摘要
核磁共振技术能够实现岩石微米—纳米级孔隙高精度、快速、无损测量,为致密砂岩孔隙结构定量表征提供新的手段。基于压汞数据刻度核磁共振T_2谱的方法,针对致密砂岩压汞进汞饱和度不足100%而造成的测不准问题,提出采取压汞曲线和T_2谱从右边界的最大孔隙向左侧小孔隙累加,选定右累加曲线中压汞测量的孔喉半径范围作为核磁共振孔喉半径的可对比区间,利用纵向插值法和最小二乘法构建T_2谱转换的孔喉半径分布曲线。选择临清坳陷东部石炭系—二叠系致密砂岩气储层为研究对象,利用改进方法获得核磁共振T_2谱和孔喉半径转换系数及孔喉半径分布,定量研究了储层孔隙结构特征,并结合岩石薄片、扫描电镜观察,探讨了致密砂岩孔隙结构差异成因及储层有效性。结果表明,利用改进方法得到的核磁共振孔喉半径曲线与压汞曲线吻合度高,显著提高了致密砂岩核磁共振测试的准确度。研究区石炭系—二叠系致密砂岩孔喉半径主要分布于0.002~2μm,总体为亚微米—纳米级孔隙,但不同类型砂岩孔喉半径分布具有明显差异:岩屑石英砂岩富硅质、贫塑性岩屑和杂基,总体以亚微米级孔喉为主,含微米级孔喉;岩屑长石砂岩和长石岩屑(富石英)砂岩石英含量高、塑性岩屑和杂基含量较低,为亚微米—纳米级孔喉(纳米级占优);而长石岩屑(富岩屑)砂岩和岩屑砂岩贫石英、富塑性岩屑和杂基,主要是小于0.05μm的纳米级孔喉。微观岩石学组分是控制孔隙结构差异和储层有效性的关键因素,储层质量宏观上可能受控于沉积微相,粗粒和细粒的点砂坝/河床滞留微相岩屑石英砂岩是最有利储层,细粒的点砂坝微相岩屑长石砂岩、分流河道和障壁砂坝长石岩屑(富石英)砂岩是较有利储层,而潮坪相长石岩屑(富岩屑)砂岩、岩屑砂岩均是孔、渗性极差的无效储层。
Nuclear magnetic resonance(NMR)provides a new method for quantitative characterization of pore structure of tight sandstone with high accuracy,fast and non-destructive measurement of micro-nano-scale pores.Based on NMR T_2 spectrum method scaled by mercury injection data,aiming at inaccurate measurement caused by the mercury injection saturation less than 100% in tight sandstone,the mercury injection curve and T_2 spectrum are accumulated from largest pore on the right boundary to small pore on the left side;it is suggested to select the pore-throat radius range of mercury injection measurement in the rightward accumulated curve as the comparative interval of NMR porethroat radius.In addition,the longitudinal interpolation and the least squares method are adopted to construct the pore-throat radius distribution curve transformed by T_2 spectrum.The Carboniferous-Permian tight sandstone gas reservoir in eastern Linqing depression is chosen as research object to quantitatively study the pore structure characteristics using the NMR T_2 spectrum,pore-throat radius conversion coefficient and distribution obtained by improved method.Based on rock thin-section and SEM observations,the difference genesis of pore structure andreservoir effectiveness of tight sandstone are also discussed.The results show that the NMR pore-throat radius curve obtained by the improved method is highly consistent with the mercury injection curve,significantly increasing the accuracy of NMR test in tight sandstone.In the Carboniferous-Permian tight sandstone of the study area,pore-throat radius is mainly distributed in the range of 0.002-2 μm,generally corresponding to submicron-nano pores.However,the pore-throat radius distribution varies obviously with different sandstone types.Lithic quartz sandstone is rich in silicon,lacking plastic debris and matrix,generally dominated by submicron pore throat,including micron pore throat.Lithic feldspar sandstone and feldspar lithic sandstone(rich in quartz)has high content of quartz,and low contents of plastic debris and matrix,generally classified as submicron-nano pore throat(dominated by nanos).Feldspar lithic sandstone(rich in lithic fragments)and lithic sandstone are poor in quartz while rich in plastic debris and matrix,mainly classified as nano pore-throat with radius less than 0.05 μm.Microscopic petrographic components are key factors controlling pore structure variability and reservoir effectiveness.On the macroscopic level,reservoir quality may be controlled by sedimentary microfacies.The coarse-and fine-grained micofacies lithic quartz sandstones stranded in the point bar or river bed are the most favorable reservoirs.Fine-grained micofacies lithic feldspar sandstones at the point bar and feldspar lithic sandstones(quartzrich)in diversion channels or at barrier dams can be considered as relatively effective reservoirs,while the feldspar lithic sandstones(rich in lithic fragments)and lithic sandstones of tide-flat facies are always invalid reservoirs with extremely poor reserving capability and permeability.
出处
《石油学报》
EI
CAS
CSCD
北大核心
2017年第8期902-915,共14页
Acta Petrolei Sinica
基金
国家自然科学基金项目(No.41372151)
国家重大科技专项(2017ZX05008-004)
国家重点基础研究发展计划(973)项目(2015CB250902)资助
关键词
核磁共振T2谱
孔隙结构
转换系数
致密砂岩
临清坳陷
NMR T_2 spectrum
pore structure
conversion factor
tight reservoir
Linqing depression