Spe yp monthly session hydraulic fracturing technology - april 2021

1. Why Frac & How it works!
2. Rock Mechanics
3. Fundamentals of Hydraulic Fracturing
4. Fracturing models
5. Design criteria for frac treatments
6. Frac Equipment
7. Frac chemicals and proppants
8. QC for Frac job
9. Hydraulic fracturing technologies and practices

• Overcome damage
• Maximize productivity
• Enhance hydrocarbon recovery
• Better communication between wellbore & reservoir
• Consistency of production
• Increase drainage radius
Hydrocarbon
flow bath
Why Frac & How it works!

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• This additional pressure drop due to skin is the
difference between the (flowing pressure with
damage – flowing pressure without damage)
• The term skin factor is used to quantify the term Skin
Effect

Propped hydraulic fracturing is aimed at raising the well productivity by increasing
the effective wellbore radius for wells completed in low permeability carbonate or
clastic formations. The radial well inflow equation:
(i) increasing the formation flow capacity (k.h)
{the fracture may increase the effective formation height (h) or connect with a
formation zone with a higher permeability (k)};
(i) bypassing flow effects that increase the skin (s) e.g. near wellbore formation
damage;
(ii) increasing the wellbore radius (rw) to an effective wellbore radius (rw’) which is a
function of the conductive f racture length Lf

If the hydraulic fracture has infinite conductivity , then:
rw = Lf/2
Thus high conductivity fractures allow fluids to flow to the
well whose effective radius has been enlarged to a value
equal to half the single wing fracture length.
Alternatively, if the actual wellbore radius is used, this
improved inflow can be expressed as a negative skin.
(P2) a well with an ideal (S=0) completion.
(P3) same well showing a positive skin due to
formation damage.
(P1) The hydraulically fractured well with the
negative skin will have the greatest
production rate.

(i) Pumping the fracturing fluid at a sufficiently high pressure
to overcome the rock stresses i.e. initiate and propagate a
fracture.
(ii) The fluid properties are adjusted to ensure efficient
fracture creation -low fluid loss and tubing head pressure
values are frequently achieved by use of a viscous, shear
thinning, water based, cross-linked gel.
(iii) The created fracture is then filled with proppant to "hold
it open" or provide conductivity for fluid flow when fluid
pumping is halted..
(iv) The viscous fracturing fluid is degraded after the
treatment to a viscosity similar to that of water by
incorporation of a chemical breaker into the fracturing fluid
formulation. This will allow it to be produced back after the
treatment, followed by the initiation of hydrocarbon
production

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Rock Mechanics

• Interpretation of the well logs
– Triple combo
– Sonic Data
– Estimated reservoir pressure &
Permeability
• Understand formation
mechanical properties
– Stresses
– Pore Pressure
– Young’s modulus
– Poisson’s ratio
– Toughness
– Permeability
Rock Mechanics

• Over burden stress
– Mass of rock above
– Average gradient (1→1.1) psi/ft
• Minimum horizontal stress
– Closure stress at pay zone
– Can be as high as overburden
• Maximum horizontal stress
– Tectonic stress added to min. horizontal stress
v
Hmax
Hmin
Rock Mechanics

Fracture Geometry Will Propagate Perpendicular to the Min. Horizontal Stress
Rock Mechanics

 According to both lab and field evidence, the best
phasing for perforating for fracturing is 60 degree
with 90 degree being an acceptable second (Abass,
et. al., SPE 28555).
 Due to the fact that most “vertical” wellbores are
not vertical by several degrees and most “vertical”
fractures naturally oriented off vertical by several
degrees, the perforated interval should be as short
as practical. This minimizes the chance of
generating multiple fractures.
 If the gross pay is very thick, limited entry
perforation with multi-staged frac is proven to give
better conductivity.
Rock Mechanics

Stimulation Type
Selection Criteria
Hydraulic Fracturing
Candidate well
Fundamentals of Hydraulic Fracturing

