特低渗透砂岩储层水敏实验及损害机理研究——以鄂尔多斯盆地西峰油田延长组第8油层为例

以鄂尔多斯盆地西峰油田延长组第8油层砂岩为例,通过铸体薄片、扫描电镜、图像分析及全岩分析等手段详细研究储层特征,应用室内岩心流动驱替实验进行水敏实验研究。与此同时,结合扫描电镜、毛管流动孔隙结构仪分别定性和定量研究水敏实验前、后岩心内部粘土矿物产状和孔隙结构参数等微观特征的变化,以此探讨水敏损害机理。研究表明,西峰油田延长组第8油层属于特低渗透砂岩油藏,其粘土矿物主要为高岭石、绿泥石、伊利石,不含蒙脱石,伊/蒙混层矿物含量少(仅为11.4%),主要体现为伊利石的化学性质。储层水敏损害程度中等偏强,膨胀性粘土矿物引起的损害程度有限,岩心水敏损害机理主要为:次生非晶态物质缩小有效喉道半径;多种粘土矿物共生结构破坏或分散;非膨胀性粘土矿物集合体的分散和单晶碎裂;孔隙杂基结构坍塌及微粒运移加剧喉道堵塞。

Water sensitivity experiment and damage mechanism of sandstone reservoirs with ultra-low permeability:a case study of the eighth oil layer in the Yanchang Formation of Xifeng oilfield, Ordos Basin

Taking the eighth oil layer of Yanchang Formation in Xifeng oilfield in Ordos Basin as an example,this paper investigates reservoir characteristics through cast thin section observation,SEM,image analysis and whole rock analysis,and studies water sensitivity through core flow displacement experiment.In addition,the changes of microscopic features within cores before and after water sensitivity experiment such as clay mineral occurrence and pore structure are qualitatively and quantitatively determined by using SEM and capillary flow porometer respectively,so as to investigate the mechanism of water sensitivity.The eighth oil layer of Yanchang Formation in Xifeng oilfield is a sandstone reservoir with ultra-low permeability.Its clay minerals are dominated by kaolinite,chlorite and illite,with no montmorillonite but some mixed-layer illite/smectite(only 11.4%).The degree of water sensitivity damage is moderate to strong.The damage from expanding clays is limited.The mecha-nisms of water sensitivity damage in cores include reduction of effective throat radius caused by secondary amorphous;damage or scattering of the paragenetic structures of clay minerals;dispersion of non-expanding clay mineral assemblage and cracking of their single crystal;collapsing of structure of matrix in pores and throat-plugging caused by migration of fine particles.