This report covers the November 15 to February 15, 2001 period and summarizes our current IPEC studies. Table 1 correlates the washing results for the low surfactant concentration of 0.1 wt % to the oil-bath interfacial tensions before and after washing. The electrolyte (NaCl), builder (Na2SiO3), and sub-CMC [surfactant] remove the oil from the cuttings as a free phase oil layer that is free of solids. This free phase oil layer is skimmed from the bath separating the oil from the cuttings and bath. For good oil removal, the bath-oil interfacial tension must remain low throughout the washing process. The builder sequesters Ca++ from the cuttings, and thus prevents loss of surfactant to cuttings while the electrolyte and surfactant give ultra-low oil-bath interfacial tensions throughout the washing process and thereby enhance the roll-up mechanism.
Table 1: Percent of oil removed from drill cuttings using roll-up and appropriate builder Na2SiO3.
| Quantity of NaCl
and Na2SiO3 | Bath-Oil Interfacial
Tension before wash. (dynes/cm) | Bath-Oil Interfacial
Tension after wash. (dynes/cm) | % by weight of oil
content in cuttings after wash |
|---|---|---|---|
| 6.0 % NaCl | 7x10-3+-0.002 | 0.18 | 8.3%+-0.3 |
| 6.2% Na2SiO3 | 0.15 | 2.4 | 8.1%+-0.3 |
| 13.0% Na2SiO3 | 5.0x10-3+-0.002 | 0.019+-0.005 | 4.1%+-0.3 |
| 8.0% Na2SiO3 +
2.5% NaCl | 9.0x10-3+-0.002 | 8.0x10-3+-0.002 | 3.2%+-0.5 |
Solubilization reduces the oil content of the cuttings to a value that is an order of magnitude lower than the builder-enhanced roll-up mechanism. For initial oil contents of 20 wt %, the builder-enhanced roll-up reduces the oil content of the cuttings to 3.2 wt % oil while water only (absence of surfactant) reduces oil content to 14%, thereby demonstrating the improvement of using a small amount of surfactant over water alone.