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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
