Example Casing Program: Marcellus Shale Well
A typical Marcellus Shale well casing program is illustrated in Figure 1.
In this example, the upper hole sections are constructed as shown in Table 1:
| Section | Top of casing, feet | Bottom of casing, feet | Top of cement, feet | Hole diameter, inches | Casing outside diameter, inches | Casing inside diameter, inches | Remarks |
|---|---|---|---|---|---|---|---|
| Conductor | Surface | 50 | Surface | 24 | 20 | 19 | |
| Surface | Surface | 250 | Surface | 17 1/2 | 16 | 15.01 | Protect shallow aquifers from contamination |
| Intermediate (1) | Surface | 700 | Surface | 14 3/4 | 11 3/4 | 10.772 | Drilled through various coal seams |
| Intermediate (2) | Surface | 2000 | 10 5/8 |
Following this, a 7.875 inch hole is drilled out of the second intermediate string. Depending on the depth of the Marcellus, this portion of the well is drilled to a depth of several thousand feet before an angle is built and the hole is deviated to horizontal – generally at about 6000 to 9000 feet TVD. The horizontal section may be maintained for several thousand more feet through the productive formation. (Wells can have measured depths of 13,000 feet or more).
Challenges to getting a good primary cement job in the horizontal section of a Marcellus well include fractures and faults, doglegs, washouts, drill cuttings, and borehole cavings. To attain adequate pipe standoff (at least 67% based on a computer simulation), two centralizers are spaced on each casing joint along the entire horizontal interval. Then, to ensure adequate cuttings removal before cementing begins, four open-hole volumes of conditioned drilling mud are circulated after the casing is run to bottom.