Modified Tinsley Curve
Kf *Wf
Xf
and/or
Kf *Wf
Xf
Tight gas k << 1 md (hard rock)
High permeability k >> 1 md (soft formation)
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Cinco-Ley and Samaniego's 1981 correlation between
effective wellbore radius and fracture conductivity
Max. r’w = 1/2 Xf
Max. Negative Skin - 7

 Formation :Sandstone (Shaley sand / sandy shale) Clays, Carbonate (Limestone / dolomite)
 Type of hydrocarbon : Oil (GOR , BPP , Dew point , paraffin , asphaltene), Gas (Condensate)
 Reservoir : Press., Temp. , porosity , permeability
 Core analysis result : Sensitivity to fluid treatment ( water , oil )
 Gross and net formation thickness. : from logs
 In - situ stress :- from core analysis pay, below and above
 Water saturation : oil wet / water wet
 Drainage radius : nearest wells
 Perforations : Gun type , phasing , No. and diameter of hole , length
 CBL: effect of cement on fracture job.
 Results of build up survey : skin factor
 Production history (initial, currently, cumulative)
 Well deviation.
Data Collection

Step Rate Test: Frac Extension Pressure
Data Frac – Mini Frac
Pump-in / Flow Back Test: Closure Pressure

Pump in/ shut in test ( press. Decline test )
Most common test used
Mini -Frac in the formation using the same fluid for frac.
With same rate , typical vol 100 – 300 bbls.
( as a rule 10 -15 % of frac. Fluid vol.)
Typical test procedures :
Established inj. Rate at designed rate
Maintain rate for 7 min.
Stop inj. And S/I the well
Measure ISIP
Monitor press. Decline from 30 min. to 4 hrs.
( until press. Versus time curve flatten)

Square Root of time
Log - Log
G - Function

Step down Test: Frac Friction

Closure stress = ISIP – PWF
Net press. = frac. Extension press. – ISIP
the pressure responsible for extending the frac. And creating width
Frac. Gradient = BHISIP / depth
P tbg ( pump press.)= BHTP + Pf + Pperf - Ph
HHP required = Pump press * required rate

Fluid efficiency = 1/ Leak off
Mini-Frac Analysis

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Net Pressure
Reservoir Pressure
Closure Pressure = Pcl
For Fracture With Tip-to-Tip Length > H
Perkins & Kern
1961
Nordgren
1972
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Models should provide the following:-
 Describe or include the basic physics of all important processes
 Ability to predict the job results
 Provide decision making capability
 Understanding the resulted Frac Geometry
 Isolate causes of problems
 Change the necessary inputs to eliminate danger
 Predict results
Assumptions are made to simplify the equations:-
 Divide the Frac geometry into segments
 Flow direction 1D, 2D & 3D
 Fracture Height
 Plane Strain (lateral over Vertical effects)
• Using a frac simulator,it’s possible to
simulate the fracture propagation
through the formation.
• The frac simulator Process
– Adjusting Wellbore Parameters
– Implement log interpretation
– Design Job volumes
– Running the model
Stage Clean Vol Dirty Vol Rate Prop Prop State time
Start End
gal gal bpm ppg ppg min type vol
bbls bbls kg/lit kg/lit lbs
1 8,000.0 8,000.0 28 0 0 6.80
190.5 190.5
2 2,000.0 2,037.3 28 0.5 1 1.73 Sand Slug (Prop 20/40) 1,500.0
47.6 48.5
3 10,000.0 10,000.0 28 0 0 8.50
238.1 238.1 0 0
4 7,000.0 7,268.8 28 1 1 6.18 Prem Prop 20/40 + Expedite 7,000.0
- 173.1 0.12 0.12
142.9 153.8 0.24 0.24
131.0 146.0 0.36 0.36
131.0 151.1 0.48 0.48
142.9 170.3 0.6 0.6
119.0 146.5 0.7 0.7
10 3,400.0 3,400.0 28 0 0 2.89 Flush
81 81 0 0
Pumping Time 54 min 119,000 lbs
Total X.Linker 55,000 gals 59,000 lbs
Total Base Gel 3,400 gals 60,000 lbs
Total 58,400 gals
Base Gel Fluid
PAD Cross-Linked Gel 45#
PAD
Cross-Linked Gel 40#
Total proppant 20/40
Total proppant 16/30
Proppant
Total proppant
Remarks
U.Safa (14876-14881) (14892-14908)
WKAL-T3
Fracture Profile
14800
14850
14900
14950
15000
.. ..
Layer Pro...
TVD(ft)
TVD(ft)
S...
S...
S...
S...
S...
S...
S...
S...
S...
S...
S...
S...
S...
S...
S...
S...
25 50 75 100 125 150 175 200 225 250 275 300 325 350 375
Concentration of Proppant in Fracture (lb/ft²)
0 0.51 1.0 1.5 2.0 2.5 3.1 3.6 4.1 4.6 5.1
ProppantConcentration (lb/ft²)
14800
14850
14900
14950
15000
0
Width Profile (in)
TVD(ft)
TVD(ft)
Fracture Length (ft)
Propped Length (ft)
Total Fracture Height(ft)
Total Propped Height(ft)
Fracture Top Depth (ft)
Fracture BottomDepth (ft)
Average Fracture Width (in)
Average ProppantConcentration (lb/ft²)
Equivalentnumber ofmultiple fractures
Dimensionless Conductivity
351.5
351.5
88.2
88.2
14857.5
14945.7
0.305
3.24
1.0
3.074
Fracturing models

