Hungary 2000

Problem:   During a workover on a well in a gas storage field control of a swab kick was lost and a blowout and fire resulted. Reservoir pressure was near seasonal high and production from the well was predicted at ~3.8Mscm/day. The gas source was a pipeline from Russia and the blowout well handled injection during the summer and production during the winter. A 6m perforated interval at 1229m MD into a Darcy+ permeability sandstone was the main production interval along with possible communication with shallower zones having gas and water. The Hungarian wild well firefighting team successfully capped the well in two weeks. However, after the bullhead operation an adjacent well cratered and the capping stack was opened to relief pressure. The casing had burst near the surface and the resulting sand erosion destroyed the capping stack and the well eventually cratered producing large volumes of formation water. Other surface options were lost.
Remedial Strategy: A relief well became the only feasible control option and the initial plan developed included a single relief well having a casing intersection followed by well killing and plugging operations. A pit and trench to divert the ~3000m3/day of water was initially constructed, but additional pits were dug to handle the effluent, which could not be allowed to enter local water systems. Many wells were present in this gas storage field and it was thought further damage to other wells, subsequent gas resources and reservoir damage would occur if the well was not controlled. A single relief well, having a ~257m offset, was chosen to intersect, kill and plug the blowing well.
Special Services: John Wright Company was contracted to provide both strategic and tactical special services. Technical assistance and onsite supervision during the initial diagnostic period and the P&A operations were provided. 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 relief well kill scenarios for possible kill operations.
Challenges: The project was complicated by the following:
  • The surface flow included both water and gas into a crater, requiring control and storage of the produced water from both deep and shallow zones.
  • The reservoir pressure was dropping considerably requiring a quick P&A .
  • RW surface location was restricted due to many wells, water trench and pits locations and other environmental conditions.
  • No surveys existed above 500m MD and the lower surveys being MSS at ~100m intervals, resulting in a positional uncertainty of ~25m radius.
  • Shallow gas charging was not expected, but was considered during planning and drilling.
  • A 257m offset wellhead required high build rates in the upper portion of the RW.
  • The relief well located the target well at ~650m and a 4m Cross-By was achieved followed by a diverging path to the intersection point. At ~1020.5m MD
  • A 6.5m slot was milled in the target well’s 7” casing to allow the P&A operations.
  • After opening the slot up, a hydraulic set packer/bridge-plug was run and set ~ 147m below the slot to stop the gas flow from the reservoir. This is the first time this had every been done from a relief well.
  • A cement plug was pumped into from the packer/plug to just below the slot.
  • A final cement plug was pumped from the slot up to the shallow zone where the casing strings were damaged