EPA Workshop on Hydraulic Fracturing, Workshop No. 1, Chemicals

Fracture Fluid Additive an

Formation Degradations

George E. King

Apache Corporation
Fracture Additive and Formati

Reactions and Degradations

Subsurface

Reactive Targets

Chemical & Phys

Reactive Targets Reaction Contro

• Rock (shale, sandstone, limestone, etc.)

– Matrix

Reaction Contro

• Access (inhibition controls)

– Permeability (can rea

each other?)

– Natural Fractures

– Hydraulic Fractures

– Fluids (non HC gases, waters,

– Area‐to‐volume ratio 

diffusion can occur?)

– Inhibition – (diffusion

coatings, form, etc.)

hydrocarbons)

• Tubulars (various alloys)

• Cement

• Reaction variables

– Flow Rate and Pressu

– Temperature

– Pressure

• Drilling components

• Fracture Additives

– Time (average frac 3 

pressure, 2 to 4 week

– Volumes

– By‐product solubility– Re‐precipitation
Well Described Shale

Reaction/ d Degra ation

Chemical Physical

• Ion Transfer, CEC

• Solution and re‐precipitation

Physical• Creep (Deenadaya

Solution and re precipitation • Osmotic

Rx w/ proppant.

Osmotic

• Dispersion (breaka• Salt imbalance

disaggregation (dr

– Resolved by more 

matching salinity.
Shale Porosity vs. Permeabi

Permeabi
Proppant Diagenesis

SPE 131782, LaFollette and Carman

• Proppants Proppants – the conductivity conductivity of a propp

propp

fracture can decompose in some condit

– Proppant Proppant decomposition decomposition from prop‐fluid r

r

– Prop embedment into the formation goug

liberates small formation formation particles particles.
Changes in Recovered Wate

Composition: Sh l a e + Prop + Fl 
Zeolites are the most common 

mineral when shales and prop

heated with salt water.
Zeolites

C Z lit

In order to be a zeolite, the ratio (Si + Al)/O must equal 1⁄2 and typically hav

vacant, interconnected spaces in their structure that form long, wide chan

varying sizes. Common Zeolites y g

The first zeolite formed is often

altered to another species.
Many Formation Degradations Directly T

pH – Low pH C d reate by CO2 or Mi 

nera 
Reduction of Conductivity Conductivity with S
Decomposition Reactions of M

Common Frac Additives (1 of 

• Proppant

– Physical

• Embedment Embedment (pushes (pushes up particles particles of fracture fracture fa• Erosive – minor effect with maximum impact o

perforations in the casing (large particles, rougsurfaces and high velocities)

– Chemical

• Diagenesis – solution and common re‐precipit

silica and some aluminum oxides. Strength los
Decomposition Reactions of M

Common Frac Additives (2 of 

• Friction Reducer

– Physical – lowers friction in pipe by 25 to 35+

(decreases horsepower & resultant emissions

– Chemical Chemical – high MW polyacrylamide polyacrylamide absorbs absorbs 

• Surfactants – (flow‐back, dispersion, IFT, e

most adsorb and are lost.

• Gellants – guar, cellulose derivatives, etc.

– Physical – increases viscosity & proppant carr

ability ability, decreases decreases leakoff leakoff, absorbs absorbs in formatio

formatio

– Chemical – breakers & temperature induced

degradation leaves partly broken polymer in p
Decomposition Reactions of M

Common Frac Additives (3 of 

• Gel Brea e s k r – a ou mm ni m pe su ate rsulfate – red

gel viscosity in lower temperature formatiThe materials remain with fluids.

• Biocides – oxidizing biocide vs. metabolic t

Best have low bioaccumulation and bio‐

d d ti egradation. Some UV use in clear fl id u s.

• Scale Inhibitors – phosphonates, phosphat

esters, Polymers Polymers – sorption sorption losses, no

degradation of phosphonate or phosphatePolymer breakdown is common degradati
Observations

Conventional Rocks

sandstone & carbonates

Unconventional 

sandstone & carbonates shales mudstones sil

• Reactions are well described in

Literature – 60+ years of data

shales, mudstones, sil

• Reactions only starting 

described in Literature

• Access is major limiter 

• Adsorption, absorption &

graded release very common.

