Abstract

Silica micro-encapsulation is a new technology that has significant economic and environmental value, since it allows disposal of oil- and/or hydrocarbon-contaminated drill cuttings, either onshore or offshore, in an environmentally safe manner.

Silica micro-encapsulation is a process by which the oil attached to the drillcuttings is physically encapsulated within an insoluble matrix of amorphoussilica. The process consists of two stages:

  1. Application of an emulsifier, in an acidic environment, to the hydrocarbon-or oil-contaminated drill cuttings. This emulsifies the oil into microscopic droplets (less than 10 microns).

  2. Application of reactive alkaline silicate to the emulsified oil. An instantaneous acid-base reaction occurs between the reactive silicate and the acid, producing a solid amorphous silica shell that surrounds and traps the micron-size oil droplets.

Specific emulsifiers are selected to cover hydrophilic-lipophilic balance (HLB)requirements for a broad range of oils, including synthetics, mineral oil, diesel, crude oil and bitumen.

Laboratory and pilot tests using silica micro-encapsulation technology for treatment of cuttings contaminated with oil or hydrocarbon show:

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    The end product is a system of microscopic oil droplets encapsulated with precipitated amorphous silica. Scanning electronic microscopy (SEM) verifies that the external surface is composed primarily of silica.

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    The droplet size of emulsified oil-in-water, measured by light scattering, is less than 10 microns. After processing, the particle size of silica-encapsulated oil ranges from 10 to 30 microns.

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    Determination of free oil on the treated cuttings via liquid-liquid extraction followed by gas chromatography/mass spectroscopy techniques indicates over 99.9% efficiency of the encapsulation of the treated cuttings in a large-scale mixer.

Results indicate that silica micro-encapsulation eliminates or minimizes the environmental impact for discharge of cuttings in onshore and offshore drilling operations. This novel technology satisfies the new environmental regulations that are under consideration at this time.

Introduction

Offshore and onshore disposal of synthetic and oil mud generated cuttings is prohibited in some areas of the world. As a result, the drilling industry has moved to second generation synthetic-base muds (SBMs). However, in some areas such as the North Sea, governmental authorities continue to change the legislation to the point that now they have under consideration the maximum allowable discharge of less than 1 % oil. This governmental movement is the consequence of the environmental impact of oil-wet drill cutting accumulations on the ocean floor ecosystem, even with the SBMs that pass all required environmental tests.

There have been various chemicals processes applied to convert these cuttings to an acceptable form so that the associated SBM or oil-base mud does not causea problem. However, the majority of those processes have logistic and technical limitations.

Silica micro-encapsulation is an onsite process in which oil is removed fromthe cuttings in microscopic droplets and then encapsulated within an inert material.

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