This presentation discusses multi-stage hydraulic fracturing, including the process, fluid flow patterns, and geomechanics. The presentation is given by Harshal Pende from IIT Madras and includes sections on introducing hydraulic fracturing, outlining the multi-stage process, describing the five distinct fluid flow patterns in fractured wells, discussing geomechanics concepts like principal stresses and fracture orientation, and providing references.

1. A PRESENTATION ON-
Multi-Stage Hydraulic Fracturing: Fluid Flow and Geomechanics
Presented by- Harshal Pende
Roll no.-PE17M005
INDIAN INSTITUTE OF TECHNOLOGY MADRAS

2. Outline
• Introduction
• Process of Multi-Stage Hydraulic
Fracturing
• Fluid Flow patterns in hydraulically
fractured wells
• Geomechanics
• References
This Photo by Unknown Author is licensed under CC BY-NC-ND

3. INTRODUCTION
• Hydraulic fracturing (also fracking) is a well
stimulation technique in which rock is
fractured by a pressurized liquid. The process
involves the high-pressure injection of
'fracking fluid' (primarily water, containing
sand or other proppants suspended with the
aid of thickening agents) into a wellbore to
create cracks in the deep-rock formations
through which natural gas, petroleum,
and brine will flow more freely. When
the hydraulic pressure is removed from the
well, small grains of hydraulic fracturing
proppants (either sand or aluminium oxide)
hold the fractures open.[1]

4. Process of
Multi-Stage
Hydraulic
Fracturing
• After the well has been drilled to target
depth,holes or perforations are made in the
production casing to provide entry points by
which fracturing fluid and proppant can enter into
the targeted hydrocarbon zones.The number and
orientation of perforations is pre determined and
designed to intersect the natural fracture system
that may be present in the reservoir.
• Hydraulic fracturing is essentially a 4-step process
• Step 1: Pressure the reservoir rock using a fluid to
create fracture.
• Step 2: Grow the fracture by continuing to pump
fluids into the fractures.
• Step 3: Pump proppant materials into the fracture
in the form of a slurry,a part of fracture fluid.
• Step4: Stop pumping and flowback the
well,leaving the proppant in place in reservoir.

5. Fluid flow
patterns in
hydraulically
fractured wells

6. • Five distinct flow patterns occur in the fracture and formation around a
hydraulically fractured well.[1] Successive flow patterns, which often are
separated by transition periods, include fracture linear, bilinear,
formation linear, elliptical, and pseudoradial flow. Fracture linear
flow(Fig. 1a) is very short-lived and may be masked by wellbore-storage
effects. During this flow period, most of the fluid entering the wellbore
comes from fluid expansion in the fracture, and the flow pattern is
essentially linear.
• Bilinear flow (Fig. 1b) evolves only in finite-conductivity fractures as fluid
in the surrounding formation flows linearly into the fracture and before
fracture tip effects begin to influence well behavior. Fractures are
considered to be finite conductivity when Cr < 100. Most of the fluid
entering the wellbore during this flow period comes from the formation.
During the bilinear flow period, BHP, pwf, is a linear function of t1/4 on
Cartesian coordinates.
• Formation linear flow (Fig. 1c) occurs only in high-conductivity (Cr ≥ 100)
fractures. This period continues to a dimensionless time of tLfD ≅ 0.016.
The transition from fracture linear flow to formation linear flow is
complete by a time of tLfD = 10–4 . On Cartesian coordinates, p wf is a
linear function of t 1/2 , and a log-log plot of (pi – pwf) has a slope of 1/2
unless the fracture is damaged. The pressure derivative plot exhibits a
slope of 1/2.

7. • Elliptical flow (Fig. 1d) is a transitional flow period
that occurs between a linear or near-linear flow
pattern at early times and a radial or near—radial
flow pattern at late times.
• Pseudoradial flow (Fig. 1e) occurs with fractures of
all conductivities. After a sufficiently long flow
period, the fracture appears to the reservoir as an
expanded wellbore (consistent with the effective
wellbore radius concept suggested by Prats et al.[2]).
At this time, the drainage pattern can be considered
as a circle for practical purposes. (The larger the
fracture conductivity, the later the development of
an essentially radial drainage pattern.) If the fracture
length is large relative to the drainage area, then
boundary effects distort or entirely mask the
pseudoradial flow regime. Pseudoradial flow begins
at tLfD ≅ 3 for high-conductivity fractures (Cr≥ 100)
and at slightly smaller values of tLfD for lower values
of Cr.

