Capillary pressure – saturation relationships for gas shales measured using a water activity meter

Abstract

Hydraulic fracturing of gas shale formations involves pumping a large volume of fracking fluid into a hydrocarbon reservoir to fracture the rock and thus increase its permeability.The majority of the fracking fluid introduced is never recovered and the fate of this lost fluid, often called "leak off," has become the source of much debate. Information on the capillary pressuresaturation relationship for each wetting phase is needed to simulate leak off using numerical reservoir models. The petroleum industry commonly employs airwater capillary pressuresaturation curves to predict these relationships for mixed wet reservoirs. Traditional methods of measuring this curve are unsuitable for gas shale's due to high capillary pressures associated with the small pores present. A possible alternative method is the water activity meter which is used widely in the soil sciences for such measurements. However, its application to lithified material has been limited. This study utilized a water activity meter to measure airwater capillary pressures (ranging from 1.3 -219.6 MPa) at several water saturation levels in both the wetting and drying directions. Water contents were measured gravimetrically. Seven types of gas producing shale with different porosities (2.5 -13.6%) and total organic carbon contents (0.4 -13.5%) were investigated. Nonlinear regression was used to fit the resulting capillary pressurewater saturation data pairs for each shale type to the Brooks and Corey equation. Data for six of the seven shale types investigated were successfully fitted (median R 2 = 0.93), indicating this may be a viable method for parameterizing capillary pressuresaturation relationships for inclusion in numerical reservoir models. As expected, the different shale types had statistically different Brooks and Corey parameters. However, there were no significant differences between the Brooks and Corey parameters for the wetting and drying measurements, suggesting that hysteresis may not need to be taken into account in leak off simulations.

Spontaneous Imbibition of a Wetting Fluid Into a Fracture With Opposing Fractal Surfaces: Theory and Experimental Validation

“…29 Gehne and Benson 30 report that the permeability of Crossville sandstone varies between 3 × 10 −18 and 3×10 −17 m 2 . The solid phase density and helium gas porosity of the cored samples were measured using the method of Donnelly et al 31 and were determined to be 2.50 (±0.01) gcm −3 and 5.85 (±0.27)%, respectively.…”

“…The samples investigated were gray in color with light gray interbedding. Their solid phase densities and helium gas porosities were determined, using the method of Imbibition in a Fractal Fracture Donnelly et al, 31 to be 2.50 (±0.01) gcm −3 and 5.59 (± 0.39)%, respectively.…”

Water Saturation Relations and Their Diffusion‐Limited Equilibration in Gas Shale: Implications for Gas Flow in Unconventional Reservoirs

“…In some studies, shales have been equilibrated in controlled relative humidity ( rh ) environments in order to obtain water vapor adsorption isotherms (Chenevert, ; Dosunmu & Okoro, ; Li et al, ; Seemann et al, ) that are beyond the range achievable with experimental techniques based on controlling differential pressures. An equivalent approach involves adjusting water contents of shales to specific levels and measuring the associated equilibrium rh values (Donnelly et al, ; Ferrari et al, ).…”

“…In our search of the literature, very few previous studies have reported desorption isotherms, and their conclusions are inconsistent. A couple of studies have reported significant hysteresis in adsorption and desorption isotherms (Chenevert, ; Ferrari et al, ), while another recent study reported negligible hysteresis (Donnelly et al, ). Moreover, to our knowledge, no previous study utilized a combination of humidity and capillary pressure control methods in order to examine the full range of water retention relations.…”

A Hysteretic Model Considering Contact Angle Hysteresis for Fitting Soil‐Water Characteristic Curves

“…For example, the Brooks and Corey (1964) model was used by Donnelly et al. (2016), Ekblad and Isacsson (2007), and Y. Liu et al. (1995), the Van Genuchten (1980) model was used by Bordoni et al.…”