Eliminate intermediate 18-in liner in deepwater well with shock and vibration expected

After drilling its first vertical exploration well in the presalt area of the Jacare field offshore Angola, Statoil aimed to eliminate the planned intermediate 18-in liner in the subsequent well. To accomplish this objective, Statoil would need to drill the 18 1/8-in section to the planned TD for the next section. This would require drilling through the salt in minimum time while opening the borehole to 21 in, and, ideally, in one run to avoid salt creep. If extended, this 18 1/8-in hole would be drilled from 2,555 m [8,382 ft] to 5,647 m [18,527 ft], passing through a layer of hard stringers at approximately 4,350 m [14,272 ft]—the original TD for the 181/8-in section.

Based on the first well drilled, Statoil anticipated shock and vibration in medium to hard salt formations that would negatively affect BHA performance. In the first well, this resulted in the need for a second bit run. Interbedded formations would likely make managing weight on reamer challenging and lead to premature cutting structure damage.

Use OptiDrill service to enhance BHA performance

Based on the length of the run and prejob modeling, Schlumberger recommended a multisegment solution with a primary focus on the use of the OptiDrill real-time drilling intelligence service. The OptiDrill service provides downhole drilling mechanics and dynamics measurement on a rigsite display for improved decision making. This information is also made available offsite for remote interpretation by the drilling team.

With increased knowledge of downhole conditions, Statoil could optimize drilling parameters to improve ROP, mitigate risk, and enhance cutting structure life. To improve management of vibration and to optimize bit and reamer weight distribution, Schlumberger recommended remote interpretation by a drilling analyst from Geoservices, a Schlumberger company. The BHA included the PowerDrive X6 RSS and Rhino system to maintain verticality and open the 18 1/8-in hole to 21 in.

Drilled 3,100 m of salt interval in one run, saving Statoil 10 days

Using the OptiDrill service and complementary technologies and services, Statoil accurately applied optimal drilling parameters. This led to enhanced BHA performance that enabled Statoil to drill through the Angolan salt at a record-breaking 30-m/h ROP and set a record for the longest salt run ever drilled in Angola. Furthermore, verticality was maintained throughout the interval, and the hole was underreamed without premature wear to cutting structures.

“We successfully drilled 3,100 m of a salt section in one run and avoided setting a potential intermediate liner in the salt, thereby saving around 10 days,” Statoil Drilling Engineer Marcel Emile Ngueguim said. “We recommend the use of the OptiDrill service where accurate information is needed to improve drilling performance and bit life, especially in deep water with hard or abrasive formations. It is also recommended in underreaming applications to accurately evaluate the weight distribution between the reamer and the bit.”