Factors affecting Conductivity:-
 Fracture Length
 Fracture Width
 Fracture Height
 Proppant Concentration, Size &Type
 Closure Stress on Proppant Bed
 Treatment Fluid Effects
Factors affecting Frac Length:-
 Treatment Volume
 Treatment Rate
 Stress Contrasts Between Layers
 Rock Properties
 Fluid Properties
Fracturing models
Uncontrollable parameters:-
1. k & Φ
2. σmin
3. BHST & Pr
4. Type of fluid (oil /Gas)
Controllable parameters:-
1. CSG, TBG & wellhead configuration
2. Down Hole equipment
3. Perforations IHD, SPF & Phasing
4. Fracture treatment design

Fracture Treatment Limitations:-
1. Spacing and well distribution, Xf
2. Maximum net pressure, W, H
3. FCD considerations (Xf, W)
4. Prop & Fluid selection/ Availability
5. Economics NPV, oil price, job volume adjustment
6. Surface and down hole equipment limitations (press., Rate)
7. Barrier zones (stress, pressure), H
8. Water Zone, H
Design criteria for frac treatments

Fracturing Fluid Requirements:-
 Compatibility with formation rock and fluids  Type
 Viscosity  Loading
-Required for proppant transport
-Controls fracture net pressures
-Fluid Loss fracture geometry (efficiency)
 Determines fracture geometry (width)  Rate
 Determines fracture geometry (Xf & h)  Pad/Vol.
 Friction: Reduce surface treating pressures.  surf. conc
 Regained Permeability breaker Conc

The fracturing fluid consists of:
 Pre-pad fluid (occasionally)
 Pad fluid 30%, Xf
 Slurry (sand laden fluid, staged or ramped)
 Flush (to displace slurry in the well bore, under flush ?
 As Pad volume increases more geometry is being created but
less Net Pressure is being gained
 As slurry volume increases the more conductivity is being
gained as well as Net Pressure but screen outs could occur
Fracturing Fluid Rheological Properties Requirements :-
 To suspend proppant, viscosity = 75 to 125 cps
 To create width and overcome fluid loss.
 Fluid viscosity is a function of polymer loading, and decreases
as a function of increasing temperature and exposure time.

