Numerical simulation of the dynamic migration mechanism and prediction of saturation of tight sandstone oil

Quantitative characterization of tight sandstone oil migration and accumulation is an emerging research frontier in the field of oil and gas exploration.In this study,a conceptual model containing multiple basic geological elements is developed,and a nonlinear seepage numerical model for tight sandstone oil migration and accumulation is established.The effects of the slip effect,overpressure driving force,buoyancy,and capillary force on the migration and accumulation of tight oil are examined.The results showed that(1)the differences in oil migration and accumulation between tight and conventional reservoirs are reflected in the growth mode of oil saturation,distribution characteristics of oil and water,and extent of the effect of the formation dip angle;(2)the slip effect has a significant impact when the average pore throat radius is less than 150 nm and the overpressure driving force and capillary force are the main mechanical mechanisms controlling oil migration and accumulation in tight sandstone,while the coupling effect of buoyancy,capillary force,and overpressure driving force controls the upper and lower limits of oil saturation.Finally,a dimensional and dimensionless identification chart for rapidly predicting the oil saturation of tight sandstone is proposed and verified using the measured data.This study provides a basis for analyzing the migration and accumulation mechanisms of tight sandstone oil and a new approach for predicting oil saturation.Additionally,we developed digital and visual analysis methods for the migration results,enriching the expression of the dynamics of hydrocarbon accumulation.

Quantitative characterization of pore structure of the CarboniferousePermian tight sandstone gas reservoirs in eastern Linqing depression by using NMR technique

Micro-nano scale pores can accurately and fastly be measured by the nuclear magnetic resonance(NMR)technique,which provides a new method to quantitatively characterize pore structures in tight sandstone.Based on the method of calibration of mercury pressure data for NMR T_(2) spectrum,for the measurement inaccuracy due to the mercury saturation less than 100%in tight sandstone,the mercury pressure curve and T_(2) spectrum is used to cumulate from the maximum pore on the right boundary to the small pores in the left,the range of pore-throat radius measured by the mercury injection in the leftward cumulative curve is selected as a comparable interval of NMR pore-throat radius,and the longitudinal interpolation method and the least square method are utilized to construct the distribution curve of pore-throat radius transformed by T_(2) spectrum.The modified method is used to obtain NMR T_(2) spectrum,conversion coefficient of pore-throat radius and pore-throat radius distribution of the Carboniferous-Permian tight sandstone gas reservoirs in the eastern Linqing depression,and characteristics of reservoir pore structures are quantitatively investigated;in addition,in combination with analysis of thin section and scanning electron microscopy,the reservoir effectiveness and cause of the pore structure variability in the tight sandstone are also well studied.The results show that the NMR pore-throat radius curve obtained by the modified method has a high consistency with the mercury injection curve,and the NMR test accuracy of tight sandstone is significantly improved.In the study area,the pore-throat radius of the Carboniferous-Permian tight sandstone mainly ranges from 0.002 to 2 mm,the pore is generally submicro-nano scale,but the pore-throat radius distribution of different types of sandstone varies significantly.The lithic quartz sandstone is rich in siliceous matter and poor in plastic detritus and matrix,generally dominated by submicro-scale pore-throats including micro-scale porethroats;lithic feldspar sandstone and quartz-rich feldspar lithic sandstone are rich in quartz and poor in plastic detritus and matrix,dominated by submicro-nano scale pore-throats(nano-scale pore-throats predominantly);the lithic fragment-rich feldspar lithic sandstone and lithic sandstone are poor in quartz and rich in plastic detritus and matrix,mainly dominated by nano-scale pore-throats smaller than 0.05 mm.Micropetrographic components are key factors to control pore structure difference and reservoir effectiveness,and the reservoir quality may be macroscopically controlled by sedimentary microfacies;the lithic quartz sandstones of coarse-and fine-grained point bar/riverbed microfacies are the most favorable reservoirs;the lithic feldspar sandstone of fine-grained point bar microfacies,the quartzrich feldspar lithic sandstone of fine-grained distributary channel and barrier bar microfacies are relatively favorable reservoirs,while both lithic fragment-rich feldspar lithic sandstone and lithic sandstone of tidal-flat facies are ineffective reservoirs with very poor porosity and permeability.

沉积正演模拟在准噶尔盆地永进地区西山窑组辫状河三角洲砂体分布预测中的应用

准噶尔盆地腹部永进地区深层侏罗系西山窑组勘探潜力大,但储层非均质性强、钻井少、地震资料品质差,利用地震资料预测有利储层难度大。采用沉积正演模拟方法,基于沉积背景和模型参数分析,构建了永进地区西山窑组辫状河三角洲相的四维沉积学模型,并预测了井间有利相带和砂体分布。研究结果表明:西山窑组发育4个湖泛面,可划分为4个四级层序;层序格架和孢粉含量垂向变化反映湖平面演化主要经历了7次湖退和6次湖侵;西山窑组沉积时期为弱氧化—弱还原环境,古水体深度较浅,平均古水深约为34.69 m;系统试错法模拟确认当河流水体沉积物浓度参数K为0.08 g/L时,6口井地层厚度吻合度均大于89%,且单井点岩性吻合度最高。沉积正演模拟揭示西山窑组沉积砂体叠加方式与规模在不同时期发生显著变化,早期发育垂向加积为主的大型河流沉积,河道复合砂体规模大,随后河流系统发育规模缩小,而沉积晚期以小型、快速横向迁移、分布范围广的河流为特征;辫状河三角洲平原分流河道是研究区优势储层相带,Y1井—Y3井和Y2井—Y6井等分流河道发育概率较高的地区可能是有利勘探目标。展示的案例研究表明,沉积正演模拟可为低勘探程度的深层储层预测提供有效工具。