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Shale gas is a promising energy source offering additional energy security over concerns of fossil fuel depletion. Injecting CO 2 into depleted shale gas reservoirs might provide a feasible solution for CO 2 storage and enhanced gas recovery. However, shale strain caused by the CO 2 injection as well as CO 2 sequestration in the reservoir needs to be considered during shale gas production. For this purpose, this paper examines the adsorption capacities, CO 2 -induced swelling, and He-induced strain of shales at 0–16 MPa and 35–75 °C. The maximum excess adsorption at different temperatures correlated with the bulk phase density: as the CO 2 temperature increased, the maximum excess adsorption density decreased. The density of the adsorbed phase, obtained using the Dubinin–Radushkevich model, was used to fit the excess adsorption data. At low pressure, the CO 2 -induced strain on shale was caused by the gas adsorption, whereas at high pressure, it was caused by gas pressure. The absolute adsorption linearly correlated with the adsorption-induced strain.

In practical applications, the chemical and physical adsorption of a polymer solution greatly affects its action mode and effect. Understanding the adsorption mechanism and its influencing factors can help to optimize the application mode and ensure application efficiency. Three types of polymer solutions—partially hydrolyzed polyacrylamide (HPAM), hydrophobically associating polymer (AP-P4), and dendrimer hydrophobically associating polymer (DHAP), which are viscoelastic liquids—were used as sorbates to study their adsorption by a sorbent such as quartz sand. The effects of the solution concentration, contact time, particle size of quartz sand, solid–liquid ratio, and fluid movement on the adsorption capacity of the polymer solutions were examined. The results showed that HPAM presents a typical Langmuir monolayer adsorption characteristic, and its adsorption capacity (per unit area) is 1.17–1.62 μg/cm2. The association enhances the interactions of the AP-P4 and DHAP solutions, and they present multilayer characteristics of first-order chemical adsorption and secondary physical molecule adsorption. Moreover, the dendrite structure further increases the adsorption thickness of DHAP. Hence, the adsorption thicknesses of AP-P4 and DHAP are four and six times that of HPAM, respectively. The adsorption of the three polymers is consistent with the influence of fluid motion and decreases with increasing fluid velocity. However, the larger the thickness of the adsorption layer, the clearer the influence of the flow, and the higher the decrease in adsorption capacity. Optimizing the injection rate is an effective method to control the applications of a polymer in porous media.

To study the relative sensitivity of permeability to pore pressure P p and confi ning pressure P c for clay-rich rocks, permeability measurements were performed on samples of four clay-rich sandstones. A new method (hereafter denoted the "slide method") was developed and used for analyzing the permeability data obtained. The effective pressure coeffi cients for permeability n k were calculated. The values of n k were found to be greater than 1.0 and insensitive to changes in pressure. These results confirmed observations previously made on clay-rich rocks. Also, the coefficients n k obtained had different characteristics for different samples because of differences in the types of clay they contained. The effective pressure law (σ eff =P c -n k P p ) determined using the slide method gave better results about k(σ eff ) than classic Terzaghi's law (σ eff =P c -P p ).

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