frac plugging and shale properties dr. william maurer maurer engineering inc austin, tx january 1,...

Frac Plugging And Shale Properties

DR. WILLIAM MAURER

Maurer Engineering Inc

Austin, TX January 1, 2016

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Proppant Placement Problems

Pinch out, proppantpillars, irregular

distribution?

Is this ribbon laterallyextensive andcontinuous for

hundreds of meters aswe model?

Uniform PackingArrangement?

VINCENT 2010A

SPE 119143

THREE POSSIBLE PROPPANT ARRANGEMENTS IN FRACTURES

LONG CONTCT WITH

WELLBORE

FLOW CONTROLLED PRIMARILY BY POOREST SECTION OF FRACTURE

SPE 119143

FRACTURE WIDTH DECREASES WHEN FRAC PRESSURE REMOVED

Proppant Plugging With Fines

MIXED SIZE FINES ARE MOST EFFECTIVE FOR PLUGGING

Fracture Plugging (Mixed Size)

SPE 119143

ASSUMING GOOD FRACTURE CONDUCTIIVITY CAN BE MISLEADING Vincent 2010

THIN SECTION FROM STIM-LAB

Small Fines Migrate To Wellbore Blauch,1999 SPE 56833

Smaller Fines Produce Tighter Packing (Blauch, 1999)SPE 56833

Pore Plugging Major Fracing Problem (Blauch, 1999)SPE 56833

MOST OF THE FRAC PERMEABILITY REDUCTION IS DUE TO PORE BRIDGING

PROPPANT CRUSHING PROBLEMS

SPHERE PACKINGSPH

Point Contacts Create High Stresses

(Point Contact(Extremely high stress)

HIGH HERTZIAN CONTACT STRESS

herheHERTZIAN FRACTURE INITIATION

High Contact Stress Creates Crushed Zone and High Tensile Stress Below

SPHERE SHATTERING

SMALL FINES WILL PROPAGATE ALONG FRAC AND PLUG CONSTRICION ZONE NEAR WELLBORE

Crushed Proppants Create Fines (Terracina, 2010)SPE 135502

404X Ceramic Proppants 10,000 psi

404X

PROPANT CRUSHING CREATES FINES THAT PLUG FRACS

Percent Fines vs. Closure Stress (Terracina, 2010)SPE 135502

6,000 psi closure stress crushes 9.5% of the proppants, producing a large volume of fines to plug fracs

Proppant Embedment Problems

Proppant Embedment Creates Fines that Plug Fracs (Terracina, 2010) SPE 135502

SPE 13550SPE 13550SPE 13550

Embedment reduces frac width and creates craters and formation fines

craters

Embedment Craters with 20/40 mesh Proppants(Weaver, 2005) SPE 94666

Sandstone Embedment Craters (Weaver, 2005) SPE 94666

Proppant Embedment (Terracina, 2010)SPE 135502

514x

EMBEDMENT CREATES FORMATION FINES THAT PLUG FRACS

Proppant Chemical Solution Problems

Proppant Dissolving Mechanism (Weaver, 2005) SPE 94666

Proppants dissolve into the frac fluid at high stress points and precipitate out atlow stress points, reducing frac width and plugging fracs

Frac Closure due to Proppant Solution (Weaver, 2005) SPE 94666

Proppant Solubility Increases with TemperatureWeaver, 2005 SPE 94666

TEMPERATURE INCREASES FRAC SOLUBILITY SIGNIFICANTLY

Proppant Solubility Increases With Fluid Pressure (Weaver, 2005) SPE 94666

50 Mpa = 7251 psi

PRESSURE INCREASES PROPANT SOLUBILITY CONSIDERABLY

Proppants Undergo Considerable Solution in 3 Days (WEAVER, 2005) SPE 94666

Precipitated Proppant Material (Terracina, 2010)SPE 135502

HIGH TEMPERATURES DISSOLVE SAND PROPPANTS AND THEN THE SILICA PRECIPITATES OUT AND PLUGS THE FRACS

Proppant Flowback Can Seal off Fracs

Proppant Flowback (Terracina, 2010)SPE 135502

AT THE

FLOWBACK CAN ALLOW FRACS TO CLOSE NEAR THE WELLBORE

BP BEST REFRACING CANDIDATES (WOODFORD SHALE) (Kari Johnson, K , World Oil, October 2015)

1. 500 foot frac spacing

2. Minimal proppant placement

3. Un-perforated pay at the “heel”

4. Significant gas in place

5. Convenient water availability

They recommend pumping a trace material to show where the proppant is located

MicroSeismic Technology

Refracs Stimulate only 50% of Fracs (Kashikar and Jbeil)June 2015 World Oil

On these two wells using diverters to isolate stages, less than 50% of the stages closest to the “heel” were stimulated.

