Experimental Study On Relationship Between Pore Structure And Oil-Water Seepage Characteristics In Tight Reservoir Of HQ Block

Tight oil reservoir has become one of the pillars of China's future crude oil production,but the permeability and porosity are poor and the existence of micro-cracks and nanopores make the tight reservoir heterogeneous,which will extreamly affect reservoir oil-water distribution and water-flooding,so studying the relationship between microscopic pore structure and seepage law of tight reservoirs is of great significance to improve the recovery of such reservoirs.The selected object in this paper is the tight reservoir in the HQ area of the Ordos Basin.The petrological properties and pore structure of the reservoirs in the study area were first classified and characterized by means of casting thin sections,scanning electron microscopy,X-ray diffraction and conventional mercury intrusion.Then,study the characteristics of rock oil and water seepage in different types of pore structure reservoirs systematically through the water flooding phase infiltration experiment,infiltration experiment and nuclear magnetic resonance technology,and the following research results are obtained:(1)The lithology of the reservoir in the study area is mainly medium-fine-grained and fine-grained feldspathic sandstone.The particle sorting degree is good/medium,the secondary edge is rounded and the structure is compact;The cement type is quartz growth and pore cementation.The interstitial content is high,and the main clay minerals are illite(4.5%)and chlorite(6.5%).The higher the content of rigid quartz particles,the better the physical properties,and the porosity and permeability of the reservoir are negatively correlated with the carbonate content.(2)The reservoir storage space in the tight reservoir of the study area has multi-scale pore structure.Four scale types mainly include macropores(3 7 ?m-208?m),micro-cracks(10?m-200?m);micropores(2?m-37?m),nanometer pores(100nm-2?m).According to the distribution and quantity of reservoir space in each scale,the micro-pore structure types of reservoirs in the study area are divided into four types:uniform large-pore type,macroporous strip type,micro-crack type and compact type.(3)The uniform large-pore type is the best type of pore structure in the study area.The macropores and micropores are relatively large,and the pores are well sorted,and the porosity and permeability are relatively high(0.24×10-3?m2-0.9×10-3?m2).The seepage capacity is obviously better than other types.The oil-water phase permeability curve has the widest co-infiltration zone,the water flooding efficiency is relatively high,and the water flooding seepage mode is uniform;The most porous structure type in the study area is strip type.The overall seepage capacity is weaker than the uniform macroporous type.The seepage capacity of this type has a great relationship with the distribution of large pore strips.Therefore,the water flooding efficiency and the phase infiltration characteristic value are different,and the macroporous strip is the advantage channel of oil-water seepage,so the water flooding seepage model is finger-in type,easy to form residual oil;Crack-type pore structure,the strongest heterogeneity,the pore throat around the crack is often nano-micropores,large pores are rare,cracks are dominant channels.The oil-water two-phase zone is obviously narrower than the uniform large-pore type and strip type,and the oil displacement efficiency is relatively low.The oil-water seepage mode belongs to the sudden-in type.The dense pore structure has small pore throat,large pores are rare,and the permeability is generally less than 0.08×10-3?m2.The flow capacity is extremely poor,and a very small number of large pores are the main seepage channels of oil and water,which control the water flooding process,and it is diff-icult to drive water,which is a weak dominant channel type.(4)The phenomenon of seepage oil absorption and water seepage in the reservoir of the study area,there are some differences in the ability of different types of pore structure to seep the oil and water.(5)The T2 spectrum is obviously different for the oil-water seepage process and the seepage of different types of pore structure cores.It is a good method to study the oil-water seepage and oil-water distribution characteristics.This paper provides a basis for the exploitation of tight reservoirs and lays a foundation for the development of HQ area and enhanced oil recovery.