BOT VACSVectored Annulus Cleaning System

Utilization in TUM-B5 for sand cleaning

Prepared by Sergey ChernenkovJuly 2014, Port Gentil, Gabon

VACS Tool - generalities• The Jet Bushing is normally positioned within 60 to 120 feet

above bottom of assembly. In TUM-B5 due to the limitation of the available wash pipe this distance was set at 90 ft.

• The tool is tripped into the well into with regular friction loss tests.

• Once circulation through the tool is established above the sediments, we start slowly washing down, once the top of the debris has been determined continue washing while reciprocating the string.

• During the washing operations the lifted debris travel up through the center of the milling shoe, up through the diverter tube where the cuttings will fall out as the workover fluid flows through the screen and out the jet bushing.

VACS Tool – 1st run• We have cleaned only 3 m before

the VACS tool generated 1,000 psi pressure.

• The pressure increase was initially taken by field personnel as generated by the screen (filter) plugging, and decision was taken to POOH.

• However, the recovered contains of the tool were very viscous, and not much of the dry sediments.

• The filters were not plugged and the chamber was not packed.

VACS Tool – Pressure analysis• The discovery of the tool in good conditions after being pulled made the

path of thinking narrower as surface inspection of the tool waved off one of the suspected problems of screen’s plugging. We realized that the Pressure rise was linked to generated U-tube while circulating at relatively high rate.

• The analysis of the pressure rise : If too much WOB is applied, the circulation at tool face stops This leads to limit the flow paths only into the perfs and up the annulus If the perfs are not taking all 5 BPM, the we see rise of the fluid level in

the annulus, and thus – overpressure onto the jets of the tool The gradual and not rapid increase of the pressure also illustrates

slowly risen fluid level, where 1000 psi corresponds to about 700-750 m of fluid level increase.

This increase will not be seen at surface as it is still much greater than what formation can stand. The last estimated PI was in range of 4.5 to 6.0 BPD/psi, which means that with 1,000 psi overbalance formation should take – in average – 3-3.5 BPM. As we are pumping at higher rates, the fluid level increase is very logical.

VACS Tool – Cleaning Optimization• The mitigating measures to improve cleaning efficiency were

applied on Run # 2 :

Pump at highest possible rate Do NOT slack off much of the weight onto the sediments! Work

with minimum WOB (as low as weight indicator will allow to control). The same principles as working with the burn shoes and wash pipe, applying around 500 lbs on the tool.

Indeed, the indication of the pressure rise in this case may vary and even be slightly higher, but we should not be scared of such due to the reasons explained above. This is only a U-tube

Results of the optimization – on the next slide:

VACS Tool – 2nd run• Approx 720 kg of sediment were removed, no water present in

the VACS

• Estimated volume of solids ~ 1.2 bbl

• Sediments are dry, compacted, and very coarse

VACS Tool – Further OptimizationThe 3rd run of VACS Tool had not progressed further than 2,400 m, which is just below the perforations.. The reasons are – as seen:

The sediments are too compacted for washing-off by circulation only

No rotating capabilities at SW-1 cannot give milling / crashing action on the tool face

Thus, there is a further possibility for improvement and optimization, when working with VACS or similar tools:

Increase the length of the VACS to potential maximum to increase the recovery per run.

Use of rotating equipment (Rotary or Power Swivel) will enhance capabilities of operations. SW-1 does not have any, and we are trying to repair and re-inspect old Power Swivel, which was damaged by wrong operations in the past.