Page 155 - A Practical Companion to Reservoir Stimulation

STIMULATION OF HORIZONTAL WELLS

EXAMPLE J-9 EXAMPLE .I-10
Performance of a Twisting Longitudinal to "ransverse Fracture
Longitudinally Fractured Horizontal Well
Suppose that a horizontal well is to be hydraulically fractured.
Using the data in Table 5-8, calculate the expected productiv- As Section 19-5.2.1 suggests, all fractures initiated from long
ity index increase (from that of a fractured vertical well) if a intervals will likely be first longitudinal, twisting later into
horizontal well of length equal to 2xf is longitudinally frac- transverse direction (if the well is drilled along the minimum
tured. horizontal stress direction). Calculate the impact of the twist-
ing action and devise a criterion to reduce the effect.
Solution (Ref. Section 19-6.2)
Figure 19-23 can provide the solution to this problem. For the Solutio6 (Ref. Sections 19-5.2.1 and 19-6)
first case (k = 1 md), If a fracture initiates as perfectly orthogonal (i.e., if the entry
point has a width equal to the fracture width), then the area of
(5-24) contact between the well and the fracture is
A, = nd,w,, (5-25)
Since L = 2000 ft (2xf), then L/h = 40. From Fig. 19-23,
(PI)H/(PI)" = 4.6. where d,, is the well diameter and w, the width of the transverse
For the second case (k = 10 md), FcD = 10, and from Fig. fracture.
19-23, (PI)H/(PI),, = 1.9. A longitudinal fracture with two wings has an area of
contact
A/ = ~Lw,, (5-26)
kfw = 1000 md-ft
where L is the length of the perforated interval and wI the
k = 1 mdor10md width of the longitudinal fracture.
To develop the criterion, the two areas are set equal, and
h = 50ft I after rearrangement,
Xf = l000ft I
Table J-8-Reservoir and fracture data for Example J-9. (5-27)

which suggests that if the perforated interval is larger than one
and one-half times the well diameter, the width of the twisting
fracture will be reduced substantially. For example, if L = 10
d,, then w/ = 0.15 w,. In such a case, the choke skin effect will
increase accordingly. In example 5-6, the (sChjc would be equal
to (0.2/0.15) = 1.3, and the resulting flow rate (at 30 days)
would be equal to 384 STB/d, which is a significant reduction.
Thus, if multiple transverse fractures are indicated, their
connection with the well must be minimized. Cutting the
casing with an abrasive jet may be the most appropriate
means for fracture initiation.

J-15