Coalbed Methane Exploration Drilling Rig Coring: CMD100 in Shulan, Jilin, China
Executive Summary
In March 2013, a geological exploration team in Shulan City, Jilin Province, carried out a coalbed methane (CBM) exploration drilling program using the CORTECH® CMD100 intelligent truck-mounted rig. Because the objective was to characterize the target coal seam rather than complete a production well, the project used a staged drilling process: a roller bit drilled efficiently through the upper strata to the 740 m target coal seam, then a PDC bit combined with wireline coring recovered 250 m of continuous coal-seam core from 740 m to 990 m. The hole reached a final depth of 1,130 m at a Φ215.9 mm final diameter and a 90° inclination, with the CMD100's 300 r/min top-drive speed fully meeting the coal-seam coring requirements and delivering intact, up-to-standard core.
Project Background & Challenge
CBM exploration coring has a specific job: bring the coal seam itself to surface, undamaged, so its gas content, thickness and structure can be measured. The challenges:
- Two different rock types, one hole: the overlying strata are drilled fast and cheaply, but the coal seam must be cored gently and continuously — a single drilling approach wastes time or ruins the sample.
- Fragile coal: coal seams fracture easily; aggressive rotary drilling can destroy the core needed for gas-content and resource evaluation.
- Deep target seam: the target coal lay at 740 m, and the coring interval ran to 990 m, so the rig needed both depth and precise, controllable coring speed.
- Exploration, not production: this program's success was judged on core quality and geological data, not on putting a well on production.
Our Solution
The exploration team selected the CORTECH® CMD100 intelligent truck-mounted rig and staged the drilling by formation:
- Upper section — fast penetration: through the overlying strata above 740 m, a roller (tricone) bit drilled efficiently to reach the target coal seam quickly, minimizing cost in non-sample ground.
- Coal-seam section — coring: from 740 m to 990 m, a PDC bit was combined with wireline coring technology to recover 250 m of coal-seam core, protecting the fragile coal from destruction.
- Controllable high-speed top drive: the CMD100's top drive reaches up to 300 r/min, fully satisfying the technical requirements for coal-seam coring and keeping the coring run smooth and steady.
- Stable, vertical hole: drilled at 90° inclination to a 1,130 m final depth and Φ215.9 mm diameter, the straight hole protected core quality and depth accuracy.
- Truck-mounted mobility: the integrated truck chassis moved the rig to the Shulan site and rigged up efficiently for the exploration campaign.
Key Results
| Metric | Value |
|---|---|
| Date | March 2013 |
| Location | Shulan City, Jilin Province, China |
| Objective | Coalbed methane exploration coring |
| Rig | CORTECH CMD100 intelligent truck-mounted rig |
| Upper-section process | Roller bit to 740 m target seam |
| Coring interval | 740 m – 990 m |
| Coal-seam core recovered | 250 m |
| Coring method | PDC bit + wireline coring |
| Max. rotation speed | 300 r/min |
| Final hole depth | 1,130 m |
| Final hole diameter | Φ215.9 mm |
| Hole inclination | 90° (vertical) |
| Core quality | Intact, up to standard, smooth coring run |
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-bit drilling above the seam and gentle PDC + wireline coring inside it balanced speed and sample integrity — the core trade-off in CBM exploration.
- 250 m of usable coal core: intact, standard-quality coal-seam core gave the exploration team the gas-content and seam data needed to assess the CBM resource.
- Speed control for fragile coal: the 300 r/min top-drive range let the team tune rotation to protect the coal interval rather than shred it.
- Replicable approach: the staged upper-drill / seam-core workflow became a reference for similar CBM exploration projects.
FAQ
What is staged drilling for coalbed methane exploration?
It matches the drilling method to the geology. In the Shulan project, a roller bit drilled the upper overburden quickly to 740 m, then a PDC bit with wireline coring recovered the coal-seam core from 740 m to 990 m — fast where no sample is needed, gentle where the sample matters.
How do you core a coal seam with PDC and wireline?
A PDC bit opens the hole through the coal interval while a wireline inner barrel retrieves the coal core without pulling all rods. In Shulan this recovered 250 m of intact coal-seam core from 740 m to 990 m, with the CMD100 running at up to 300 r/min.
What is the difference between CBM exploration coring and well completion?
Exploration coring's goal is to recover representative coal-seam core and measure gas content and seam geometry. Well completion focuses on getting the well ready for production. This Shulan case is an exploration coring project; the same CMD100 platform is also used on CBM production and completion work.
How deep was the Shulan CBM exploration hole?
The CMD100 drilled the vertical (90°) CBM exploration hole to a final depth of 1,130 m at a Φ215.9 mm final diameter, coring 250 m of coal seam between 740 m and 990 m.