Siddiqui Mohammed Abdul Qadeer, Salvemini Filomena, Ramandi Hamed Lamei, Fitzgerald Paul, Roshan Hamid
School of Minerals and Energy Resources Engineering, UNSW Australia, Kensington, Sydney, 2052, Australia.
Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights, NSW, 2234, Australia.
Sci Rep. 2021 Jan 25;11(1):2152. doi: 10.1038/s41598-021-81004-1.
Understanding fluid flow in shale rocks is critical for the recovery of unconventional energy resources. Despite the extensive research conducted on water and oil flow in shales, significant uncertainties and discrepancies remain in reported experimental data. The most noted being that while oil spreads more than water on shale surfaces in an inviscid medium, its uptake by shale pores is much less than water during capillary flow. This leads to misjudgement of wettability and the underlying physical phenomena. In this study, therefore, we performed a combined experimental and digital rock investigation on an organic-rich shale including contact angle and spontaneous imbibition, X-ray and neutron computed tomography, and small angle X-ray scattering tests to study the potential physical processes. We also used non-equilibrium thermodynamics to theoretically derive constitutive equations to support our experimental observations. The results of this study indicate that the pre-existing fractures (first continuum) imbibe more oil than water consistent with contact angle measurements. The overall imbibition is, however, higher for water than oil due to greater water diffusion into the shale matrix (second continuum). It is shown that more water uptake into shale is controlled by pore size and accessibility in addition to capillary or osmotic forces i.e. configurational diffusion of water versus oil molecules. While the inorganic pores seem more oil-wet in an inviscid medium, they easily allow passage of water molecules compared to oil due to the incredibly small size of water molecules that can pass through such micro-pores. Contrarily, these strongly oil-wet pores possessing strong capillarity are restricted to imbibe oil simply due to its large molecular size and physical inaccessibility to the micro-pores. These results provide new insights into the previously unexplained discrepancy regarding water and oil uptake capacity of shales.
了解页岩中的流体流动对于非常规能源的开采至关重要。尽管对页岩中的水和油流动进行了广泛研究，但报告的实验数据仍存在重大不确定性和差异。最值得注意的是，在无粘性介质中，油在页岩表面的铺展比水更广泛，但在毛细管流动过程中，页岩孔隙对油的吸收远少于水。这导致对润湿性和潜在物理现象的误判。因此，在本研究中，我们对富含有机质的页岩进行了实验和数字岩心相结合的研究，包括接触角和自发渗吸、X射线和中子计算机断层扫描以及小角X射线散射测试，以研究潜在的物理过程。我们还使用非平衡热力学从理论上推导本构方程，以支持我们的实验观察结果。本研究结果表明，与接触角测量结果一致，预先存在的裂缝（第一连续介质）吸收的油比水多。然而，由于水向页岩基质（第二连续介质）的扩散更大，水的总体渗吸量高于油。结果表明，除了毛细管力或渗透力外，页岩对水的更多吸收还受孔径和可及性的控制，即水分子与油分子的构型扩散。虽然在无粘性介质中无机孔隙似乎更亲油，但由于水分子尺寸极小，能够穿过此类微孔，因此与油相比，它们更容易让水分子通过。相反，这些具有强毛细作用的强亲油孔隙仅仅由于油分子尺寸大且无法进入微孔而限制了对油的吸收。这些结果为页岩对水和油吸收能力方面先前无法解释的差异提供了新的见解。
