Vietgazprom faced a challenge with an exploration well in a thick carbonate section offshore Vietnam. SLB suggested OptiWell™ well construction performance service to analyze data from the well, determine the thickness and location of loss zones, and develop a lost circulation material (LCM) strategy. The technology reduced losses by 50% when opening the well in the 20-in section. The well was drilled, opened, and cased sucessfully.

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.

Throughout this process, the well operations analyst provided continuous monitoring and insight so that the drilling team could see the effect that pumping the various LCM pills had on the losses in real time. This detailed information also enabled the drilling team to pump and squeeze a FORM-A-BLOK™ high-performance, high-strength lost circulation pill into the fractured carbonate section.

Reduced mud loss by 50% while opening the well to 20 in

The combination of the information provided by the OptiWell service, the collaboration with the well operations analyst, and the ability to see the loss reaction in real time gave Vietgazprom the information needed to complete the section. Ultimately, the OptiWell service assisted Vietgazprom in reducing losses by 50% while opening the well to 20 in. The section was drilled, logged, opened to 20 in, and cased with 16-in liner successfully and on schedule.