Study on Oil Recovery Mechanism of Polymer-Surfactant Flooding Using X-ray Microtomography and Integral Geometry

Abstract

Understanding pore-scale morphology and distribution of remaining oil in pore space are of great importance to carry out in-depth tapping of oil potential. Taking two water-wet cores from a typical clastic reservoir in China as an example, X-ray CT imaging is conducted at different experimental stages of water flooding and polymer-surfactant (P-S) flooding by using a high-resolution X-ray microtomography. Based on X-ray micro-CT image processing, 3D visualization of rock microstructure and fluid distribution at the pore scale is achieved. The integral geometry newly developed is further introduced to characterize pore-scale morphology and distribution of remaining oil in pore space. The underlying mechanism of oil recovery by P-S flooding is further explored. The results show that the average diameter of oil droplets gradually decreases, and the topological connectivity becomes worse after water flooding and P-S flooding. Due to the synergistic effect of “1 + 1 > 2” between the strong sweep efficiency of surfactant and the enlarged swept volume of the polymer, oil droplets with a diameter larger than 124.58 μm can be gradually stripped out by the polymer-surfactant system, causing a more scattered distribution of oil droplets in pore spaces of the cores. The network-like oil clusters are still dominant when water flooding is continued to 98% of water cut, but the dominant pore-scale oil morphology has evolved from network-like to porous-type and isolated-type after P-S flooding, which can provide strong support for further oil recovery in the later stage of chemical flooding.

Pore‐Scale Modeling of Pressure‐Driven Flow and Spontaneous Imbibition in Fracturing‐Shut‐In‐Flowback Process of Tight Oil Reservoirs

“…In last decades, due to its rapid development, X-ray CT imaging has been widely used to obtain the microstructure of different kinds of rocks. In contrast to FIB-SEM, the industrial microfocus CT [30][31][32][33][34][35] is a nondestructive measurement device that uses X-rays to penetrate rocks from different angles. FIB-SEM is limited to depicting small sample sections, making it difficult to accurately investigate the differently sized structures in tight rock.…”

Effects of Core Size and Surfactant Choice on Fluid Saturation Development in Surfactant/Polymer Corefloods

“…Interpretation of corefloods is typically solely dependent on effluent analysis; this, inherently, is a limited viewpoint and can lead to uncertainty about in situ behavior such as emulsification or polymer degradation. − To this aim, direct imaging has proven invaluable in developing a greater understanding of both flow and transport within these complex systems . Microfluidics and micro X-ray computed tomography (CT) have allowed for insights into a range of microscale phenomena such as stability of emulsions and pore-scale distribution of fluids. , However, by nature, these two approaches are restricted in both sample and viewing size and, as such, are often used as prescreening experiments, or in combination, to corefloods; promising exception being larger micromodels capturing macroscale behavior successfully . Medical X-ray CT, on the other hand, allows for imaging of representative core samples and, most commonly, extraction of saturation profiles. , Despite this, only rarely have these studies expanded on the direct imaging results, notable cases being the incorporation of internal profiles in evaluating modeling approaches and the provision of insights into the existence of instabilities in the underlying displacement process …”

“… 37 Microfluidics and micro X-ray computed tomography (CT) have allowed for insights into a range of microscale phenomena such as stability of emulsions 38 and pore-scale distribution of fluids. 39 , 40 However, by nature, these two approaches are restricted in both sample and viewing size 41 and, as such, are often used as prescreening experiments, or in combination, to corefloods; 42 promising exception being larger micromodels capturing macroscale behavior successfully. 43 Medical X-ray CT, on the other hand, allows for imaging of representative core samples and, most commonly, extraction of saturation profiles.…”