Reduce NPT by mitigating circulation loss and shallow gas hazards
The formation in two Indonesian fields consists
of interbedded shale and sandstone with coal
stringers, and the unconfined compressive
strength is 2,000–5,000 psi with low to medium
levels of impact and abrasion. However, these
fields are also are known for presenting
challenging tophole sections where NPT is often
caused by massive circulation loss. One well,
for example, suffered 3 days’ NPT from lost
circulation on the surface section. There was
also a shallow gas hazard necessitating pilot-hole
drilling. In fact, 17.5- or 12.25-in surface sections
usually require 8.5-in pilot holes to prevent
shallow gas hazards. The operator in these fields
sought to mitigate the lost circulation problem
and eliminate the need for pilot holes to avert
shallow gas hazards.
Eliminate pilot-hole drilling
Schlumberger engaged with the operator to conduct technology sharing sessions with the drilling
engineer, geologist, and subsurface team. The Allegro XCD-Pro service technology provides a plastering
effect by smashing cuttings against the bore wall by the casing body—strengthening the wellbore.
As the well is cased during drilling, a casing drilling operation also enables the casing to be placed
when the drillstring reaches TD, eliminating the need for a pilot hole.
Significantly improved drilling efficiency
The operator used Allegro XCD-Pro service to drill a 121/4-in section with a 95/8-in casing. This eliminated
need for the 8.5-in pilot hole due to shallow gas hazards. Compared with AFE, the casing-while-drilling
operation saved 24 h.
In a second well, the 17.5-in section was drilled using a 13 3/8-in × 17 1/2-in XCD casing-while-drilling
bit. In addition to also eliminating the pilot hole, it enabled the operation to continue while
having some circulation loss without any NPT. Compared with previous well, estimated potential
saving by casing drilling was 2.5 days.
Both wells demonstrated the Allegro XCD-Pro service as a significant solution to overcoming
lost circulation and shallow gas hazard problems without adding any risk. Casing drilling saved
the operator 3.5 days by eliminating the pilot-hole drilling runs and multiple cement plugs.