Reduce unexpected mud loss in exploration well
While drilling a 12 1/4-in pilot hole for Well VGP-130-TD-1X, the bit
encountered a 350-m-thick carbonate section. After a severe mud loss in several
zones in this section, Vietgazprom recognized that action had to be taken.
Vietgazprom was using a synthetic-based mud that was difficult and expensive to
transport, making mud loss physically, temporally, and economically detrimental
to the project. Because the well was an exploration well, the exact thickness
and condition of the carbonate section was unknown. Therefore, it was critical
to analyze data, identify the potential loss zones within the carbonate
section, and plan the loss mitigation accordingly.
The goal was not only to drill the 12 1/4-in pilot hole but also
complete the entire suite of wireline logging, open the well to 20 in, and
complete the section with the 16-in liner run. To complete the section
successfully, the exact location of the loss zones needed to be identified and
an LCM strategy needed to be planned. After the results of the LCM strategy
were analyzed, Vietgazprom could make the necessary changes to the plan to
complete the section on schedule.
Identify losses and implement an LCM strategy
Vietgazprom chose the OptiWell service to analyze the data. The well
operations analyst assimilated subsurface and surface data and accurately
identified loss zones within the carbonate section. The analyst was then able
to determine that the experienced losses correlated with breakouts or fractures
in the formation. This information was presented to Vietgazprom, and an LCM
strategy was created.
As part of this strategy, a 50-ppb LCM pill was pumped through the bit
around the loss zone. The static losses reduced, though as the circulation was
increased, the loss rate increased. A higher concentration of LCM at 120 ppb
stemmed the losses.