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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 associated problems. 

             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 problems.  The Alberta 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 production.