Pore Network Model Construction Of Sandstone Reservoir And Application

Effective water control and maximum enhanced oil recovery have become the most important technical problems for high-efficient development of sandstone reservoir.Accurate reservoir assessement and micro seepage mechanism are both key factors and foundation to sovle those problems.Due to the complex of sandstone reservoir and seepage process of polymer in porous media with large specific surface and complicated structure,the tradition method and experiment is limited.Therefore,accurate assessement of sandstone reservoir pore structure,pore network model,related numerical simulation method and microstructure mechanism need to be established to accurately describe electrical properties and seepage process of microscopic oil displacement,which are extremely meaningful for reservoir assessment and maximum enhanced oil recovery.This paper established digital core based on the micro-CT scanning experiment and image processing technology,analyzed basic rock physical property by extracting pore space from digital core with skeleton extraction algorithm.Based on these digital models,several reconstruction methods for the pore network model is conducted,including the pore network reconstructed via the 3D digital core and genetic algorithm,the dual pore network which contained different scales pore radius distribution.According to those pore structure models,many experiments were simulated to obtain the influence of pore structure and micro pore structure parameter on micro-electrical properties,polymer solution single-phase flow and multiphase flow,he best time inject the ploymerisate in the progress of water displacing oil.The main results and understanding are listed as follows:(1)Establish a set of technique of refining pore structure modeling suitable for the sandstone.The Micro-CT images were smoothing and noise reduction after the filter processing.The pore structure of the image can be segmented by the binarization method which threshold according to the rocks' experiment—measured porosity.Using the skeleton extraction algorithm to obtain the pore and throat radius distribution,the author verified the equivalence significance of the pore network and digital cores and offered the parameter for the model reconstructing.(2)Based on the pore network model by tradition genetic algorithm,actual measurement value of porosity,as constraint condition,is inserted into ojective function to prevent from too earliy convergence.The recursive optimization is applied into random network model,to establish 3D pore network model of sand core.This method is suitable for the heterogeneity sandstone rock's micro modeling.(3)For rheological properties in polymer,author discussed the relationship between the Darcy velocity and apparent viscosity,and the multiphase flow is simulated.The results show that,in certain pressure gradient,oil phase has bigger effect on water phase,compared to shear rate.Water phase's relative permeability decreases with rising of pressure gradient.Besides,with pressure gradient increasing,shear rate is having bigger effect on water phase.At this point,with gradient increasing,water phase's relative permeability is rising.In relative high or low pressure gradient,relative permeability of water phase is close to relative permeability of Newtonian fluid.The ratio of water phase's relative permeability and Newtonian fluid's relative permeability integral in the pressure gradient show a trend of increasing in certain water saturation with the viscosity of ploymerisate increasing.The ratio of the water phase's relative permeability is larger if the fluid has smaller thinning.The water phase relative permeability trend is not obviously changing with the water saturation increasing.(4)The different time injection of the ploymerisate in the progress of water displacing oil is studied with pore network model.The author has analyzed the water ratio and mobility ratio change trend with the water saturation.The results indicate that ploymerisate injected in the early or late displacement processing has the best time to improve the oil recovery.The reservior with greater coordination number and pore radius distribution,increment of oil recovery is less.The reservior with greater the pore radius ratio,residual oil saturation is less after first oil displacement.In certain range,the reservoir with small radius is easy to have the potential of polymer and improve oil recovery.(5)For 2 different permeability sand reservoirs in pore space,the different scales pore parameters distribution is obtained by the Micro-CT and the casting thin section to establish dual pore network model with different pore diameter distribution.Microscopic seepage experiment is simulated after establish of dual pore network.The results have shown that dual model increases connectivity in model.So in imbibition process,it can decline residual oil saturation in model.Therefore this model can offere basis for micro simulation in this type reservoir.(6)Based on dual pore network model,author has established pore network model with different scales,and considered the models' scale how to affect the rock electrical parameters.The simulation results show that the lithological correlation coefficient and saturation and correlation I-Sw coefficient R2 have obvious scale effect.The lithology coefficient has litter scale effect.The cementation index has certain scale effect influenced by the pore holes in the network model.The cementation index is increased with the model's scale increasing.For the accurately reservoir evaluation about the hole development sandstone reservoir,the physics experiments should choose large scales rock.