Inflow and Production
Impairments from Loss of Solution Gas
in Cold Production
by Dr. Franklin Foster, 2006
[note: this article made possible by support and funding
from the Petroleum Society of CIM, Lloydminster Section]
Cold production (the producing of oil bearing sand to the surface using
progressing cavity pumps) has become an important and successful technique
in heavy oil fields. The process has several positive
characteristics. Among these are that sand production creates so
called “wormholes”. These are long channels that develop when less
dense sand flows toward the well while more dense sand remains in
formation. Since these channels can extend far from the well bore
they provide greatly enhanced access to the pay zone. As well, since
wormholes create increased permeability, they greatly enhance oil
production, at least in the short term.
Among the factors that drive the cold production process are the gases in
solution in the crude oil. As the well is produced, an area of lower
pressure is created and the gas in solution literally drives the oil
toward the well bore, again, at least in the short term. What
happens, that eventually creates problems, is that the tendency of the
most gasified oils to “rush toward production” means that increasingly
denser and denser, and therefore more viscous material is left behind.
Gases also come out of solution, leaving dense “dead oil” behind. As well,
the long, rambling wormholes undermine the integrity and homogeneity of
the reservoir. The flow toward the well bore can drag debris and
other blocking material to the well. In short, while producing the
more mobile portions of the reservoir, the less mobile substance become
less and less mobile. This situation leads eventually to sharp drops
in the production levels of wells. It is, therefore, one of the
current research areas to attempt to better understand cold production
processes and develop appropriate remediation processes to deal with
Blocking debris can consist of introduced materials such as drilling mud
or cement; or reservoir materials such as shale,
pyrite or chert which has been able to migrate due to the removed sand.
Some of these problems can be remedied using traditional workover
procedures while others will need new approaches.
The unbalanced reservoir also allows migration of waters and gases which
can also compromise oil production. As solution gases continue to be
lost, either through production, or through changes in the reservoir, the
remaining oil becomes more and more viscous or “dead”, lacking the means
to contribute to its production.
Faced with a cold production well that has experienced a dramatic drop off
of oil production, the first step is to properly diagnose the problem.
Is it the result of blockages of debris, or have insolution gases been
exhausted to the point of leaving only highly viscous dead oil? The
latter case may respond to treatment by heat or chemicals or both.
Of course, since crude oil is a complex chemical mixture, the choice of
remedial chemicals must be done with care. Once the chemicals are
chosen, they are often pulsed into the well (a technique somewhat
analogous to using a plunger to unclog a drain) and left to “work” for a
period of days. Following this period, the well may be swabbed or
bailed to remove debris as well.
Various case studies have been performed on wells with severe inflow
Research Council is doing leading edge research in this area by
providing diagnostic fluid sample analysis to measure emulsion, density,
and viscosity characteristics.
In conclusion, it can be seen that the loss of insolution gasses
compromises the key drive mechanism in cold production. Perhaps, the
eventual drop in well production can be avoided by carefully monitoring
insolution and exsolved gases to arrive at optimal levels in order to
maintain production. [This may include isotope analysis –
see article]. While these
steps may ameliorate problem rates, there continues to be a need to design
innovative remedial procedures to deal with the new range of problems
arising from this new and important production technique – cold