Lost circulation is one of the main causes of nonproductive time during
drilling and impacts the success of cementing operations. Losses into the
reservoir not only impact drilling, they potentially impact the reservoir, due
to influx of quantities of drilling fluids that are potentially damaging, or
will influence the production rate. Existing solutions are mainly based on
particulates, which are often added to drilling fluids to plug fractures or
build up filtercake to cure losses. When applied for curing losses in reservoir
sections, it is desirable that the plugging materials maintain stability for
sufficient time to allow well completion but eventually self-degrade to leave
undamaged formation for hydrocarbon production. The main challenges are the
design of the lost-circulation material to cure losses into fractures of
various widths, and to provide plug stability and cleanup within a desired time
frame over a broad bottomhole temperature range.
Fibers have shown good fracture-plugging behavior. Parameters affecting
fiber performance include, but are not limited to, fluid viscosity fiber
concentration, fiber geometry, flow rate, effect of the wall, and fracture
width. To effectively apply fibers as lost-circulation applications, a novel,
fiber-laden fluid was designed for easy preparation on on surface, allowing
compatibility with bottomhole assemblies (BHAs). The decrease velocity inside
the fracture enables fibers to bridge and then plug the fracture, thus
regaining circulation. The fibers are specially designed to degrade in an
adjustable time frame sufficient to ensure plug stability until the well is
completed. With time, the plug undergoes further degradation, leading to
nondamaged formation for production.
This novel degradable solution has been successfully proven during field
trials in various drilling scenarios ranging from severe to total losses with
effective and efficient loss mitigation, without issues on placement through
BHA and bit nozzles, and mitigating further reservoir damage.
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