INTRODUCTIONThe extraction of resources from geologic formations, including geothermal energy, oil and gas, and in-situ mineral recovery relies on the ability to communicate hydraulically (through fluid) with the formation. Many, if not most, of these formations must be accessed through relatively low permeability rock. Extracting these resources requires gaining access through drilling and stimulation (enhancing fracture conductivity) techniques. The ability to characterize, develop, and control complex fracture networks through geologic formations is essential to the extraction of geologic assets. It is estimated that >50% of the rate decline in the production of oil and gas from tight reservoirs is due to closure of unpropped fractures due to natural closure forces as fluids are removed from the fractures. Hydraulic stimulation is used to create and extend fractures to create a greater drained area at great expense, while proppants and acid treatments are used to maintain conductivity. The ability to initiate, extend, maintain, and control fracture formation and conductivity over the life of a well is essential to improved efficiency in subsurface development.

This project is investigating the formation, application, and subsurface and production effects of novel, high modulus, swellable (expandable) proppants. The development of multifunctional proppants, such as expandable proppants, can be enabling in development of subterranean resources. Expandable proppants are theorized to provide the following benefits:

� Enhanced transport: smaller, lighter proppants can be transported farther into the formation, and into fractures perpendicular to main flow channels.

� Fracture Initiation and extension: Expandable rigid proppants with GPa modulus can apply 1000-10,000(+) PSI force while retaining permeability and fluid access. These forces are sufficient to initiate and extend fractures.

� Offset closure forces: Expanding proppants can apply force, and increase contact area to offset embedment and closure forces, shifting the production decline curve.

� Control proppant flowback: Expandable proppants can be used to quickly lock in proppant packs, reducing or preventing proppant

� Impart and control formation stresses. The targeted delivery of force can be used to manipulate formation stresses

FabRICaTIONSwellable proppants are prepared as a nanocomposite of a water-reactive metal or compound with a hydrolysis-resistant polymeric binder. The original proof of principle used iron particles in a polysulfone polymer, appropriate for 150-180°C formation conditions. Above about 150°C under anaerobic conditions, the iron reacts with water and forms black Fe3O4, undergoing a 217% volumetric expansion. Other reactions evaluated included hydration of oxides such as CaO and MgO, hydration of lamellar materials such as clays, and hydration/oxidation of reactive metals such as Zn, n-Si, and Ca. Different polymers including epoxies, nylons, polycarbonate, and polyurethanes were evaluated for stability and properties. For typical oil and gas conditions of 70-90°C, CaO-epoxy systems were selected for further development.

aPI CONDUCTIvITy TEsT CEll REsUlTsAn API conductivity test cell was fabricated and used for conductivity tests. The press was modified to enable a constant load to be applied while enabling expansion of the platens, which were instrumented with extensometers.

sImUlaTION aND mODEllINgA rigid sphere model was developed to evaluate effective porosity and safety margins of baseline XOProp™ versus commercially available ceramic and ultralight proppants.

Proppant size: 400 micronFracture Load: 2,000 psi

Elastic Modulus

Yield Strength of the Proppant

a (load press contact

face, radius)

Applied load to proppant face full

cubic packing

Percent failure over

loadPorosity

Gpa Mpa inches psi

Fused Silica 41 1108 0.000918045 187328.2273 17% 0.209209

Bauxite (Al2O3) 165 2100 0.000577161 473954.4606 56% 0.212483

Nylon 6 2.3 55 0.002398185 27451.48711 244% 0.175246

Polycarbonate 2 70 0.0002512554 25009.24893 146% 0.171279

FracBlack (ROM theoretical ave. upper and lower) 4 125 0.001994215 39699.70805 119% 0.188132

XOProp (ROM theoretical ave. upper and lower)epoxy + CaO (20% vol)

9.37 162 0.00150157 70022.94616 198% 0.199919

XOProp expanded (experimental) 2.51 75 0.002328673 29114.83238 169% 0.177824

The impact of using expandable proppant on well production was simulated using production simulation by FracGeo, using its geosimulation codes. Contributions from crack extension were analyzed, as well as increasing fracture width in slowing the decline curve by offsetting crack closure due to formation stresses. Using estimated closure-stress applied over time due to fluid depletion versus fracture width and permeability, production curves for a typical carbonate unconventional formation were simulated.

