Investigation of sand consolidation using steam for the Tar Zone, Wilmington field, California

Abstract

An experimental study was carried out to better understand and optimize the process of sand consolidation using high-pH steam in wells of the Wilmington field, California. The apparatus consisted of a vertical 18 in. long aluminum cylindrical cell with an ID of 1.5 in. into which loose sand of the Wilmington Tar Zone was tamped. The top half of the cell was thermally insulated while the bottom half was cooled by means of a cooling jacket. Steam was injected at the top of the cell and fluids produced at the bottom of the cell. Steam at 250-260 degrees C and 700-800 psig was injected at rates of 5 cc/min and 20 cc/min. Steam with pH of 7 and 12 were used, the latter obtained by addition of sodium carbonate. Temperatures along the cell axis, and inlet and outlet pressures were measured. The cell contents were removed after each experiment and analyzed to determine if sand consolidation occurred. Thin sections of samples before and after the steam treatment were analyzed using an electron microphone to determine any change in texture and composition of the sand. Xray diffraction analysis was performed to determine the crystallographic characteristics of the "cement'' binding the sand grains where consolidation had occurred. Results showed sand consolidation did not occur for steam with pH of 7. However, for steam of pH 12, the sand was consolidated particularly at the top part of the cell in only hours instead of weeks as reported in the Wilmington field. Analysis showed both needle-like and equant crystals of sodium-aluminum-carbonate-silicates being formed between the consolidated sand grains. Contrary to the previous postulate that precipitation of dissolved quartz or feldspar "cement'' the sand grains, the results indicate that the mechanism of sand consolidation is probably more complex. Further research is planned to fully understand and optimize the technology.