Study On Numerical Simulation Of CO₂ Flooding In Horizontal Wells For Ultra-low Permeability Reservoir Of H1 Wellblock

In recent years,the proportion of low permeability and extra-low permeability reservoir reserves is as high as 65% above in our country.Inter alia,the proportion of extra-low permeability reservoir is more 50%.Due to the complicated reservoir and existent split,pertinence theory reference on development and design of oilfield is absent,great development difficulties,poor benefit,compared with the high penetrative reservoir,the understanding degree and development level of the extra-low permeability reservoirs has a significant gap.Hence,in order to resolve these technique problem,it need to correctly understand the characteristics of extra-low permeability reservoir,and fully comprehend the distribution law of remainder oil and effectively combine tapping technique and measure on.Then advisable pertinency exploitation plan is draw up.The reserves could sufficiently employed and developed.In this paper,extra-low permeability reservoir of H1 wellblock in Daqing oilfield is taken for research object.The area of H1 wellblock is large,but there are just 9 horizontal wells with natural energy that leads to absence dynamic and quiescent data.The complex reservoir,thinner layer,narrow-small sand body,and local fracture lead to bad understanding degree.Because of differential length and well spacing in the horizontal wells,that results in difficult pattern disposition and difficult development.Traditional development theory and method for low permeability reservoir is not fit for H1 wellblock.The development design absences purposeful theory foundation.In order to resolve these problems,on the basis of sufficient investigation,the comprehensive study on multidisciplinary,multi-technology and multi-method was carried out in view of H1 wellblock,and a comprehensiveness method of CO₂ flooding for extra-low permeability reservoir of H1 wellblock was proposed.The following studies have been developed:（1）The minimum start-up pressure gradient and the minimum miscible pressure of CO₂ and crude oil in H1 wellblock are measured by laboratory experiments,combining with filtration theory on extra-low permeability reservoir to establish three-dimensional and three-phase multiple medium components non-darcy seepage flow model on CO₂ flooding in extra-low permeability reservoirs.After that,the simulation software on CO₂ flooding for extra-low permeability reservoirs is formulated,which consummate simulate CO₂ flooding process.（2）Combining with available drilling data and log information of H1 wellblock,with the combination of drilling-logging-seismic and the H1 wellblock reservoir seismic interpretation work from the dot,line,plane and space,teh reliability of the seismic interpretation layers are ensured.Based on the well breakpoint,combining with the abundant well information,the fault recognition is more exact by technique measure of coherence and azimuth property and dip property.Based on preprocessing of the seismic-logging data and sensitivity analysis,the distribution of predicted sand body is real and nature by optimizing geostatistics inversion method.（3）Based on well-to-seismic combination and reservoir inversion resul,the 3D elaborate geological model for H1 wellblock is established.The model can fully reflect the 3D variation and distribution characteristics of geological feature,provide a reliable geological basis of the following sophisticated numerical simulation study.（4）By fully considering the factors of horizontal well length location and contiguity relationship,partition on well pattern disposition is designed for the 9 horizontal wells with CO₂ flooding after natural depletion.Based on the factors of horizontal well length and crack scale,combining with development technique and measure on extra-low permeability reservoir,well pattern and injection-production parameters of are optimized by simulation software on CO₂ flooding for extra-low permeability reservoirs,combining with economic benefit evaluation measure to confirm the optimum CO₂ flooding development plan.The the optimal parameters are well pattern of disposition method of combination of vertical and horizontal wells,partition placement of injection-production pattern of seven-spot and nine-spot,gas-water alternate injection,cycle is 0.5 years,gas-oil ratio is 1:1,daily CO₂ injection volume is 1500m³.The program’s recovery percent is 5.28% in 10 years.According to the research in this paper,an entire tapping method on CO₂ flooding in horizontal wells for extra-low permeability reservoir,after natural recovery,is suppled for H1 wellblock.This method could supply theory steering and technical support for effective development to the same extra-low permeability reservoir.