NEWS FROM SPE/IADC 2013: TBS technology optimizes Bakken shale drilling
BY KURT ABRAHAM, Executive Editor
AMSTERDAM -- Since 2010, drilling in the North Dakota sector of the Bakken shale has seen an industry changeover to longer laterals (greater than 7,500 ft), with the majority being closer to 10,000 ft. As explained in a technical paper presented by two Weatherford International authors at the SPE-IACD Drilling Conference in Amsterdam, these longer laterals require a tremendous engineering effort. They create several issues with hole cleaning, ledging and reduced ROP. To improve performance in these laterals, operators have been looking for a while now, for an economic alternative to rotary steerable systems (RSS’s), while still retaining their basic benefits.
Lead author Wendell Bassarath said that a new system to achieve 3D directional control was developed to improve drilling efficiency, using targeted bit speed (TBS) technology. The system uses a conventional positive displacement motor with a bent housing and an MWD tool that mimics many of the features offered by an RSS. The steering technique was achieved by accurately modulating the flow of the drilling fluid through the drillstring.
This allowed rapid variations in the drilling parameters to accurately control the bit speed along the desired toolface setting. If wellbore objectives could not be achieved in rotary mode using TBS technology, then the mud motor could be oriented in a conventional manner to follow the well plan.
To test these various assertions, said Bassarath, two horizontal wells were drilled in North Dakota. Well #1 was drilled in a northerly direction, to a TD of 19,632 ft, with 10,217 ft of lateral leg. It had a total of four bit runs in the lateral leg, with an average ROP of 38.08 ft/hr. Well #2 was also drilled in a northerly direction, with a TD of 18,232 ft, with 8,956 ft of lateral leg. It had two bit runs in the lateral leg, with an average ROP of 30.67 ft.hr.
As drilling progressed, these wells required frequent directional updates, due to formation faults. Consequently, this required many target changes for geosteering. ROPs in the first Bakken well were higher than the second well, since more time was spent sliding to correct the well path on #2 without TBS technology. Use of TBS technology on Well #1 enabled the operator to have precise steering control and drill a smoother wellbore. The second well reached TD early, due to an inability to overcome high frictional forces in the lateral leg.
As a result of the smoother wellbore, the operator had a trouble-free casing run in Well #1. The system consistently achieved more than 93% rotation in the lateral in both wells. This was a significant improvement from previous wells, which achieved roughly 70% rotation. On the first well, sliding time was reduced from 30% to 8%, saving seven days of rig time and the associated drilling costs.