Vincent, Proppant Performance, Diagenesis, SPE 139875

7/26/2019 Vincent, Proppant Performance, Diagenesis, SPE 139875

1/18

Montana Tech

April 14, 2011

Long Term Proppant Performance

Is diagenesis a significant concern?

Mike Vincent

[email protected]

Fracwell LLC

SPE 139875

Proppant Diagenesis IntegratedAnalyses Provide New Insights into

Origin, Occurrence, and Implications forProppant Performance

R. Duenckel, CARBO CeramicsM. W. Conway, Stim-Lab

B. Eldred, CARBO CeramicsM. C. Vincent, Consultant

Acknowledgements


2/18

Problem Statement

Compelling evidence that fractures are not asconductive or durable as we thought:

Surprising refrac success [SPE 134330, 136757]

Benefit of increasing frac conductivity beyond whatpredicted by models [SPE 119143]

Loss of lateral hydraulic continuity betweenadjacent wellbores connected by a frac [119143]

Infill drilling on very close spacing

Loss of vertical hydraulic continuity betweenstacked reservoir layers [146376]

Laboratory testing

Extended duration

Harsh conditions to promote or accelerate damage

Outline Extended duration testing Benign conditions in lab

Testing to promote diagenesis

Diagenesis defined

Analysis methodology

Zeolites

Static testing

Conductivity testing

Actual proppant recovered from wells

Summary


3/18

Does Conductivity Degrade?

0

0.2

0.4

0.6

0.8

1

0 15 30 45 60 75

PermeabilityRatio

Days at Constant Stress

IDC at 10,000 psi (69 MPa)

LWC at 10,000 psi (69 MPa)

Sand at 5000 psi (35 MPa)

Cobb, 14133200F, 5000/10,000 psi [93C, 35/69 MPa]

All non-corrodible surfaces, prop inTeflon tube, continuous flowing 2% KCl

McDaniel , 15067275F, 8000 psi [135C, 55MPa]

showed importance of using silicasaturated, deoxygenated brine

Similar damage shown with dry nitrogen!

100

1000

10000

0 10 20 30 40 50

Conductivity(md-ft)

Days at Constant Stress, 8500 psi

IDC - Intermediate Density Ceramic

Proflow - Precursor to LWC

RCS - Resin Coated Sand

Ottawa Sand

0

20

40

60

80

100

0 30 60 90 120 150 180 210 240 270

%

OriginalCondu

ctivity

Days at Constant Stress, 5000 psi

20/40 Sand at 75F

10/20 Sand at 250F

Hahn, SPE Drilling 1986300F, 8500 psi [149C, 59 MPa]Teflon tube, continuous flowing 2% KCl,

Non-silica saturated

Montgomery (12616) 198475/250F, 5000 psi [23C/121C, 34 MPa]

API short term cell: Metal plates,continuous flowing 2% KCl,

Non-silica saturated

6

Does Conductivity Degrade?


4/18

Handren 110451250F, 6000 psi [121C, 41MPa]

Modern conductivity cell, Ohio SandstoneDeoxygenated, Silica Saturated 2% KCl,

All data

showdegradation.

No modelsconsider

this!

Does ConductivityDegrade?

Is replacingdegraded

proppant amajor factor

in refracsuccess?

These historical tests suggest Even with relatively benign conditions, proppantsdegrade.

Occurs regardless of fluid (brine, water, oil, nitrogen)

Occurs faster with larger diameter materials [StimLabdata not summarized here]

Occurs faster with lower strength proppants

This would suggest the degradation in these caseswas due to mechanical, not chemical mechanisms

However, can we make it worse by invokingchemistry?


5/18

Diagenesis in Propped Fractures

Dissolution and reprecipitation process Key variables according to 118174 and related papers

Reservoir type

Temperature, closure stress Fluid chemistry Proppant type Proppant coating

Diagenesis example-Precipitants on high strength ceramic

after exposure to shale and syntheticwater at 500F for 7 days

SPE 118174

New Work - Analysis Methodology Extended high temperature static tests to

evaluate interactions between proppants,shales and fluids

Testing of proppants after exposure todiagenetic conditions

Conductivity testing (flowing) at high stress andtemperature with shale cores

Investigation of flowback fluid and proppantrecovered from wells


6/18

Static cells

More than 70 static tests conducted Various combinations of proppant, shale and fluids

held at 400F for up to 154 days

Post-exposure tests include SEM, EDS, strength testsof proppant, bulk density, water analysis

Proppants tested included ceramics, sands and RCS Also included inert steel beads and glass rods

