Mr. Erik Milito - The House Committee on Natural Resources ...

ISOLATING POTENTIAL FLOW ZONES DURING WELL CONSTRUCTION 61
0
2000
4000
Mud Weight
Fracture Gradient
16"
Design Fracture Gradient
6000
Depth, ft
8000
11.75"
10000
12000
Pore Pressure
D
C
B
9.625"
7.625"
14000
If large disparities exist between the offset well information and the predicted values, further investigation may be
warranted. This graph will become the design basis for the well.
B.2.3 Casing Plan
8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00 19.00
EMW, ppg
Figure B.1—Casing Shoe Depths with Pore Pressure/Fracture Gradient Graph
<strong>The</strong> appropriate selection of shoe depths and consequently, the required number of strings is critical to the well
design. General guidelines are given here for the selection of shoe depths. Local practices, regulatory requirements
and experience should also be used to fine-tune this process.
Initial shoe depth determinations are made as follows (see Figure B.1).
— Starting at the drilling fluid weight at the well’s TD (point A), draw a vertical line upwards until it intersects the
design fracture gradient curve (point B). This is the approximate shoe depth of an intermediate casing.
— Draw a horizontal line from point B leftwards until it intersects the drilling fluid weight curve (point C) and then
upward until it intersects the design fracture gradient curve (point D). This represents the approximate shoe
depth of the next casing string.
— Repeat this process until all shoe depths dictated by drilling fluid weight and fracture gradient constraints have
been established.
After the preliminary shoe depths have been established, an additional check should be made based on kick
tolerance. <strong>The</strong> kick tolerance is the maximum size kick of a specified intensity that can be circulated out of the hole
without causing the formation to fracture in the open hole section (often near the shoe). It may be necessary to adjust
casing shoe depths to conform to kick tolerance limits.
A