Feasibility of Application of Thermal Shocking by In-situ Generation of Hot N₂/CO₂ for Development of Unconventional Reservoirs

Thermal shocking technology by generation of in-situ gases (N₂/CO₂), heatwave, and hot acid can overcome challenges due to permeability and viscosity while developing unconventional hydrocarbon resources. The source of thermal shock is the exothermic reaction of the aqueous solution of ammonium nitrate, urea, and sodium nitrite. To investigate the thermobaric characterization of the reaction, a series of experiments in a high-pressure high-temperature (HPHT) reactor was designed to define the optimum ratio of the chemicals. The gaseous products of the reaction were sent to gas chromatography to study the volume of released nitrogen and carbon dioxide. In the next step, the effect of reaction products on the viscosity and SARA components of a heavy oil from Russian company was studied. In parallel, the effect of generated thermal shock on the breakdown pressure of both sandstone and carbonate rocks was studied and compared with ordinary hydraulic fracturing technology. Rock samples were introduced to 4D tomography to study the shape of fractures created by hydraulic fracturing technology and thermal shocking. Experimental works show that a molar ratio of 1:1:1 of three components gives pressure and temperature of 3768 psi and 252 °C. The main components of gaseous products are nitrogen and carbon dioxide. The initial pH of the aqueous solution was 6.5 and after reaction decreased to 1. In addition, the results show that due to released heat, oil viscosity was reduced by 6 folds, from 600 to 100 cP. Either, it was found that dissolution of gaseous products of the reaction in oil reduces oil viscosity from 250 to 50 cP. SARA analysis shows that due to thermal shock, the volume of heavy components in heavy oil such as asphaltenes and resins dramatically decreased from 10.9 and 21.2% to 5.9 and 15.7%, respectively. Analyses showed that by replacing ordinary hydraulic fracturing technology with thermal shock, breakdown pressure reduces repeatedly. Thermal shocking technology by the in-situ generation of hot N₂/CO₂ can be used as high efficiency, eco-friendly and waterless technology for the development of unconventional hydrocarbon resources. Of course, this technology is no sole solution, but in many cases can be used as a replacement for hydraulic fracturing and thermal EOR methods.