Static Cells- 11 length, 450ml volume Fill with proppant or equal volumes

proppant and shale Water filled intergranular porosity

Sealed and placed in oven at 400F

Proppant Properties

ISO Crush (%)

Proppants BD(g/cm3)

SG SPC(ksi)

% Stress (psi)

20/40 High strengthceramic

2.06 3.62 37.4 4.0 15k

20/40 Light weightceramic

1.58 2.72 24.0 3.3 7.5k

40/80 Light weight

ceramic

1.48 2.58 -- 3.1 7.5k

20/40 Sand 1.56 2.66 13.0 2.3 5k

40/70 RCS 1.52 2.59 -- 1.2 5k

20/40 RCS 1.59 2.59 -- 0.7 5k


7/18

Ceramic Proppant Chemistry

Chemistry, wt. %

Proppants Al2O3 Fe2O3 K2O SiO2 CaO MgO TiO2

High strength

ceramic78.1 11.2 0.007 8.2 0.02 0.006 2.24

Light weight

ceramic49.7 1.06 0.06 46.7 0.02 0.01 2.22

Ceramic Proppant Mineralogy

Mineralogy, wt. %

Proppants Corundum Mullite CristobaliteAmorphous

silica

High strength

ceramic75 25 - -

Light weight ceramic - 75 20 5


8/18

Shale Chemistry

Chemistry, wt. %

Shale SiO2 Al2O3 Fe2O3 K2O+Na2O CaO+MgO

Pinedale 66.2 20.0 3.2 5.3 3.8

Steamboat 77.0 13.9 2.1 3.0 3.1

Hnysvl/Bssr 1 57.5 20.3 4.9 5.9 10.2

Hnysvl/Bssr 2 61.4 15.5 4.6 5.1 12.7

Shale Mineralogy

Mineralogy, wt. %

Shale Illite Quartz Kaolinite Calcite Muscovite

Pinedale 48.6 34.9 11.0 -- --

Steamboat 26.1 56.5 9.3 -- --

Hnysvl/Bssr 1 34.2 25.2 1.5 16.6 17.4

Hnysvl/Bssr 2 29.1 33.4 4.9 14.0 14.9


9/18

Static Tests ResultsExamples of zeolite precipitants high strength ceramic

400F, 14 days, Pinedale

Shale, DI water

Al2O3 Fe2O3 K2O SiO2 MgO TiO2 C

Spot 1 HSC 63.5 17.5 0.6 15.0 0.4 2.2 0

Spot 2 Precipitate 35.8 7.0 4.6 45.6 1.8 1.6 0

Static Tests ResultsExamples of zeolite precipitants frac sand


Shale, DI water


Spot 1 Sand 2.6 0 0 97.4 0 0 0

Spot 2 Precipitate 18.4 7.5 5.0 66.7 2.0 0 0


10/18

Static Tests ResultsExamples of zeolite precipitants RCS


Shale, DI water


Spot 1 RCS 9.0 0 0 19.6 0.7 0 70.7

Spot 2 Precipitate 23.9 20.1 4.3 47.4 2.7 1.7 0

Static Tests ResultsExamples of zeolite precipitants on steel and glass rods

400F, 154 days,Haynesville/Bossier

Shale, DI water


11/18

Static Tests Results

Diagenetic precipitants were observed with all 4 shalesamples to varying degrees

Diagenetic activity only occurred when shale was present

Diagenetic precipitants were observed on all proppanttypes tested including inert materials

The diagenetic precipitants were alumina silicates andmay be classified as zeolites

In the case of the sands and inert materials the aluminawas sourced conclusively from the shales

Static Tests ResultsIncrease observed in post static

test crush

Proppant Type Average % Increase in CrushAfter Exposure

20/40 HSC 31

20/40 LWC 94

20/40 Sand 61

Testing of the post static test proppant showed an increasein ISO crush and reduction in characteristic strength of thepellet


12/18

Conductivity Testing of AgedProppant Samples

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 2000 4000 6000 8000 10000 12000 14000

Stress (psi)

LongTerm

Conductivity(mD-ft)

Sample 2

Sample 1

Crush

Sample Type Exposure at 400F%

(% Incr.) Stress, ps i

1 20/40 HSC None 4 15k

2 20/40 HSC Static cell- 14 days DI water 4.8 (21) 15k

0

80

160

240

320

400

480

2000 4000 6000 8000 10000 12000

Stress (psi)

