The geology of offshore drilling through basalt sequences: Understanding operational complications to improve efficiency

J. M. Millett*, A. D. Wilkins, E. Campbell, M. J. Hole, R. A. Taylor, D. Healy, D. A. Jerram, D. W. Jolley, S. Planke, S. G. Archer, A. Blischke

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

39 Citations (Scopus)


Offshore drilling in basins with a significant basaltic component poses a number of complications to drilling operations. These include slow and variable rates of penetration (ROP), drilling fluid losses, drill bit or string sticking, overpressured formations, wellbore spalling and collapse. In this contribution we investigate features of large igneous province (LIP) volcanic facies that may directly contribute to drilling complications. Combining borehole and field based examples we identify highly vesicular brecciated lava flow tops and hydro-volcanic facies as a major potential cause of catastrophic drilling fluid losses. The risk for drilling losses is generally higher in the upper parts of thick volcanic successions where hydrothermal secondary mineralization and alteration may be less pervasive. We demonstrate how these facies may be identified early by integrating real time mud logging data with characteristic drill cuttings and LWD (logging while drilling) wireline data as it becomes available. We highlight the potential of basaltic formations to maintain porosity and permeability to greater depths than is typical for sediments due to the high compressive strength of crystalline basalt frameworks. The heterogeneous sub surface distribution of key volcanic facies commonly includes intimate mixing and layering of hard and dense with soft and weak volcanic rock which may promote complex in-situ stresses to develop during burial compaction. Where this occurs, wellbore stability predictions such as the fracture and wellbore collapse gradients for volcanic sequences may deviate from those expected in basin equivalent sedimentary sequences. Examples of swelling volcanic clay horizons, unstable volcaniclastic sequences, and intrusion related ledge effects are used to characterize the main causes of drill bit and string sticking. A greater understanding of drilling complications encountered within prospective areas containing volcanic sequences is needed if better pre-drilling risk assessment, cost prediction, real-time identification and mitigation is to be achieved.

Original languageEnglish
Pages (from-to)1177-1192
Number of pages16
JournalMarine and Petroleum Geology
Early online date9 Aug 2016
Publication statusPublished - Nov 2016

Bibliographical note

This manuscript was improved by insightful reviews by Christian Koeberl and an anonymous second reviewer. Anand Kale is kindly thanked for editorial handling. This work was developed, in part, through the Volcanic Margin Petroleum Prospectivity project (VMAPP - run by VBPR, DougalEARTH ltd. and TGS), and the StratLIP research project at the University of Aberdeen. D. Jerram and S. Planke are partly supported by Research Council of Norway Centres of Excellence project (number 223272, CEED). Chevron are thanked for permission to present selected well data on behalf of Co-Venture partners OMV, Faroe Petroleum and Indemitsu.


  • Basalt
  • Drilling
  • Offshore
  • Volcanic margins
  • Large igneous provinces
  • Volcanic fades
  • Faroe-Shetland Basin
  • Columbia river basalts
  • NE Atlantic
  • Hyaloclastite deposits
  • facies architecture
  • volcanic reservoirs
  • oceanic-crust
  • flood basalts
  • igneous rocks
  • lava flows


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