FRaCTURE ExTENsIONExtending fractures offers the opportunity to intercept high angle natural fractures and enhance the amount of formation accessed by stimulation. Three phases of natural fracture expansion: Phase I - fracture opening and proppant transport due to hydraulic forces, Phase II - fluid removal/drawdown, fluid pressure equal to closure force. Phase III - fracture opening due to proppant expansion.

OFFsETTINg EmbEDmENTA major issue with softer formations is the embedment of proppants into clay-bearing or more flexible systems. Empirical Exxon embedment data was used.

ImPaCT ON PRODUCTIONThe net impact on production due to the delayed closure of the natural fractures is eroughly 23% for the well modelled.

lEss ThaN mONOlayER COvERagEIn lower strength formations, polymer and expandable proppants outperform hard proppants at less than monolayer coverage due to embedment/rock fracture. This is illustrated using a rock failure point of 2000 psig.

FUTURE wORkproppant conductivity testing with different rock types. Evaluation and modelling of embedment in simulated real rocks, evaluation of proppant transport into far field and natural fractures, optimizing proppant design (modulus/deformability) in different unconventional formations. Evaluating production effects with FEA simulated embedment and real (not rigid) rock properties.

www.tervesinc.com

swEllablE PROPPaNTs FOR IN-sITU sTImUlaTIONDOE sbIR Contract DE-sC0013242

andrew sherman and brian werry, Terves Inc, Euclid, Oh. www.tervesinc.com Mastering the Subsurface Through Technology Innovation, Partnerships and Collaboration: Carbon Storage and Oil and Natural Gas Technologies Review Meeting, August 1-3, 2017

API conductivity test cell results showing expansion under loan

and permeability retention

Effect of closure force on fracture width expansion for 28% CaO-epoxy swellable proppant

CONTaCT andrew sherman, Chief Technical Officer, Terves Inc.Phone: (216) 404-0053, x103 Email: asherman@tervesinc.com

Increase in fracture opening during proppant placement, flowback, and expansion for 45 and 30 degree natural fractures

With sand. Closure at lower stress (6242 psi vs 6755 psi), or shorter time (4300 versus 5300 units)

CONTROllED ExPaNsION

Spherical proppants using bead-forming technology, and proppant expansion of beads.

UNEXPANDED PROPPANT, Without Reinforcement

0 psi 3000 psi 5000 psi

EXPANDED PROPPANT, Without Reinforcement

0 psi 3000 psi 5000 psi

ExPaNDED

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darcy)

Load: 2000psi / Temp: 80CPer ISO 13503-5

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Fracture Load Stress Impact on Expansion~28 vol.% CaO-Epoxy

3M pellets

16/20 mesh size

8/16 mesh size

6/8 mesh size

Phase I

Phase IIPhase III

Proppant enters the fracture

Before expansion

Maximum expansion and start of fracture propagation

Time

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ture

Ope

ning

, mm

Phase I

Phase IIPhase III

Proppant enters the fracture

Before expansion

Maximum expansion and start of fracture propagation

Frac

ture

Op

enin

g, m

m

Time

Phase I

Phase IIPhase III

Initiation of Regional Stress

Frac

ture

Ope

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Time

Phase IV6755 psi

0.316 mm

5300

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Initiation of Regional Stress

Phase IV

6242 psi

0.295 mm

4300

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ecov

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Time, years

Expandable Proppant Contribution to Stimulating Well Recovery

Expandable Proppant Conventional Proppant

Illustration of proppant embedment in natural fractures in different strength rocks, versus deformable proppant. Effect of expansion shown.

0%

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Proppant SpreadSand embedment into 34MPa C.S. Rock

Sand embedment into 200MPa C.S. Rock

Sand embedment into 71MPa C.S. Rock

Polymer deformationat 0, 20, 40% vol.expansion.

Sand embedment into 41MPa C.S. Rock

Comparing Sand vs. Polymer propping at partial fracture filling, @ 2,000psi fracture stress, 1mm proppant

Poster_Subsurface-Conference.indd 1 7/28/2017 12:24:37 PM