鄂尔多斯盆地南梁—华池地区长81致密储层微观孔喉结构及其对渗流的影响

鄂尔多斯盆地南梁华池长81油藏孔喉结构多样、渗流特征复杂,成藏及油水关系认识不清,制约了该区石油勘探突破及规模开发进程。通过铸体薄片、恒速压汞、核磁共振、油水相渗测试等方法,系统研究了南梁—华池地区长8₁储层微观孔隙结构,对比分析了该区不同物性样品微观孔喉结构差异及其对油水渗流特征的影响。结果表明:①储层物性越好,微观非均质性越强,可动流体饱和度越大,无水期驱油效率先增后减,最终水驱油效率越高。②当渗透率大于1.000 mD时,渗透率贡献率主要依靠少数半径大于6.00μm的连通喉道;当渗透率小于1.000 mD时,渗透率贡献率主要由喉道半径峰值区间的小喉道决定。③连通喉道半径小于0.10μm的孔隙流体为不可流动的束缚流体,储层物性越好,半径大于0.50μm喉道控制的孔隙体积越大,可动流体饱和度越高。④研究区油水相渗特征可以分为3类,其中Ⅰ类相渗物性最差、驱油效率最低;Ⅱ类相渗喉道半径为0.50~1.00μm,两相共渗范围较宽,无水期驱油效率和最终驱油效率均最高;Ⅲ类相渗喉道半径多大于1.50μm,含水上升较快,无水期驱油效率最低,但最终驱油效率只略低于Ⅱ类相渗最终驱油效率。喉道半径的分布、连通特征决定了储层渗透率和可动流体饱和度大小,影响油水两相渗流规律,对石油充注、成藏以及开发均有重要的影响,是该区油水关系复杂的重要因素之一。该研究成果对分析岩性油藏油水关系、预测有利储层分布具有一定指导意义。

Micro pore throat structure and its influence on seepage of Chang 81 tight reservoir in Nanliang-Huachi area,Ordos Basin

Chang 81 reservoir in Nanliang-Huachi area of Ordos Basin is characterized by various pore throat structures,complex seepage characteristics,unclear understanding of reservoir accumulation and oil-water relationship,which restricts the process of oil exploration breakthrough and scale development.The micro pore structure of Chang 8₁ reservoir in Nanliang-Huachi area was systematically studied by means of casting thin section,constant velocity mercury injection,nuclear magnetic resonance and oil-water relative permeability test,and the difference of micro pore throat structure of samples with different physical properties in the study area and its influence on oil-water seepage characteristics were compared and analyzed.The results show that:(1)The better the reservoir physical properties of the reservoir,the stronger the micro heterogeneity,the greater the movable fluid saturation,the displacement efficiency in the anhydrous period increases first,then decreases,and the higher the final water displacement efficiency.(2)When the permeability is higher than 1.000 mD,the permeability contribution mainly depends on a few connected throats with radius greater than 6.00μm,while the permeability is lower than 1.000 mD,the permeability contribution is mainly determined by the small throats in the peak range of throats radius.(3)The pore fluid in the radius of connected throat less than 0.10μm is immovable fluid.The better the reservoir physical properties are,the larger the pore volume controlled by the throat with the radius greater than 0.50μm is,the higher the saturation of movable fluid is.(4)The characteristics of oil-water relative permeability in the study area can be divided into three types,among which the physical property of type I is poorest and the oil displacement efficiency is the lowest.The throat radius of typeⅡis 0.50-1.00μm,and the permeability range of the two-phase is wide,the oil displacement efficiency and final oil displacement efficiency are highest in anhydrous period.The throat radius of typeⅢis greater than 1.50μm,the water cut rises rapidly,the oil displacement efficiency is lowest in anhydrous period,but its final oil displacement efficiency is slightly lower than that of typeⅡ.The distribution and connection characteristics of throat radius are one of the important factors of complex oilwater relationship in this area,which determine the permeability of reservoir and the saturation of movable fluid,affect the rule of oil-water two-phase flow,and have an important influence on oil filling,reservoir accumulation and development.The research results have certain guiding significance for analyzing oil-water relationship of lithologic reservoir and predicting favorable reservoir distribution.