• Access – the 0.1 to 5000+ mD

Access is major limiter 

– Shale perm 100 to 50

(0.0001 to 0.0005 mD

fluid movement to m

– Shale pore size of 0.3 

perm & Area‐to‐Volume ratios

of 20,000 to 30,000 are major

chemical & physical reaction

t l

p

water entry into the m

– Area‐to‐volume ratio

the 100 to 1000:1 ran

30,000+:1 of a matrix 

controls 100 000:1 range of gr

• Meaningful work done on core

and appears reflective of what

happens in the rock

100,000:1 range of gr

particles.

– Reaction studies invo

shale are highly susp

possible (unachievab

happens in the rock. p ( 
Support Slides (for the reco

reco

• Shale Characteristics• References
Molecular Diameter

Freeman, 
pH 5 Fluid Effect on Haynesville Haynesville S

pH at Various Various Points in the Flow 
Proppant Diagenesis Conclusions from SPE 1
Changes in Recovered Wate

Composition: Prop + Fl d ui Te

Test of Onset of Proppant Diagen

requires formation formation to be prese

prese

Diagenetic materials formed on all types of proppant – sand, ceramic, glass, r

materials, steel balls, etc.
Same Test with Another Sha
Shale Reactivity

• Shales reactive reactive in the following following manner

manner

– Chemical Reactivity

• Shale units are highly laminated laminated and contain contain a

soluble minerals

• Acid soluble minerals are homogenized in the 

bulk matrix and natural fractures

• Reactive fluids may be capable of etching the 

shale fractures.

• Aluminum oxide, Al2O3
Water Chemistry Changes

• Water chemistry chemistry in the presence presence of sha

(Haynesville) changed out to 240 days

– Ca++ Si+/‐ Cl‐ HCO ‐ – Ca , Si increases sharply and 

/ , Cl , HCO3 increases sharply and 

decreased=>dissolution followed by precip

– The formation formation initially initially weakens weakens, then stren

stren

– There is about a 10% to 20% net strength 

that may be due to changes changes in moisture moisture le

adjustment of mineral structures to salinit
Additive & Formation Degradation Conc

• Several Several chemical chemical and physical physical actions actions o

o

over time

• Short time tests may be misleading misleading

– Re‐precipitation and Prop/Shale strengthe

observed

– Additives often disappear to absorption,

adsorption, precipitation precipitation or modification modification

– “Lost” additives may or may not come bac

extremely dilute solutions.
Proppant Changes

After 120 days of exposure, all the silica in the proppant had been leached o

aluminum oxide behind. Precipitation of minerals on the proppant grains wa
Variables that Influence Influence Rock Ty

1. Porosity2. TOC3. Quartz4. Calcite5. Dolomite6. Illite7. Mixed Clay

8. Siderite

9. Total feldspar10. Total Carbonate

11. Total Clay Content

The first three

principal components

explain almost 70% ofthe variation in the

data set.
Interactions of Componen

Exposure to Flowback Wate

LaFollette, SPE 140110

TDS = 158,000 w/ barium, strontium, sodium and calcium. pH = 5.8.
Petrofacies Variation
Shales ‐ Composition

• Sedimentary in Nature

– Seal and gumbo shales high clay content – 

clays, Organic Organic content content of 10 to 30+%

– Gas productive shales – called a shale beca

particle particle size. Actually Actually a siltstone siltstone or mudst

mudst

<10 to 30% clay and TOC usually 1% to 8%

– Young’s modulus of gas p p ros ective shales 

with tight gas sands – distinctly different f

and gumbo shales (Britt, 2009)
Core Chemistry / Mineralo

Mineralo
References

• Al‐Bazali, T. M., et.al.: “An experimental Investigation on the Impact of Capillary Pressure, Diffusion Osmosis, and Chemical Osmosis on the Stability and Res

of Shales,” SPE 121451 paper and presentation, SPE Offshore Europe Oil and Gas Conference and Exhibition, Aberdeen, UK, 8‐11 September 2009.

• Beihoffer, T.W., Dorrough, D.S., Schmidt, D.D.: “The Separation of Electrolyte Effects from Rheological Effects in Studies of Inhibition of Shales with Natural M

63rd Annual Conference and Technical Exhibition, Houston, 2‐5 October 1988.

• Britt, L.K., Shoeffler, J.: “The Geomechanics of a Shale Play: What makes a Shale Prospective!” SPE 125525, Presented at 2009 SPE Eastern Regional Meeting, 

September 2009.

