Iptc 14285 Presentation

IPTC 14285

Exposure to Phosphate-Based Completion Brine

Under HPHT Laboratory Conditions Causes

Significant Gas Permeability Reduction in

Sandstone Cores

John Downs

Cabot Specialty Fluids

2011 International Petroleum Technology Conference

Alkali metal phosphate brines

Potassium phosphate brine - K2HPO4/KH2PO4

Max density = 1.77 g/cm3

K Phosphate (g/100 g H2O)

KH2PO4 (%)

K2HPO4

(%)pH Density

(g/cm3)

25.19 100 0 4.01 1.15

34.84 75.13 24.87 5.58 1.20

48.12 58.56 41.44 6.19 1.28

73.52 43.18 56.82 6.92 1.40

124.31 28.93 71.07 8.06 1.58

201.89 15.63 84.37 9.51 1.77

173.32 3.24 96.79 10.39 1.72

165.72 0 165.72 10.98 1.72

2011 International Petroleum Technology Conference 2

Also cesium phosphate brine - Cs2HPO4/CsH2PO4

Max density = 2.80 g/cm3

Potassium phosphate brine used as completion fluid by Pertamina, 2008-9 (SPE 139169)

• Used in 5 exploration wells

• Fluid density up to 1.67 g/cm3

•HPHT wells up to 335oF, up to 20,000 ppm H2S and 35% CO2

•NPT due to elastomer failures, DST tool failures, tubing

connection failures, incompatibility with brines and cements

•Formed a film on downhole metal surfaces

•No mention of testing for formation damage


HPHT laboratory core flooding test with phosphate brine

The objective of the core flooding test was to find out if potassium phosphate brine is compatible with sandstone gas reservoirs under HPHT conditions

•To determine the effect of potassium phosphate brine invasion on

the gas permeability of sandstone under HPHT conditions

•To determine the cause/mechanism of any change in the gas

permeability of sandstone after exposure to the phosphate brine

Use cesium formate brine (a standard HPHT well completion fluid)

as a control substance, for comparison


Potassium phosphate brine, 1.637 g/cm3, pH 9.32

- Analysis (by ICP and ion chromatography)

Analyte in solution Concentration(mg/l)

K 248,742

PO4 481,196

Na 131

Cl 96

NO3 45

SO4 45

Ba, Ca, Sr, Mg < 1

Pb < 23

Al, Cd, Cu, Hg, Mn, Mo, Ni, Zn <5

Fe < 0.5

Cr 6.1

B 8.1


5

Cesium formate brine, 2.20 g/cm3, pH 10.5

- Analysis (by ICP and ion chromatography)

Analyte in solution Concentration

(mg/l)

Cs 1,261,000

K 17,850

Rb 7,621

Na 7,836

Li 1,516

Cl 938

S 201

NO3, SO4, PO4 <5

Ca 14.3

Ba, Sr, Mg < 2

Zn 3.4

Al, Cd, Cu, Hg, Mn, Mo, Ni, Cr, Pb <1

Fe 0.08

P 35

B 11.5


6

HPHT core flooding test rig – Corex, Aberdeen


HPHT laboratory core flooding test for determining

effect of phosphate brine on gas permeability

Key features of methodology

•Clean core, saturate with reservoir water, then centrifuge to irreducible •Measure permeability to gas (30 mD) under HPHT conditions • Forward flow of 10 PV test brine, followed by 48 hour soak period

•Realistic drawdown build-up, simulating production start-up

•Flow large volume of gas under drawdown to achieve clean-up

• Measure permeabilityunder HPHT conditions with humidified gas

• Do SEM on core samples to identify source of any damage


HPHT core flood test with phosphate brine

Programme - Measure initial permeability to gas at Swi under HPHT conditions

- 10 PV flush with test brine at 1 ml/minute- Soak for 48 hours at balance under HPHT conditions- Drawdown ramped up in stages to 100 psi (5,700 psi in wellbore)

using 2,000 PV of humidified gas - Measure return permeability to gas under HPHT conditions- Examine core (dry/cryo SEM) for any signs of damage

Test conditions - 175o C - 5,800 psi pore pressure - Clashach sandstone core flooded with North Sea reservoir water and then centrifuged to irreducible saturation


