Page 124 -

Mud Hydraulics Optimization 101

(ID = 12.715 in) was set at the depth of 10,000 ft. The open hole has a
diameter of 14.5 in. The total depth of this vertical well is 15,000 ft. The
mud weight is 11 ppg, with a plastic viscosity of 20 cp and a yield point
2
of 15 lb/100 ft . The weak zone is at 15,000 ft, with a pore and fracture
pressure gradient of 10.6 ppg and 11.5 ppg, respectively.
The goal is to run 5,500 ft of liner (11¾-in OD, 60 lb/ft, 10.772-in
ID) to the bottom. The autofill float equipment has an orifice with a
total flow area (TFA) of 4.91 sq. in. The challenge is to run the liner
through the casing and the open hole section without fracturing the for-
mation. Note that the annular radial clearance between the casing and
the liner is 0.4825 in.
We will first use SurgeMOD to calculate the surge and swab pressures
for a given tripping speed. Figure 4.10 shows the simulated bottomhole
equivalent mud weight (EMW) versus the string depth during the trip-in
operation at 50 ft/min. If the pipe is closed at the end, the loss of circula-
tion would occur when the liner reaches 5,000 ft. A liner with autofill
float equipment (TFA = 4.91 sq. in) could be run to TD without frac-
turing the formation. If a circulation sub is placed above the liner, this
trip speed would be safe for the entire wellbore as well. EMWs for both
closed and open pipe decrease after the pipe passes 10,000 ft due to the
larger diameter of the open hole section. We can see that a fixed tripping
speed of 50 ft/min may be safe at total depth (TD), but it would have
already fractured the formation before it reaches TD for closed pipe.

Autofill Closed Circulation sub Fracture
0

String Depth (ft) 10000
5000

15000
10.0 10.5 11.0 11.5 12.0 12.5 13.0
EMW (ppg)
Figure 4.10 Calculated bottomhole EMW for trip-in operation. Surge EMW @ 15,000 (ft);
spd = 50.0 (ft/min).