Fracturing Proppant Selection Methodology:-
 Calculate the required kf(in-situ fracture permeability)  Prop Size
 Select proppant from proppant table as a function of closure
stress and in-situ fracture permeability.  Prop Type
 Knowing the expected Xf and Hf we could Calculate the Prop
amount based on required Av Prop conc.  Prop Conc
Prop. Amount = 2 * H * Xf (lb/sq.ft)
Fracturing Proppant Selection Methodology:-

Fracturing Equipments description and Rigging up on location
Frac Tanks:-
 Used for batch mixing linear gel.
 500 BBL capacity each.
 Equipped with intake line and discharge manifold.
 Must be cleaned after every job.
Hydration Unit :-
 Used for mixing linear gel on fly.
 constantly measuring fluid viscosity.
 can heat Frac water prior to mixing.
 No contamination of water tanks.
 No wasted chemicals or mixing time.

Blender:-
Blenders measure and mix Proppants with Liquid and Dry chemicals at the desired
ratios in the fracturing fluid and pump the fluid to High pressure pumps.
Blender Components
 Suction Centrifugal Pump
 Discharge Centrifugal Pump
 Flowmeters
 Densometer
 Mixing Tub
 SandScrews
 Liquid Additive
 Dry Additive
 Liquid Additive Storage Tank
 Chemical Transfer Pump

Sand Screw
 Lift sand from the hopper into the tub
 Comes in two sizes 12” and 14” cut down screws
 Optical encoders are mounted on the screws to count the revolution
 Must be calibrated with an open loop calibration
 12” can deliver from 291 lbs till 10,000 lbs per Minute
 14” can deliver from 469 lbs till 16,000 lbs per Minute
Mixing Tub agitators:-
 Hydraulically driven turbine agitators
 Two sets of blades on a shaft
 Keeps proppant suspended in fluid without entraining air
 Default setting is 40 rpm without proppant
 Add another 4 rpm per pound of proppant added
Mixing Tub (Capacity: 6-10 bbls):-
 Mixes additives and proppant with linear gel
 Tub level float : Keep tub level Constant
 Tub level valve: Maintains a constant suction pressure
 Electronically open or closed valve
 Keep 40-60% open

Centrifugal Pumps :-
 Used to draw fluids out of Frac tanks or Gel-Pro
and convey sand laden fluids to high pressure
pumps.
 One pump located on the suction side and one
on the discharge side.
 Discharge side used mainly as boost for high
pressure pumps
Flow-meters:-
 Have to be inserted with the arrow in the flow
direction
 Have calibrated vanes inside
Denso-meter :-
 Using a nuclear source, this device can
measure the density of pumped fluids into the
well.
 Fluid density can be interpreted as prop
concentration on the monitoring screens.

Liquid additive pump:-
 Used to pump liquids on the fly through injection inputs on the suction of
both centrifugal pumps
 They are very accurate
 There rates are measured with a tachometer or micromotion
 They are calibrated by performing bucket test
 There should be a head of fluid above it to insure accuracy
 Should be checked before and after each job
 The progressive cavity pump is more accurate than the other pumps
Dry Additive
 Used to add dry additives to the blender tub
 Additive moved by screw feeders into tub
 Additives are sack fed into the hopper
 Capacity of hoppers are 2 sacks each
Chemical Transfer Pump
 Transfer chemicals from Drums to tanks or uprights on the blender truck
Liquid Additive Storage Tank
 Stainless Steel
 75 and 30 gal Tank

Mountain Mover / Sand sheave / Silo
 5 compartments (1st and 5th are 560 ft3, 2nd,3rd,and 4th 460)
 Comes to site empty and is loaded by one truck per compartment
 Uses conveyor belts to move sand from compartments to blender
 We always empty closest compartment to the blender first and then
from front to back.
 Silo is used when one prop. Size will be pumped in the Frac job

Manifold Trailer
 Save time on rig up and rig down
 Provide symmetrical flow, reduce friction losses and
provide balance flow
 to provide discharge headers adequate for high rate
(70 bbl/min, 185.5 L/s) and/or high working pressure
(15,000 psi, 103 420 kPa) stimulation treatments.
Frac Pumps:-
It is a positive displacement pump used for simulation
or cementing to pump fluid from surface down to the
formation at respectively high rates and under
respectively high pressure. It consists of three major
parts: Engine, Transmission and pump.

