Formation heat treatment is a process that has great potential as a method to increase the permeability of a formation, remove the damage caused during operations such as drilling, completions, and work-overs, and/or partially destroy the structure of clay in the near wellbore area. Published experimental work examining this technique confirms that, as a result of formation heating, blocking water can be vaporized, the clay structure may become dehydrated, the structure of the clays can be partially destroyed and, at temperatures above 600 °C, microfractures can be generated in the sandstone. The few field studies utilizing this technique which have been reported list excellent results. However, the combination of high energy requirements and the use of specialized equipment make the technique costly so that its application in the field has not been accepted widely.
Research into the combustion of gases in porous media at the University of Calgary is being carried out with the aim of applying the concept to the process of formation heating. Gaseous combustible mixtures may be injected and dispersed homogeneously through the entire matrix, ensuring a uniform treatment of the formation as well as potential modification of the formation's structural and fluid mechanical properties. In the field applications of this technique, the exothermic reaction will take place within of the formation so that the well bore will not be exposed to high temperatures, and the only energy requirements for the operation will be for the compression and injection of the gases.
A gas combustion tube has been designed, constructed and commissioned in order to evaluate the effects of controlling parameters such as operating pressure, gas flow rate, type and pore size of media, and concentration of gas fuel on combustion characteristics. Experiments have been carried out using two different porous media, and the effects of operating pressures from atmospheric (88.5 kPa or 12.8 psia) to 777.7 kPa (112.8 psia) have been studied. Lean mixtures of natural gas and air (5.4% to 5.6%, by volume) were used. It will be shown that it is possible to reach temperatures above 600oC within of the porous media. The size of the region exposed to temperatures greater than 600 °C increases as the pore size decreases. The velocity of the front, and the maximum temperature, have both been found to increase as the relative velocity of the gases increases.
Formation damage can occur at any stage during the lifetime of a well. Operations such as drilling, completion, workovers, and stimulations expose the formation to fluids that may be almost all incompatible with the formation and its original fluids. These situations can cause a reduction in the permeability of the formation around the well bore, and/or a reduction in the production of fluids. This problem is usually severe in horizontal wells, because of longer exposure of the wellbore to the incompatible fluids. A detailed description of the formation damage mechanisms is presented in the literature(1). The most popular method currently used to remedy formation damage is hydraulic fracturing of the matrix.
