Microscopic Heterogeneity Characteristics Of Tight Sandstone Reservoirs-microscopic Comparison Of Chang 6 Reservoirs In Wuqi And Surrounding Area

The Chang 6 reservoirs in Huaqing area and Wuqi area belong to typical tight sandstone sandstone reservoirs,which are the representative one for exploration and exploitation globally.Conventional experiments are difficult to effectively recognize and evaluate the microscopic characteristics of the reservoirs,which in turn limits the exploration and development process and theoretical understanding of the research area.In this study,petrophysics and physical properties of reservoirs were studied using physical properties tests,casting thin sections,and image analysis.Combined with scanning electron microscopy and CT scans,the reservoir diagenetic features and pore types in the study area were qualitatively described.Conventional and constant-rate mercury injection experiments were used.The classification of capillary pressure curve types and the analysis of influencing factors were carried out.At the same time,the relationship between them and the pore throat structure from the perspective of the distribution of movable fluids and oil and water were explored,and the constraints of oil displacement efficiency from the perspective of micro heterogeneity were discussed.Finally,various microscopic heterogeneity features have been used to evaluate the productivity response of different quality reservoirs.Mainly achieved the following understanding:?1?The Chang 6 formation of Huaqing area is mainly composed of feldspathic sandstones.The composition of the rocks is low in maturation,the average porosity is 9.89%,and the average permeability is 0.024×10^-3?m².The Chang 6 formation of Wuqi area is mainly composed feldspar and rock debris sandstones.The sandstone is dominated with an average porosity of 8.57%and an average permeability of 0.30×10^-3?m²,which are all typical tight sandstone reservoirs.?2?Typical types of diagenesis in the reservoirs in the study area include compaction,cementation and dissolution of clay minerals;the stronger compaction and cementation of Chang 6 reservoirs in Huaqing area than in Chang 6 reservoirs in Wuqi area.The strengths of later diagenetic alterations are different,resulting in the differences in microscopic pore structure and permeability characteristics of fluids in the two reservoirs.?3?The Wuqi area has a relatively high percentage of pipe bundle throats in Chang 6formation,with larger throats and better connectivity.The dissolved pore-to-grain pore type reservoir dominates,and the Chang 6 banded and granular throat in Huaqing area.The proportion is relatively high,the throat is small and the connectivity is poor,and the ratio of dissolved pore-to-grain pore type reservoirs is high.?4?The high-pressure mercury-infused capillary pressure curve forms reservoirs into Class I,Class II,Class III,and Class IV.The nature of Chang 6 in the Wuqi area of the same type of reservoir is better than that of Chang 6 in Huaqing area.The size of throat throat and pore throat radius distribution are the most critical factors controlling the porosity and permeability of reservoirs in the study area.The relationship between the physical properties of the Chang 6 formation of the Wuqi area and the throat throat radius is more closely related.In the case where the overall assessment trend is not clear,more significant laws will be harvested with classification assessment.?5?The increase in the proportion of larger porosity is one of the reasons for better reservoir quality in the Chang 6 formation in Huaqing area;the Chang 6 formation in Wuqi area has better pore connectivity,less microporosity,better pore throat structure quality,and throat radius.The pore radius,pore-throat ratio,separation coefficient and mercury saturation are the main constant mercury intrusion micro-heterogeneity parameters for controlling the physical properties;the seepage ability of the Chang 6 formation in the Wuqi area is more obviously controlled by the pore throat configuration relationship.?6?For the curve of the same T₂ spectrum morphology,the Chang 6 formation of the Wuqi area contains more intergranular pores,and the development of the intergranular pores of the Chang 6 section in Huaqing area is less than that of the Chang 6 formation of the Wuqi area.This is one of the reason why the former reservoir quality is inferior to the latter.When the throat is small,the Jiamin effect will cause the fluid to block through the throat,resulting in the decrease of the movable fluid saturation as the face rate decreases;when the throat increases to not affect the flow of the fluid,the throat The channel is essentially the same as the pore,and the larger the value is,the higher the fluid saturation is.?7?Regardless of the type of oil displacement or water displacement,the types of displacement can be divided into three types:uniform,reticulate and finger displacement;The oil displacement efficiency shows a good positive correlation.Different pore types have different displacement ranges;The oil in the relatively large pores are displaced in the non-water stage,and further pressurized water injection causes the oil in the small throat to be displaced.The relationship between displacement efficiency and throat radius is even closer;the microscopic heterogeneity of the reservoir seriously affects the expansion and widening of the seepage channel,and it is difficult to affect the injection of water in relatively dense areas.