Published: 05/02/2018
Published: 05/02/2018
An operator was drilling the 12 1/2-in section of a new well in Pakistan and reached 3,325 m [10,900 ft] to the top of the Lockhart Formation with a final OBM weight of 2.03 g/cm3 [16.9 lbm/galUS]. As the 9 5/8-in casing was run, the well experienced total losses.
The presence of the casing in the well limited the operator's options to stop the losses. Pumping multiple high-concentration LCM pills would increase the risk of choking the check valves on the casing. In addition, any significant circulation would increase the risk of destabilizing the open hole, which would jeopardize the entire cementing operation.
The use of OBM added to the challenge because circulating multiple LCMs wastes large volumes of expensive mud, and the friction properties of the mud reduce an LCM's ability to create a bridge or additional cake at the formation face. Instead, the operator asked Schlumberger to cure the losses and cement the well in a single operation without mud circulation.
The engineers were prepared for a Losseal Natural Fracture treatment with a composite blend of OBM-compatible fibers and solids that create a strong, impermeable grid, stopping mud or cement from flowing into natural 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 OBM-compatible pill.
Well data were also input into CEMENTICS software to design the spacer train and cement slurry within the limited pressure window. The result was a tight density range from spacer system (2.04 g/cm3 [17.0 lbm/galUS]) to the cement slurry (2.16 g/cm3 [18.0 lbm/galUS]).
The cementing crew delivered the pumping the 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, restoring returns to surface, including approximately USD 55,000 in OBM.
After the operation, the cement bond log confirmed the top of cement and consistent cement bond across the interval, saving the operator an estimated USD 205,000 by eliminating the need for remedial cementing.
Challenge:
Cement 9 5/8-in casing across
fractured formation despite total losses of oil-based mud (OBM) that preclude
circulation.
Solution:
Results:
