Abstract

Interest in the unconventional shale gas plays continues to grow in Western Canada. The Montney formation found in North Eastern British Columbia can be particularly challenging due to drilling in the Canadian Foothills. Wells in the area are known for deep, hard, abrasive and abnormally pressured formations. Further challenges include unexpected fractures, lost circulation and coals seams. The combination of these drilling issues can cause a significant increase in expected drilling times (slow ROP and NPT).

Following some difficulty drilling offset wells due to well control issues, future designs incorporated a higher, more conservative mud weight. This let to slower ROP and corresponding NPT.

A new approach with MPD and lighter mud weight was proposed. For the intermediate sections, the first well changed from a weighted to un-weighted invert emulsion. The second well was drilled with a pure base oil system to lower the fluids solids content. The horizontal section was initially planned to drill with a density of 1400kg/m3 weighted invert. A MPD program was proposed drilling with a 1250kg/m3 weighted invert for the next two wells and adjusting backpressure to match the required bottom hole ECD.

The key operational objectives for the operator were increased ROP and a reduction of NPT. This was accomplished by lower ECD associated with lower mud densities, lower drilled solids and lower viscosities. A secondary benefit was the reduction of whole mud losses. Mud losses were reduced in manner that allowed for fast safe well control in the event a pressured fracture (kick) was encountered.

A reduction of more than 7.4 days vs AFE from spud to rig release was largely attributed to utilizing MPD technique and the team work of everyone involved on location. NPT was reduced from 100 hours to 8 hours on the final well of the project. The second MPD well of the project was considered a big success, with the following results (refer table 1).

Table 1

MPD2 vs Best Conventional well Performance Data

Intermediate Hole PerformanceMain Hole Performance
MPD#2 WellBest Conventional WellMPD#2 WellBest Conventional Well
Bit Runs 3 4 3 8 
Depth Length (m) 918 880 3080 2368 
Time (hr) 41 77.5 243.75 290.3 
ROP (m/hr) 26.5 11.55 11.3 8.025 
Intermediate Hole PerformanceMain Hole Performance
MPD#2 WellBest Conventional WellMPD#2 WellBest Conventional Well
Bit Runs 3 4 3 8 
Depth Length (m) 918 880 3080 2368 
Time (hr) 41 77.5 243.75 290.3 
ROP (m/hr) 26.5 11.55 11.3 8.025 

As the activity in NE British Colombia's Montney play continues to grow, it is important that other operators learn the benefits of utilizing MPD. This includes safely decreasing days on the well by increasing ROP and reducing influx and losse related NPT caused by excessive mud weight.

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