Drilling cuttings are waste products from the oil drilling industry. They consist of oil, water and mineral substances of various compositions. The consistency thereof may vary from liquid to a pasty concentrate.

At present the only possibility for the oil producers on the Norwegian continental shelf to get rid of such a waste product is to send it to Denmark for destruction, something which, however, is expected soon to be forbidden. Thus, searches are made in order to utilize said waste product or to have it destroyed in some other way.

The present invention provides a method wherein the drilling cuttings are utilized in an advantageous way in the preparation of products comprising different fractions of stone and mineral filler to be dried and heated. The drilling cuttings are used as part of the filler material, said drilling cuttings first being purified and subsequently processed in order that the mineral substance contained in the drilling cuttings has a satisfactory grain size for the purpose. The oil contained in the drilling cuttings wholly or partly provides the fuel for heating and drying the stone materials.

Before the drilling cuttings can be used in the process of the invention it has to, as mentioned above, be purified and processed in order that the mineral substance contained therein will have a grain size that fulfils the requirements for filler (mineral substance) in the relevant production. Free water is eliminated from the drilling cuttings. . To the drilling cuttings is then added diesel oil or

_ another fuel oil according to nedd in order that the viscosity

/

¹ will be low enough for the mixture to be reasonably pumpable at normal temperatures. Thus, the amount of oil to be added will depend on the viscosity of the drilling cuttings as supplied from the oil drilling field and, naturally, will also

be temperature dependent.

The processed drilling cuttings are used as fuel for the oil burner in drying drums or similar production equipment. The mixture is used either as a fuel per se, enriched through the admixing of fuel oil/diesel oil according to need in order to obtain the required heating value, or as a supplementary fuel that is sprayed through a separate nozzle into the flame from the ordinary burner nozzle. The amount of oil that is added depends on which one of said two methods is selected, and is adapted to the requirement for the heating value of the fuel according to the drying and heating process which shall take place, as well as the volume capacity of the plant. The man skilled in the relevant production art will easily be able to find out which blending ratios that are favourable under specific conditions and can set the controls of the plant in accordance herewith. The choice of temperature level will then automatically determine the amount of fuel mixture required.

The mineral substance that iε released from the drilling cuttings mixture when the oil burns and the water evaporates will constitute part of the filler to be contained in the product.

By "filler" is meant a small grained mineral substance having a grain size < 0,075 mm. Filler, per se, is a commercial product and is used as an additive in various products such as asphalt, cement, etc. The amount of filler added for instance to asphalt, depends on the type of main material and the amount of filler substance present in the gravel material itself. Generally, the amount of filler varies by between 1 and 10 per cent of the total weight of the finished composition.

Stone materials are dried in a drying drum by heating with fuel oil fed through an oil burner. By adding some of the filler material to the fuel substance (fuel oil) one may then utilize the fine matter as well as the oil in drilling cuttings.

In the following are presented some examples of embodiments of the invention.

Example l: Burning test

Drilling cuttings which, by weight, consisted of about 1/3 mineral substance, about 1/3 diesel oil and about 1/3 water was purified of coarse particles, processed, stirred, passed through a fine mesh filter (abount 1mm mesh width) and admixed with further about 33 per cent diesel oil so that the total oil content was about 50 per cent by weight. The mixture was charged into a steel pressure container. The container was pumped up to an overpressure of about 6 bars through a valve.

A burner pipe having an opening of 3 mm was welded to the bottom of the pressure container. No nozzle was mounted into the burner opening, however a valve had been fit onto the burner pipe. When the valve was opened, the drilling cuttings mixture waε forced out through the burner pipe as a "thick" stream. Without a nozzle the spreading and atomizing of the mixture was minor, however, with a propane flame the stream could easily be ignited and burnt with a steady flame as long as the propane flame was maintained.

During the test, the oil in the mixture waε combuεted completely. Mineral substances and water vapour were released directly into the air. In a production plant this process will take place within the drying drum; and filler, dust and water vapour will be retained in the mixture and the filter.

The experiment shows that drilling cuttings is usable as a fuel substance in a drying drum for drying stone materials, whereby the mineral filler can be integrated into the final product.

Example 2: Experiments in asphalt plants

A. Drilling cuttings used as an independent fuel.

B. Drilling cuttings used as a supplementary fuel. In all cases satisfactory resultε were obtained.