Reducing Drilling Risks in J bend Wells Targeting basement in - PowerPoint PPT Presentation

Reducing Drilling Risks in J bend Wells Targeting basement in Tectonic Area through Geomechanical Solutions Presenter: Rahul Talreja Geomechanics Engineer, Schlumberger Author Rajeev Ranjan Kumar, Schlumberger

Index Mechanical Earth Model and its Validation ■ Introduction to Area ■ Pore Pressure Profile ■ Wellbore Stability Analysis ■ Comparison of Borehole Condition ■ Summary ■

Wellbore Failure in Stress Field Factors determining wellbore stability Pore pressure ■ Mud Weight and Casing* ■ Rock Mechanical Properties ■ Stresses ■ Wellbore trajectory* ■ *Factor under human control

Mechanical Earth Modelling (MEM) and Its Validation History Matching Density log Kicks / Flows MDT/RFT Stable Mud Weight Window test P Fluid XLOT / Frac test Stresses Pressure Induced fractures and Breakouts Mechanical Properties Sonic logs Mechanical core tests

Introduction Structurally complex field of North-East, India Well-C Well-B Well-C Well-B Well-D Well-A Well-A Well-D S Shaped and J Shaped Deviated Wells

General Lithology and Drilling Challenges Namsung and Girujan • No major issues at 70pcf Tipam • Cavings and Pickoff Effects on Drilling • Tight spots and Stuck Operations Barail Pipe • Excessive reaming and wiper trips • Fishing Kopili • Loss of Equipment • High Pressure, Cavings, • Sidetracks pack-offs, washouts • Inability to running casing to planned depth • Poor ROP Prang and Narpuh • Hydrostatic pressure, Differential sticking Lakadong • Tight hole *Mathur et.al 2001; Murthy, 1983 and Petroconsultants, 1996

Pore Pressure Profile Well Test Well test/MDT data is available to calibrate the pore pressure • • Pore pressure increases in Kopili from 63pcf to 73-74pcf. There is pore pressure reversal trend from Prang to Narpuh (69-70pcf)

Wellbore Stability Analysis Over-gauged hole condition due to shear • failures in weak shale layers of Tipam, Barail, Kopili, Prang, Narpuh and Lakadong formations. Several tight hole/held-up incidents while • RIH and POOH operations. Schlumberger-Private

Wellbore Stability Analysis in Koipili, Prang and Lk+Th Alternate layers of low and high strength formation

Variation of Shear Failure (Collapse Pressure Gradient)

Comparison of Basic Logs and Hole Condition Well-A Well-B Well-C Well-D

Relative Improvement in Hole Condition Well-C Well-D Drilled with 73pcf Saved 5 Rig Days Increased to 78.5pcf Drilled with 73pcf

Summary Formation pressure gradient shows increasing trend from Barail (63pcf) to Kopili (74-75pcf) and • reversal from Prang to Langpur (69-70pcf). • Tight holes and tool stuck incidents are prominent in Kopili shales, Barail shales, Prang and Lakadong. • Mud weight of 70-73pcf should be used while drilling Tipam and Barail. 9-5/8in casing shoe should be set as deep as possible inside Kopili S hale to minimize exposure of shale for • longer duration. • Mud weight of 76-81pcf is planned for drilling deeper formations below over p ressured Kopili S hale t o basement for avoiding shear failure at higher well deviation. Proper hole cleaning with appropriate mud chemical composition to be used to reduce fluid invasion in sand • to avoid differential sticking. Way Forward: Chemical stability study of Kopili S halewith WBM optimization. •

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