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This work represents a method to stimulate illitic sandstone formations using in-situ generated hydrofluoric acid (HF) in the presence of thermochemicals. Using traditional mud acid for stimulating such reservoirs would cause a huge damage to the formation rather than enhancing its permeability. In this study, HF acid precursor reacts with an oxidizer in the presence of an exothermic reaction to generate HF acid downhole. Besides the high temperature generated inside the near-wellbore area, the pressure will build-up due to produced nitrogen gas from the thermochemicals reaction. The high pressure provides enough energy to flows back the well and removes any resulted precipitate. Firstly, the solubility of quartz and clay minerals in the new chemical mixture was tested. After that, core flooding tests were run for Scioto sandstone cores of 6-inch length and 1.5-inch diameter. Two different approaches were adopted for this treatment; (1) to remove the core damage and enhance its permeability using the acid generating fluids, (2) to stimulate the core using both the acid generating fluids and the thermochemicals. The core petrophysical and mechanical properties are evaluated before and after the acidizing process using core flooding tests, NMR scans and scratch tests. The core permeability got enhanced by about 37.5% after being treated with the acid generating fluids. The Inductively Coupled Plasma (ICP) analysis of the core flooding effluent showed that the total chelated amount of Si4+ ions from the core reached 49 mg. The scratch test showed a decrease in the Scioto core strength after the acid treatment by about 770 psi. Moreover, the core dynamic Young's modulus and Poisson's ratio were reduced by 550 ksi and 0.01 respectively. On the other hand, the NMR scanning for Scioto core showed an enhancement in the core total porosity after the acid treatment. The generated pressure pulse from the thermochemicals pushes the acid generated deeper into the formation and highly increased the stimulation process efficiency. Upon application of this new stimulation technology, the true production potential of sandstone reservoirs can be achieved, corrosivity will be minimized and handling hazardous chemicals (HF) will be avoided. • New method to generate in-situ HF acid was introduced. • Solubility experiments showed the effectiveness of the generated acid to react with both clays and quartz. • Coreflooding experiments showed good improvement in core permeability. • The generated acid created micro fractures in addition to its dissolving power. • The generated acid did not change that much the rock integrity. [ABSTRACT FROM AUTHOR]