Experimental investigation of sand consolidation using high-temperature alkaline solution

Abstract

An experimental study was conducted to better understand the sand consolidation process under high-temperature alkaline solution. Wilmington Tar sand samples were successfully consolidated in the laboratory using high-temperature (250-260⁰C) solution of sodium carbonate (pH 11-12). The sample was placed in a vertical 18 in. long aluminum cylindrical cell with an ID of 1.5 in.. The top half of the cell was thermally insulated while the bottom half was cooled. Hot alkaline solution was injected at 20 ml/min for 3-4 hours at the top of the cell and liquid produced at the bottom of the cell. After each experiment, the cell contents were removed and analyzed to determine if sand consolidation occurred. Both aggregates of sand grains and sectioned and polished epoxy-mounted sand grains were examined and analyzed using an electron microprobe to determine any change in shape, size, or composition of the sand pack and precipitation and growth of secondary phases. To better understand the process, experiments were subsequently conducted using samples of pure quartz, pure feldspar, and a 50:50 (by weight) mixture of quartz and feldspar. In each case, both varied 20-40 mesh and 50-250 mesh grain size samples were used. For the 20-40 mesh cases, zeolites and a mixture of amorphous silica and sodium carbonate were deposited on grain surfaces but were insufficient to cause overall sand consolidation. However, when a finer, poorly sorted (50-250 mesh) 50:50 mixture of feldspar and quartz was used, sand consolidation was obtained in 2.5 hours. At the top, hotter part of the cell, equant and acicular zeolite crystals (sodium aluminum silicates) weakly bound the sand grains. At the bottom and cooler part of the cell, the sand grains were strongly bound by a mixture of amorphous silica and sodium carbonate. Results to-date indicate that both zeolite and silica may be cementing agents, the grain-bonding strength depending on the grain surface area. This investigation is part of an ongoing research. The temperature, injection rate, and pH of the alkaline solution, treating time and "soaking period" are considered important process parameters that need to be further investigated.