Case Studies on Operational Failures Due to Poor Geological Planning

Geological planning is the foundation of a successful drilling operation, as formation properties determine well design, equipment used, and strategies for support teams. However, errors in geological data interpretation or planning can lead to costly operational failures, from wellbore collapses to lost circulation. This chapter analyzes real-world case studies that illustrate how poor geological planning has caused operational issues, highlighting key lessons to improve safety and sustainability. By studying these cases, we connect geological fundamentals, well lifecycle, and interdisciplinary collaboration with future drilling trends.

Importance of Geological Planning

Geological planning utilizes seismic data, well logs from previous wells, and geological maps to design the well trajectory, select drilling fluid, and anticipate risks such as unstable shales or high-pressure zones. Poor planning can lead to issues such as:

• Wellbore collapse: Collapse of the well walls due to unstable formations.
• Lost circulation: Absorption of drilling fluid by porous or fractured formations.
• Kicks: Influx of formation fluids into the well due to misestimated pressures.
• Stuck pipe: Obstruction of the drill string due to reactive formations or collapses.

These issues not only delay operations and increase costs (AFE), but also compromise safety. The case studies below illustrate these risks and the lessons learned.

Case Studies

Case 1: Wellbore Collapse in Unstable Shales – Vaca Muerta, Argentina

Context: In 2018, an operator in the Vaca Muerta formation, known for its hydrocarbon-rich shales, faced a wellbore collapse during the drilling of a directional well. The shales, highly reactive to water-based fluids, swelled, causing the well walls to collapse.

Cause: Geological planning underestimated the shale’s reactivity, relying on incomplete seismic data and insufficient prior well logs. The drilling fluid engineer selected a water-based mud instead of an oil-based one, which would have stabilized the clays.

Impact:

• Operational delay: The operation was halted for two weeks to clean and stabilize the well.
• Additional cost: Unplanned expenses in the AFE, including new mud and cleaning tools, exceeded $500,000.
• Safety risk: The collapse increased well pressure, requiring activation of the BOP.

Lessons learned:

1. Improve geological characterization: Use more data from nearby wells and laboratory tests to assess shale reactivity.
2. Interdisciplinary collaboration: The wellsite geologist and drilling fluid engineer must collaborate to select the appropriate fluid.
3. Pre-job meeting review: Include discussions on specific geological risks in safety meetings.

Connection to the curriculum: This case highlights the importance of formation properties and collaboration between the wellsite geologist and drilling fluid engineer.

Case 2: Lost Circulation in a Carbonate Reservoir – Gulf of Mexico

Context: In 2015, a fixed platform in the Gulf of Mexico experienced severe lost circulation while drilling an exploratory (wildcat) well in a carbonate reservoir with natural fractures.

Cause: Geological planning failed to adequately identify fractured zones due to limited seismic data interpretation. The drilling fluid, designed for standard pressures, was absorbed by the fractures, halting mud circulation.

Impact:

• Mud loss: Thousands of barrels of mud were lost, with costs exceeding $1 million.
• Delay: Drilling was paused for 10 days while lost circulation materials were implemented.
• Environmental risk: Partial mud spills threatened compliance with HSE regulations.

Lessons learned:

1. High-resolution seismic data: Invest in 3D seismic to detect fractures before drilling.
2. Prior testing: Conduct pilot tests in similar formations to anticipate losses.
3. Contingency planning: Include lost circulation materials in the mud design and AFE.

Connection to the curriculum: This case underscores the importance of geological maps and HSE protocols to mitigate environmental impacts.

Case 3: Kick in an Offshore Well – North Sea

Context: In 2017, a drillship in the North Sea experienced a severe kick while drilling a deepwater well, caused by a misestimated pore pressure in a sandstone formation.

Cause: Geological planning relied on outdated pressure models, underestimating the reservoir pressure. The drilling fluid engineer did not adjust the mud density in time, and the driller failed to detect warning signs in the MWD data.

Impact:

• Blowout risk: The kick required immediate BOP closure, preventing a major incident.
• Operational cost: Delays and control measures exceeded $2 million.
• Reputation: The operator faced strict regulatory audits due to failures in HSE protocols.

Lessons learned:

1. Updated geological models: Use real-time LWD data to adjust pressure models.
2. Driller training: Enhance training to interpret kick warning signs in controls.
3. Effective communication: Strengthen pre-job meetings to align the wellsite geologist, drilling fluid engineer, and driller.

Connection to the curriculum: This case connects interdisciplinary collaboration with communication and safety.

The following table summarizes the case studies:

Summary

The case studies demonstrate that poor geological planning can cause collapses, lost circulation, and kicks, with economic, operational, and safety impacts. Integrating accurate geological data, interdisciplinary collaboration, and effective communication in pre-job meetings is essential to mitigate these risks. These cases connect geological fundamentals, well types, equipment, and roles with future trends in automation and sustainability.

Practical Exercise

1. Reflection question: How could better geological planning have prevented the wellbore collapse in Vaca Muerta, and what role does communication play in this process?
2. Research task: Investigate a drilling incident (e.g., Macondo in the Gulf of Mexico) and write a paragraph describing how poor geological planning contributed to the issue.
3. Technical question: Explain how seismic data and LWD logs could prevent lost circulation in a fractured reservoir.

Bibliography

• Books used:

  • Hyne, N.J. (2012). Nontechnical Guide to Petroleum Geology, Exploration, Drilling & Production. PennWell Books.
    Explains geological risks and operational failures in an accessible manner.
  • Bourgoyne, A.T., Millheim, K.K., Chenevert, M.E., & Young, F.S. (1986). Applied Drilling Engineering. SPE Textbook Series.
    Details the technical causes of drilling failures.

• Recommended books:

  • Mitchell, R.F., & Miska, S.Z. (2011). Fundamentals of Drilling Engineering. SPE Textbook Series.
    A technical resource on geological planning and risk mitigation. Available at: https://store.spe.org/Fundamentals-of-Drilling-Engineering-P113.aspx.
  • Azar, J.J., & Samuel, G.R. (2007). Drilling Engineering. PennWell Books.
    Ideal for deepening knowledge on operational failures. Available at: https://www.pennwellbooks.com/drilling-engineering/.

• Direct links:

  • SPE (Society of Petroleum Engineers): Resources on geological risks and failures. https://www.spe.org/en/.
  • IADC (International Association of Drilling Contractors): Information on drilling incidents. https://www.iadc.org/.
  • PetroSkills: Courses on drilling risk management. https://www.petroskills.com/en/training/courses/drilling-practices---dp.