The surface wettability and morphology of shale may both be modified by SiO2 nanofluid (SNF), directly influencing the capillary force and CO2 geo-storage. However, the literature requires more ...information and studies with respect to nanoparticles’ effect on shale surface at reservoir conditions of high pressure and temperature. Here, we investigate the stability of nanoparticle layers formed by SNF on Longmaxi (marine) and Yanchang (continental) shale in ScCO2 and nanoparticles’ efficiency of wettability reversal at different nanofluid aging times and concentrations. Besides, low-pressure nitrogen gas adsorption (LP-NA) was performed to evaluate the effect of nanoparticles on shale pore structures after ScCO2 exposure. Results indicate that the nanoparticle structure could be stable in ScCO2 and render the wettability of shale samples to be more hydrophilic, while the quartz-rich Longmaxi shale surface shows a denser nanostructure than the clay-rich Yanchang shale surface does and presents a stronger water wettability. More micropores are transformed into mesopores or macropores for ScCO2- and SNF-treated Longmaxi samples than solely ScCO2 samples, but the pore structure parameters show trivial alteration in Yanchang samples after SNF treatment. The difference in the capillary force recovery between Longmaxi (recovered by 660.5%) and Yanchang (recovered by 500.6%) shale implies that silica nanofluid may be more suitable for Longmaxi formation in the CGS application.
CO2 geo-sequestration (CGS) is crucial in tackling global climate change, and the safety of CO2 storage within the reservoir is intricately linked to wettability. The utilization of ...nanofluids-surfactants for adjusting reservoirs’ wettability has emerged as a promising approach to enhance the security of CGS. However, the mechanism underlying their impact on reservoir wettability and carbon sequestration remains elusive. Regarding nanoactive fluid (ASNF) compounded with nano-SiO2 and AOS, to explore its potential for wettability reversal of CO2-exposed shale under in situ conditions, comparative experiments were conducted with Longmaxi Formation shale as the subject. The chemical structures and microstructures of shale before and after the experiments were comprehensively characterized. The results showed that a maximum of 67.93 % enhanced the water wettability of samples co-treated with ASNF and ScCO2. The primary reason for shale wettability reversal was increased hydrophilic chemical groups and enhanced interaction energy between organic matter and water molecules, stemming from nanoactive particle retention on the shale surface. The alteration in wettability decreased the mobility of CO2 and increased the distribution of surface water films, enhancing the carbon sequestration capabilities of the trapping mechanism. These findings provided an important foundation for improving the effectiveness and safety of CGS in shale reservoirs.
•The reversal effect of ASNF on the wettability of CO2-exposed shale has been experimentally investigated.•The ASNF demonstrated significantly superior performance compared to SNF at compounding ratios not exceeding 1.•The effect of nanoactive fluids on the chemical structure and microstructure of shale after ScCO2 exposure is elaborated.•Nanoactive particles can avianize the negative effect of CO2 on structural trapping and potentiate the positive effects of CO2 trapping in shale.
CO2–slickwater hybrid fracturing technology is an essential part of shale gas recovery and CO2 geo-storage. However, the exposure to supercritical CO2 (ScCO2) and slickwater can result in potential ...changes of the pore structures and surface wetting behavior, which affect the gas transportation and CO2 sequestration security in shale reservoirs. Therefore, in this paper, X-ray diffraction (XRD), low-pressure nitrogen gas adsorption (N2GA), mercury intrusion porosimetry (MIP), and fractal analysis were used to describe the pore characteristics of shale before and after ScCO2–slickwater coupling treatments. Shale’s surface wettability was confirmed by contact angle measurements. After the ScCO2–slickwater treatments, the number of micropores (<3.5 nm) and mesopores (3.5–50 nm) increased, while that of macropores (>50 nm) declined based on the N2GA and MIP experiments. Combined with fractal analysis, we argue that the pore connectivity diminished and the pore structure became more complicated. By analyzing the results of XRD, shale pore changes occurring after the ScCO2–slickwater treatment can be explained by the adsorption of polyacrylamide (PAM). Contact angle measurement results showed that the shale’s surface treated by ScCO2 and slickwater was more hydrophilic than that treated by ScCO2 and water, and indirectly prove our argument above. Hence, the coupling using effect of ScCO2 and slickwater can impair the negative effect of CO2 on the shale capillary force to improve shale gas productivity, but it can negatively affect the security of CO2 sequestration in shale reservoirs.
