||Problem: An old well in
a prospective gas storage field was improperly plugged and abandoned. The 8-5/8"
casing was cut and pulled at 825' MD, followed by a cement plug. The prospective storage
reservoir, a sandstone formation at 3000' MD, was exposed to the open hole up to the
8-5/8' casing shoe at 992' MD. In order to utilize the sandstone formation as a storage
reservoir the openhole must be properly plugged and abandoned. After several unsuccessful
attempts, re-entry into the well at the top of the casing stub utilizing conventional
methods became futile. See Figure 1.
|Remedial Strategy: The
leaking well would have to be plugged by unconventional techniques. A remedial operation
was planned to parallel the existing casing and to mill a slot just above the casing shoe.
The intersection would be achieved using electromagnetic ranging techniques, steerable
motors and an integrated rate gyro steering system. Re-entry into the well would be
attempted, and if allowed, a string of 4-1/2" casing would be run to cover the
openhole section to the reservoir. If re-entry could not be obtained, a cementing
operation to plug the well would commence See Figure 1.
|Special Services: John
Wright Company (JWCO) was contracted to supervise the special services. This would include
pre-planning and on-site supervision of: directional drilling, surveying, casing
detection, milling, and re-entry into the well. Directional drilling and wellbore
surveying services were contracted from Scientific Drilling Controls. Vector Magnetics
provided electromagnetic ranging services and worked together with JWCO and SDC to create
a single team.
|Challenges: The project
was complicated by the following:
- There were no borehole surveys of the 8-5/8" casing
- Short casing stub complicated the ranging operations.
- The formations were very soft where the slot was to be
- The angle of incidence had to be less than 4° to run the 4
1/2" liner in the slot.
- Window had to be started below a collar to prevent
separation during milling.
- Drilling parallel and alongside existing casing with poor
surveys would require precise directional control and accurate casing detection
- Team concept for special services was successfully and
- Existing wellhead was successfully utilized for the remedial
- Electromagnetic ranging techniques were critical for success
of the operation.
- Remedial well intersection was made at 800 ft with 3°
- Casing was milled from 800 ft to 835 ft with a custom
- 4-1/2" casing was run to 3000' MD and cemented in the
- The well became suitable for use as an injector/withdrawal
well, saving the cost of new well.