Fluid End
 Double Guided Hardened Valves
 High Sand Concentrations
 Rates to 17.5 bpm per pump
 Pressures to 20,000 psi

Emergency Relief Valve:-
 Emergency relief valves provide over-
pressure protection for equipment
operating under high pressure, high flow
conditions.
 The valves rely on the system's hydraulic
pressure to open when a preset pressure
is exceeded and automatically snap shut
when the pressure drops.
 The valves are externally adjustable to
operate from low pressure/ medium
flows. Emergency relief valve utilizes an
internal spring to activate opening and
closing.

Frac Head :-
 Connects the surface lines to Frac string.
 Double gate valves are usually used.
 flanged connections are required for more safety.
Well Head Isolation Tool:-
 Used when the job is performed with X-mass tree.
 Saves the tree from erosion during the job.
 Sleeve is stroked down and cups will engage the TBG
one the pressure is applied.

Frac Head
Gate
valves
PKR
SLP
JT
PTV
Frac String:-
 It could be D/P, EUE/PH-6 TBG or even 5” CSG.
 size & connection are selected based on the max. expected WHTP.
 Tapered string could be used to lower friction pressure @ high rates.
 PKR pressure and temperature ratings are carefully selected based on
Max Prop. Conc. & Reservoir Temp.
 String must be pressure tested before starting the job.
 TBG movement calculations have to be reviewed based on actual fluid
weights and PKR Dept.
 Slip Joints are used to avoid PKR unset due to TBG contraction, enough
WT is being slacked on the PKR after setting.
 CSG pressure should be monitored during the hole job and could be
increased to decrease the differential pressure on the PKR.

Fracturing Equipment description and Rigging up on location

Gelling Agent
BACTERICIDE
high Temp Gel Stabilizer
Crosslinker
Crosslinker Accelerator
Crosslinker Delay Agent
Breaker
Breaker
Breaker Activators
Buffer
Buffer
Surfactant
AntiFoam Agent
Fracturing Chemicals and proppant

water oil Foam
Safe
Available
Economical
Controlled Break Times
Wide Temperature Range
Non-damaging to clays
Low interfacial tension
Compatible with formation
fluids
Typically 60 to 80% N2 or CO2
Good viscosity
Good temperature stability
Good proppant transport
Good fluid loss control
Low water on formation
High fracture conductivity
Minimum damage fluid
Clay Control
High Interfacial Tension
Compatibility Issues
Expensive
Hazardous
Harder to control Fluid
Properties
Functions of Fluid System:-
 Transport Proppant.
 Create Fracture Width.
 Create Fracture Length.
 Easy to be Recovered.
 Control Fluid Loss.
 Minimize Friction
 Clay stabilizer
Ideal Fluid System Properties:-
 Low Viscosity While Pumping.
 Maximum Required Viscosity In the
Fracture.
 Little or No Fluid Loss to Formation.
 Formation Friendly.

Polymers

Base Gel Formation:-
Dry polymer is added to water to swell
(hydrate) the polymer, forming a viscous
base gel fluid.
Polymer Properties: Viscosity
 Resistance to Flow
 Creates Fracture Width
 Transports Proppant

pH Control:-
pH expresses the degree of Acidity or alkalinity of solution.
pH Measured by
 narrow range pH paper
 or pH meters.
Importance of pH Control
 Polymer Hydration Rate
 Crosslinking Rate
 Gel Stability
 Gel Break Rate
 Prevent Bacteria Growth

Cross-linker Types
 Borate
 Zirconium
 Titanium
Cross-linkers
 Cross-linkers interconnect polymer chains, multiplying
molecular weight
 Increased molecular weight gives more viscosity and better
proppant transport
 Rapid crosslinking gives high pumping pressure and shear degradation
 Delayed cross-linking reduces pumping pressure and shear degradation of fluid
 Fluid should crosslink before perfs Activated by temp., pH & conc.

