Bangladesh 2001

Problem:   After drilling to TD on this HPHT exploration well, the string was being tripped for logging when the BHA became stuck 140m below the last casing shoe. During the subsequent operations a blind back-off was made above the BHA. While tripping out this string the well began flowing. A high pressured water flow from near bottom fractured into a weak sandstone formation just 50m above the bit. After connecting the drillstring back, a temperature survey was run to identify the crossflow. To make the well safe for further operations, a polymer GUNK plug was pumped to initially halt the flow , followed by a permanent cement plug. A temperature survey was run to confirm that the flow was stopped around the BHA. The water flow could not be confirmed stopped below the BHA however. Since the water flow could damage the reservoir a plan to re-enter the open hole below the fish and permanently plug the well was required..
Remedial Strategy:  The initial plan selected included the sidetracking below the 13-3/8 casing after the casing has been cut, milled and pulled and then re-enter below the bit. During the milling operation, however, holes were found in the 13-3/8 and 20 strings. A new relief well location was chosen and offset ~40m from the blowout wellhead and was planned to intersect the openhole just below the bit @ 3849m. After entering the openhole, the bit would be run to bottom to clean out the openhole interval and the e-logs would be run to identify an economic formations for future developments.
Special Services:  John Wright Company was contracted to provide both strategic and tactical special services. Technical assistance and onsite supervision during the initial crossflow period kill and plugging design and supervision were provided. Later, JWCO supervised the special services required for the relief well intervention project. This included pre-planning and on-site supervision of directional drilling, surveying, kill operations and casing detection. Vector Magnetics, responsible for electromagnetic ranging, was coordinated through JWCO on this project and worked together as one team. Well Flow Dynamics was instrumental in the diagnostic investigation and in simulating various kill scenarios for possible kill operations, both surface and relief well kills.
Challenges: The project was complicated by the following:
  • The underground flow was halted at the BHA but could not be proven deeper.
  • The water depth was ~11m and very few HPHT drilling units were available.
  • The well temperature was in excess of 135 C and the BHP >13500psi
  • Several sidetracked holes were present just below the 13-3/8 shoe.
  • Casing design was critical with only one contingent string available for the project.
  • The possibility of encountering the 4500m MD pore pressure at the intersection point was not expected, but must be planned for.
  • The original hole must be cleaned out to allow effective logging operations using a rotating BOP with no returns taken at surface.
Results:
  • A 40m offset wellhead minimized well design constraints.
  • The relief well located the target well just below the 13-3/8 shoe and a 2-5m proximity was successfully maintained for ~600m until the intersection point.
  • An openhole intersection occurred as planned at the bit of the target well
  • A rotating head BOPE was utilized to intersect and clean out the hole to TD
  • Polymer GUNK pill was found at the intersection point and for ~80m MD in the openhole, proving that this new type of reactive plug is competent
  • Below the GUNK plug the high pressured water flow was found and heavy mud was circulated into the loss zone, using the rotating head, until TD was reached and circulation to surface was possible.