Engineered Solid Package Enables Lifting Cement in the Permian Basin
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
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.