Research On EOR Mechanism And Optimization Of SAGD With Different Well Types In Thin-layer Oil Sands Reservoir

Steam assisted gravity drainage(SAGD)is one of the most efficient techniques to develop oil sands.However,when using the traditional SAGD technique,the steam chamber development is usually of insufficiency due to the high longitudinal sweep rate of steam,which seriously influences the SAGD performance for developing thin layer oil sand reservoirs(reservoir thickness is 15～20 m).In order to better improve the recovery of the thin layer of oil sands,this paper proposed the different well type of SAGD to develop thin layer of oil sands,including dislocation well and infill well SAGD,respectively by using 2D visualization and 3D physical simulation experiments to study the production mechanism,and for each well type was optimized to obtain the best production effect.In this paper,the contact between the onsite and the laboratory model parameters was established through selecting the similarity criteria,which laid an important foundation for the subsequent physical simulation experiments.Based on traditional SAGD technology,three groups of SAGD physical simulation experiments with different horizontal dislocated distances(0 cm,10 cm and 20 cm)between two wells were designed.The effects of different horizontal well spacing on the development of steam chamber were studied,with the help of 2D physical simulation device,and the optimal well spacing was optimized.On this basis,the 3D physical experiment was carried out to verify the production mechanism.The results show that the lateral sweep area of steam was increased obviously and the form of steam chamber was changed.In the 2D experiment,the recovery factor of the horizontal well spacing with 10 cm was 5.6% and 3.6% higher than that of the other two groups,respectively the generation of appropriate horizontal well spacing can combine the effect of steam displacement and gravity drainage better and improve the sweep efficiency of steam.Nevertheless,the overlarge horizontal well spacing can hinder the steam chamber development because that the strength of steam overlap is weakened.Subsequently,the physical simulation experiment of SAGD in infill wells was carried out,two pairs of injection-production wells were simultaneously encrypted in the early stage and in the late stage of production respectively.The effects of different encryption methods on the development of steam chamber and recovery were analyzed and compared.The results displayed that the infill well SAGD made the use of multiple well groups that can make the steam chamber develop more fully and the swept area also can be enlarged obviously.Adjacent steam chambers can quickly connect between the injection and production wells,creating an "arch bridge" that collaborates with downward heating of the interwell cold oil zone to significantly improve recovery.The early encryption is a sufficient condition for the balanced development and rapid connection of adjacent steam chambers,while the later encryption will greatly reduce the oil-steam ratio,resulting in the waste of injected steam resources and reduced economic benefits.The early encryption is a sufficient condition for the balanced steam chamber development,while the later encryption will greatly reduce the oil-steam ratio,resulting in the waste of steam and reduced economic benefits.