Journal of Canadian Petroleum Technology
Volume 48,
Number 8,
August 2009,
37-41
Abstract
Shale formations are used to serve as hydraulic and thermal barriers in steam
stimulated processes such as steam-assisted gravity drainage (SAGD) and cyclic
steam stimulation (CSS). They are potentially subjected to swelling and
softening when they are exposed to fresh water. A conventional swell test on
clay shale is very slow and it can take months or years. In this study, an
accelerated swell test is proposed, which applies an electrical potential
gradient through the specimen. The applied external electrical field
accelerates the ionic flows and subsequently speeds up the swelling process.
Experimental results of this study on reconstituted bentonite specimens
saturated with sodium chloride solution have proved the proposed idea. Possible
electrochemical reactions and their influence on the experimental set up have
been discussed. A mathematical model based on coupling the flow equations in
micro and macro levels has been developed to quantify this process.
Introduction
Multi-component mass transport under electrical, chemical and hydraulic
gradients is gaining increasing attention and interest in different fields of
engineering. Acar and Alshawabkeh(1-3) applied an electrical field
through soils to extract contaminant ions from the soil. Roy and
Cooper(4) and Cooper and Roy(5) proposed the application
of an electrical field to prevent the bit balling during the drilling process.
In this study, the electrical field is applied to accelerate the swell test in
shale specimens.
Shale formations are used to serve as an hydraulic and/or thermal barrier in
oil production. The high tendency of shale to absorb fresh water and its high
swelling potential may cause problems, such as drilling bit
balling(6) or wellbore instability(7). Fresh water can
access shale formations in different ways from different sources. Practical
examples include: the use of steam and water in the oil recovery processes and
the use of water-based drilling mud in borehole drilling. Control of swelling
is critical in these practical applications, and thus, characterizing the
swelling behaviour in shale formations is of great importance in these
engineering activities. However, a conventional swell test on shale is very
slow and it can take months or years(8). Thus, an accelerated swell
test could be very helpful to overcome this problem in cost and time
savings.
Ion extraction from macro voids in shale and the subsequent induced
concentration gradients along the macro voids and inter-particle micro channels
are the main sources of swelling in shale. However, due to the low permeability
of shale, the ion transport through the bulk fluid of this material is a time
consuming process(8). Consequently, the fluid flow towards the
inter-particle micro channels has a very low rate. If the ion extraction from
the bulk fluid is accelerated, the fluid flow towards the micro channels will
occur faster and the specimen swells more quickly.
In this study, an electrical potential gradient is applied to accelerate the
ion removal from shale which finally leads to a quick swell test. Experimental
results on reconstituted pure bentonite specimens saturated with NaCl solution
proved this idea.
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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History
- Original manuscript received:
24 June 2008
- Meeting paper published:
17 June 2008
- Revised manuscript received:
22 April 2009
- Manuscript approved:
2 July 2009
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