Case Study: KJO Achieves Performance Step Change with Integrated Horizontal Reentry Strategy in Complex Offshore Formation

Drilling solution developed at local PetroTechnical Engineering Center (PTEC) delivers eight wells to TD through unstable shale zones, saving 50 days

Challenge: Drill reentry horizontal wells in challenging offshore shale environment while ensuring wellbore stability and minimizing rig time.

Solution: Deploy a customized drillstring that included advanced directional drilling and logging while drilling servicesas well as a customized drill bit from Smith Bits and an enhanced water-base drilling fluid from M-I SWACO.

Result: Completed eight wells and saved a total of 50 days off plan using new horizontal reentry campaign.

Demanding reentry requirements in complex offshore reservoirs

Khafji Joint Operations (KJO) is developing the offshore Khafji oil field in which horizontal wells have proven to be an effective development strategy. Because installing new offshore structures requires excessive time and costs, sidetracking from older vertical wells serves as an economical solution for further field development while minimizing the cost per foot required for well delivery.

Most of the existing wells’ 7-in casing was tied back and cemented to surface, resulting in insufficient conventional casing string options for drilling ahead or inadequate mechanical barriers for isolating the field’s unstable shale zones. The field also comprised collapsible coal layers as well as zones at risk of severe lost circulation. Another limiting factor in these reentries was the unavailability of oil-base mud because of the absence of preparation and premixing facilities.

Most of the reentry wells would be targeting three shallow reservoirs located close to the sidetracking point, leaving little room for landing the section and requiring high build rates. Geosteering would be required in hole sizes from 5 7/8 to 6 1/8 in. Because of these stringent geosteering, formation evaluation, and completion objectives, slimming down the well design was not an option.

Previous sidetracking campaigns in the field suffered from numerous wellbore stability events and stuck pipe. These technical challenges so severely affected operations that the majority of wells failed to meet the initial objective, and sidetracking activities were suspended for two years.

New drilling strategy featuring fully integrated solution

Schlumberger experts at the local PetroTechnical Engineering Center (PTEC) collaborated with KJO about its well delivery goals and determined the key enabling technologies that would most effectively meet objectives despite the operation’s technical complexity.

First, the team conducted a geomechanics study of the offset wells to determine the mud weight that would help avoid wellbore breakout while minimizing the risks of losses. Considering the results of the geomechanics study and the stipulation that no oil-base mud could be used, PTEC experts selected M-I SWACO KLA-SHIELD enhanced-polymer water-base drilling fluid system to address the wellbore stability challenges. The system was enhanced using bridging material and sealing agents to drill through the porous reservoirs.

The PowerDrive Archer high build rate rotary steerable system (RSS) was chosen to deliver the build rates required while avoiding the risks of sliding in these unstable formations. The team also used the IDEAS integrated drillbit design platform to engineer a customized 6 1/8-in PDC bit. Casing windows were performed using the TrackMaster CH cased hole whipstock system, which features premium mills that enable quality window exits in cemented casings. The proposed drilling solution enabled performing the sidetrack and drilling the lateral in a single hole size. Contingencies were developed using an expandable liner or finishing the lateral in a 3 7/8‑in hole size.

Performance step change meets sidetracking objectives, saves 50 days

KJO resumed its sidetracking campaign using the integrated approach developed with the PTEC team. The customer drilled eight wells—three in Reservoir A, two in Reservoir B, and three in Reservoir C—and each achieved its target objectives.

In Reservoir A, the goal was sidetracking an existing vertical 7-in liner and landing at the sandstone reservoir, then geosteering for 700 ft [213 m]. The landing section required an average dogleg severity of 10°/100 ft through the unstable shale layers to land on target. The PowerDrive Archer RSS and the KLA-SHIELD mud system helped overcome the wellbore stability issues, provide proper hole cleaning, and avoid stationary time in front of the shale. The well was drilled to TD in one hole size with no wellbore stability issues and achieved all the logging and directional requirements. The 4½-in liner was then smoothly run to bottom and cemented in place for perforation. The well was finished 5 days ahead of plan.

The goal in Reservoir B was sidetracking an existing vertical 7-in liner, landing in the sandstone reservoir, and geosteering for 600 ft [183 m]. This landing section required an average 7°/100 ft to land on target. The integrated drilling system drilled the well to TD in one hole size and achieved all logging and directional requirements. The 4½-in liner was also run to bottom and cemented in place for perforation. This well was delivered 10 days ahead of plan.

Finally, in Reservoir C, the requirement was sidetracking the existing liner, landing with 8°/100 ft at the limestone reservoir, and steering for 2,000 ft [610 m]. The customized BHA drilled to TD in one hole size but required lost-circulation management pills and multiple curing runs. Thereafter, the 4 1/2-in liner was run smoothly to required depth and cemented in place off bottom to isolate the loss zone and to allow openhole completion. The well was finished 15 days ahead of plan.

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