Snorre in-depth water diversion using silicate

Arne Stavland, Hilde Jonsbråten, Olav Vikane, IRISKjetil Skrettingland and Herbert Fischer, Statoil

FORCEWater based EOR diversion techniques

20 January 2010

Table of content• Introduction• Chemical reactions• Gelation kinetic• Bulk gelation time• Permeability reduction

– Filter experiments– High permeability sand– Dynamic experiments in high permeability sand

• The possibility of designing systems for field treatment

• Operator’s plan

Introduction• Sodium silicate is an alkaline liquid• Diluted, the viscosity is water like• Upon reaction, triggered by

temperature, or concentrations, silicate gel is formed

• Can be used for water shut-off or as diversion agent

• Sodium silicate is on the PLONOR list

Dissolution of ionsReservoir minerals mixed with silicate or NaOH• NaOH dissolves Al3+

while silicate did not• Both NaOH and silicate

dissolved Ca2+ (5-28 mg/l)

• No Mg2+ was dissolved. Precipitation of Mg(OH)2 at high pH

• For NaOH the final pH was lowered while remained constant in silicate samples

2

34 )()(02.0

OH

OOHSiOHAlK

NaOH-HCl Acid-Base titration

8

9

10

11

12

13

14

0.001 0.01 0.1 1 10

mmole H+ added

pH

[NaOH]= 0.002M

[NaOH]= 0.01M

[NaOH]= 0.25M

3% SiO2

Silicate and divalent cations

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

8 9 10 11 12 13 14

pH

Rel

on

cen

trat

ion

in

so

luti

on

0

0.2

0.4

0.6

0.8

1

Rel

co

nce

ntr

atio

n p

reci

pit

ated

Mg2+ Ca2+ Mg(OH)2 Ca(OH)2

Precipitation of Mg(OH)2, while Ca2+ and Ba2+ will be soluble in alkaline brineCore floods demonstrated higher mobility reduction when silicate displaced SSW.When mixed in SSW, front plugging was observed.

Gelation kinetic• As for most chemical gel system, the

gelation kinetics

• By assuming independent variables, the following model is suggested

• Need to define– The constant A and the exponents, , , and Ea

,....),,,(/1 pHsalinityCTftk

RTEaCaHClSig eeeeAt /2

Bulk gelation time• Define gel codes ranging from 0-3

• Variables:– Silicate concentration, 3-5 wt%, K40 from BIM– Make-up water, distilled water, tap water, SSW– Temperature, 20-80°C– Acid, HCl, pH ~10.5-11.5

• Visual inspection of samples versus time– Gel code and syneresis

Code Bulk studies Flood experiments

0 Blank Good injectivity

1 Cloudy Filtration and pressure increase

2 Cloudy, increased viscosity

Filtration and pressure increase

3 Rigid Gel Complete blocking after shut in

Gelation time versus Ca2+

– Gelation time decreases by increasing calcium concentration– Tap water with 20 ppm Ca2+ has gelation time 1.6 times lower than in distilled

water

Gelation time versus Ca-concentration

y = 2.0683e-0.092x

R2 = 0.8664

y = 8.769e-0.1319x

R2 = 0.9756

0.1

1

10

0 5 10 15 20

Calsium concentration, ppm^1/2

Ge

lati

on

tim

e, d

ay

s

40°C code 1, days

60°C code 1, days

pH versus HCl concentration

– Linear relationship between HCl added and pH– Can design silicate system by controlling HCl added

pH = -0.944x + 11.427

R2 = 0.9971pH = -0.7783x + 11.513

R2 = 0.9952

pH = -0.0591x + 11.529

R2 = 0.9943

10.6

10.7

10.8

10.9

11

11.1

11.2

11.3

11.4

11.5

11.6

0 2 4 6 8 10

wt% 2 M HCl

pH

3% pH

4% pH

5% pH

Linear (3% pH)

Linear (4% pH)

Linear (5% pH)

Gelation time, experiment versus prediction

4wt% silicate

0.1

1

10

100

1000

0 1 2 3 4 5 6 7 8

wt% 2 M HCl

gel

tim

e, d

ay

s (

1)

4%, 20°C 4%,40°C 4%, 60°C4%, 80°C 4% 3 micron filter 60°C 20 °C, 4%40 °C, 4% 60 °C, 4% 80 °C, 4%

Mobility reduction during silicate injection

Injection of 3% silicate matched with piston like displacement of viscous fluid

1

1.05

1.1

1.15

1.2

1.25

0 1 2 3 4 5 6

Porevolumes injected

RF

RF exp

RF-mod

Permeability reduction 4 wt% silicate• After shut-in

permeability was measured by water injection

• Low silicate concentration (3 wt %) could not withstand high pressure gradients

• Higher silicate concentrations show proper stability, RRF in 9 Darcy sand of ~102-103

Permebility reduction in sand packs, 4% silicate

1

10

100

1000

10000

100000

0 20 40 60 80 100 120 140

time, days

RR

F

RRF12

RRF13

RRF9

RRF8

Dynamic flood experiments• 3 x 75 cm columns, pv = 2100 ml, high permeability

quartz sand• 6 P sections• Temperature = 55°C• 4 wt% silicate + acid + tap water, injected from piston cell• Flow rate

