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

Author Rajeev Ranjan Kumar, Schlumberger Presenter: Rahul Talreja Geomechanics Engineer, Schlumberger

Index

■

Mechanical Earth Model and its Validation

■

Introduction to Area

■

Pore Pressure Profile

■

Wellbore Stability Analysis

■

Comparison of Borehole Condition

■

Summary

Factors determining wellbore stability

■

Pore pressure

■

Mud Weight and Casing*

■

Rock Mechanical Properties

■

Stresses

■

Wellbore trajectory* *Factor under human control

Wellbore Failure in Stress Field

Mechanical Earth Modelling (MEM) and Its Validation

Fluid Pressure Mechanical Properties Stresses

P

Density log Induced fractures and Breakouts Mechanical core tests XLOT / Frac test Sonic logs MDT/RFT test Kicks / Flows

History Matching Stable Mud Weight Window

Well-A Well-B Well-C Well-D Well-A Well-B Well-C Well-D

Introduction

Structurally complex field of North-East, India S Shaped and J Shaped Deviated Wells

• No major issues at 70pcf

Namsung and Girujan

• Cavings and Pickoff

Tipam

• Tight spots and Stuck

Pipe Barail

• High Pressure, Cavings,

pack-offs, washouts

• Poor ROP

Kopili Prang and Narpuh

• Hydrostatic pressure, Differential

sticking

• Tight hole

Lakadong

Effects on Drilling Operations

• Excessive reaming and wiper trips
• Fishing
• Loss of Equipment
• Sidetracks
• Inability to running casing to planned

depth

General Lithology and Drilling Challenges

*Mathur et.al 2001; Murthy, 1983 and Petroconsultants, 1996

• 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)

Pore Pressure Profile

Well Test

Schlumberger-Private

• 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.

Wellbore Stability Analysis

Alternate layers of low and high strength formation

Wellbore Stability Analysis in Koipili, Prang and Lk+Th

Variation of Shear Failure (Collapse Pressure Gradient)

Well-A Well-B Well-C Well-D

Comparison of Basic Logs and Hole Condition

Relative Improvement in Hole Condition

Well-C Well-D

Drilled with 73pcf Drilled with 73pcf Increased to 78.5pcf

Saved 5 Rig Days

• 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 Shale to minimize exposure of shale for

longer duration.

• Mud weight of 76-81pcf is planned for drilling deeper formations below overpressured

Kopili Shale to 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 Shalewith WBM optimization.

Summary

Thank You