Effect of Near Wellbore Effective Stress on the Performance of Slotted Liner Completions in SAGD Operations

Abstract

In SAGD wells, the gap between the oil sand and the sand control liner closes or collapses over time due to such factors as the oil sand thermal expansion, the melting of bitumen and the ensuing loss of the apparent bonding between the grains. The result is the buildup of effective stresses and the gradual compaction of the oil sands around the liner. Current practices for the sand control design do not account for the effect of time-dependent effective stress variation around the liner on the sand control performance. In this paper, we outline the results of an experimental study on the effect of near-liner effective stress on the performance of slotted liners. This study builds on existing experimental procedures and investigates fines migration, sand production and clogging tendency of slotted liner coupons in large-scale unconsolidated sand-packs. Sand-packs with controlled properties (grain size distribution, grain shape, and mineralogy) are packed on a multi-slot sand control coupon in a triaxial cell assembly. Varying levels of stress are applied to the sand-packs in directions parallel and perpendicular to the multi-slot coupon. For each stress level, brine is injected into the sand-pack from the top surface of the sample towards the coupon. Test measurements include pressure drops across the sand-pack and the coupon as well as the produced sand/fines mass for each stress level. Post-mortem analysis is performed to measure fines/clay concentration along the sand-pack as a direct measure of fines migration. Experimental results show that under the subsequent increase in effective stresses, sand-packs experience considerable deformations in directions parallel and perpendicular to the multi-slot coupon; which result in a drastic drop in the porosity and retained permeability. Test results show that the maximum reduction in permeability occurs in the vicinity of the multi-slot coupons due to the fines accumulation and the higher compaction in that region. In comparison to experiments with no confining stress, the application of confining stress results in lower retained permeability in the sand-packs as well as reduced sand production. This paper presents, for the first time, the effect of near wellbore effective stress on clogging tendency and sand retention characteristics of slotted liner completions. The tests allow the assessment of the adequacy of the use of existing design criteria over the life cycle of the well under variable stress conditions around the liner.

CFD-DEM Simulation Of Multi-Particle Arching At Sand Filter Opening

“…They concluded that the higher stresses help stabilize the sand bridges over the slots which result in less sand production. Fattahpour et al [24] also studied the effect of the increasing stress on the performance of the sand filter. They applied varying levels of stress to the sandpacks around the slotted liner in parallel and perpendicular to the multi-slot coupon.…”

Effect of Slot Width and Density on Slotted Liner Performance in SAGD Operations

“…The central phenomena considered in the slotted liner design are the inflow performance and sand control. Considering these two factors, the current design criteria are proposed in terms of slot aperture window in relation to one or more attributes of the formation sand PSD [10][11][12][13][14][15][16][17]. The OFA is another important parameter that can influence the flow performance [18].…”

“…Mechanisms of sanding and plugging in sand control devices have been subjected to many studies over the past decades. Most of the design guidelines proposed earlier are based on one or more parameters of the formation of sand particle distribution [9][10][11][12][13][14][15][16][17][18][19][20][21][23][24][25][26][27][28]. Additionally, slot density which is described by numbers of slots per volume, has been used to investigate the interaction between slots.…”

“…In this study, the effect of stress on sand production has been investigated together with slot width and density, and is incorporated in the design criteria for slotted liners in SAGD operations. In order to do so, a novel sand control testing facility (scaled completion test, SCT) is utilized to study the performance of sand control tools for different stress regimes (triaxial compression/extension) [16,29]. The stress levels correspond to stress 218 variations during the life cycle of a SAGD production well.…”

“…The experimental apparatus used in this study (Scaled Completion Test, SCT) [16,29,30], accommodates the sand-pack sample on top of a sand screen coupon. Compared to conventional SRT set-ups, it has the versatility to use multi-slot liner samples which is an improved design to replicate the actual flow regime and streamlines near the sand control device/slotted liner of a production well.…”