Study On The Hydrocarbon Mobility Under The Geological Conditions Of Low Porosity And Permeability And Prediction On Movable Resource Potential In Nanpu Sag

Only those movable fluids,which can participate in the flow in the low porosity and permeability reservoir,have exploration and development values.Therefore,clarify the movable fluid distribution rules in different porosity,permeability and pore conditions,will help to improve the accuracy of low permeability reservoir evaluation,exploration target optimization and improve the development effect of low permeability oilfield.Many scholars pay more attention to the upper limit of tight oil reservoir,and less about the lower limit of the movable oil properties.Clarify the lower limit of the physical properties and the movable fluid distribution rules of tight oil reservoir can provide support for the selection of "sweet point" and productivity evaluation.The recoverable coefficient of a stratum in the same oil field or block is generally the same empirical value,hence,the uncertainty of the calculated recoverable resources is relatively high.Therefore,it is important to study the oil and gas mobility under the geological conditions of low porosity and permeability for the reservoir effectiveness evaluation and the forecast of movable resource quantity.In this paper,the effectiveness of the reservoir in the Nanpu Sag of the Bohai Bay Basin is studied by using the irreducible water saturation method,the minimum flow pore throat method and the oil bearing method.The results show that the lower limit of porosity is 2.3%,and the corresponding depth,permeability and pore throat radius are 6185 m,0.01 m D and 0.038?m respectively.Based on the comprehensive analysis of Es33 source rocks and reservoirs in the Gaoliu area of Nanpu Sag,it is concluded that the reservoirs and source rocks are intimate contact and the reservoirs are tight,the hydrocarbon expulsion is great,which are favorable for tight oil accumulation.In order to explore the mobility of hydrocarbons in low porosity sandstone reservoirs,especially in tight sandstone reservoirs,the cores of effective sandstone reservoirs in the Es33 V sublayer are selected to carry out nuclear magnetic resonance experiment,water/oil displacement,high pressure mercury intrusion experiment and constant pressure mercury intrusion experiment.The distribution characteristics of movable oil under different porosity,permeability and pore size were analyzed.For a reservoir with a porosity of less than 10% and a permeability of less than 0.2m D,the proportion of movable oil is generally less than 20%.With the increase of the pore size,the ratio of the movable oil to the oil phase increases in certain pore size ranges,and the larger pore size is more enriched movable oil.The ratio can be as high as 75% in the pore size range of >100 ?m.From the relation between the movable oil in certain pore size range and the total movable oil in the sample,the ranges of 0.1~1?m and 1~10?m are the most abundant movable oil,the ratios are 44% and 38%,respectively.As the reservoir property becomes tight,the right peak of the movable oil distribution curve decreases gradually until disappears,and the pattern of movable oil distribution curve gradually changes from the double peak to the single peak.The pore size of the reservoir controls the mobility of the oil and the amount of movable oil is mainly determined by the porosity.The microscopic pore structure of reservoir leads to different characteristics of movable oil distribution.The calculation results show that the lower limit of permeability and pore size of the movable oil of the Es33 V sublayer are 0.025 m D and 0.058?m,respectively.The relationships between the movable oil proportion and the porosity and permeability of tight sandstone reservoir are established in the Gaoliu area.With the decrease of porosity and permeability,the movable oil proportion decreases.The calculated results show that the movable oil proportion in Es33 V sublayer is 16.5% and the corresponding movable resource is 660×104t.The calculation method is applied to the adjacent blocks and adjacent horizons.The amount of movable oil resources is calculated to be 2568×104t,which is 38.8% higher than that of the fourth-round assessment of hydrocarbon resources in Nanpu Sag.The movable oil proportion in the first section of Shahejie Formation(Es1),Es34 and Es35 was 7.8%,16.5% and 12.5% respectively,and the amount of movable oil was 1029×104t,478×104t and 400×104t respectively.Compared to the fourth-round assessment of hydrocarbon resources,in this study,the the recoverable resources of Es1 and Es33 V sublayer,Es34 and Es35 are increased by-1.9%,106%,108% and 60% respectively.Therefore,the mobile oil proportion of Es33 and Es34 is relatively high and the development difficulty is relatively small.The Es1 has the maximum amount of movable oil and the development potential is high.