An oil field located in the northern Campos basin has been producing since 1995. It is located in water depths ranging from 1500 to 2100 m and presents hydrocarbon accumulation in sandstone formations comprised of ten units. While conducting infield drilling, depleted zones with severe lost circulation issues were expected. Cementing operations in such conditions can be challenging and require special attention to cementing the drillstring and completely achieving zonal isolation objectives. During preplanning, foamed cement was considered based on its ability to mitigate formation compaction caused by formation depletion, the capability to fill lost-circulation voids compared to nonfoamed slurries, its excellent displacement properties, and good cement bond results, making it an excellent solution for this challenging scenario.
This paper presents a case history where foamed cement was used for a production casing in an ultradeepwater well in Brazil. The 12 1/4-in. production section was drilled to total depth (TD) using managed pressure drilling (MPD) technology and synthetic-based mud (SBM) at a density of 8.7 lbm/gal + surface backpressure (SBP). The goals for the cementing operation were the same as for the other production wells:
Provide a 200-m casing-to-casing barrier
Achieve an 830-m height of cement (HOC) and top of cement (TOC) at 2900 m
Evaluate the cement sheath using a bond log
Provide complete zonal isolation across the reservoir
Displace the drilling fluid across the annulus and place a competent cement slurry
Provide hydraulic isolation between future fracturing stages
Prevent isolating the perforation at 2710 m [annular pressure buildup (APB) mitigation]
The cementing challenges were significant and required the use of lightweight slurry to remain within the operational pressure window. Cementing best practices were closely followed, helping ensure a good bond was obtained under these conditions. Finally, the post-job cement bond log showed excellent bonding to the formation and pipe, which meant competent zonal isolation and wellbore were delivered for production.