RIASSUNTO
Abstract
The use of coil tubing in fishing operations has been limited to date. This paper discusses a coil tubing fishing operation on a 4000 m, 30% H2S gas well with 27 MPa surface pressure. A 12.5 metre wireline tool string was stuck inside the production tubing at 1770 m, with 76 m of elemental sulphur fill on top. The need for 23 m of lubricator during coil tubing fishing operations was eliminated by designing a pump through Pressure Deployment System, along with a pump-off sub. Problems encountered with the Pressure Deployment BOPs will necessitate periodic inspection of the BOP stack on future high pressure, sour well work.
Advances in coil tubing technology have made coil tubing an economical alternative for many oil field operations. Fishing operations can now be performed on live wells without long sections of lubricator. Coil tubing has increased to 88.9 mm (3 1/2"") in size, has become more H2S resistant and is now continuous without butt welds. The components of the coil tubing unit, such as the injector have also increased in strength allowing work in deeper and higher pressure wells.
Introduction
Esso's Obed Field near Hinton, Alberta is comprised of five sour gas wells, three of which are completed in the Nisku formation and the remaining two in the Leduc formation. A gauge ring with a junk catcher was run into Esso et al. Obed 11-13-54-23 W5 in an attempt to determine the amount of sulphur and iron sulphide scale buildup on the 114.3 mm tubing.
The gauge ring became stuck due to sulphur scale buildup at 1770 m and was left in the hole. An unsuccessful attempt was made to fish for the gauge ring using braided line. During the fishing attempt the fish could not be pulled free and the fishing tool would not release from the fish so the braided line was pulled out of the rope socket. This left a resulting fish of 12.5 m in the well. An impression block run later revealed that 76 m of sulphur had piled on top of the fish.
This 4000 m, 8% CO2, 30% H2S gas well had a bottom hole pressure of 38 MPa and 27 MPa surface pressure. Figure I is a schematic of the well,
FIGURE 1: Subsurface schematic: Esso et al. OBED 11-13-54-23 WSM. (Available in full paper)
wellbore, shear events near the well bore (combined P and S phases, too close to be distinguished), or shear events far away from the wellbore (S phase only, P phase completely absorbed). It is interesting to note that most of the signals are oriented within the N30-40 °E window (Figure 6). which is close to the expected orientation of the main fracture. The results also show that the best polarization is obtained within the first quarter-period of the wave and degenerates quickly afterwards. This can be explained if one assumes that the events are occurring close to the wellbore. The first part of the waveform would be mostly a P-wave that would become gradually contaminated by S-waves.