Abstract
Low-permeability (unconventional) hydrocarbon reservoirs exhibit a complex nanopore structure and micro (µm) -scale variability in composition which control fluid distribution, displacement and transport processes. Conventional methods for characterizing fluid-rock interaction are however typically performed at a macro (mm) -scale on rock sample surfaces. In this work, innovative methods for the quantification of micro-scale variations in wettability and fluid distribution in a low-permeability oil reservoir was enabled by using an environmental scanning electron microscope. Live imaging of controlled water condensation/evaporation experiments allowed micro-droplet contact angles to be evaluated, while imaging combined with x-ray mapping of cryogenically frozen samples facilitated the evaluation of oil and water micro-droplet contact angles after successive fluid injection. For the first time, live imaging of fluids injected through a micro-injection system has enabled quantification of sessile and dynamic micro-droplet contact angles. Application of these combined methods has revealed dramatic spatial changes in fluid contact angles at the micro-scale, calling into question the applicability of macro-scale observations of fluid-rock interaction.
Highlights
Recent advances in imaging technologies such as focused-ion-beam scanning electron microscopy (FIB-SEM)[4] have revealed important details regarding the nanopore structure in shales[5], an important UHR
Focusing attention on the dolomite grain, it can be observed that micro-droplet growth occurs on the grain until Frame 7, after which an evaporation cycle initiates
Frame 4 is selected for droplet profile extraction (Fig. 3a) because the contact angle in later frames is affected by pinning and the micro-droplet wetting and merging with a micro-droplet growing on an offset grain (Frames 5–8)
Summary
Recent advances in imaging technologies such as focused-ion-beam scanning electron microscopy (FIB-SEM)[4] have revealed important details regarding the nanopore structure in shales[5], an important UHR This pore structure information has been used in the population of pore-scale models to predict important shale reservoir properties affecting fluid storage and flow properties such as porosity and permeability[6]. It is possible that these pore-scale models may even be able to predict important reservoir properties affecting multi-phase flow of gas, water and oil in UHRs, such as relative permeability and capillary pressure. While imaging of rock nanopore structure is routine, imaging of fluid-rock interaction at this scale, necessary for quantifying multi-phase fluid distribution and flow, is not
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