Abstract Pore-fluid is directly related to the reservoir quality. Three-dimensional (3D) nuclear magnetic resonance (NMR) can be used for charactering pore-fluid due to its sensitivity to fluid components saturated in sedimentary rocks. In this paper, taken a tight sandstone as an example, investigating pore-fluid characterizations and microscopic mechanisms through 3D NMR. Firstly, a commonly used 3D NMR pulse sequence, tri-window pulse sequence, in actual oilfield was presented and its data processing workflow was exhibited briefly. Then, random-walk method was modified to simulate the pulse sequence measurements at different pore-fluid cases in tight sandstone, such as pure water case, oil-water case, and gas-water case. Finally, pore-fluid 3D NMR responses were exhibited and their microscopic mechanisms were explored. The results show that 3D NMR can identify different fluid components saturated in sedimentary rocks; wetting fluid saturation directly affect wetting fluid relaxation time, but the non-wetting fluid relaxation information is independent of fluid saturation; wetting fluid has an obvious restricted diffusion as a lower saturation; an obvious difference between gas signal and water or oil signal in two-dimensional relaxation spectra due to high longitudinal to transverse relaxation time ratio of pore gas. These simulations provide a theoretical basis for interpreting 3D NMR macroscopic responses, which should be helpful for pore-fluid identifying in tight oil and gas reservoirs.

中文翻译：

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三维核磁共振沉积岩孔隙流体特征及微观机制：以致密砂岩为例

摘要 孔隙流体直接关系到储层质量。三维 (3D) 核磁共振 (NMR) 可用于表征孔隙流体，因为它对沉积岩中饱和的流体成分敏感。本文以致密砂岩为例，通过3D NMR研究孔隙流体特征和微观机制。首先介绍了一种在实际油田中常用的3D NMR脉冲序列——三窗脉冲序列，并简要展示了其数据处理流程。然后，改进随机游走方法以模拟致密砂岩中不同孔隙流体情况下的脉冲序列测量，例如纯水情况、油水情况和气水情况。最后，展示了孔隙流体 3D NMR 响应并探索了它们的微观机制。结果表明，3D NMR可以识别沉积岩中饱和的不同流体成分；润湿流体饱和度直接影响润湿流体弛豫时间，但非润湿流体弛豫信息与流体饱和度无关；润湿液由于饱和度较低，扩散受限明显；由于孔隙气体的纵横向弛豫时间比高，二维弛豫谱中的气体信号与水或油信号之间存在明显差异。这些模拟结果为解释 3D NMR 宏观响应提供了理论基础，有助于致密油气藏孔隙流体识别。但非润湿流体弛豫信息与流体饱和度无关；润湿液由于饱和度较低，扩散受限明显；由于孔隙气体的纵横向弛豫时间比高，二维弛豫谱中的气体信号与水或油信号之间存在明显差异。这些模拟结果为解释 3D NMR 宏观响应提供了理论基础，有助于致密油气藏孔隙流体识别。但非润湿流体弛豫信息与流体饱和度无关；润湿液由于饱和度较低，扩散受限明显；由于孔隙气体的纵横向弛豫时间比高，二维弛豫谱中的气体信号与水或油信号之间存在明显差异。这些模拟结果为解释 3D NMR 宏观响应提供了理论基础，有助于致密油气藏孔隙流体识别。