Energy & Fuels最新文献

This study presents a highly novel and meticulously designed experimental approach to investigate oil recovery due to natural depletion and cyclic huff-n-puff gas injection in fractured, ultratight reservoirs. To this end, we performed a series of core-flooding experiments on a fractured reservoir whole core sample under elevated pressure and temperature conditions, and using the reservoir live fluids. The whole core setup provides a sufficiently large pore volume in low-porosity core samples and helps minimize uncertainties associated with fluid saturation measurements. The experimental procedure included flow experiments that eventually restored the core back to the reservoir conditions, in terms of pressure, temperature, and fluid saturation, in the presence of propped/unpropped fractures. The core sample was subsequently subjected to several depletion stages to pressures above and below the bubble point pressure. Ultimately, a cyclic huff-n-puff gas injection was employed to quantify incremental oil production after the depletion processes. An initial depletion of 13.75 MPa at a pore pressure above the bubble point resulted in a recovery of approximately 5.8% of the original oil in place (OOIP). This value was consistent with the theoretical estimate based on the rock compressibility and fluid expansion. As the pore pressure dropped below the bubble point, the hydrocarbon gas evolved from the oil phase in the matrix and displaced oil toward the fracture by the solution gas drive mechanism, eventually resulting in an additional recovery of 12.71% of OOIP. After the primary production, a single huff-n-puff gas injection cycle was conducted over the same pressure range of the depletion process, which yielded an incremental recovery of nearly 8% of OOIP. This finding clearly highlighted the promisingly profitable oil volume additionally recovered from the tight matrix system by the huff-n-puff gas injection mode. It was also observed that a subsequent cycle of gas injection did not significantly increase oil production, which indicated that the initial cycle effectively maximized the recovery potential in this ultratight reservoir system.

This study examines the lithofacies characteristics of the Silurian Wufeng–Longmaxi Formation black shale in the southern Sichuan Basin and their influence on gas content. The analysis integrates core observations, organic matter content measurements, X-ray diffraction (XRD) analyses, and field gas data. Seven shale lithofacies were classified based on mineral composition and total organic carbon (TOC) content. Vertically, the bottom section of a single well is dominated by organic-rich siliceous shale interbedded with thin mixed shale, characterized by considerable thickness, high TOC content, high gas content, and stable lateral distribution. The middle section features organic-rich clay-siliceous shale interbedded with siliceous shale, while the upper section consists primarily of organic-rich siliceous shale and clay-siliceous shale with lower organic matter and gas content, as well as frequent vertical lithofacies changes that lead to strong lateral heterogeneity. In the lower deep-water organic-rich siliceous shale, biogenic silica and organic matter evolve together. Siliceous support enhances hydrocarbon formation and preservation, leading to a gas enrichment model dominated by adsorbed gas. This results in high total gas content, a large proportion of adsorbed gas, and a brittleness index favorable for shale gas storage and hydraulic fracturing. Due to the relatively high organic matter content, the organic-rich clay-siliceous shale lithofacies also displays high gas content, coupled with an increased proportion of free gas. Based on four distinct lithofacies-based shale gas enrichment models, the organic-rich siliceous shale and organic-rich clay-siliceous shale facies are recognized as the most favorable targets for shale gas storage and development.

