Summary Hydraulic fracturing is used to obtain economical rates from tight and unconventional formations by increasing the surface area of the reservoir within the flowing distance to a high-conductivity pathway. However, a significant fraction of the fracturing fluid is never recovered, and thus may reduce the hydrocarbon permeability near the fracture. Here, we experimentally mimic the water-invasion process during fracturing, and measure the effective permeability changes in a low-permeability core. Measurements of water flowback and effective permeability as a function of interfacial tension (IFT), flow rate, and shut-in time suggest that water is being held at the fracture face because of the capillary discontinuity (i.e., when the water leaves the matrix and enters a space with minimal capillary pressure). This effect arises from the capillary interaction between the matrix and the fracture, and is akin to the capillary end effect in coreflood experiments. The results show that this effect, although only a laboratory experimental artifact for conventional reservoirs, can be a significant source of effective hydrocarbon-permeability reduction by fracturing-fluid invasion into the formation in unconventional and tight reservoirs.
Significant amounts of fracturing fluid are lost during hydraulic fracturing operations and it is believed that this fluid can hinder hydrocarbon production. For this reason, higher fracturing fluid recovery (flowback) might be desirable. One way to enhance the flowback is to reduce the capillary force within the formation. While the applicability of surfactants in conventional reservoirs that operate in tertiary production phase is fairly well understood, it is unclear whether these techniques can enhance the production in unconventional reservoirs that operate in the primary phase; and the magnitude of the enhancement that can be expected by using the surfactants as fracturing fluid additives. Here, we designed a coreflood sequence that simulated fracturing fluid invasion, flowback and hydrocarbon production in order to quantify the permeability damage due to fluid invasion. Furthermore, we evaluated the enhancements in hydrocarbon permeability due to the use of IFT reducing agents. Our results revealed a mechanism of permeability damage and indicated that improvements in hydrocarbon permeability observed with surfactant-supplemented fracturing fluids were due to the reduction of water trapping through matrix-fracture interaction and not to the capillary desaturation of the rock.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.