| After years of exploration and development in the Lamadian oilfield,most of them are now in the middle and late stages of development.The distribution law of microscopic residual oil is not well understood,and the residual oil tapping and recovery rate improvement of the reservoir in the study area has certain limitations.Therefore,through precise research and understanding of the microscopic pore structure of the reservoir,it is important to clarify the fugacity and distribution pattern of the microscopic remaining oil.This thesis takes the Portugal reservoir formation in the Lamadian oilfield as an example.Through core observation,physical analysis,ordinary thin section,cast thin section,scanning electron microscopy,X-diffraction,high-pressure mercury pressure,oil-water phase percolation,nuclear magnetic resonance and other experimental techniques,we firstly clarify the depositional characteristics,lithological characteristics and physical characteristics of the sandstone reservoir in the Portugal reservoir formation,and on this basis,conduct a comprehensive study and analysis of the reservoir microscopic pore structure,percolation characteristics and the distribution pattern of remaining oil.On this basis,the reservoir micro-pore structure,seepage characteristics and residual oil distribution patterns were studied and analyzed.The study shows that:(1)The sandstone type in the study area is mainly feldspar sandstone,with less lithic feldspar sandstone and feldspar lithic quartz sandstone.The fill composition is dominated by colluvium,mainly including authigenic clay minerals,siliceous colluvium and carbonate colluvium.The average porosity of the study area is 33.07%and the average permeability is 2.47μm~2,which is a very high porosity and high permeability reservoir.(2)The sandstone of the reservoir in the study area is in the middle orogenic stage A.The rock-forming action is mainly destructive compaction and cementation and late dissolution.The pore type is mainly a combination of multiple pores forming different combinations of pore types.(3)There are mainly two types of capillary pressure curves,the physical properties of type 1 are better,the pore throat size is coarser and more uniformly distributed,and both types of pore throat structures show higher discharge pressure,better maximum inlet mercury saturation and better pore throat connectivity.(4)The reservoir bound water saturation and residual oil saturation are lower,the movable fluid saturation is higher,the capillary resistance to micro seepage is lower,and the reservoir fluid micro seepage ability is better.The influence of reservoir pore structure on percolation capacity is stronger.The interval with pore throat radius less than 0.644μm is the immovable interval,between 0.644μm～5.571μm is the inefficient seepage zone,between5.571μm～9.54μm is the normal seepage zone.(5)The study area mainly consists of pore throat filling type and pore throat semi-filling type residual oil,followed by pore wall film type residual oil,with relatively little residual oil content in the throat lagging type,corner type and dispersed oil droplet type.Based on the analysis of the comprehensive evaluation results,it can be seen that the microscopic residual oil content of the type II reservoir is higher and is the main target for further residual oil exploration. |
