Coalbed Methane Well Coring Drilling Rig: CMD100 Sectional Drilling to 1,130 m

A coalbed methane (CBM) well program called for a rig that could drill efficiently through overburden, then switch to controlled coring once the target seam was reached. The CORTECH® CMD100 large-diameter drilling rig drilled the well to a finished depth of 1,130 m at a final hole diameter of 215.9 mm. Drilling began with roller-cone bits to 740 m, where the target seam was encountered; at the client's request, the crew then ran a coring program in the seam interval, switching to a PDC bit and crossing through the seam at 990 m to complete coring. Total core recovered was 250 m — a clean, staged well-construction job that combined fast overburden penetration with precise seam sampling.

Project Background & Challenge

Not every interval of a CBM well needs the same drilling method. Overburden above the seam rewards fast, low-cost penetration, while the coal seam itself must be preserved and sampled to confirm seam thickness and quality. The challenge was therefore operational discipline:

• Different methods, one well: the upper interval needed rapid roller-cone drilling, then the rig had to transition into controlled coring without delay.
• Client-specified coring point: coring was requested only once the seam was found at 740 m, requiring accurate depth control.
• Core through the seam: the coring run had to cross the seam at 990 m and recover a continuous representative core interval.

Our Solution

The CMD100 handled the whole sectional program with its flexible top-drive drilling capability:

• Roller-cone drilling to 740 m: roller-cone bits drilled the overburden quickly and economically, opening the hole at the planned 215.9 mm final diameter.
• Seam coring on demand: once the seam was encountered at 740 m, the crew followed the client's instruction to run coring in the seam interval, demonstrating the rig's ability to shift from production drilling to coring mode.
• PDC bit through the seam at 990 m: switching to a PDC bit, the assembly drilled through the seam at 990 m, completing the coring run and recovering a 250 m total core length.

Key Results

For the full technical specifications of the CORTECH® CMD100, see the CMD100 product page.

Customer Value & ROI

• Right method at the right depth: fast roller-cone drilling through overburden cut cost, while controlled coring in the seam delivered the sample quality the client needed — no need to over-spend on coring the whole hole.
• Depth accuracy: finding the seam at 740 m and coring on instruction shows the precision that staged well construction depends on.
• Representative 250 m core: a continuous 250 m core interval gave the client the seam data needed for completion decisions.
• One rig, two tasks: the same CMD100 handled roller-cone, coring and PDC drilling, avoiding extra rig mobilization.

FAQ

How is core recovered from a coal seam in a CBM well?

The rig drills overburden first, then runs a coring assembly once the seam is reached. Here the CMD100 roller-coned to 740 m, then cored the seam interval and crossed through it at 990 m with a PDC bit, recovering 250 m of core.

What is the difference between roller-cone and PDC drilling in CBM wells?

Roller-cone bits drill overburden quickly and economically; PDC bits deliver steady, controlled performance when the assembly needs to cross the seam during coring. The program used both in sequence for cost and sample quality.

What borehole diameter is typical for a CBM well?

This well was finished at 215.9 mm diameter to 1,130 m — a representative diameter for a CBM production well on the CMD100 platform.

How much core can be recovered from a coal seam interval?

In this program the coring run recovered a total of 250 m of core from the seam interval, drilled between the 740 m seam encounter and the 990 m through-seam crossing.

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