Previous laboratory study has demonstrated that adequate sand control can be obtained even though the gravel is much larger than 5-6 times the formation grain size conventionally used as a sizing criteria. In a formation of interest, the −16+20 Ottawa sand was shown to be effective in preventing the production of a formation sand in spite of a 16:1 ratio of gravel to mean sand grain size as determined by sieve analysis. Mechanism studies indicate that the formation sands were clusterized by illite/smectite mixed-layer cementing bonds, and were subsequently mobilized as agglomerates rather than individual sand grains. The critical size parameter for the formation appears to be the mean diameter of the agglomerates and not that of the sand grains. The use of larger gravels, which provides much higher well productivity due to increased permeability, remains consistent with the Saucier's rule.

The long-termed stability of sand control using −16 + 20 Ottawa sand is evaluated in this continuation study. Experiments were performed in flow cells using carcass material and core plugs from a friable sandstone reservoir. Impacts of physical forces such as intermittent pressure surges and long-duration two-phase flow on sand control are investigated. The effects of chemical treatments using common oilfield chemicals, completion brines, and acidizing with HCl, HF, or HBF4 acids are also included.

The results show no deterioration in sand control ability of −16+20 Ottawa sand when subjected to intermittent pressure surges, nor degradation with time during long-duration two-phase flow. The use of diesel, IPA, common completion brines, and seawater has no effect on the sand control. However, exposure to fresh water and acidizing using HF acid resulted in loss of sand control. Permeabilities of the core plugs also became significantly decreased after these treatments. These observations can be explained by the breaking of mixed-layer clay cements due to swelling/dispersing by fresh water or dissolution by the HF acid.

Treatments with HBF4 or HCl acids did not affect the sand control ability of −16+20 Ottawa sand, although some permeability impairments to the core plugs or gravel packs were observed during two-phase flow after HBF4 treatment. Acid treatment with HCl increased the permeability of formation sand significantly, however, the permeability gain diminished somewhat during the onset of two-phase flow.

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