“This is a common occurrence where operators must rely on diverters to isolate perf clusters”

”HYBRID WELL” - Combined Refracing and Drainholes

“

Drainhole (Proposed)

In well 2, a proposed drainhole could be used to stimulate the fracs in the last half of the horizontal well

This type of “Hybrid Well” may be a good way to combine the best features of refracing and drainholes to maximize production and minimize fracing costs

SPE 119636

SPE 119636

Barnett Shale Well A Refracing

REFRAC

SPE 119636

Well A Microseismic Events – 2 stage

SPE 119636

Well A Microseismic Events Distribution

SPE 134330

BARNETT SHALE WELL REFRAC - Microseismic

11ST FRAC - GELL (1000 MCF/D)

2ND FRAC - SLICK WATER (1500 MCF/D)

CIPOLA 2005

SPE 134330

BARNETT SHALE STIMULATION

CIPOLA 2005

SPE 119636

Well B Microseismic Events – 3 stage

SPE 119636

REFRAC

Barnett Shale Well B Refracing (MicroSeismic)

MIMPLEMENTATION TEAM

Maurer Engineering – Drainhole Concepts and Patents

Drilling Engineering Firm – Field Engineering and Drainhole Designs

Microseismic – Field Instrumentation and Candidate Well Selection

SHALE PROPERTIES

Natural Fractures in Shale

Lateral Heterogeneity (macro scale)?

• If natural fissures are a significant component of fluid flow in the formation… How are they distributed? Can we avoid damaging them?

Single PlaneHC expulsion fissureslacking well-developed

conjugate set (LeighPrice, Bakken)

Conjugatelike we envision in CBM (face

and butt cleats) or BarnettShale

SwarmsSPE82212

James LimeVINCENT 2010A

Oil is Produced Through Voids in the Shale Not Natural Fractures

• At 10,000 feet depth, the vertical rock stress = 10,000 psi and the horizontal stress = 4000 psi

• These high rock stresses close all natural fractures in shale

• The natural fractures cannot be propped open because of their small width and proppant embedment

• Oil is therefore produced through voids which remain open under high stresses

10,000 PSI

4,000 PSI PSI

NATURAL FRACTURES VOID SPACE

Void Spaces in Shale

Eagle Ford

Pearsall Shale, S. TX (Loucks, 2010)

Eagle Ford, Ingrain IncAlbany, Ingrain Inc

Haynesville, Loucks, 2010

Haynesville, E.TX (Ingrain) From Loucks, et al, GCAGS, April 2010 Eagle Ford, Ingrain Inc

Flow is through large pore spaces as shown in four different commercial shales

EAGLE FORD SHALE(WALLS AND SINCLAIR, 2011)

1000m nD = 1 mD

EAGLE FORD SHALE POROSITY IS UP TO 12 PERCENT AND PERMEABILITY IS UP TO 100 mD

EAGLE FORD SHALE

EAGLE FORD SHALE

This shows the relative size of oil molecules to the pore size

Shale Oriented Core For Measuring Horizontal Permeability (Soeder,1988)SPE 15213

EAGLE FORD SHALE KEROGEN (OIL)

Shale Properties

This shows distributions of minerals and organics In Devonian Shale(Note high calcite content)

EAGLE FORD SHALE CORE

Note the small natural fractures filled with silica and other minerals

Woodford Shale OutcropSome reservoirs

pose challenges toeffectively breach

and prop through alllaminations

Our understanding of fracbarriers and kv shouldinfluence everything fromlateral depth to frac fluidtype, to implementation VINCENT 2010A

THIS SHALE HAS GOOD HORIZONTAL AND POOR VERTICAL CONTINUITY SHOWING THE NEED FOR HYDRAUIC FRACING

OIL FLOW IN SHALE

• The pressure to push oil though the shale into the frac comes from an expanding gas cap or water drive.

• Oil flow rate is proportional to the shale permeability and the pressure drop between the fluid

in the shale and in the frac (drawdown pressure)

•.As fracs plug, the pressure in the frac away from the damaged decreases rapidly, causing the rapid decline in shale wells (50% first year, and 70% the second year)

•Drain holes should never plug (due to their large flow area) so they should completely eliminate the rapid decline due to frac plugging•

Eagle Ford Shale Outcrop (35 feet)

Eagle Ford fracs are typically 50 to 200 feet highThis shows layering that provides horizontal permeability The tall cliff shows the high strength of Eagle Ford shale

THE END wcmaurer@aol.com

512-263-4614