The Characteristics Of Pore-throat Structure And Its Respond Mechanisms With Recoverable Capacity Of Chang 8 Tight Sandstone Reservoir Of Huaqing Area In Ordos Basin

Since the global demand for fossil energy grows rapidly,the exploration,development and utilization of unconventional oil and gas have attracted extensive attention.Tight oil has been developed commercially in China because of its realistic in all kinds of unconventional oil and gas reservoirs.Huaqing Area in Ordos Basin is the area with the most abundant tight oil reserves in China.Due to the complexity of pore structure,Chang 8 layer in this area has a complicate oil-water relationship and the difference between production performance is large.A deep and comprehensive understanding of the characteristics and controlling factors of pore structure is the basis of clarifying the recovery ability of tight oil sandstone.At present,there are abundant researches on characteristics of pore structure in tight sandstone reservoir.However,the research on multi-method joint characterization of pore structure is relatively weak.Based on the survey of research background,several experiments have been conducted to make a full study of petrological and physical characteristics,diagenesis and burial-filling history of Chang 8 layer in Baibao-Huachi Area and Heqi-Maling Area in this thesis.The size,distribution and complexity of pore structure have also been analyzed and classified based on the combination of experiments such as constant-pressure mercury intrusion,constant-rate mercury intrusion and nuclear magnetic resonance and fractal theory.The movable ability of fluid in tight sandstone reservoir have been studied on the data obtained from experiments including magnetic resonance image and relatively permeability.The recovery ability of reservoir has been researched through combining the movable ability and production information.Finally,differences of pore structure and its controlling factors between various kinds of reservoir with different recovery ability have been analyzed and the relationship between pore structure and recovery ability of reservoir have been established.The content of feldspar is higher in Baibao-Huachi Area and the chlorite films is welldeveloped.The Heqi-Maling Area has a higher lithic fragment and a lower physical property than Baibao-Huachi Area.Compaction is stronger in the Heqi-Maling Area because of a deeper burial.The dissolution and late-cementation are also higher in the Heqi-Maling Area.The Baibao-Huachi Area has a higher facial porosity and inter-granular pores due to the history of sedimentary and diagenesis.The types of capillary curve in Baibao-Huachi Area are mainly ? and ?,which in Heqi-Maling Area is mainly ??? and ?.The capillary curve of constant rate mercury intrusion shows that pore-throat structure is better in the Baibao-Huachi Area which curve is dominated by pores.The deficiencies in different kinds of experiments used to characterize pore structure can be eliminated by joint characterization through which pore structure of whole sizes can be better presented.Base on whole-size analysis,the interval of pore-throat distribution and average throat size become smaller from type ? to ?.The fractal dimension can be used to clarify the complexity of pore throat structure,the larger the fractal dimension is,the higher the complexity of pore throat structure is.The pore structure of reservoir in two areas can both be classified into 4 types,and the pore structure gets worse from type ? to ?.The recovery ability and movable fluid saturation decrease as changes from type 1 to 4.Besides,the signal distribution area in T1-T2,relative permeability and displacement efficiency are also decrease from type 1 to 4.The production analysis indicates that the oil production and stable production cycle becomes smaller from type 1 to 4 and Baibao-Huachi Area has a better performance than the Heqi-Maling Area in production which because the differences in pore structure.The main types pf pore changes from inter granular pores to inter crystal pores as reservoir changes from type 1 to 4 and the dissolution pores have been found in both types.The maximum pore-throat radius,average throat radius gets smaller and fractal dimension get larger which indicates that the pore-throat gets smaller and more complex from type 1 to 4.The main controlling factors of pore structure are sedimentary and diagenesis.Content of quartz decreases while the content of interstitial fillings increases as reservoir type changes.The significant characteristics of each type of reservoir is that the type 1 has a higher content of chlorite films and type 2 has a stronger dissolution and compaction than type 1.The severest compaction has been found in type 3 reservoir because of a high content of plastic material.Large number of carbonate cementation have been found in type 4 reservoir which results in the least porosity.The Baibao-Huachi Area has a better pore structure which results from a good preservation of inter granular pores due to a weak compaction and a better development of dissolution pores.