1. DesignofPseudo 3-DHydraulicFracturingTreatments
Hydraulic Fracturing Theory Manual
T h i s s e c t i o n d i s c u s s e s t h e v a l u e s f o r t h e fluidlosscoefficient and spurtloss
u s e d i n f r a c t u r e d e s i g n and/or analysis.The amount of fluid lost to the formation during a
treatment is a primary design consideration. Thelost fluid is essentially wasted and represents a
significant portion (i.e., generally 30 to 70%) of thetotal fluid and cost of treatment.The rate of
fluid loss is described by the expression
where C is the fluid loss coefficient, A is the fracture wall area and t is the time since the area
A was exposed to fluid. The loss coefficient depends on three separate effects as shown onFig.
5.15and each of the three have the square root of time relationship given inEq. (5.3).These
effects andhow they are determined are discussed below.The best estimate of fluid loss is
obtained from the pressure decline analysis of a calibration treat-ment (discussed in Chap. 8).
Fluid Loss Coefficient, C t The composite fluid-loss coefficient depends on three separate linear
flow mechanisms with theseparate coefficients, C I - fracturing fluid viscosity relative
permeability effects, C II - reservoirfluid viscosity-compressibility effects, and C
III
- wall building effects. In any fracturing treatment,each of these mechanisms acts
simultaneously to varying extents and complements the other.These mechanisms act
analogously to a series of electrical conductors and their coefficients arecombined as shown in
the following equation:
(5.4)
The fracturing fluid viscosity and relative permeability (i.e.,
filtrate
) effect can be obtained fromthe following equation:
2. Spurt Loss
The total fluid lost when wall building dominates is a combination of the fluid lost before a
filtercake has begun to form (spurt loss) and the fluid lost through the filter cake during the
treatment.Thepoint wherethefluid loss curveintersects theordinateon afluid
loss plotis known as thespurt loss (see Fig. 5.16).For fluids that build effective wall
cakes and low permeability formations, thespurt loss is low. In this case, a value of zero (0) is
used for spurt loss if the permeability is verylow (i.e., less than 0.05 md).Generally, the service
company supplies the spurt loss values for their various fluids.Table 5.1isan example from the
Dowell “Fracturing Fluids” book showing
C
3. III
(i.e., C
w
)
and spurt for anon-
wallbuildingfluidforvarioushighpermea
bilityrocks(i.e.,relativelyhighspurt)and
amountsof silica flour. Spurt loss can be
significant for moderate to high
permeability formations. Forexample,
assume a 500 ft fracture radius, 50 ft fluid
loss height, and 5 md permeability.Table
5.1shows 20 gals/100 ft
2
spurt loss even with 20 lb/1000 gal silica
flour. This equates to an additional20,000
gal of fluid loss which must be included in
the treatment design.
Fig.5.17-Wall Building for Various Fluid
Systems.
4.
5. Hydraulic Fracturing Theory ManualFluid
Loss
5-25
December 1995
Fig.5.18-Silica Flour for Moderate to
High Permeability.Table 5.1-Spurt Loss
Dependence on Permeability and Additives.
FLUID LOSS OF FLUIDS
PREPAREDWITH J160
THICKENERJ160(lb/1,000
gal)Temperature(F)K(md)J84(lb/1,000 gal)
(Silica Flour)C
w
X 1000(ft/Spurt(gal/100 ft
2
)
2020201251251252.21.522.50205030.09.96
.00.07.959.030301251251.04.820205.04.21.
819.540401251251.04.820205.04.21.819.56
0601251252.93.120204.94.115.519.880808
8. Design of Pseudo 3-D Hydraulic Fracturing
Treatments
Hydraulic Fracturing Theory Manual
5
5-26
December 1995
FLUID LOSS PROBLEMFind:
The Combined Fluid Loss Coefficient
Given:
Gas Reservoir: 170 F;
P
r
= 2300 psi,;
S
g
= 0.50;
k
= 0.1 md (buildup test);
BHTP
9. = 4000 psi
Lab Data:
@ 150 F(For Water Filtrate: 0.45 cp @
150 F0.21 cp @ 250 F)
°Φ
HC
0.125=
µ
g
0.0174
cp
=
C
III
0.001
ft
/
min
=
°°°
10. UFCIII:Calculate Total Fluid Loss
CoefficientR e s F l u i d
V i s c ( c p ) 0 . 0 1 7 F i l t r a t e
V i s c ( c p ) 2 . 4 Formation
Temp(deg F)170.P r e s s u r e
D i f f ( p s i ) 1 7 0 0 . C -
I I I 0 . 0 0 1
P e r m e a b i l i t y ( m d )
0 . 1 0 0 P o r o s i t y ( f r a c
t i o n ) 0 . 1 2 5 Compressibility
(lbs/gal)200.0((Clos Pres + 500(psi)-
Res Pres)@ T e s t
T e m p ( d e g F ) 1 5 0 . C - I =
0 . 0 0 4 4 6 3 C - I I = 0 . 0 2 6 5 1 7 C - I I I =
0 . 0 0 1 0 9 0 f t / m i n * * . 5 a t 1 7 0 .
( d e g F ) Harmonically Weighted Ct =
0.00085P F 3 C o n t
i n u e P F 1 2 E
x i t 0 9 : 2 3 : 4 0 0 3 / 0 4 / 9 2
F i l e : U F D E M O S F R C W e l l
N a m e : C A R T H A G E ( C O T T O N V
A L L E Y ) F I E L D UserID: ZWXY01U
L T R A F R A C 2 . 0
