Microfluidic Diagnostics of the Impact of Local Microfracture Connectivity on Hydrocarbon Recovery Following Water Injection

Abstract

Microfractures originate in hydrocarbon reservoirs and groundwater aquifers either in the form of pore‐scale authigenic apertures or secondary openings during well stimulation. Microfractures are often difficult to detect and can act as an invisible impediment when predicting hydrocarbon recovery. We use microfluidics to identify the flow conditions at which microfracture connectivity with macrofractures becomes impactful. The analysis focuses on fluid displacements at unfavorable mobility ratios, which are difficult to capture with high‐order numerical methods. Two configurations of microfracture type with the porous matrix, either dead‐end (only connected to one macrofracture) or connecting two macrofractures, were investigated as case examples for both water and oil‐wet conditions. Our findings confirm that improvements in hydrocarbon recovery are not universal due to the presence of microfractures but rather are a function of capillary number, wettability, and microfracture connectivity. We find that, regardless of wettability, a capillary number threshold for a connected microfractured system exists beyond which the effects of microfractures on recovery, fluid dendrite morphology, and oil ganglia number diminish considerably. However, substantial geometry‐dependent differences in recovery are observed below this threshold. A connected microfracture generally decreases hydrocarbon recovery and suppresses coalescence of viscous fingering dendrites regardless of wettability. In contrast, a dead‐end microfracture causes wettability‐dependent effects with (1) minimal impact on hydrocarbon recovery at water‐wet conditions and (2) both decreasing and increasing recovery effects at oil‐wet conditions. Furthermore, dead‐end microfractures become somewhat impactful to the divergence of viscous dendrites when capillary number increases but are overall ineffective to the trapped ganglia numbers.

Effect of Surfactant‐Assisted Wettability Alteration on Immiscible Displacement: A Microfluidic Study

“…The box‐counting method was adopted to determine the fractal dimension of displacing fluids, and the grains in images need to be removed to perform fractal dimension determination. Therefore, the “Dilate” and “Erode” functions were typically used to remove grains in images before performing the fractal dimension measurements (Du et al., 2020). Because NAPL in binary images is black in color, we performed dilation on the images to remove the white grains.…”

“…Images of the same experiments at different times were converted into stacks for processing. The “Enhanced Local Contrast” plugin was utilized to enhance the local contrast of each image in stacks for quantitative analysis (Du et al., 2020). Color images were converted to grayscale mode and binarized using “Otsu” thresholding method (Islam et al., 2014; Mehmani et al., 2019).…”

“…Immiscible displacement is of vital importance in many subsurface processes, such as carbon sequestration, enhanced oil recovery (EOR), nonaqueous phase liquid (NAPL) remediation (Al‐Raoush, 2009; Detwiler et al., 2001; Du et al., 2020; Hu et al., 2017; Yamabe et al., 2015; Zhang et al., 2011; Zhong et al., 2003). Wettability is an important factor affecting immiscible displacement in porous media.…”

Wettability effect on oil recovery using rock-structured microfluidics

“…38 In the petroleum field, brine-flooding experiments have been performed (using crude-oil-aged cores mostly or micromodels very recently) to investigate wettability's effect on oil recovery, where the surface wetting conditions are altered or varied by changing the brine composition, oil type or aging temperature. 17,24,39 The experimental results have revealed that the recovery factor (RF) varies nonmonotonically when the core changes from oil-wet to waterwet conditions. 24 Studies have recently shown an improved oil recovery from low-salinity flooding [40][41][42][43] since the lowsalinity flood can alter the rock wettability by inducing surface charges at oil/brine/rock interfaces.…”

A Coreflood‐on‐a‐Chip Study of Viscoelasticity's Effect on Reducing Residual Saturation in Porous Media

“…Microfluidics is a fast screening tool for investigating flow dynamics at the pore-scale and even representative elementary volume scale (Anbari et al, 2018;Lifton, 2016;Mehmani et al, 2020). It is commonly used to study multiphase flow processes encountered in subsurface environments, such as NAPL displacement (de Castro et al, 2015;Phenrat et al, 2011;Zhong and Mayer, 2001) and hydrocarbon recovery (Du et al, 2020;Li et al, 2020;Mejia et al, 2019;Yun et al, 2020).…”