LongTermPerm

eability(D) Sample 3

Sample 4

Sample 5

Crush

Sample Type Exposure at 400F

%

(% Incr.) Stress, ps i

3 20/40 LWC None 3.3 7.5k

4 20/40 LWC 2.5 hours DI water 7.2 (118) 7.5k

5 20/40 LWC Static cell - 21 days DI water 6.5 (97) 7.5k

Conductivity Testing of Aged

Proppant Samples


13/18

Long term testing of post static tests proppantsyields identical conductivities

Increased post test crush observed is related tostress corrosion not diagenesis

This stress corrosion effect already built-intolong term conductivity tests

Conductivity Testing of AgedProppant Samples

Extended Conductivity Tests (flowing)

Using Haynesville/Bossier Core

Static tests do not address possible acceleration ofdiagenesis due to closure stress

Extended conductivity testing performed withHynsvl/Bssr core and compared to Ohio SS

Test conditions: 325F, 12k closure stress, 1#/ft2 loading

Proppants tested: 40/80 LWC and 40/70 RCS

Held at 12k for 21 days Conductivity measured, post test proppant pack

examined for evidence of diagenesis


14/18

0

200

400

600

800

1000

1200

2000 4000 6000 8000 10000 12000

Stress (psi)

LongTermC

onductivity(mD-ft)

40/70 RCS- 1 ppsf Shale 325F

40/80 LWC- 1 ppsf Shale 325F

47/70 RCS 1 ppsf OHSS

40/80 LWC - 1 ppsf OHSS

Extended Conductivity TestsUsing Haynesville/Bossier Core

Both LWC and RCS showed lower conductivity with

Hville/Bssr core vs Ohio SS

Conductivity reduction continued with time at 12k

stress After 21 days between Hville/Bssr core, 12k, 325F:

40/70 RCS 2 md-ft 40/80 LDC 71 md-ft

Post test examination of proppant pack yielded noevidence of diagenetic precipitants after 21 days of

flow

Conductivity reductions attributed to embedment,

spalling, and continued breakage

Extended Conductivity Tests

Using Haynesville/Bossier Core


15/18

Identity of Precipitants from Static Tests From SEM examination of structural appearance of

diagenetic materials present in prior studies and currentstatic testing: zeolites

Zeolites: crystalline structures with interconnectedcages

Zeolite chemistry: (Si + Al)/O = , Si/Al varies widely

Industrial use as molecular sieves

Zeolites: 46 naturally occurring and > 150 syntheticallyprepared

Zeolites will not form in acidic conditions

What is the pH downhole? High CO2 in hot reservoirs! [Grimes & McNeil,Bross]

We pump high pH gels, but pH quickly drops toacidic conditions upon flowback of frac fluids!

Deep Bossier: pH 6.2

CVL- pH 6.4

Haynesville- pH-6.0

Deep Bossier- pH 6.4

James Lime- pH 7.0

Bakken in situ - pH 4.3-5.8 [Smith 2010]


16/18

Flow back Analysis

Examination of proppant flow back samplesfrom GOM, S. Tx, Rockies, Canada show nodiagenetic activity

Area 2

No evidence ofdiagenesis

No evidence of zeolite

precipitation was observed onany ceramic fragmentsrecovered

Proppant Recovered from Actual Wells

No evidence of zeolite precipitation was observed on any

ceramic fragments recovered after > 1 year downhole. Ironoxide, salts, carbonate and sulfate scales visible on some

sand, RCS and CER samples.


17/18

Summary

High temperature static testing ofproppants in the presence of formationmaterial shows:

diagenetic precipitants may form when formationmaterial is present

these precipitants will form on all proppant typesand inert materials

the precipitants formed may be classified as zeolites

the precipitants always include alumina. In the case

of sand, RCS and inert materials the alumina wasclearly sourced from the formation, NOT theproppant

Summary After aging proppants do show strength

degradation the degradation is related to a stress corrosion mechanism

common to oxides after exposure to water

the degradation appears unrelated to diagenetic processes

stress corrosion attacks silica bonds in both sand and ceramic

proppants

resin coating did not isolate the sand particles from stresscorrosion effects

this degradation is already incorporated in the referenceconductivity testing


18/18

Summary Zeolites did not form under extended conductivity testing

under flowing conditions

High temperature reservoirs in which zeolite formationhas been speculated appear to be too acidic fordeposition

Inspection of proppant recovered from wells did notindicate the presence of zeolites

Zeolite precipitation does not appear to pose asignificant concern for propped fractures in manyapplications

There are numerous damage mechanisms that justify an

increased investment in conductivity. However, it doesnot appear that diagenesis poses a significant concernin most reservoirs, nor that proppant coatings willeliminate zeolite precipitation

Montana TechApril 14, 2011

Long Term Proppant Performance

Is diagenesis a significant concern?

Mike Vincent

[email protected]

Fracwell LLC

Documents

Vincent, Proppant Performance, Diagenesis, SPE 139875