Experimental Investigation on Sand Production during Non-Diagenetic
Hydrate-Bearing Sediments Depressurization Production in Vertical Well
with Crustal Stress
Abstract
Sand production is the process in which formation sand and gravel would
migrate into the wellbore by the flow of reservoir fluids. This is a
problem that endangers the safety of hydrate exploitation. The aim of
this study is to understand sand production in during hydrate
exploitation. A novel experimental apparatus was constructed to examine
sand production in the hydrate-bearing sediments by applying the
depressurization method. The maximum pressure of apparatus is 30 MPa,
the temperature could be controlled from -253.15 to 313.15 K. The pore
pressure, crustal stress, production pressure, gas flow rate, water
production volume and subsidence rates could be measured. The vertical
wellbore comprised liner 1 (ø32 mm × 135 mm, 3 mm holes, arrangement:
36°, holes row gap: 10 mm) and liner 3 (ø24 mm × 135 mm, 2.5 mm holes,
arrangement: 36°, hole row gap: 10 mm) with a sand screen. Besides gas
in from top, the sediment chamber (ø158 mm × 120 mm) had a middle mesh
screen that allowed gas and water enter or vacuumize the chamber
circumferentially around the sediments (ø158 mm × 100 mm). Sand
production situation was recorded by HD camera through the visual window
on the gas-solid-liquid separator. Hydrate production was divided into
three periods: water, gas with water drops, and gas. We found fine sand
production in the first period and sand grains production in the second.
The sand production behaviours through the different gas production
rates in two production method - depletion gas production curve and
stable gas production curve were discussed. The grain sizes of sand
production were increasing in the production period with hydrate
saturation decreasing. The temperature related characteristics of the
hydrate layers differed during different stages of hydrate production.
The unique sputtering occurring owing to the decomposition of the
hydrate might have provided the driving force for sand migration, and
water gas bubbles or gaseous water drops from the decomposed hydrate
might have enhanced sand carrying capacity. The subsidence of
hydrate-bearing sediments was influenced by sand production, whereas the
maintenance of crustal stress possibly influenced the rate and magnitude
of subsidence. The stimulation at late production in low hydrate
saturation might conduct the subsidence and sand production increased
dramatically.