HPHT core flood test with potassium phosphate brine

Core from Clashach sandstone, quarried near Edinburgh, Scotland

Core sample

Coring Depth

(m)

Length (cm)

Volume (cc)

Pore volume

(cc)

Porosity (%)

Grain density (g/cc)

Gas permeabilit

y(mD)

#1 n/a 4.78 23.802 2.07 8.7 2.62 27.6

#2 n/a 3.97 19.919 1.98 10.0 2.63 34.0


Core dimensions and properties

10

Appearance of core face under SEM – before exposure to brine


Fine/medium grained sand (D50=190µ), with grain-coating and pore-filling illite clay, chlorite, quartz and calcite. Pore throat D50=6 µ (<1 -11 µ range)

11

Low magnification High magnification

Ionic composition of the reservoir water*

NaCl content of 79,330 mg/l and TDS of 89,260 mg/l

Principal scaling ions : Ca, Mg and Ba

*Simulation of reservoir water from Franklin field (HPHT gas)

in UK North Sea

Ion concentration (mg/l)

Na K Ca Mg Ba Fe Cl HCO3

31,190 300 2,300 350 1,000 10 53,500 610


12

Output of DownHole Sat scale prediction – phosphate brine mixing with formation water


Red = definite chance of scale formation (calcium and iron products)

13

Phosphate brine in mix (% v/v)

Scale 0 16.67 33.33 50 66.67 83.33 100

Calcite CaCO3 0.538 0.0638 0.0223 0.00907 0.00335 < 0.001 0

Aragonite CaCO3 0.401 0.0476 0.0166 0.00676 0.0025 < 0.001 0

Witherite BaCO3 0.0409 0.0484 0.0206 0.00848 0.00285 < 0.001 0

Strontiante SrCO3 0 0 0 0 0 0 0

Magnesite MgCO3 1.16 0.00457 0.00103 < 0.001 < 0.001 < 0.001 0

Anhydrite CaSO4 0 0 0 0 0 0 0

Gypsum CaSO4*2H2O 0 0 0 0 0 0 0

Barite BaSO4 0 0 0 0 0 0 0

Celestite SrSO4 0 0 0 0 0 0 0Tricalcium phosphate 0 223472 111060 58608 26373 6628 0

Hydroxylapatite 0 2.80E+01 7.30E+09 2.20E+09 5.30E+08 4.90E+07 0

Fluorite CaF2 0 0 0 0 0 0 0

Silica SiO2 0 0 0 0 0 0 0

Brucite Mg(OH)2 2.12 0.00404 0.00139 < 0.001 < 0.001 < 0.001 0

Magnesium silicate 0 0 0 0 0 0 0

Ferric hydroxide Fe(OH)3 254 45.69 24.51 14.92 8.8 4.26 0

Siderite FeCO3 9.07 3.47 1.25 0.508 0.184 0.0409 0

Strengite FePO4*2H2O 0 3.20E+07 2.80E+07 2.10E+07 1.40E+07 6418781 0

Halite NaCl 0.00591 0.0109 0.0171 0.0243 0.0316 0.0334 0

Thenardite Na2SO4 0 0 0 0 0 0 0

Iron sulfide FeS 0 0 0 0 0 0 0

HPHT core flood testing with potassium phosphate brine


24-carat gold film wrapped around circumference of core to create a barrier to gas diffusion/leakage under hydrothermal conditions

Encased with layers of PTFE tape, heat-shrink tubing and an outer Kalrez sleeve before mounting in core holder

14

HPHT humidifier for gas used in core flooding

2.75"

22.50"

Dry nitrogen gas enters base of humidifier, passes through column filled with high surface area spheres saturated with water, and exits from top.

Pressure vessel mounted vertically in oven at test temperature/pressure.