• Dacy, J.M.: “Core Tests for Relative Permeability of Unconventional Gas Reservoirs,” SPE 135427 paper and presentation, SPE Annual Technical Conference a

19‐22 September 2010.

• Deenadayalu, C., Suarez‐Rivera, R.: “The Effect of Horizontal Completions on the Breakdown Pressures of Anisotropic Gas Shale,” ARMA 10‐477, Salt Lake Ci

• Duenckel, R., et. Al.: “Proppant Diagenesis – Integrated Analysis Provide New Insights into Origin, Occurrence, and Implications for Proppant Performance,” 

presentation, SPE Hydraulic Fracturing Technology Conference and Exhibition, The Woodlands, TX, USA, 24‐26

• Freeman, Freeman, C.M.: A Numerical Numerical Study of Microscale Microscale Flow Behavior Behavior in Tight Gas and Shale Gas Reservoir Reservoir Systems, Systems,” SPE 141125 paper and presentation, presentation, SPE Ann

Exhibition, Florence, Italy, 19‐22 September 2010.

• Grieser, B., Wheaton, B., Magness, B., Blauch, M., Loghry, R.: “Surface Reactive Fluid’s Effect on Shale,” SPE 106815, 2007 SPE Production and Operations Sy

USA, 31 March – 3 April 2007.

• Kale, S., Rai, C.S., Sondergeld, C.H.: “Rock Typing in Gas Shales,” SPE 134539 paper and presentation, SPE Annual Technical Conference and Exhibition, Floren

2010.

• King, G.E.: “Thirty Years of Gas Shale Fracturing: What Have We Learned?, SPE 133456 paper and presentation, SPE Annual Technical Conference and Exhibit

September 2010.

• King, G.E., Lee, R.M.: “Adsorption and Chlorination of Mutual Solvents Used in Acidizing,” SPE 14432, SPE Production Engineering, May 1988, p205‐

• LaFollette LaFollette, R. F., Carman, P. S :. “Proppant Proppant Diagenesis: Diagenesis: Results Results So Far,” SPE 131782 presentation presentation and Paper, SPE Unconventional Unconventional Gas Conference, Pittsburgh Pittsburgh, 

• LaFollette, R. F., Carman, P. S.: “Long Term Stability of Proppants Exposed to Harsh Shale Reservoir Conditions,” SPE 140110 paper and presentation, SPE Hyd

Conference and Exhibition, The Woodlands, TX, USA, 24‐26

• Milner, M., Petriello, J., McLin, R., Gathogo, P: “Imaging Texture and Porosity in Mudstone and Shale: Findings from Petrographic, Secondary, and Ion‐Milled 

4th B.C. Unconventional Gas Technical Forum, April 2010.

• Muniz, E.S., da Fontoura, S. A. B., Lomba, R.F.T.: “Development of Equipment and Testing Methodilogy to Evaluate Rock‐Drilling Fluid Interaction,” ARMA/NA

America Rock Mechanics Symposium, Houston, TX, 5‐9 June 2004.

• Muniz, E.S., da Fontoura, S. A. B., Durate, R.G., Lomba, R.F.T.: “Evaluation of the Shale‐Drilling Interaction for Studies of Wellbore Stability,” ARMA/USRMS 0

Anchorage, Alaska, 25‐29 June 2005.

• Sarwar, MU: . . “Gel Degradation Degradation Studies Studies of Oxidative Oxidative and Enzyme Breakers Breakers to Optimize Optimize Breaker Breaker Type and Concentration Concentration for Effective Effective Break Profiles Profiles at Low an

Ranges,” SPE 140520 paper and presentation, SPE Hydraulic Fracturing Technology Conference and Exhibition, The Woodlands, TX, USA, 24‐26 January 2011

• Tutuncu, A.N.: “Anisotrophy, Compaction and Dispersion Characteristics of Reservoir and Seal Shales,” ARMA 10‐344, Salt Lake City City, UT, 27‐30 June 2010

• Van Oort, E., Hale, A.H., Mody, F.K.: “Manipulation of Coupled Osmotic Flows for Stabilization of Shales Exposed to Water‐Based Fluids,” SPE 20499. Annual 

Exhibition, 22‐25 October 1995.