Study On Pore Structure And Lower Limit Of Reservoir In Tight Oil Reservoirs In Xiagou Formation,Qingxi Depression

Qingxi Sag is an oil-rich sag located in the Jiuquan Basin,and tight oil exploration prospects are good.Mudstone in Xiagou Formation is the main reservoir.Because the unclear microscopic characteristics of reservoirs restrict the development of tight oil,it is very important to study the microstructure of the reservoir.Most of the mudstone reservoirs in the Xiagou Formation are low porosity and low permeability,and the mineral components include brittle minerals,carbonate minerals,and clay minerals.The development of intergranular pores,intercrystalline pores,dissolved pores,and microfractures improves the connectivity of reservoirs.Organic pores are generally isolated pores.Various types of throat,including necked throat,flaccid throat,point throat,etc.High-pressure mercury injection experiment to determine reservoir classification,The porosity of type ? reservoirs ranges from 3.11% to 11.59%,and the permeability is from 1.12 to 2.71 mD.The porosity of type ? reservoirs ranged from 2.86% to 9.17%,and the permeability ranged from 0.21 to 0.99 mD.The porosity of type ? reservoirs ranges from 0.42% to 1.59%,and the permeability ranges from 0.05 to 0.09 mD.The pore throat size and pore-throat connectivity all affect the seepage capacity of the reservoir.The pore throat distribution has a complex effect on the permeability;the size,distribution and connectivity of the pore throat have no significant effect on the reservoir capacity.The micro-nano-CT was used to determine the parameters of the throat.Through analysis of the laryngeal hole ratio,throat cross-sectional area,pore throat coordination number and other parameters,it was shown that the size of the throat and the matching relationship between the throat and the pores were also the key factors affecting reservoir seepage capacity.The lower limit of porosity of the reservoir is 2.65% and the lower limit of permeability is 0.15 mD by applying the oil test method,the method of oil production,and the minimum flow radius method.Type ? reservoirs are ineffective reservoirs,and Type I and Type ? reservoirs are effective reservoirs.