High Temperature Heat Treatment In Tight Sandstone Gas Reservoir To Alleviate Water Phase Trapping Damage

With the continuous development of unconventional natural gas exploration technology,the newly proven natural gas reserves increase year by year,and tight sandstone gas reservoirs play a decisive role.Tight sandstone gas reservoirs have become the focus area of unconventional natural gas development nowadays.During the development of tight sandstone gas reservoirs,water phase trap induced by water retention is one of the most important damage types,which seriously restricts the development of tight sandstone gas reservoirs.It is of great practical significance for the development of tight sandstone gas reservoir to alleviate the damage of reservoir water phase trap and improve the permeability of reservoir.In this paper,using the typical tight sandstone of Ordos Basin and the Western Sichuan as the research object,based on the laboratory experiment,the test of permeability and porosity of rock samples before and after heat treatment under simulated in-situ stress conditions has been carried out.Simulating the changes in the seepage capacity of the water bearing rock core during the process of hot gas flooding at different temperatures.The heat treatment experiments of dry rock samples,saturated distilled water,saturated 3%KCl solution and saturated simulated formation water were carried out at increasing temperature.The self-priming and returning capacity of the core before and after heat treatment were measured.The basic mechanism of heat treatment to alleviate the damage of water phase trap was analyzedThe main control factors of formation heat treatment to alleviate the damage of the water phase trap are analyzed from geology and engineering.Geological factors include the physical properties of tight sandstone,pore structure,clay mineral characteristics and water saturation.The engineering factors include the temperature of heat treatment,the way of heating and the properties of the engineering fluid.The heat treatment experiment of tight sandstone gas reservoir under simulated original conditions is carried out.Experiments show that before reaching the threshold temperature of tight sandstone heat treatment,the expansion of core will lead to compression of pore throat and decrease permeability,and the permability of core will increase rapidly after reaching the thermal threshold temperature.In the process of high temperature thermal displacement,the water in the core of water core rapidly evaporated and evaporated and decreased the water saturation of the core,which enhanced the permeability.The stress sensitivity of the rock heart is enhanced after heat treatment.The heat treatment experiment of tight sandstone under different water content has been carried out.The permeability of core with distilled water after heat treatment is obviously higher than that of dry core.The core with high salinity simulated formation water has obvious salting out after heat treatment.The infiltration rate after heat treatment is between the core of dry rock and the core containing distilled water.The water bearing state of the core also has a certain effect on the thermal threshold temperature during the heat treatment of the core.The thermal threshold temperature of water bearing core is obviously lower than that of dry core.The change of self-absorption and rearrangement capacity of core before and after heat treatment was evaluated.The core after water absorption capacity after heat treatment is improved significantly,a self-priming time after desorption and self imbibition rate improves after heat treatment,and in the process of flowback,flowback efficiency will be raised in the core after heat treatment.The main mechanism of the formation heat treatment to alleviate the water phase trap in the tight sandstone reservoir is analyzed.High temperature can evaporate the pore water,reduce reservoir water saturation.Liquid phase vaporization can produce huge steam pressure to increase gas output capacity.High temperature can remove moisture from clay minerals,relieve hydration and expansion of clay minerals and release seepage channels.Under high temperature,rock will generate thermal cracking to form new fracture network and enhance reservoir percolation capacity.