致密砂岩储层微观孔喉分布特征及对可动流体的控制作用

为分析致密砂岩储层多尺度微观孔喉分布对可动流体的控制作用，以鄂尔多斯盆地伊陕斜坡东南部三叠系延长组长6、长7和长8油层组为例，将高压压汞与核磁共振技术结合，研究致密砂岩储层多尺度微观孔喉分布特征，将离心实验与核磁共振T₂谱分析技术相结合，探讨致密砂岩储层可动流体的分布特征，两者结合研究致密砂岩储层孔喉分布对可动流体的控制作用。研究区延长组致密砂岩储层微观孔喉半径分布范围宽，分布在0.6~3 050.8 nm，主体分布在10~500 nm，表明该致密砂岩储层主要发育微、纳米级孔喉，主体为纳米级孔喉；致密砂岩储层中可动流体饱和度为9.83%~25.64%，平均值为17.53%，普遍较低。储层孔隙度和储层渗透率与可动流体孔隙度具有较好的正相关性，表明储层物性条件对致密砂岩储层可动流体分布具有较好的控制作用；大于50 nm孔喉占全部孔喉比率、大于100 nm孔喉占全部孔喉比率、最大孔喉半径、峰值孔喉半径等参数与储层可动流体孔隙度均具有较好的正相关性，表明储层中相对较大孔喉，尤其大于100 nm孔喉的分布对致密砂岩储层可动流体含量具有重要的控制作用；孔喉的分选系数与可动流体含量表现为正相关，这主要与致密砂岩储层中孔喉半径分布较宽且分选好的致密砂岩主要以细小孔喉为主有关。

Microscale pore-throat distributions in tight sandstone reservoirs and its constrain to movable fluid

To understand the constrains of multiscale microscopic pore-throat distributions to the movable fluid in tight sandstone reservoirs,highpressure mercury injection and nuclear magnetic resonance(NMR)were employed to obtain the distribution characteristics of microscale pore-throat distributions of Chang 6,Chang 7 and Chang 8 oilbearing sections of the Yanchang Formation in the southeastern part of the Yishan slope,Ordos Basin.The occurrences feature of movable fluid in tight sandstone reservoirs were also investigated by centrifugal experiment and the T2 spectrum analysis of NMR.Results show that the microscopic pore-throat radius distribution in the tight sandstone reservoirs of Yanchang Formation has a wide distribution(ranging from 1.13 to 3050.80 nm),mainly distributed from 10 to 500 nm,referring to microand nanoscale pore-throats and mainly were nanoscale.The movable fluid saturation in tight sandstone reservoirs ranged from 9.83%to 25.64%with an average value of 17.53%,indicating a low content in tight sandstone reservoirs.The porosity and permeability of studied reservoirs were positively correlated to the pore-throats having movable fluid,indicating the physical properties of reservoirs playing a role in controlling the distribution of movable fluid in tight sandstone reservoirs.The ratio of pore-throat which greater than 50 nm,and ratio of pore-throat greater than 100 nm,the maximum pore-throat radius,peak pore throat radius etc.,showed a positive correlation with the porosity of movable fluid in tight sandstone reservoirs.It can be indicated that the distribution of relative larger pore-throasts,especially those larger than 100 nm,have strong controlling affection to the relative content of movable fluid in tight sandstone reservoirs.The sorting coefficient of pore-throat is positively correlated with the content of flexible fluid due to the wellsorted tight sandstones with a wide pore-throat radius distribution in tight sandstone reservoirs are dominated by fine pore-throats.