致密油藏储层微观孔隙特征与可动用性评价

Micro-Pore Characteristics and Recoverability of Tight Oil Reservoirs

致密油储层主要包括致密灰岩和致密砂岩,两者微观特征差异明显.但目前针对致密灰岩和致密砂岩的对比研究相对较少,因此开展致密油藏不同岩性微观孔隙结构特征及可动用性研究具有十分重要的意义.利用低温氮吸附比表面、核磁共振、压汞等方法,从纳米级、亚微米级、微米级孔隙等不同尺度表征了致密灰岩和致密砂岩孔隙结构差异,分析了不同孔隙对渗透率的贡献和对流体赋存的影响,研究了启动压力梯度的差异和喉道对启动压力梯度的影响.以川中灰岩和长庆砂岩为例,结果表明渗透率大于0.01mD储层具备开发潜力,致密灰岩中的亚微米和微米级孔隙是重要的储集和流动空间,致密砂岩中微米级孔隙是重要的储集和流动空间.基于微观实验分析和低渗透油藏评价方法,提出了致密油藏分级评价参数,并给出了分级评价界限,对确定致密油藏攻关目标和优选区块新建产能意义重大.

Tight oil reservoirs mainly include tight limestone and tight sandstone,and there are significant differences in their microscopic characteristics.However,there are relatively fewer comparative studies on tight limestone and tight sandstone,so it is very important to study micro-pore characteristics and recoverability of different lithology tight oil reservoirs.By combining cryogenic nitrogen adsorption surface area,nuclear magnetic resonance and high pressure mercury technology,this paper comprehensively described the pore structure differences between tight limestone and tight sandstone from various scales including nano scale,submicron scale and micro scale,analyzed the effect of pores at different scales on permeability and fluid occurrence state,and studied the difference of the starting pressure gradient and the effect of throat on the starting pressure gradient.Taking the central Sichuan limestone and Changqing sandstone as an example,the results show that the tight oil reservoirs have development potential with permeability of more than 0.01 mD,in tight limestone,the submicron and micron scale pores are important reservoir and flow spaces,and in tight sandstone the micron scale pores are important reservoir and flow spaces,which are key to effective development.Based on numerous microscopic experimental analysis and low permeability reservoir evaluation methods,8 grading evaluation parameters of tight reservoir were proposed and grading evaluation boundaries were determined,which is of great significance to determine the target of tight reservoirs and select the preferred blocks to build capacity.