In the Talara basin, the cementing of the production section represents a challenge to achieve effective zonal isolation around the pay zone and ensure an efficient hydrocarbon production. For this purpose, well cement design must be tailored to accomplish specific goals. Challenges related to depleted intercalation zones, gas-bearing formation, highly recycled drilling mud, and marginal economic incentives push operators to build a multidisciplinary team with cementing and drilling fluid service companies to optimize well cement design. The objective of this article is to present cementing lessons learned from a recent drilling campaign in the Peruvian northwest area.
Cementing jobs in the Block IV of the Peruvian northwest area is usually complex due to poor zonal isolation according to cement bond evaluation tools (sonic logs). The lack of good cement quality is related to micro-channeling and loss of well integrity. In fact, things get more complicated due to the requirement of recycling of the drilling mud to cut costs. Highly recycled mud sticks to the formation walls, complicating its removal. Various measures have been taken to understand the issues behind poor cementing jobs. Proper cementing design and placement through continuous improvements in both drilling fluid and cement formulations resulted in successful cement placements with consistent outcomes in several wells.
The formulation and designing of the pre-flushes, and the optimization of their rheological properties and wellbore exposure time, resulted in effective mud removal. For an 8.5 in hole, which was cased with a 5.5 in casing, the minimum wellbore exposure time of the pre-flush considered in the design was 2.5 minutes, each ending with a washer allowing the mud cake to disperse. Centralization was kept high with a standoff greater than 85%. The slurry design considered 14.7 ppg tail and 14.2 ppg lead slurries specifically tailored for the current conditions. Also, mechanical reciprocation of the casing string for about 10 ft-long strokes enabled more effective mud removal. Excellent results were obtained by the cement bond log based on the sonic principle. This log was taken 72 hours after the cementing job showed a 10 mV reduction in amplitude through the entire target zone, resulting in a 90% bonding index.
The challenges related to the cementing complexities were finally overcome with a multidisciplinary team of engineers from both operating and service companies working together diligently. During this process, a low-cost and effective cementing job design was developed through continuous improvement. The design resulted in good repeatability and consistency in the cementing job.