Gamma rays are bursts of high-energy electromagnetic waves that are emitted naturally by some radioactive elements. Laboratory experiments were undertaken to assess the influences of gamma irradiation on thermal decomposition and petrophysical properties of carbonate rocks of aquifers and oil reservoirs. A constant gamma ray dose of 9 MGy was applied on identical calcium carbonate core samples, extracted from actual oil reservoir. The core samples were analyzed using thermogravimetric analysis (TGA), differential thermal analysis (DTA), infrared spectrum (IR) and scanning electron microscope (SEM) before and after application of gamma ray irradiation. The attained data was used to interpret thermal decomposition, phase transition and mechanical stability of calcium carbonate rocks. Furthermore the effect of gamma irradiation on pertophysical properties of porosity and permeability were studied experimentally for water and oil saturated carbonate rocks.
Chemical composition of the carbonate core samples was determined using titration method and its sulfur content was determined using precipitation method. Application of Differential Thermal Analysis (DTA) proved the purification of the used core samples. Chemical analysis indicated that the core ha 99.8 % calcium carbonate. The Infrared (IR) indicated that no chemical changes of irradiated core samples have been observed. The analysis using DTA and TGA indicated that gamma irradiation enhanced thermal decomposition of carbonate rocks of oil reservoirs. The obtained results indicated that calcium carbonate rocks are stable rocks. In addition, the gamma ray irradiation has been proven to have almost no effect on porosity and permeability of these reservoir rocks.
Applications of the attained results are expected to have real impact on deep understanding of rock stability, using gamma ray tools and measuring gamma ray levels in oil fields, and improvements in future interpretation of attained data from gamma ray measurements such as gamma ray log.