Sand Control 175
for the slot width, whilst a less aggressive suggestion much used in the Gulf of
Mexico is 1 D10. Markestad et al. (1996) concluded from experimental evidence
that 2 D10 generally produces sand, whilst 1 D10 may or may not. Markestad
concluded that D10 was not a reliable measure on its own of sand retention in a
screen and a further parameter based on the sorting of the sand was required. These
screen size selection rules may be appropriate where very limited particle size data is
available, but under-sizing risks plugging and over-sizing risks sand production,
screen erosion and failure. Physical testing is preferred.
Figure 3.33 shows a typical test set-up for testing plugging and sand retention
potential.
A polymer is used to suspend a representative sample of the formation sand. It is
required to ensure that the heavier particles do not settle out before reaching the
screen. Heavier particles are key to effective bridging. The suspended solids flow
down to a circular sample of screen. The pressure drop versus the weight of the sand
reaching the screens is measured as are periodic measurements of the weight of
solids being transported through the screen.
The tests should be performed with representative samples of the ‘worst’
(highest uniformity) sand across a range of screen types and sizes. This may require
substantial amounts of core. It is not usually possible to reuse slurries either from
particle size analysis or from previous slurry tests – fine particles in particular are
lost, but pieces of core from failure studies will suffice. Screen selection is then based
Water for dilution
Screen
sample
‘Dead’ space
before screen Sand slurry
(viscosified)
Differential Positive
transducer displacement pump
(computer logged) (computer controlled)
Water
Trap
Piston chamber
Figure 3.33 Screen test set-up. Source: After Ballard (1999), Copyright, Society of Petroleum
Engineers.
