Research On Damage Mechanism Of Geothermal Reservoir In Beijing Area

Beijing area is rich in geothermal resources. But because of the certain sensitivity minerals in geothermal reservoirs, some damage will be caused in drilling, completion and production process. Study of geothermal reservoir damage mechanism is of great theoretical and practical significance for efficient, safe and sustainable exploitation and utilization of underground hot water resources in Beijing area.Carbonate rocks geothermal reservoir in Beijing is acted as object in the paper. Damage mechanism of geothermal reservoir is studied through selecting some field samples as well as experiments in laboratory, for example:physical properties of rock, fluid sensitivity, sensitivity to stress, damage assessment of drilling fluids to rock specimen. The main conclusions and innovative results are as followsGeothermal reservoir in Beijing area belong to ultra-low permeability reservoir, Geothermal reservoir level of velocity sensitivity is weak low～medium, level of sensitivity to water is medium-low～medium strong, level of sensitivity to alkali is low～medium-weak, sensitivity to stress is extreme strong. The extent of damage of drilling fluid to reservoirs is medium-weak under environment simulated geothermal well. Rock permeability decreases as the temperature increase, the amount of fluid loss, pressure difference increase. High-temperature, low loss and low density drilling fluids are used during the drilling process for reservoir protection.Potential factors of reservoirs damage are environment, rocks, fluid of reservoirs. The formation of downhole pressure difference, time and changes of fluid parameters in the process of operation will make reservoir damage become a realityThe particle transport model of heat reservoir damage is established. Particle diffusion amount per unit of time and the fact that the migration velocity of particle diffusion varies with invasion depth of particles have been got.By analyzing the model of the well circumferential stress changing damage geothermal reservoir, influence factors of critical flow and the method to determine are established. It is put forward that the plastic zone can be limited within a reasonable range by controlling the flow, seeking a balance between production rate and reservoir protection.Point at the characteristics of poor performance using a drilling fluid temperature in work-site, developed a geothermal reservoir protection improvement of polymer drilling fluid system, poly-sulfonate system, effectively improve the volume of drilling fluid filtrate cake quality, developed the capacity of drilling fluid resisted heat.