Schlumberger

Technical Paper: Engineered Solid Package Enables Lifting Cement in the Permian Basin

Society: AADE
Paper Number: 14-FTC-54
Presentation Date: 2014
 

Abstract

Cementing in the Permian basin has been historically challenging due primarily to highly depleted zones and naturally fractured formations. The problems associated with lost circulation (LC) are well known in drilling and cementing but low cement tops are especially critical due to the exposure of the casing to highly corrosive zones, besides regulatory compliance. Failing to cover such corrosive zones has proven to be expensive to the operators in terms of remediation, lost production and potential liabilities. 

It is not uncommon in the Permian Basin to drill and cement wells without mud returns; the Permian lithograph (Chart-1) shows the Upper and Lower Spraberry formations, one of the main thief zones. The average and maximum fracture widths for the Upper and Lower Spraberry formations are shown in (Charts 2 and 3) with 1.35 mm as the largest fracture width for both formations. The upper Spraberry formation is located just below the San Andres formation which needs to be isolated for local regulatory compliance due to its corrosive nature. Lifting cement over the Upper Spraberry formation proved to be quite challenging. 

To cement across depleted and corrosive formations it is common to pump specifically designed pills loaded with LCM ahead of the cement slurries which exhibit high viscosities, making difficult to displace them to the thief zone without channeling through. 

Due to limitations in the surface equipment volume, LCM pills tend to be smaller than what is needed to fully cure the losses leading to scattered results and ultimately to discontinue its use. The effectiveness of the LCM is further reduced by the contamination suffered at the interfaces with other fluids. 

The considerations above presented lead to an engineered combination of a placement technique and specifically shaped and sized materials added to cement slurries, that when used in a specific sequence has made possible to lift cement in the Permian basin to the designed targets. The performance of the new solid package has been validated through lab testing, with differential pressures up to 1000psi, and cement bond logs. Other logging tools such as distributed temperature sensing (fiber optics) has been complementary in the identification of thief zones for further job optimization. 

The unprecedented results obtained with the new solid/fiber package has made possible lifting cement to the depths specified by regulatory entities, besides providing long term zonal isolation and long term casing protection across the corrosive formations in the Permian basin.

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