Hydraulic fracturing is an essential technique to increase reservoir permeability and enhance the production of shale gas. When the dip angle is steep and geological condition is complex, hydraulic ...fractures may behave complexly, and research on this topic is critical for the shale gas industry. This paper reports a case study of hydraulic fracturing in a shale reservoir with a steep dip angle. We monitored pump data, including the injection rate and fluid pressure. Microseismic monitoring was also used to record the seismic events and monitor the hydraulic fracture propagation. Our results validated that microseismic monitoring is a feasible technique to monitor the hydraulic fracture propagation in shale reservoirs with steep dip angles. Moreover, the variation in depth of shale reservoir induces significant alternation of local in situ stress states, in which cases the fracture propagation pathway is more complex, and where microseismic monitoring is necessary to acquire the hydraulic fracture distribution. Besides, all sound sources, including quarries and rivers, should be eliminated during microseismic station arrangement to improve accuracy of microseismic signals. Moreover, the relationship between the maximum magnitude of seismic event and fluid injection volume was validated further in this study. Finally, unexpected faults and aquifers may affect hydraulic fracture propagation due to the steep dip angle of the target shale reservoir. Thus, a comprehensive geological survey is essential for better hydraulic fracturing design. Our results provide first-hand in situ hydraulic fracturing data and provide important implications for shale gas development, especially for those shale reservoirs with steep dip angles.
Reducing net carbon emissions is of great significance for sustainability. Carbon capture, utilization, and storage (CCUS) technology is regarded as one of the most effective approaches to reducing ...net carbon emissions. A prerequisite for the implementation of the CO2 geological storage project is the assessment of the storage potential of the storage site. In this study, a calculation method of storage potential was proposed to estimate the CO2 storage potential of the Yanchang shale gas reservoir in the Ordos Basin, China. In this method, the CO2 sealing capability of the caprock is taken into account, which determines the maximum CO2 storage pressure of the reservoir. The overall CO2 storage potential consists of four types of storage states (free-state, adsorption, dissolution, and mineralization). The maximum CO2 storage pressure of the Yanchang shale gas reservoir is 13.4 MPa via breakthrough pressure experiments, and the corresponding theoretical storage potential is 7.59 × 1011 t. The potential for free-state, adsorption, dissolution, and mineralization sequestration are 8.42 × 1010 t, 6.88 × 1010 t, 2.45 × 109 t, and 6.05 × 1011 t, respectively. Due to the difficulty in completing mineralization within the engineering time scale, the mineralization potential should not be taken into account when estimating the available CO2 storage potential. The available CO2 potential (including free-state, adsorption, and dissolution) of the Yanchang shale gas reservoir is 1.54 × 1011 t, which is a considerable amount. The Yanchang shale gas formation will be able to accommodate 41.49% of global annual CO2 emissions (according to the data in 2021) if the available CO2 storage potential of the Yanchang shale gas reservoir is fully exploited.
Reducing net carbon emissions is of great significance for sustainability. Carbon capture, utilization, and storage (CCUS) technology is regarded as one of the most effective approaches to reducing ...net carbon emissions. A prerequisite for the implementation of the COsub.2 geological storage project is the assessment of the storage potential of the storage site. In this study, a calculation method of storage potential was proposed to estimate the COsub.2 storage potential of the Yanchang shale gas reservoir in the Ordos Basin, China. In this method, the COsub.2 sealing capability of the caprock is taken into account, which determines the maximum COsub.2 storage pressure of the reservoir. The overall COsub.2 storage potential consists of four types of storage states (free-state, adsorption, dissolution, and mineralization). The maximum COsub.2 storage pressure of the Yanchang shale gas reservoir is 13.4 MPa via breakthrough pressure experiments, and the corresponding theoretical storage potential is 7.59 × 10sup.11 t. The potential for free-state, adsorption, dissolution, and mineralization sequestration are 8.42 × 10sup.10 t, 6.88 × 10sup.10 t, 2.45 × 10sup.9 t, and 6.05 × 10sup.11 t, respectively. Due to the difficulty in completing mineralization within the engineering time scale, the mineralization potential should not be taken into account when estimating the available COsub.2 storage potential. The available COsub.2 potential (including free-state, adsorption, and dissolution) of the Yanchang shale gas reservoir is 1.54 × 10sup.11 t, which is a considerable amount. The Yanchang shale gas formation will be able to accommodate 41.49% of global annual COsub.2 emissions (according to the data in 2021) if the available COsub.2 storage potential of the Yanchang shale gas reservoir is fully exploited.