Accurately determining the stability of shale gas reservoirs requires an understanding of the mechanical behavior and microstructural changes exposed to both short-term and long-term water–rock interactions during hydraulic fracturing. After soaking Longmaxi shales in slick water for 0, 5, 15, 30, 60, 120, and 180 days, we use laboratory uniaxial and triaxial compression experiments across T–P_c (high temperature and high pressure) conditions to examine these changes. The results indicate significant differences in the effects of long-term versus short-term water–rock interaction on the mechanical properties of shale. Furthermore, as the duration of water–rock interaction increases, the correlation among mechanical properties, brittle mineral content, and various fractal dimensions gradually diminishes, especially after immersion exceeding 15 days. In contrast, the correlation between surface roughness, pore structure, and shale mechanical properties remains consistently stable, with surface roughness being particularly notable. Based on surface roughness, we propose a multiscale quantitative characterization method for rock damage using the analytical hierarchy process (AHP) calculation method, grounded in fractal damage mechanics theory (covering macroscopic and mesoscopic scales). Consequently, a shale damage evolution model under water–rock interaction is formulated, which can predict and assess the degree of damage in shale gas reservoirs following different durations of water–rock interaction. In addition, we propose the mechanisms to demonstrate how the microstructure and mechanical behavior of shale vary depending on the duration of the water–rock interaction: (1) surface hydration and ionic hydration (mineral dissolution and detachment, ion exchange), predominantly occurring under conditions of short-term water–rock interaction, and (2) osmotic hydration (pore pressure fluctuations, alterations in stress distribution, crack propagation, and clay swelling), which typically takes place over a longer duration and is primarily observed in long-term water–rock interaction scenarios.

Accurately predicting the content of adsorption gas and free gas in nanopore structures, as well as the dynamic production of adsorption gas and free gas, is of great importance for the production of coalbed methane wells. However, the storage and transport of adsorption gas and free gas in different nanopores are still unclear. In this study, the molecular adsorption simulation results and pore size distribution data were combined to calculate the amounts of adsorption gas and free gas in different pore sizes of the coal sample. The molecular mechanism for the adsorption gas and free gas in tunnels of different sizes during the transport behaviors is proposed. The results indicate that in pore sizes smaller than 1 nm, the amount of adsorption gas is 18.85 cm³/g, which is up to 74.31% of the total amount of adsorption gas, hardly any free gas is present. At 1–2 nm pores, the amount of adsorption gas is 4.14 cm³/g, and then the amount of free gas is 1.20 cm³/g, which provides about 71.59% of the total amount of free gas. In other types of pores (2–5, 5–10, and >10 nm), the amounts of adsorption gas are 0.30, 0.23, and 0.17 cm³/g and the amounts of free gas are 0.05, 0.07, and 0.35 cm³/g, respectively. By transport simulation, a molecular mechanism for the adsorption gas and free gas in tunnels of different sizes during the transport behaviors was provided. In the first stage, with more free methane molecules stored in the macropores and fractures expelled from the coalbed, the gas production from coalbed methane wells has risen sharply at the beginning of the stage. Subsequently, the dramatic depletion of free methane molecules results in the desorption and migration of adsorption methane molecules. In the second stage, more adsorption gas is desorbed and migrates into the micropores, thereby providing a stable increase in gas production. In the last stage, only a small amount of free gas is initially stored in the macropores and fractures and the adsorption gas desorbs from the micropores and begins to slowly migrate through different size tunnels; the gas production in coalbed methane wells will gradually decrease.

Synthesis of solid scale inhibitors with a sustained-release function has become one of the most promising scaling control methods in the oil and gas industry. It is still a challenge to synthesize a low-cost, high-efficiency, and long release period solid scale inhibitor. In this study, diatomaceous earth (DE) was used to adsorb amino trimethylene phosphonic acid (ATMP) to get ATMP-DE solids, which were then double-coated with aluminum cement (AC) and poly(vinyl alcohol)-glutaraldehyde (PVA-glut) step by step to synthesize ADAP microspheres (ATMP-DE/AC@PVA-glut). Scanning electron microscopy (SEM) was used to verify the adsorption of ATMP onto DE, and the double-coating structure of the ADAP microspheres. The optimized mass ratio of AC/ATMP-DE (first coating) was determined to be 2:1. At this mass ratio, the ATMP release lifetime starts to level off, indicating that a nearly complete encapsulation was achieved. The optimized mass percentage of PVA-glut (second coating) was determined to be 1.5% when the release lifetime stops increasing and a complete secondary coating of ATMP-DE/AC was achieved. The controlled-release property of the ADAP microsphere has been tested under laminar and turbulent flow conditions using static and dynamic sampling methods from 20 to 80 °C, to simulate different working conditions during oil and gas production. Under laminar flow conditions, the release time ranges from 300 to 200 h and from 220 to 140 h from 20 to 80 °C using static and dynamic sampling methods, respectively. Under turbulent flow conditions and 60 °C, the release time decreases to 120 and 70 h using static and dynamic sampling methods, respectively, showing the acceleration release kinetics with more agitation. Under the most severe conditions (dynamic sampling under turbulent flow conditions), the scale inhibition efficiency of released ATMP has been tested. Within 60 h, the scale inhibition efficiency of the released sample solution is over 90%, and from 60 to 80 h, it drops to 90 to 70%. Such good scaling efficiency shows great potential of the newly synthesized ADAP microspheres in the oil and gas industry.

