Effect of Stress Build-up around Standalone Screens on the Screen Performance in SAGD Wells

  • Author(s) / Creator(s)
  • Steam Assisted Gravity Drainage (SAGD) is the primary thermal recovery technology currently
    employed to extract heavy oil and high-viscosity bitumen from Alberta oil sands. In the nearwellbore region, the initial stresses are nearly zero, and as the SAGD chamber grows, the stresses
    tend to build up due to the thermal expansion of the formation. Also, melting of the bitumen and
    subsequent loss of the bonding between the grains leads to the collapse of the gap between the
    formation and sand control liner over time. The result will be effective stress buildup and gradual
    compaction of the oil sands around the liner.
    Slotted liners have been extensively used as a sand control device in SAGD wells. Slotted liners
    must allow free flow through the slots with minimal plugging and acceptable amounts of sand
    In our study, large-scale unconsolidated sand was packed over a multi-slot coupon of the slotted
    liner. The sand-pack wassubjected to several stress conditions corresponding to the evolving stress
    conditions during the life cycle of a SAGD producer well. The testing program employed several
    multi-slot coupons to examine the flow performance under typical encountered stresses in SAGD
    wells. Cumulative produced sand was measured at the end of testing as an indicator of the sand
    control performance. The permeability evolution of the sand in the near-coupon zone was
    calculated by measurements of pressure differentials and considered as a measure of screen flow
    performance. Fines/clay concentration along the sand-pack was also quantified after the test to
    investigate the fines migration, a phenomenon which is considered to be the main reason for
    reduced wellbore productivity.
    Experimental results show that the liner performance is significantly affected by the normal stress
    buildup on the liner. Experimental observations indicate sand-pack compaction due to the increase
    of effective stress around the liner leads to a lower porosity and permeability. The situation near
    the liner is further complicated by the fines accumulation that results in pore plugging and further
    permeability reduction. When it comes to sanding, however, higher stresses help stabilize the sand
    bridges behind the slots, leading to less sand production.
    As for the design criteria, the lower and upper bounds of the slot size are governed by plugging
    and sand production, respectively. Considering the stress effect on plugging and sanding, testing
    data indicate that both the lower and upper bounds should be revised to larger slot aperture sizes.

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    Article (Draft / Submitted)
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    Attribution-NonCommercial 4.0 International