Microfracture and Surfactant Impact on Linear Cocurrent Brine Imbibition in Gas-Saturated Shale

Abstract

During and after hydraulic fracturing, fluid–shale interaction has a prominent impact on liquid retention and thus on gas phase permeability and gas productivity. By providing a low surface tension or wettability alteration, surfactants are widely used to decrease liquid retention after fracturing. To evaluate the liquid intake of a rock sample, an imbibition experiment is commonly used, especially when it is treated by a surfactant. However, conventional imbibition experiments with gas shale could not quantitate the imbibition behaviors as it does with conventional rocks because of the low porosity and extremely low permeability of gas shale. In this paper, a comprehensive experimental method was successfully developed to study the liquid imbibition in shale samples. Bulk shale easily fell apart during imbibition experiments. However, samples prepared with the coating method decribed herein remained intact except for fractures generated in them during the first imbibition. On each imbibition curve with imbibed mass as a function of time, two imbibition rates were identified: first imbibition rate at early stage and the second imbibition rate at later stage. For each sample, the imbibition experiment was performed three times. The sample was treated by surfactant between the second and the third imbibitions. All fractures were generated during the first imbibition. The characteristics of these fractures, such as quantity and distribution, are described in detail. In order to avoid the microfracture impact, the second and the third imbibition data were used to study the surfactant impact on the liquid intake in shale. The surfactant worked well to reduce the mass gain in shale. The effects of the existence of fractures, sample length, surfactant concentration, and treatment methods on the first and second imbibition rates were all studied in detail.

A critical review of water uptake by shales

“…Recently, many publications have reported that micro-fractures, which can take up a significant amount of water, are created due to swelling of clays by absorbing water molecules (Makhanov et al 2014;Roshan et al 2015;Sun et al 2015;Zhou et al 2016;. As expected, imbibition of oil should create fewer micro-fractures compared to imbibition of water, and this was demonstrated by Makhanov (2013) as shown in Figure 2.…”

Experimental investigation of shale imbibition capacity and the factors influencing loss of hydraulic fracturing fluids

“…The cumulative imbibed volume increases with time. However, the rate of water intake obviously slows down with increasing time, and the rate approximately reaches zero, which represents the equilibrium condition (Sun et al 2015). However, some curves may have ''upward tails,'' which demonstrate an obvious diffusion effect and may be related to the complex pore structure in these rock samples, as shown in Fig.…”

Effect of Surfactant Adsorption on the Wettability Alteration of Gas-Bearing Shales

“…The ultimate fate of the lost hydraulic fracturing treatment water (*70% of total injected volume) and the role that these fluids may have in altering reservoir gas production remain an open question (Cheng, 2012;Jackson et al, 2014). Previous studies and industry experience suggest that liquid imbibed into tight rocks is easily trapped near the fracture face and is not usually drained during production due to the strong capillary forces (Bennion et al, 1996;Dehghanpour et al, 2013;Sun et al, 2015). Increased liquid trapping and water saturation in the rock near the fracture would thus reduce gas relative permeability and impair reservoir gas productivity (Bennion et al, 1994).…”