Norbornadiene (NBD), or bicyclo[2.2.1]hepta-2,5-diene, plays a key role in the development of high-grade liquid hydrocarbon aviation fuels. It serves as a model for synthesizing various organic compounds and understanding through-space (TS) interactions in strained hydrocarbons. NBD is also notable for applications such as liquid organic hydrogen carriers (LOHCs), solar energy conversion via isomerization, and high-energy-density (HED) e-fuels. It is also important to study the pyrolysis mechanism and kinetics of quadricyclane fuel. To advance HED e-fuels, understanding the quantitative structure–property relationship (QSPR) is essential, which requires precise electronic structure data. However, the outer valence binding energy and Dyson orbitals of NBD have yet to be conclusively confirmed, despite numerous studies. Photoelectron spectra typically assume that Dyson orbitals correspond to quantum-mechanically calculated energies that match measured binding energies. This assumption may be inaccurate if the quantum mechanical method is approximate. By combining accurate quantum mechanical calculations with high-resolution synchrotron-sourced photoelectron spectroscopy (PES) and electron momentum spectroscopy (EMS), this study confirms the Dyson orbital of NBD’s highest occupied molecular orbital (HOMO) at 8.77 eV as b₁ and HOMO – 1 at 9.48 eV as a₁. The TS interaction in the 8–10 eV region splits the 6b₁ and 10a₁ Dyson orbitals by up to 0.80 eV. This insight enhances the understanding of TS interactions in the NBD, aiding the development of strained hydrocarbons for HED aviation fuels.

In jet fuels, sulfur-containing compounds (SCCs) contribute to beneficial (i.e., lubricity) and adverse characteristics (i.e., fuel instability, emissions). Previous qualitative methods relied heavily on the combined use of sulfur-specific detectors and mass spectrometers (MS) to complete compositional analysis of SCCs in jet fuels. As the methods required measurements of known SCCs to facilitate identification, qualitative analysis was significantly limited. With SCCs influencing important fuel properties, novel qualitative methods are warranted. In this study, a method was developed to complete the qualitative characterization of SCCs in jet fuels by using positive-ion mode atmospheric pressure chemical ionization (+)APCI coupled to an orbitrap. Prior to fuel measurements, SCCs exhibiting different functionalities were measured to determine dominant ionization reaction(s). Tandem mass spectrometry measurements were also employed on ionized SCCs to determine the extent of structural information achievable and applicability for structural elucidation of SCCs. Upon MS¹ fuel measurements, the elemental compositions, range and average m/z values, carbon numbers, ring and double bond equivalent values, and relative abundances for ionized SCCs in each identified homologue ion series (ions of the same empirical formula increasing by 14.01565 Da, a CH₂ unit) were determined for each jet fuel. New ion series were identified. Further, the most abundant ion series were represented by empirical formulas of C_nH_2n+1S, C_nH_2n–1S, and C_nH_2n–3S. Furthermore, the detected SCCs exhibited greater ranges in carbon number (i.e., 7–19 carbons) and molecular weights than previously recorded. Kendrick mass defect plots were also made, which demonstrated clear qualitative differences for the fuels. Overall, the method was successful at providing more compositional information than past analytical methods and required only a simple dilution (S-methylation, extractions, and high-performance liquid chromatography (HPLC) separations were not required). Access to such detailed compositional data will likely prove critical for linking the SCC composition to fuel properties, such as emissions and fuel stability.

