Abstract:

The pore throat of tight sandstone reservoir block is narrow, and during the whole process of gas reservoir development, the water phase trapping damage is easy to prone, which restrict the development process of tight gas. The field test and laboratory experimental study have proved that the heat treatment technology for reservoirs can remove this damage and increase the permeability, but it has not been popularized and applied because of the unclear reservoir physical properties. Therefore, typical tight sandstone cores in Kuqa Depression, Huimin Depression and Jidong Depression are selected in order to simulate the fracture surface where heat treatment fracturing fluid stays or the near-wellbore zone where water phase gathers in the production process. A thermal shock experiment is carried out with 3 % KCL solution completely saturated experimental cores, the permeability of tight sandstone with different reservoir quality coefficient RQI before and after thermal shock is tested, and the relationship between the reservoir quality coefficient RQI and the increasing permeability is analyzed. The researches show that the permeability of tight sandstone samples does not change obviously when heated from room temperature to 100 ℃, but decreases slightly when heated to 200 ℃, and increases by 200 %~500 % when heated to 300~400 ℃, but the permeability of some samples does not change obviously, which is related to the reservoir quality coefficient RQI of the samples. The critical value of quality coefficient of water-bearing tight sandstone reservoir suitable for thermal surge permeability is 0.25. When RQI value is less than 0.25, the thermal surge permeability amplitude of rock samples is monotonically decreasing with RQI value. When RQI value is constant and heat shock temperature is greater than 200 ℃, the higher the temperature, the better the effect of thermal surge infiltration.

Key words: tight sandstone, thermal stimulation, water phase trapping damage, reservoir quality index, fracturing fluid