8. GEOMECHANICS
• In the classic well-stimulation scenario, hydraulic fracturing
occurs when the pressure of fluid injected into a formation is
sufficient that the force generated exceeds the tensile strength of
the rock, as Hubbert had postulated. Failure of the rock allows
fractures to propagate along the path of least resistance; this path
is primarily influenced by the three-dimensional stress state
within the rock. In order to understand how fractures develop, an
understanding of stress in the Earth’s upper crust is essential.
• In a simplified form, the stress regime within the Earth’s crust at
some material depth can be resolved into three orthogonal force
vectors: a vertical stress component and two horizontal stress
components commonly denoted as SV, SHmax and SHmin. These
are referred to as the three principal stresses. Vertical stress
arises primarily as a function of the weight of overburden
whereas the horizontal stresses result from tectonic effects, such
as crustal compression or extension caused by plate movements.

9. • Although simple hydrostatics would suggest that these three stresses might be
equal, the long history of mobility and deformation in the Earth’s crust (folding
and faulting) demonstrates that this cannot be the case. To account for such
deformation, there must be substantial differences between the three principal
stresses.
• Under this paradigm of unequal stress, it follows that pressure injection of fluid
will cause the rock to fail in a plane perpendicular to the direction of the least
principal stress (Hubbert and Willis, 1957). Because SHmax is by definition
greater than SHmin, the least principal stress is necessarily either SHmin or SV 2
.
• It is useful to visualise the hydraulic fracturing scenario referred to above in
terms of the pressurised planar fracture pushing apart the rock. It is evident
that this will occur in the direction of the lowest stress, thereby constraining
the path of least resistance for fracture propagation irrespective of what the
orientation of bedding or cleavage planes might be. Figure 2.1a below shows an
example with SHmin as the least principal stress and Figure 2.1b shows an
example with SV as the least principal stress.

10. • Figure 2.1 Stress and fracture plane development
• A) B)

11. • Based on this theory, and an understanding of the relative magnitude of
these stresses, we can confidently predict the orientation of hydraulic
fractures. So, in the case where SHmin is the smallest of the three
stresses, it follows that fractures must develop in a vertical plane as in
the case for Figure 2.1a, whereas if SV is the smallest stress then
fracturing must occur in a horizontal plane as illustrated in Figure 2.1b.
• Although the preceding discussion is focussed on the intentional
hydraulic fracturing of rock, it should be noted that fracturing can also
occur unintentionally. An example of this is during drilling operations if
the drilling mud density is allowed to rise excessively for the depth of the
uncased formation. It can also occur during waste water injection if flow
rates and pressures are high enough. Hydraulic fractures also occur
naturally and are thought to propagate as a result of critical
pressurisation of pore fluid.

12. References
• McGuire, W. J., Jr., Harrison, E., and Kieschnick, W. F., 1953, The
mechanicso f formation fracture induction and extension:A m.
Inst. Min. Met. Eng., Petroleum Br., Paper 318-G. (Dallas,
Texas,O ct. 19-21.)
• McHenry, Douglas,1 948, The effect of uplift pressureo n the
shearings trength of concrete:P reprint of Paper for Internat.
• Cong.o n large dams. Miles, A. J., and Topping, A.D., 1948,
Stressesa round a deep well: Petroleum Tech- nologyJ our.,
Technical Paper 2411, v. 11, no. 6. (Nov.)
• Phillips, Dr. D. W., 1947, Safety in mines: ResearchB oard
(Sheffield, Great Britain) contribution to the Symposiumo n
Rock Pressure,S ymposium Heerlen. (June)
• ReynoldsJ, . J., Bocquet,P . E., and Clark, R. C., Jr., 1954, A
methodo f creating vertical hydraulicf ractures: Drilling and
ProductionP ractice, p. 206. Schoemaker,R . P., 1948, A review
of rock pressurep roblems: Am. Inst. Min. Met. Eng. Tech. Pub.
2495. (Nov.)
• Scott, P. P., Jr., Bearden, Wm., Jr., and Howard, G. Co,1 952,
Rock rupture as affected by fluid properties:A m. Inst. Min. Met.
Eng., PetroleumB r., Paper 205-G. (Oct.) Teplitz, A. J., and
HassebroekW, . E., 1946

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