Abstract
Oil-based drilling fluids are essential for challenging drilling operations.
However, their use requires costly handling, treatment and disposal.
Supercritical fluid extraction is herein investigated as a novel technology to
treat this waste. Supercritical fluid extraction employs a substance above its
critical temperature and pressure as a solvent. In this state, the substance
has both liquid- and gas-like properties that can be controlled by the pressure
and temperature of the extraction process.
In this paper, results of studies using supercritical carbon dioxide to remove
the base oil from drilling waste are presented. Current work investigates the
extraction of hydrocarbons (i.e. base oil) from a synthetic oil-based
centrifuge underflow drilling waste. Extraction efficiencies as high as 98%
have been observed. Additionally, results of both past and current studies
indicate that the hydrocarbons are unchanged by the extraction process and that
they may be recovered and potentially reused.
Introduction
In rotary drilling, drilling fluids are essential to lubricate the drill bit
and circulate the drill cuttings to the surface. It is well documented that
oil-based drilling muds (OBMs, sometimes referred to as non-aqueous drilling
fluids or NADFs) have several advantages over their water-based
counterparts(1, 2). OBMs have a higher natural lubricity, making
them suitable for challenging drilling operations. Also, OBMs are less reactive
with clays and shales, thereby preventing hole enlargement, resulting in
smaller overall waste volumes. However, OBMs must be carefully handled and
treated prior to disposal due to their potential negative environmental
effects.
There are a number of options available to treat and dispose of OBM drilling
wastes (for example, land spreading and landfilling), however the cost of
handling and disposing of drilling waste is increasing. The drilling industry
is now turning to novel approaches for the treatment and disposal of drilling
wastes in order to meet more stringent environmental
guidelines(3).
Supercritical fluid extraction (SFE) is an extraction technique that uses
substances at or above their critical pressure and temperature as solvents. In
the vicinity of the critical point, the liquid and vapour phases of the
substance merge, producing a fluid with gas-like diffusivity and viscosity and
liquid-like density(4, 5). These properties provide for favourable
mass transfer of soluble waste components (i.e. hydrocarbons) from solid
matrices to the bulk supercritical fluid. The density of the fluid is defined
by the pressure and temperature; small changes in processing conditions can
fine-tune the solvating power of the fluid(6). Additionally,
supercritical fluids have zero surface tension, thereby allowing easy
penetration into most matrices(4).
Several studies have documented the treatment of OBM drilling waste using SFE.
In 1984, a patent by Eppig et al. detailed a system suitable for the removal of
organic contaminants from inorganic matrices(7). This patent
specifically lists the treatment of oil contaminated drill cuttings as an
application of the technology, and indicates that propane, Freon and carbon
dioxide would be suitable supercritical fluids for this purpose.
A later study by Eldridge investigated the use of a pilot-scale SFE system to
treat oil contaminated drill cuttings from North Sea drilling
platforms(8).
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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History
- Original manuscript received:
31 March 2006
- Meeting paper published:
13 June 2006
- Revised manuscript received:
2 March 2009
- Manuscript approved:
4 May 2009
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