Challenge: Drill shallow extended-reach well to drain methane gas from Australian coal mine.
Solution: Provide integrated services, including
Result: Successfully drilled gas drainage well to TD at 3,659 m MD and 170 m TVD and intersected existing vertical wells as planned to achieve good drainage.
A company mining coal in the Hunter Valley region of New South Wales, Australia, was losing production. The cause was gas-outs that occurred when methane gas reached a level that necessitated shutting down the longwall mining machines and sending their eight-man crews to the surface. To keep the crews and machines working 24 hours a day to achieve its yearly quota, the company wanted to drain the methane gas by drilling an extended-reach well that would intersect ten 8-in vertical wells connecting with the coal seam being worked.
Drilling the long lateral at a shallow TVD would be challenging due to goaf—ground subsidence that occurs after longwall mining—and the possibility of pipe buckling. In addition, the lateral would have to be steered precisely to intersect the existing vertical wells, and hole cleaning would be difficult because the freshwater used as drilling fluid lacked viscosity.
Schlumberger directional drilling, well-plan engineering, and prewell planning were instrumental in successfully meeting all the challenges. Engineering and drilling assistance included determination of any limitations that extended-reach drilling (ERD) with fit-for-purpose rigs would place on hydraulics, pipe size and connections, torque and drag, well control, and BHA design. In addition, Schlumberger and Smith Bits, a Schlumberger company, assisted with the initial design and supplied tools and equipment needed for implementation, such as a rotating control device, casing centralizers, integral-blade stabilizers, drill bits, and drillpipe with high-torque connections.
The ERD rig was anchored to a 500-tonUS concrete pad at 65° from vertical, and a 21-in conductor pipe, 12 m long, was set at the same 65° angle. Schlumberger then drilled the 17 1/2-in surface hole, building angle to 90° before landing in the target zone. After the 13 3/8-in casing was set, Schlumberger drilled the long lateral to TD at 3,659 m MD and 170 m TVD, with a BHA that incorporated a 12 1/4-in Smith Bits standard M613 PDC bit, a Schlumberger mud motor with
12-in stabilizer, a DPM dynamic pressure module, and HDS-1L fixed-collar directional service.
The highly trained crews achieved this ERD success using a horizontal directional drilling rig
with a 300-tonUS pull-down capacity and a Slider automated surface rotation control system that enhanced ROP and improved directional control while sliding the mud motor. RADAR real-time analysis of drilling and advanced ranging provided the distance and direction to existing vertical wells, enabling steering and sidetracking of the lateral to intersect them as planned.
This shallow, 3,659-m-long extended-reach well was drilled successfully using integrated services from Schlumberger. By draining methane gas, the well
will help the coal mining company avoid production delays caused by gas-outs and meet
its yearly quota.
Download: Integrated Schlumberger Drilling BHA Achieves World-Record Extended-Reach Well (0.70 MB PDF)