Method for the removal and recovery of the oil component from drill cuttings

A sample of drill cuttings deriving from the use of oil-based mud, was taken from a drilling well, downstream of the coarse material separation by means of shale shaking.

The sample, thus consisting of drilling mud and cuttings of a clay nature, was characterized by an oil content equal to 10.5% and a degree of humidity of 2.8%. 500 g of this sample were charged into a two liter glass flask equipped with a blade stirrer and treated with 500 g of ethyl acetate and stirred for 15 minutes. The suspension was centrifuged at 2,500 revs for two minutes, separating 445 g of solid to be subjected to subsequent washings.

The liquid phase, consisting of ethyl acetate and the oil extracted from the cutting, was distilled in a rotating laboratory evaporator at 90° C., 10,000 Pa, recovering ethyl acetate without hydrocarbons (gas chromatography) in the head fraction, which was used in the subsequent extraction treatment.

The tail fraction, collected in the distiller boiler, consisted of the oil-base used for the preparation of the drilling mud.

The solid residue obtained from the centrifugation was subjected to a further two washing cycles with the ethyl acetate recovered as described above, obtaining at the end of the extraction operations, the following streams:

435 g of dry cuttings, classifiable as non-dangerous waste, according to D.M. 5-2-98, as they contain 600 ppm of residual hydrocarbons and less than 5 ppm of aromatic polycyclic hydrocarbons, or, on the basis of the same characteristics, as reclaimed earth according to the acceptability limits for soil destined for residential/industrial use according to Tuscan Region regulation Nr. 36 of 16-3-93.

51 g of oil without solvent, re-usable for the preparation of fresh drilling mud.

700 g of a sample analogous to that used in example 1, characterized by an oil content of 15% and the same water content, were treated with 700 g of ethyl acetate in a 2 liter flask equipped with a blade stirrer. After 15 minutes of stirring, the suspension was decanted for 30 minutes, the coarse fraction being deposited in the flask and the supernatant, consisting of the extraction solvent, extracted oil and fine clay fraction of the cutting, being sucked up.

The supernatant was subjected to centrifugation at 2,500 revs for 2 minutes, recovering a fine solid fraction and a supernatant which was distilled under the same conditions described in example 1.

The solvent recovered from the distillation was added to the decanted solid in the flask, which was then extracted as in the first cycle.

The separation of the solid and liquid fractions was then repeated as in the first washing cycle, recovering at the end of the operations:

402 g of cuttings containing 680 ppm of total hydrocarbons and less than 5 ppm of aromatic polycyclic hydrocarbons, re-usable according to the Law provisions cited above.

173 g of fine dry clay material, containing 500 ppm of total hydrocarbons and less than 5 ppm of aromatic polycyclic hydrocarbons, classifiable as non-dangerous waste according to the same criteria or usable for the preparation of fresh mud.

105 g of oil without solvent re-usable for the preparation of fresh mud.

700 g of the same sample used in example 2 were treated with 700 g of ethyl acetate under the same conditions. After 30 minutes of sedimentation, the supernatant was sucked up and distilled directly, without effecting the separation of the fine clay material.

The solvent thus recovered was recycled to a second washing of the solid material remaining in the flask; the separation of the fractions was carried out using the same procedure adopted for the first cycle.

At the end of the operations the following products were obtained:

400 g of cuttings, containing 720 ppm of total hydrocarbons and less than 5 ppm of aromatic polycyclic hydrocarbons, re-usable according to the previous criteria.

280 g of oil/clay mixture, re-usable for the formulation of fresh drilling mud.

Considering the fact that in many cases the mud leaves the drilling well at a temperature higher than the environmental value (generally between 40 and 80° C.), an extraction test was carried out operating at 80° C.

For this purpose, the extraction flask was equipped with a water-cooled reflux cooler, in order to condense the solvent vapors.

The operating procedure is identical to that described in example 3, obtaining at the end of the operations:

394 g of cuttings, containing 500 ppm of total hydrocarbons and less than 5 ppm of aromatic polycyclic hydrocarbons, re-usable according to the previous criteria.

283 g of oil/clay mixture, re-usable for the formulation of fresh drilling mud.

The same procedure is adopted as described in example 3, using n-hexane as extraction solvent.

700 grams of the same sample used in example 2 were treated with 700 g of n-hexane at 80° C. in the reflux flask used in example 4. After 30 minutes of sedimentation at room temperature, the supernatant was sucked up and distilled directly, without effecting the separation of the fine clay material.

The solvent thus recovered was recycled to a second washing of the solid material remaining in the flask; the separation of the fractions was carried out using the same procedure adopted for the first cycle.

At the end of the operations the following products were obtained:

402 g of cuttings, containing 742 ppm of total hydrocarbons and less than 5 ppm of aromatic polycyclic hydrocarbons, re-usable according to the previous criteria.

281 g of oil/clay mixture, re-usable for the formulation of fresh drilling mud.