Mitchell Jonathan, Lyons Kyle, Howe Andrew M, Clarke Andrew
Schlumberger Gould Research, High Cross, Madingley Road, Cambridge CB3 0EL, UK.
Soft Matter. 2016 Jan 14;12(2):460-8. doi: 10.1039/c5sm01749a. Epub 2015 Oct 19.
Viscoelastic polymer solutions flowing through reservoir rocks have been found to improve oil displacement efficiency when the aqueous-phase shear-rate exceeds a critical value. A possible mechanism for this enhanced recovery is elastic turbulence that causes breakup and mobilization of trapped oil ganglia. Here, we apply nuclear magnetic resonance (NMR) pulsed field gradient (PFG) diffusion measurements in a novel way to detect increased motion of disconnected oil ganglia. The data are acquired directly from a three-dimensional (3D) opaque porous structure (sandstone) when viscoelastic fluctuations are expected to be present in the continuous phase. The measured increase in motion of trapped ganglia provides unequivocal evidence of fluctuations in the flowing phase in a fully complex 3D system. This work provides direct evidence of elastic turbulence in a realistic reservoir rock - a measurement that cannot be readily achieved by conventional laboratory methods. We support the NMR data with optical microscopy studies of fluctuating ganglia in simple two-dimensional (2D) microfluidic networks, with consistent apparent rheological behaviour of the aqueous phase, to provide conclusive evidence of elastic turbulence in the 3D structure and hence validate the proposed flow-fluctuation mechanism for enhanced oil recovery.
当水相剪切速率超过临界值时，已发现粘弹性聚合物溶液流经储层岩石可提高驱油效率。这种提高采收率的一种可能机制是弹性湍流，它会导致被困油滴的破裂和运移。在此，我们以一种新颖的方式应用核磁共振（NMR）脉冲场梯度（PFG）扩散测量来检测孤立油滴运动的增加。当预计连续相中存在粘弹性波动时，数据直接从三维（3D）不透明多孔结构（砂岩）获取。所测量的被困油滴运动的增加为完全复杂的3D系统中流动相的波动提供了明确证据。这项工作提供了真实储层岩石中弹性湍流的直接证据——这是传统实验室方法难以轻易实现的测量。我们通过对简单二维（2D）微流体网络中波动油滴的光学显微镜研究来支持核磁共振数据，水相具有一致的表观流变行为，从而为3D结构中的弹性湍流提供确凿证据，进而验证所提出的用于提高采收率的流动波动机制。
