Surfactant-Enhanced Treatment of Oil-Contaminated Soils and Oil-Based Drill Cuttings

Description:

Third Quarterly Progress Report:

This report covers the June 15, 2001 to September 15, 2001 period and summarizes our current IPEC studies. A Coulter LS230 was used to find the size distribution of washed Baroid drill cuttings that passed a 20 mesh screen. The Coulter LS230 uses laser light scattering with a wavelength of 750 nm to size particles with diameters from 0.4 mm to 2000 mm by light diffraction. The collimated laser beam propagates through a sample cell where 20 mesh washed Baroid drill cuttings suspended in water scatter the incident light in characteristic patterns that depend on their sizes. The scattered light intensity is plotted as a function of scattering angle, and this plot is termed a diffraction pattern. This diffraction pattern is measured by 126 detectors at varying scattering angles. The particle size distribution is computed from the diffraction pattern based on the Fraunhofer model of particle light scattering.

Figure 1, showing oil content of Baroid drill cuttings for water-only, 2-component surfactant formulation, and 3-component surfactant formulation for a 30 minute contact time and 150 shakes per minute, should be compared to Figure 2, showing the average particle size of the washed drill cuttings for water-only, the 2-component surfactant formulation, and the 3-component surfactant formulation as a function of contact time at 150 shakes per minute. From Figure 1, the optimal washing formulation was the 3-component formulation of builder, alfoterra, and sulfobetaine (1.7% residual oil after wash). This optimal washing formulation produced the smallest average particle size (3 mm for 30 minute contact time) as shown in Figure 2. It is hypothesized that the "cleaner" cuttings are also smaller because agglomerates of clay particle and oil are broken apart most effectively by the optimal surfactant formulation, thereby liberating the most oil.

Figure 3 shows the percentage of washed cuttings passing a 20 mesh screen as a function of contact time for the most optimal 3-component formulation. A table shaker frequency of 150 shakes per minute was used in these experiments. For a 15 minute contact time, which is sufficient to produce a residual oil content of 1.7%, 10 % of the washed cuttings are smaller than 20 mesh. A contact time of 480 minutes results in no further reduction of Baroid cuttings' oil content. However a 480 minute contact time increases the percent of cuttings smaller than 20 mesh to 50%. Therefore, in the field demonstration, the bath-cuttings contact time would be minimized to decrease the fines accumulation while maximizing oil detachment from the cuttings.

Figure 1. Residual Oil content of oil-based Baroid drill cuttings after washing with one, two, and three component combinations of 13.5 % builder, 0.1 % alfoterra, and 2 % sulfobetaine.

Figure 2. Particle size distribution of washed Baroid cuttings 20 mesh and smaller for water-only, two-component formulation of 0.1 % alfoterra and 13.5% builder, and 3-component formulation of 0.1 % alfoterra, 13.5% builder, and 2 % sulfobetaine.

Figure 3. Percent of washed soil particles sized 20 mesh and under as function of contact time using table shaker at 150 shakes per minute.