Impact of de-ionized water on changes in porosity and permeability of shales mineralogy due to clay-swelling

Abstract

Hydraulic fracturing is widely applied for economical gas production from shale reservoirs. Still, the swelling of the clay micro/nano pores due to retained fluid from hydraulic fracturing causes a gradual reduction of gas production. Four different gas-bearing shale samples with different mineralogical characteristics were investigated to study the expected shale swelling and reduction in gas permeability due to hydraulic fracturing. To simulate shale softening, these shale samples were immersed in deionized (DI) water heated to 100 °C temperature and subjected to 8 MPa pressure in a laboratory reactor for 72 hours to simulate shale softening. The low-temperature nitrogen adsorption and density measurements were performed on the original and treated shale to determine the changes in micro and nano pore structure. The micro and nano pore structures changed, and the porosity decreased after shale treatment. The porosity decreased by 4% for clayey shale, while for well-cemented shale the porosity only decreased by 0.52%. The findings showed that the initial mineralogical composition of shale plays a significant role in the change of micro and nano pores and the pore structure alteration due to retained fluid from hydraulic fracturing. A pore network model is used to simulate the permeability of shale used in this study. To define pore structure properties, specific factors such as porosity, pore size, pore throat distribution, and coordination number were used. Furthermore, the anisotropy characteristics of shale were integrated into the model via a coordination number ratio. Finally, the change in permeability due to shale softening was determined and compared with untreated with the progress of shale softening. The simulation showed that the permeability of Longmaxi shale could decrease from 3.82E–16 m2 to 4.71E–17 m2 after treatment.

Per- and Polyfluoroalkyl Substance Release from Aqueous Film-Forming Foam Impacted Solids Exposed to Stormwater and Saltwater

“…CaCl 2 was added to deionized water to decrease the diffuse double layer and thus solid swelling. 34 To ensure effective sorption, each column was loaded over the course of 6 days by recycling the loading solution through the column. Initial and final concentrations of the loading solution were collected and measured (Table S11).…”

Prediction of gas production rate from shale gas reservoirs using a micro–macro analysis

“…The pore diameters and porosity values were obtained from the experimental data presented before and shown in Table 1 . In a previous study, different tests (X-Ray Diffractometer Analysis (XRD), Scanning Electron Microscope (SEM) Analysis, Thermo Gravimetric Analysis (TGA), Computer Technology (CT) and Pore Size Distribution Analysis using the Brunauer–Emmett–Teller (BET) gas adsorption method) were conducted to obtain pore structures of the four shale formations studied in this research under laboratory conditions 23 . Other parameters, including the coordination numbers and anisotropic ratios, were set based on previous research on shale 12 .…”

“…Table 1. Shale sample parameters 23,24 . www.nature.com/scientificreports/ or reflection boundary was set at the left boundary and a constant pressure equal to wellbore pressure was set as the right boundary (outlet).…”

Experimental Study of True Triaxial High Pressure Subcritical Water Impact Fracturing

“…In order to improve fracturing efficiency and form a novel fracturing technology system, many scholars have proposed new alternative fluids to fracturing fluids, including CO2 11,12 , liquid nitrogen 13 , and highenergy gas 14 . The reduction of water use can solve the challenges of shale gas extraction in arid and water-scarce regions, while preserving precious water resources 15,16 . Advantages of supercritical CO2 fracturing are: low fracture initiation pressure, complex fracture-causing fractures, and easier communication of microfractures 17,18 ; three aspects of fracture initiation pressure, fracture distribution, and microfracture extension are currently studied experimentally 19,20 ; fracture extension was observed by CT, scanning electron microscopy, and acoustic loss measurement instruments 21,22 .…”