Working
withshales:
asticky
situation
PhilipWatson, Michael Skriba
and StephenWAlmond,
MWV Specialty Chemicals, USA,
explore the importance of using
correctly formulated drilling fluids
whenworking in shalewells.
S
haleshavehistoricallypresentedchallengestotheoiland
gas industryduringthedrilling,completion,stimulation
andproductionphases of awell’s life. Themajorityof
these challengeshavebeen causedby the interactionof the
fluids usedduring thesephaseswith the shales themselves.
For example, the interactionof an improperly formulated
water‑baseddrilling fluidwith reactive shale can lead to
problemswithborehole stability, drilling fluidproperties
and formationdamage. Figure1 shows theeffect of an
improperly formulatedwater‑based fluidwhen itmeets
reactive shale, leading todisaggregationof the shale
sample. Inextreme cases, fluid/shale incompatibilities
have resulted in the loss of thewell throughborehole
collapseduringdrillingor caused severe losses inwell
productivityafter stimulation. Therefore, water‑based
fluid formulationswhich contact shale formationsmust be
formulated to reduceormitigate incompatibilities.
Tounderstand shale/fluid incompatibilities, it is
important tounderstand themineralogical composition
of the shale. A typical shale is composedof clayminerals
andquartz grains, and the colour is normallygrey. The
inclusionof otherminor constituents alters the colour
of the rock; for example, black shale results from the
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