Abstract:
As known, fracture's capacity and penetration are two key factors for fulfillment of the fracturing jobs including conventional and acid fracturing process. Penetration of acid into existing fractures can improve fracture capacity by etching of fracture surface. Increasing temperature of reservoir rock results in reduction of breakdown pressure. Thermo-gas-chemical technology by in-situ releasing of extra hot gases (N2 and steam) and acid provides a series of network with long fractures and permanent conductivity. A series of experiments in high-pressure and high-temperature (HPHT) reactor were designed to understand the performance and effectiveness of thermo-gas-chemical reaction and determine the optimum binary composition in order to release maximum temperature, pressure and acid generation to provide long conductive fractures. In parallel, dependence of breakdown pressure and temperature was modeled. Moreover, to understand the geometry and propagation of fractures, the effect of thermo-gas-chemical method was studied on core samples in core holder and then cores were scanned by 4D tomography. The preliminary results showed that during the thermo-gas-chemical reaction temperature in reaction zone reaches 207 ℃ and pressure 893 psi due to reaction products. It was found that reaction initiates just after the injection of activator and temperature and pressure increased instantly. This phenomenon acts as a strong impact to break formation rock. The pH of aqueous solutions during the reaction decreased from 8 to 1 and below which provides etching the surface of existing and new fractures. Observed that thermobaric parameters of reaction closely depend on the concentration and reaction activator. Experimental results show that the application of thermo-gas-chemical fluid instead of ordinary fracturing fluid, results in reduction of breakdown pressure from 3400 psi to 121 psi, due to induced thermobaric shock. Experiments on core samples and 4D tomography confirmed the formation of new fractures and expansion of existing ones. Thermo-gas-chemical technology by generation of in-situ hot gases and acid can provide a new high efficiency, cost-effective and eco-friendly method of EOR method for tight low permeability reservoirs and even depleted reservoirs without increasing water cut.
