High losses challenge liner cement job
An operator was drilling the 8 1/2-in section of a new well in Pakistan
with mud weight of 1.07 g/cm3 [8.9 lbm/galUS] and encountered a weak
formation. Attempts to cure losses with conventional LCMs (sawdust and cotton
seed) were minimally effective, resulting in 1,130 m3 [7,100 bbl] of
mud being lost in 10 days. Despite the losses, the hole was drilled to
approximately 3,700 m [12,100 ft] and the 7-in liner run into the hole.
The liner limited the operator’s options to stop the losses
because any significant circulation would increase the risk of destabilizing
the open hole, which would jeopardize the cementing operation. Cementing
without controlling the losses would likely result in losses of cement to the
formation. Both of these cases would require expensive remedial cementing to
achieve zonal isolation objectives.
The operator asked Schlumberger for a competent solution to control the
losses while cementing.
Expert software optimizes LCM-while-cementing strategy
Based on prior experience in the field, the engineers were prepared for
a Losseal Natural Fracture treatment with a composite blend of fibers and
solids that create a strong impermeable grid, stopping mud or cement from
flowing into naturally fractured zones. The engineers input well fluid
information, loss rates, and other well data into the Lost Circulation Control
Advisor software, an expert decision-tree application used to analyze and solve
lost circulation problems, to generate a fit-for-purpose treatment design that
would cure the losses with a single pill as part of the spacer train.
Well and pill data were also input into the CEMENTICS software, which
was used to design thecomplete spacer train and cement slurry within the
limited pore-to-fracture pressure window.
Pill cures losses, enabling successful cementing
The cementing crew delivered the pumping operation as designed. When the
Losseal Natural Fracture treatment reached the loss zone, the surface pressure
and mud pit volume began to increase, indicating the pill had cured the losses
and restored returns to surface. As a result, the operator recovered about USD
23,000 in WBM.
After the operation, a cement bond log confirmed the TOC and consistent
cement bond across the interval, saving the operator USD 197,000 by eliminating
the need for remedial cementing.