Electrochemical oxidation of 5-hydroxymethylfurfural (HMF) is an environmentally friendly and economical method to produce valuable 2,5-furandicarboxylic acid (FDCA). While great efforts have been devoted to developing non-noble-metal electrocatalysts for the HMF electrooxidation reaction (HMFOR), the activity still needs to be improved. Herein, taking Co₃O₄ as the model electrocatalyst, we demonstrate oxygen defect engineering as an effective method to enhance the HMFOR activity. Various concentrations of oxygen vacancies are introduced into Co₃O₄ by electrochemical reduction. The HMFOR performance exhibits a volcano dependence on the concentration of oxygen vacancies. Under the optimal reduction condition of −1.8 V (vs Hg/HgO) and 5 min, the HMF conversion rate and faradaic efficiency of FDCA are enhanced by 3.7- and 2-fold, respectively. Theoretical calculations further demonstrate that the presence of oxygen vacancies promotes the adsorption of HMF and decreases the reaction energy barriers during HMFOR. Our results provide critical insight into the role of oxygen defects in determining the HMFOR activity, and the method can be applied to the synthesis of highly active electrocatalysts for the electrochemical oxidation reactions of other biomasses.

Kinetic hydrate inhibitors (KHIs) are a class of low-dosage hydrate inhibitors (LDHIs) and are used mainly to prevent gas hydrate formation and flow restriction in oil and gas production lines. At the same driving force, structure I methane hydrate formation is notoriously harder to prevent with a KHI than a gas that preferentially forms a structure II hydrate. The oil industry has struggled to find KHIs that will inhibit structure I hydrate formation of gases at 10 °C or more for several days. Here, we present the first study on sI methane hydrate inhibition using blends of poly(N-vinyl caprolactam) PVCap with acyclic and cyclic amine oxides. Tri-n-pentyl amine oxide (TnPeAO) was the best synergist with PVCap. Low dosages (1000–2500 ppm) of TnPeAO were shown to give superb synergistic performance in both slow constant cooling and isothermal tests, even with very low concentrations of PVCap (30–125 ppm). For example, at 98 bar and 2 °C (ca. 11.1 °C subcooling), a blend of 125 ppm of PVCap and 1000 ppm of TnPeAO gave no hydrates in 2 days.

High-voltage electric pulse (HVEP) technology holds significant potential in enhancing the permeability for coalbed methane extraction, and the introduction of ionic solutions greatly amplifies its fracturing effectiveness. To elucidate the optimization effects of different ionic solutions in HVEP technology, this study systematically compared the improvement in coal samples conductivity after treatment with KCl, MgCl₂, and FeCl₃ solutions. Physical experiments on HVEP-induced coal fracturing were conducted to reveal the evolution of pore and fracture structures in coal and the associated permeability changes. The results demonstrate that: (1) ionic solution soaking significantly improves the conductivity of coal samples, reduces the difficulty of electrical breakdown, and enhances energy utilization efficiency. The improvement effects vary among solutions, with FeCl₃ showing the best performance for XT anthracite and MgCl₂ being more effective for SSP bituminous coal. (2) Compared to distilled water, ionic solution-treated coal samples exhibit significantly increased porosity and average pore size after breakdown, with an enhanced internal fracture network. The number of macropores and mesopores increases, while micropores and nanopores decrease, resulting in improved pore-throat connectivity. (3) In terms of permeability enhancement, the effects of the three ionic solutions surpass those of distilled water. Consistent with the conductivity improvement trend, FeCl₃ and MgCl₂ solutions demonstrated optimal permeability enhancement for XT and SSP coal samples, respectively. Therefore, when combining ionic solution treatment with HVEP technology for coal seam fracturing and permeability enhancement, it is crucial to consider the specific characteristics of the coal to select the most suitable ionic solution and achieve higher efficiency in permeability improvement.