Biocides
Chemicals that destroy bacteria and prevent their growth
1st chemical to be added to the accepted water in clean frac tanks

Review of frac chemical additives and proppants
Gel Breakers
The gel breaker functions by breaking the long chain polymers into shorter chain
segments allowing the fluid more mobility with controlled & predictable viscosity
Decrease enabling:-
Breakers Types:-
Acid Release Oxidizers Enzymes
Soluble Persulfates Soluble
Encapsulated Encapsulated Persulfates Encapsulated
High Temp Non- Persulfates
 Controlled viscosity reduction
 Maintain geometry & prop transport
 Provide rapid fluid cleanup
 Maximize production
 Temperature effects
 pH effects

Clay Control Methods
 Temporary: KCl, NaCl
 Permanent: Clay Stabilizers
Fluid Loss Control
Aim to reduce fluid loss to increase fluid efficiency, hence helping the proppant to be
placed in the formation and making the job successful
Fluid Loss Control via two main stages:
 Spurt Loss: Measure of how much fluid has to leak off for a gel cake to build up
 Filter Cake Build Up: The fluid loss controlled by resistance of the filter Cake, Cw
Surfactant Properties
 Reduce surface tension and capillary pressure
 Stabilize or break emulsions
 Prevent water blocks
 Aids in fluid recovery

Proppant Requirements
 Spherical
 Monosize
 Withstand stress
 Inert to acids (HCl and HF)
 Flow back??
How to Control Flow Back?
 Fibers
 stabilize proppant
 fill the space
 Resin
 consolidate proppant
 require certain pH
 loose pore space
 Deform particles

How to perform and QC Hydraulic Fracturing Treatments

Water Analysis Tank-1 Tank-2
Tank Condition
WTR in Tank
PH
Iron
S.G
Carbonate
Phosphate
Bicarbonate
CL--
Bacteria
Sulfate

Linear Gel test Tank-1 Tank-2
Fluid Name
Gel Loading
Fluid temp.
Shear rate
RPM
Dial reading
Viscosity
PH
Delayed X-Link time

Understanding important criteria in fracture design

Review of hydraulic fracturing new technologies and practices

Pinpoint Multistage Fracturing ,CT
Fiber-Optic, Coiled Tubing

High way : Infinite conductivity

Conductivity Enhancement ,Chem
Proppant Flowback Control,Chem

Shall Gas Frac / Horizontal / Multi Stage

 Foam Frac is the process of combining the normal conventional frac
fluid with energized gas like N2 or CO2.
 The Frac fluid will have different properties and rheology based on
the base fluid properties and the gas portion in the Mixture (Foam
Quality)
• Excellent Fluid Loss Control
• Good Proppant Transport
• Built In Gas Assist (fast fluid recovery after
placement)
• Low Liquid Content

Foam Properties
 Composition of Foam Frac:
 External Phase. Fracturing fluid (gel)
 Internal phase (Gas & Proppant)
 Surfactant Foamer (Foaming Agent).
 Gases:
 Nitrogen.(N2)
 Carbon Dioxide.
(CO2)
 Binary (CO2 & N2)
 Foamable Fluids:
 Water and Gels.
 Alcohol.
 Acids.
 Hydrocarbon.
 Typically 60 to 80 % N2 or CO2
 Good Viscosity
 Good Temperature Stability
 Good Fluid Loss control
 Less Water in Formation
 High Fracture Conductivity
 Minimum Damage Fluid

Acid Fracturing
 Acid fracturing is the preferred stimulation methodology of
carbonate reservoirs when required acid solubility, differential
reactivity and rock stability are appropriate.
 Acid fracturing is a complex process coupling chemical and
mechanical processes, accordingly, comprehensive lab tests should
be done to provide accurate inputs to the treatment simulation
including “ acid spending rate, created fracture length, leak-off and
fracture conductivity.
 More careful evaluation of rock properties and reaction kinetics can
improve performance and job efficiency. This can provide an idea to
the best fluid system to be used for the acid frac and optimizing the
job design.
Formations that are Best Candidates to Fracture Acidize
 > 85% Soluble
 Heterogeneity
 Hard formations (High Young’s Modulus)
 Closure < 8,000 psi
 Permeability < 5 md

Spe yp monthly session hydraulic fracturing technology - april 2021

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