The Integrated Drilling Technology to Solve Well Construction Challenges in the Pre-Salt Reservoirs of Ultra-Deep Water
Authors: Liqiu Ping , Xi Wang , Xiuling Zhang , Chenchao Liu , Rui Yang 
Published: March 2018

The well construction operation in the pre-salt reservoirs of Santos basin faced great challenges such as the drill string stuck in big-thickness salt formation (more than 2000m) and low penetration rate in the reservoir formation from the beginning of X. Project. The average actual well construction duration of four wells completed in 2015 was 7 days behind the planed period caused by the above-mentioned problems. The well construction cost was more than the approved budget due to the delayed well construction duration. So efforts was concentrated to integrate drilling technology in ultra-deep water to solve drilling challenges in the pre-salt reservoirs to decrease well construction duration and increase exploration and development benefit.

This paper presents an integrated drilling technology to solve drilling challenges in pre-salt reservoirs of ultra-deep water. The combination of near bit reamer stabilizer and synthetic-based mud can prevent the salt formation creeping and decrease the drill string stuck frequency. The optimization of drilling parameters based on mechanical specific energy concept can clearly identify the transfer from the anhydrite formation to the salt formation and drilling penetration rates can be improved in salt formation by optimizing WOB, rotate speed and pump rate, etc. The combination of MPD, turbine drill and impregnated bit can control the mud losses and increase the penetration rates in the carbonate reservoirs which possess poor drillability. All the above-mentioned drilling technology has been applied in two wells and successfully solves the drilling challenges in the pre-salt reservoirs of X. Project.

The combination of near bit reamer stabilizer and synthetic-based mud has decreased the drill string stuck NPT from 11.7d to zero in two wells of X. Project. The average ROP record of the two wells by use of the integrated drilling technology is 24.6 m/h that has been improved 3.4 times comparing the completed four wells in 2015. The drilling duration for 2062m salt section has decreased to from 14 days to 7 days which saved about 14 millions dollars for the two wells. The average ROP in the reservoir formation of the two wells has been increased to 3.45m/h which was about 1.5 times of the four wells' average ROP completed in 2015. The reservoir section has been completed 4.6 days ahead of the planed duration and the comprehensive drilling cost has been saved 5 millions. The integrated drilling technology in pre-salt reservoirs in ultra-deep water made the average well construction duration of the two wells finished in 2016 have decreased to 111 days, however, the average well construction duration of the four wells completed in 2015 was 162 days.

The fastest record of the one well's construction duration was 76 days establishing a new benchmark in pre-salt reservoirs in ultra-deep water. The method to solve well construction challenges in the pre-salt reservoirs of Santos Basin of this paper presented will make a reference for deep water salt formation drilling and offshore oilfields high efficiency development.