      saturaXon  and  pressure  profiles  in  a  verXcal  monitoring  well      

N. B. Nagel 2000

Sulphate  adsorbes    

Megawati, M., Hiorth, A., Madland, M.V., (2012), The impact of surface charge on the mechanical behaviour of high-porosity chalk, Rock Mechanics and Rock Engineering-Springer

Increasing adsorption

SO4  

Highlight  •  Discuss  water  weakening  

–  Pore  fluid  important  for  rock  strength  –  Ekofisk  field  vs  lab    

•  Explained  by  –  Physical  effects  

•  Surface  tension  –  Chemical  effects  

•  DissoluXon,  precipitaXon,  adsorpXon  

•  Upscaling  –  TranslaXng  core  data  to  field