Severe losses in carbonate reservoir – unable to maintain primary well barrier
IOGP Well Control Incident Lesson Sharing #23-11
Experienced severe losses while drilling carbonate reservoir using MPD in Constant Surface Back Pressure mode. Lost control over bottom hole pressure, closed BOP and observed pressure increase indicating gas migration. Attempted to kill well with bullheading without being able to remove annulus pressure trend. Changed to PMCD mode and successfully resumed drilling as per contingency plans.
The Wells Expert Committee/Well Control Incident Subcommittee believes that this incident description contains sufficient lessons to be shared with the industry. We further encourage the recipients of this lesson sharing to share it further within their organization.
Note: Original alert wording from IOGP Member Company.
Water Depth: 2800 m, Drilling 8 ½" section in MPD mode (Constant Surface Back Pressure mode) with intermittent / partial losses (up to 700 lpm), pumping LCM at connections and according losses.
At +/- 4000 mRT, faced severe losses, couldn't maintain Surface Back Pressure (SBP) and suspected a drop of ECD at bottom - below Pore Pressure.
Could not observe a clear sign of influx due to losses rate, no ECD reading: decision taken to shut-in the well and close BOP (UAP).
Observed progressive increase of pressure (200 psi over 2 hours), indicating gas migration. Bullheaded the annulus volume with 850lpm. Observed the same annulus pressure increase trend after bullheading.
Decision made to switch to PMCD mode (Pressurized Mud Cap Drilling), part of contingent operation program considering a constant annulus injection to mitigate gas ingress. Resumed drilling.
What Went Wrong?:
Severe losses: Drilling in carbonate with suspected fractures and high porosity. Unable to maintain primary well barrier - i.e. hydrostatic column (Drilling mud + surface back pressure).
Corrective Actions and Recommendations:
Good reaction to shut-in the well on BOP, despite no clear sign of influx (safe anticipation).
PMCD contingency was planned on the operation program and correctly implemented.
safety alert number: 360
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/
Disclaimer
Whilst every effort has been made to ensure the accuracy of the information contained in this publication, neither the IOGP nor any of its members past present or future warrants its accuracy or will, regardless of its or their negligence, assume liability for any foreseeable or unforeseeable use made thereof, which liability is hereby excluded. Consequently, such use is at the recipient's own risk on the basis that any use by the recipient constitutes agreement to the terms of this disclaimer. The recipient is obliged to inform any subsequent recipient of such terms.
This document may provide guidance supplemental to the requirements of local legislation. Nothing herein, however, is intended to replace, amend, supersede or otherwise depart from such requirements. In the event of any conflict or contradiction between the provisions of this document and local legislation, applicable laws shall prevail.