– D1-D2: 0.24 ml/min, residence time of 6 days– D3: decreasing from 12 – 0.03 ml/min, residence time varies

from 0.04 – 17.1 days • Objectives

– Compare dynamic plugging time with bulk gelation time– Demonstrate that plugging time and location can be

controlled– Silicate retention in porous media– Contribute to design field pilot

Experiment D1• From gelation model define a system which

has bulk gelation time = 3.2 days – 4.76 wt% HCl– Did not form gel after 7 days at 55°C– Increased temperature to 64 °C, gel formed after

total injection time of 13.5 days– In terms of residence time (at 55°C) gelation at

11.6 days, which is 3.6 time longer than predicted• It was observed that effluent silicate concentration was

~70% of injected, (corresponds to a factor of 2)• High perm sand assumed to show longer plugging time

than low perm sand (factor of ~1.3)

D1, Pressure profile

-10

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14 16

Cumulative time, days

DP

4,

5, 6

, m

bar

0

1000

2000

3000

4000

5000

6000

7000

DP

, 1,2

, 3, m

ba

r

DP4

DP5

DP6

DP1

DP2

DP3

Fig. 4.3.4 Pressure profiles versus injection time, D1.

Experiment D2• Adjust gel model with a factor of 3.6 to

produce plugging at 3.4 days – 6.5 wt% HCl• Plugging was observed at 4.6 days, sections 3

and 4, strongest in section 4 (residence time = 3-4 days)– Silicate front has reached section 5 but no gel,

probably because of diluted silicate in the front– Good agreement with prediction

• Post water injection show stable permeability reduction for more than 2 months

• No permeability reduction in sections 1 and 2

D2, Pressure profile

-5

-3

-1

1

3

5

7

9

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

time, days

DP

, m

bar

0

5

10

15

20

25

30

DP

, to

t, b

ar

DP1 DP2

DP3 DP4

DP5 DP6

Dpberea Dptot

Fig. 4.3.8 Differential pressure across the 6 section in flood experiment D2, first 5 days of silicate injection.

Experiment D3• Rerun D1 – 4.76 wt% HCl• Initially the flow rate was 12 ml/min, step

wise decreased to 0.03 ml/min• According to adjusted model, plugging at

residence time of 11.6 days– Observed plugging in section 2 at total

residence time of 13.6 days– No plugging in section 1, residence time > 6.8

days

• Effluent concentrations depend on residence time

D3, pressure profile

0.01

0.1

1

10

100

0 2 4 6 8 10 12 14 16 18 20

Residence time, days

q, m

l/min

-1000

0

1000

2000

3000

4000

Dif

fere

nti

al p

ress

ure

, mb

ar

q, ml/min

DP2

D3, Effluent concentrations

0

1

2

3

4

0 1 2 3 4 5 6PV

Rel

ativ

e C

a o

r re

sid

ence

tim

e, d

ays

0

0.2

0.4

0.6

0.8

1

1.2

C/C

0

res time, days Ca/Ca0 rel OH- Al/Al0 Si/Si0

Fig. 4.3.13 Produced silicate, calcium and aluminium, experiment D3

Al and Si concentration decreases as residence time increases

D3, Silicate retention vs residence time

0

10

20

30

40

0 1 2 3 4 5 6

PV injected

Ca

, Al,

pp

m o

r re

s ti

me

, day

s

0

20

40

60

80

100

120

140

mm

ol S

ilic

ate

reta

ined

res time, days Al, mg/l Ca,mg/l Al + Ca +Si-decay Si ret, exp

Fig. 4.3.14 Comparison of experimental and predicted silicate retention.

retainedretainedt

retained mCanAleSiSi )1(0

Dynamic experiments - summary

Conclusions• Sodium silicate is a good buffer and show good

injectivity prior to gelation• A gelation model controlled by pH, temperature,

concentrations and salinity matches bulk gelation experiments

• The gelation model, accounted for silicate retention and high permeability, predicts plugging time observed in dynamic flood experiments

• It is possible to design a silicate system with given gelation time by controlling the concentration of HCl

• In dynamic flood experiments RRF was in the order of 103-104 and somewhat lower in static experiments

• Silicate gel can be dissolved by high pH

Snorre in-depth water diversion using Silicate

2009 Work completed– DG0 – Large scale implementation– Laboratory program - phase 1

2010 Operator’s plan– Laboratory program - phase 2 – P07 single well Silicate injection pilot 2q2010

• Operational experience from preparing and injecting Sodium Silicate• Confirm placement of an in-depth permeability reduction approx. 30-50 m

from the wellbore

2011+ Operator’s preliminary plan– Two well pilot– Requirements

• Successful single well silicate injection pilot in P07• Positive results from laboratory program phase 2• Suitable area/well pair – IOR potential, response measurement and cost

Acknowledgements

•Snorre Partnership:–Statoil AS (Operator)–ExxonMobil Exploration & Production Norway AS–Hess Norge AS–Idemitsu Petroleum Norge AS–Petoro AS–RWE Dea Norge AS–Total E&P Norge AS