|Middle East 1996
||Problem: A production
well drilled in 1980 was abandoned in 1992 after an unsuccessful workover. The workover
resulted in an unintentional sidetrack through the existing casing and made it impossible
to re-enter the well below the sidetrack. The casing was open to the low pressured
reservoir and flow to surface resulted above the casing break. The uncontrolled flow
consisted of toxic and flammable mixtures of hydrogen sulfide and methane gases. The
associated risks of any surface remedial operations within close proximity to the wellhead
was considered unacceptable.
|Remedial Strategy: The
flowing well would have to be killed and plugged by drilling a relief well due to the
unacceptable risk associated with a surface operation. The kill point selected was the top
of the producing limestone reservoir at 2118' TVD. After setting the 5" kill casing
string within 2-5' proximity of the blowout well, the relief well would drill into the
perforations. Once the well was killed, a retainer would be set and cement pumped for the
final plugging. The relief well would be spudded at least 250' from the problem well due
to safety concerns and wellpath geometric constraints.
|Special Services: John
Wright Company (JWCO) was contracted to supervise the special services for the project.
This would include pre-planning/engineering and on-site supervision of drilling rig
operations, directional drilling, surveying, casing detection, kill pumping, and
cementing. Vector Magnetics, responsible for electromagnetic ranging worked together with
JWCO to create a single team.
|Challenges: The project
was complicated by the following:
- There were no borehole surveys of any kind on the flowing
- High concentrations of Hydrogen Sulfide and Methane gases
required a 250' surface displacement and 24 hr safety monitoring, including evacuations.
- A shallow loss zone prevented directional work prior to the
setting of the 9-5/8" casing at 1060' TVD.
- Kill string must be set within 2-5 of the target well
at the top of the reservoir.
- Wellpath constraints required high dogleg rates for build
- Team concept for special services was successfully and
- S-shaped wellpath was modified continuously by
electromagnetic ranging results.
- Surface excitation and electromagnetic ranging techniques
- A "By-Pass" located the well at 1724' TVD,
displaced 32' from the wellhead.
- Build up rates of 10-12°/100' and drop off rates of
8-10°/100' were required.
- The target well was intersected at the perforations and
losses resulted (Figure2).
- Calculations showed that cement was circulated back to the