Flocculation and settling properties of discharged drilling waste

Niu, Haibo (2003) Flocculation and settling properties of discharged drilling waste. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (4MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

In order to determine the potential environmental effects of offshore discharges of synthetic based drilling fluids (SBFs) and associated drilling cuttings, it is necessary to understand the physical transport mechanisms of SBFs associated with drilling discharges in the marine environment. The purpose of this work was to study the flocculation and settling properties of SBFs associated with drilling cuttings in both freshwater and seawater and provide more appropriate equations for existing transport models. -- A digital imaging system was employed in this research to study the flocculation and settling processes. The effects of particle shape and size on the settling mechanism and the effects of salinity, fluid shear, discharge concentration and oily components on the rate of flocculation and the settling speeds of floes were studied. -- The cutting sample for this study was collected from an exploration oil well in the east coast of Canada. The settling velocities of coarse particles from both untreated and thermally treated cuttings were measured in a 2.5m high and 14cm inner diameter Plexiglas settling column using both freshwater and seawater. The flocculation of fine grain particles was performed using a laboratory paddle stirrer in both freshwater and seawater. The applied shears ranged from 25 to 200 s⁻¹, and the concentrations ranged from 25 to 200mg/L. In order to study the effects of oily components on flocculation, a thermally treated sample was also used. From the experimental results it was shown that the untreated cuttings tend to clump together and settle fast while the treated cuttings settle as individual particles with relatively low speeds. The settling velocities of treated and untreated coarse particles were found to be functions of both particle sphericity and diameter following a power law. It was demonstrated by the flocculation tests that the steady state median floc size decreases as the shear stress and concentration increase, and the particles flocculate faster in seawater than in freshwater. For the same diameter and salinity, the flocs formed at high fluid shears have a higher settling velocity than do flocs formed at low shears. It was also shown that the flocs formed by untreated cuttings settle faster than flocs formed by thermally treated cuttings in the same conditions (shear rate and concentration) under which the flocs were produced.

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