Materials all in Hastelloy C-276


HPHT core flood test results with potassium phosphate brine – Brine injection phase


Pressure development across core during injection of 10 PV ofphosphate brine @ 1ml/min (frontal advance rate of 80 cm/hour)

Differential pressure did not stabilise

16

0 1 2 3 4 5 6 7 8 9 100.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

Chart Title

Cumulative brine throughput (pore volumes)

Dif

fere

nti

al p

ress

ure

(p

si)

HPHT core flood test results with potassium phosphate brine

Drawdown pressure (psi)

Cumulative gas throughput

(ml)

Cumulative gas throughput

(PV)

Stabilised flow rate (ml/min)

10 150 75.6 0.41

25 500 252 4.24

50 900 454 13.4

75 1700 857 26.0

100 4000 2017 39.7


Drawdown pressure ramping, gas volume throughput and stabilised flow rate

17

HPHT core flood test results with potassium phosphate brine – Drawdown flow profile


Gas flow rates and cumulative throughput during the drawdown sequence

2,017 PV (4,000 cm3) of gas pulled through core in 566 minutes (118 mins at 50-100 psi drawdown)

18

0 500 1000 1500 2000 2500

0

5

10

15

20

25

30

35

40

45

DRAWDOWN PRESSURE UP TO 100psi

DRAWDOWN PRESSURE AT 100psi

Cumulative gas throughput ( pore volumes)

Ga

s flo

w r

ate

(m

l/min

)

HPHT core flood test results with cesium formate brine – Drawdown flow profile


Gas flow rates and cumulative throughput during the drawdown sequence

1,931 PV (4,000 cm3) of gas pulled through core in 23 minutes (11 minutes at 50-100 psi drawdown)

19

200 400 600 800 1000 1200 1400 1600 1800 2000 2200

0

50

100

150

200

250

300

350

400

DRAWDOWN PRESSURE UP TO 100psi

DRAWDOWN AT 100psi

Cumulative gas throughput ( pore volumes)

Ga

s fl

ow

ra

te (

ml/m

in)

Gas flow rate profile during drawdown-Comparison of

cores flooded with phosphate and formate brines


HPHT core flood test results with potassium phosphate and cesium formate brines

Completion brine system

Test Temperature

(oC)

Initial Permeability

(mD)

Final permeability

(mD)

Change in permeability

(%)

Phosphate 175 10.2 0.86 -91.6

Formate 175 23.0 24.8 +7.8


Exposing the core to phosphate brine reduced its permeability to gas by > 90%

21

Appearance of core face under SEM – before and

after exposure to phosphate brine and gas

drawdown


Sand grains and pore throats covered in blanket of phosphate scale after testEDS analysis of the scale shows potassium, phosphorus, sodium and chloride

22

Before test After test

Appearance of internal surface of core under SEM–

after exposure to phosphate brine and gas

drawdown


Retained phosphate scale coating onto area of illite clay

23

Changes in ion content of fluids during HPHT core flood

test with potassium phosphate brine

•Calcium and magnesium depleted, both in wellbore fluid and filtrate. PO4

levels reduced . Suggests precipitation and/or scaling onto surfaces

•Sodium and chloride also depleted (> x 40 diluted) in filtrate •pH of filtrate dropped from 9.7 to 8.75 after passage through core •Phosphate brine picked up 9-35 mg/l each of Cr, Fe, Ni and Mo during test

Analyte Concentration in fluid (mg/l)

Formation water

Phosphate brine

Wellbore fluid post-test

Filtrate fluid post-test

PO4 3.8 481,196 449,911 438,250

Na 31,265 131.7 < 195 <195

Cl 51,341 96.3 57.9 72.6

Ca 2,050 <1.0 <2.7 < 2.4

Mg 337 0.3 2.2 0.9



Conclusions •Flooding a sandstone core with potassium phosphate brine under

HPHT conditions reduced its gas permeability by > 90% after

clean up by 2,000 PV drawdown. •SEM/EDS analysis of core samples indicates that the main cause

of formation damage was phosphate scale formation blocking

pore throats

- Scale deposits concentrated on surfaces coated with illite clay

- Reduced levels of Ca,Mg, PO4, Na and Cl in fluids post-test

• Flooding a similar core with cesium formate brine under same

HPHT conditions resulted in a slight improvement in permeability •Precipitation of phosphates onto mineral surfaces is a well-known

phenomenon, and is the desired result of scale inhibitor squeezes



Acknowledgement

I would like to acknowledge and thank Ian Patey, Murdo Munro and the

laboratory staff of Corex in Aberdeen who planned, managed

and executed the experimental programme described in this paper


Iptc 14285 Presentation

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