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Technical Paper: Solving Swelling Clay Issues: Modeling Effort/Concentric Reamer Saves Operator Over Seven Days Rig Time vs. Plan, UK North Sea

Society: SPE
Paper Number: 158958
Presentation Date: 2012
 Download: Solving Swelling Clay Issues: Modeling Effort/Concentric Reamer Saves Operator Over Seven Days Rig Time vs. Plan, UK North Sea (0.77 MB PDF) Login | Register

 

Abstract

The operator requires a 12 1/4-in tangent borehole through interbedded shale, chalk/sandstone that contains hydratable montmorillonite clay, Auk North field, UK North Sea. The swelling clay and long open-hole section have proven troublesome creating hole cleaning issues, frequent wiper trips and stuck pipe events.

A comprehensive modeling project was initiated with the aim of reducing vibration whilst improving rate of penetration (ROP) by selecting the best drive system, bottom hole assembly (BHA) configuration and combination of operating parameters. A rock strength program was run and indicated unconfined compressive strength (UCS) of the Oligocene/Eocene formations at 2-10 kpsi. Analogous formation samples were selected from the rock library and laboratory tests were conducted to replicate actual drilling conditions. The resulting data was then entered into the finite element analysis (FEA) based modeling system. A 12 1/4 x 14-in concentric reamer equipped with three polycrystalline diamond compact (PDC) triple row cutter blocks, a pilot PDC bit and a rotary steerable system (RSS) were selected for the investigation. Dynamic simulations were preformed with various operating parameters to observe how changes influenced BHA performance. 

The analysis provided valuable insight when the bit and reamer are drilling non-homogeneous formations.  The weight-on-tool fluctuation creates BHA instability which can be mitigated by managing parameters. A driller’s roadmap was produced showing optimum weight on bit (WOB)/revolutions per minute (RPM) combinations that would produce stable drilling for different formation scenarios.     
 
The integrated BHA was run with the recommended parameters and drilled 5889 ft in three runs at an average ROP of 77ft/hr.  The BHA met all directional objectives with low lateral vibration and medium stick-slip levels. All cutting structures used showed minimal wear. The successful run enabled the operator to complete the section seven days ahead of authority for expenditure (AFE) plan.

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