Rapid imbibition of water in fractures within unsaturated sedimentary rock

Abstract

2The spontaneous imbibition of water and other liquids into gas-filled 3 fractures in variably-saturated porous media is important in a variety of 4 engineering and geological contexts. However, surprisingly few studies have 5 investigated this phenomenon. We present a theoretical framework for 6 predicting the 1-dimensional movement of water into air-filled fractures 7 within a porous medium based on early-time capillary dynamics and 8 spreading over the rough surfaces of fracture faces. The theory permits 9 estimation of sorptivity values for the matrix and fracture zone, as well as a 10 dispersion parameter which quantifies the extent of spreading of the wetting 11 front. Quantitative data on spontaneous imbibition of water in unsaturated 12 Berea sandstone cores were acquired to evaluate the proposed model. The 13 cores with different permeability classes ranging from 50 to 500 mD and 14 were fractured using the Brazilian method. Spontaneous imbibition in the 15 fractured cores was measured by dynamic neutron radiography at the 16 Neutron Imaging Prototype Facility (beam line CG-1D, HFIR), Oak Ridge 17 National Laboratory. Water uptake into both the matrix and the fracture 18 zone exhibited square-root-of-time behavior. The matrix sorptivities ranged 19 from 2.9 to 4.6 mm s -0.5 , and increased linearly as the permeability class 20 increased. The sorptivities of the fracture zones ranged from 17.9 to 27.1 21 mm s -0.5 , and increased linearly with increasing fracture aperture width. The 22 dispersion coefficients ranged from 23.7 to 66.7 mm 2 s -1 and increased 23 linearly with increasing fracture aperture width and damage zone width. 24 Both theory and observations indicate that fractures can significantly 25 increase spontaneous imbibition in unsaturated sedimentary rock by 26 capillary action and surface spreading on rough fracture faces. Fractures 27 also inrease the dispersion of the wetting front. Further research is needed 28 7

Effects of microstructure on water imbibition in sandstones using X‐ray computed tomography and neutron radiography

“…The Bond number ( B o ) is a dimensionless value that can be used to demonstrate the gravity that can be neglected under the conditions of our tests [ Cheng et al ., ]. The equation for Bond number is B O = ρ ⋅ g ⋅ k w / σ .…”

“…Ignoring the maximum and minimum values, the average sorptivity is 0.5643 mm s −1/2 for X1 and 0.5673 mm s −1/2 for C1. These sorptivity results are much smaller than those reported for Berea sandstone matrix sorptivities ranging from 2.90 to 4.55 mm s −1/2 , which were captured within very early time of imbibition [ Cheng et al ., ]. This means that the conclusion proposed by Cheng et al .…”

“…This means that the conclusion proposed by Cheng et al . [] that sorptivities increased linearly with the increase of the permeability does not apply in the current investigation. Moreover, it was found that the sorptivities are almost the same, although there is a dramatic difference in porosity and pore size distribution between X1 and C1.…”

“…More recently, Cheng et al . [] presented the results of water imbibition in the fractures of Berea sandstones specifically in the initial stage of imbibition. Kang et al .…”

Quantitative investigation on the characteristics of ions transport into water in gas shale: Marine and continental shale as comparative study

“…This trend is probably related to microfractures development in the shale. The large particles may contain microfractures that can significantly increase imbibition rate (Cheng et al, 2015;Ghanbari et al, 2013).…”