Study On Water Injection Development Mechanism And Fine Water Injection Control In Ultra-low Permeability Reservoir

The reserves of ultra-low permeability reservoirs account for a large proportion of the newly proved reserves in China.Efficient development of such reservoirs is of great significance to national energy security.Fracturing and water injection development are the main stimulation technologies at present.Because the pore throat structure of ultra-low permeability reservoir is complex,the reservoir heterogeneity is strong,and the micro fractures are developed,coupled with the artificial fractures formed by transformation,the problem of water channeling and flooding of oil wells is prominent due to the injection of water,the original oil in the matrix is difficult to be effectively used,and the water drive recovery is low.The water injection development is faced with the technical problem of "fracture is easy to water channeling,and the matrix cannot drive".Based on a series of methods of seepage mechanics,reservoir engineering,physical simulation and numerical simulation,this paper has deeply carried out studies on the development mechanism and fine water injection regulation of ultra-low permeability reservoir in H area of Yanchang Oilfield.Through microfluidic imbibition experiment and two-dimensional plate dynamic imbibition experiment,the micro imbibition mechanism under different pore throat combination modes is revealed,and the main controlling factors affecting the development effect of water drive and the contribution of infiltration are defined.By using long core displacement experiment and NMR high temperature and high pressure displacement experiment,the pressure propagation law and the dual action mechanism of imbibition and displacement in the water injection process of ultra-low permeability reservoir are explored;Also,by means of reservoir engineering method and numerical simulation technology,the control technology of fine stratified water injection control technology is formed.The main results are as follows:(1)The micro models of double depth all glass chip and silicon bottom deep etching micro chip are designed,which systematically simulated the effects of throat size,pore shape,pore throat ratio,throat pore connection position and coordination number on the infiltration process of ultra-low permeability reservoir and obtained the main factors affecting the flow of imbibition film.The results show that wetting angle is a key parameter affecting film flow.The film flow increases with the decrease of wetting angle and oil-water viscosity ratio and the existence of film flow reduces the theoretical infiltration time by 10%-20%.(2)A two-dimensional plate dual-media model is designed,which studied the effects of matrix permeability,natural fractures,artificial fractures,interlayer heterogeneity,the number of small layers,the development degree of interlayer and water injection rate on water drive effect and imbibition contribution,and obtained the main controlling factors of imbibitions.The results show that natural fractures and water injection rate are the main factors affecting the contribution rate of matrix imbibitions,matrix permeability and artificial fractures are the secondary influencing factors and the development degree of interlayer and the number of small layers are the least influential factor.(3)Based on the nuclear magnetic resonance(NMR)high temperature and high pressure displacement experiment,the spontaneous imbibition of single pore medium and the imbibition-displacement experiment of fracture-pore dual medium were carried out,which deepened the dual mechanism of imbibition and displacement in ultra-low permeability reservoir,and indicated that fractures make a prominent contribution to oil displacement efficiency in the process of imbibition displacement.In addition,the differential characteristics of oil displacement efficiency of pore-throat-fracture system are quantitatively evaluated,which indicated that imbibition is dominant at low injection rate and displacement is dominant at high injection rate,and clarified the reasonable spontaneous imbibition time.(4)Based on reservoir engineering theory and numerical simulation method,a fine water injection regulation technology of layered water injection has been established and the technology is applied to H area of Yanchang oilfield,which greatly improved the producing degree of water flooding and the recovery of water injection development.