Summary
The handling of drill cuttings and other wastes generated by drilling
operations is both an environmental and economic issue. With ever-tightening
environmental regulations and the green operation initiatives of operators,
drill cuttings reinjection (CRI) into subsurface geology is often the preferred
option, allowing operators to achieve zero discharge because oily cuttings are
returned to their place of origin.
When the technology was introduced about a decade ago, injection into a
single well had a maximum slurry volume of approximately 30,000 bbl. Now,
particularly in very large projects, several million barrels of slurry can be
injected into a single well. This represents more than 1,000 times the volume
of a typical hydraulic fracturing job, or more than 100 times that of earlier
cuttings reinjections. In some cases, the success of the CRI operation is
critical, either because there are no backup options or because the economic
and environmental impacts are too significant.
This paper describes the challenges faced in CRI projects, along with recent
advances and experience gained in tackling these challenges through modeling,
cuttings slurry and operational procedure design, monitoring, and verification.
For example, much progress has been made recently in slurry rheology design and
operational procedure selection such as suspension and displacement to avoid
loss of injectivity and to maximize disposal capacity and minimize health,
safety, and environment (HSE) issues.
The authors will also present a risk-based approach that integrates
deterministic software and tools, available data, knowledge, and experience,
for modeling of geological and operational uncertainties and potential risks to
increase quality assurance. Case examples will be presented to illustrate the
value of this integrated approach. Best-practice guidelines and recommendations
will be provided for data collection, design and engineering, operation, and
monitoring.
Introduction
Oil and gas E&P companies are responsible for recycling, storing, or
disposing of drilling wastes in a safe and environmentally acceptable fashion
that complies with regulatory requirements. Tightening environmental
legislation worldwide and operators’ environmental policies are reducing
options for disposal or are increasing discharge costs to the extent that
discharging of drilling wastes may not be a future option. Injecting drilling
and other associated E&P wastes through hydraulic fracturing has been
successful and has led to the adoption of the technique as a routine disposal
method.
CRI operations started in the late 1980s with small volumes of
drill-cuttings slurry using either tubular or annular injections (Abou-Sayed et
al. 1989; Malachosky et al. 1993; Minton and Secoy 1993; Sirevag and Bale 1993;
Moschovidis et al. 1994; Willson et al. 1993; Louviere and Reddoch 1993).
However, as more experience was gained through these smaller-volume waste
disposal operations, the scale of drill-cuttings injection operations increased
dramatically (Schmidt et al. 1999; Baker et al. 1999; Guo et al. 2003). For
example, in terms of disposal volumes, by 2002 CRI operations had increased
from thousands of barrels of slurry per well to millions of barrels per well
(Guo et al. 2003). CRI operations moved from onshore to offshore fixed
platforms to deepwater mobile offshore drilling modules (Abou-Sayed and Guo
2002; Minton and Secoy 1993; Saasen et al. 1998; Saasen et al. 2001). It has
been operated worldwide within a wide range of different environments.
A drill-cuttings injection operation involves the collection and
transportation of waste from solids-control equipment on the rig to a
slurrification unit, where the cuttings are ground (if necessary) to small
particles in the presence of water to form a slurry. The slurry is then
transferred to a holding tank for final rheological conditioning. The
conditioned drill cuttings slurry is pumped through a casing annulus or tubing
into subsurface fractures created by injecting the slurry under high pressure
into the disposal formation. The waste slurry is often injected intermittently
in batches into the disposal horizon, followed by a period of injector shut-in.
Each batch injection may last from less than an hour to several days or even
longer, depending upon the batch volume and the injection rate.
© 2007. Society of Petroleum Engineers
View full textPDF
(
2,030 KB
)
History
- Original manuscript received:
3 November 2004
- Revised manuscript received:
30 November 2006
- Manuscript approved:
27 January 2007
- Version of record:
20 June 2007
View Cart
