Ensuring reliable zonal isolation in high-temperature geothermal wells is a pivotal barrier to the scalability of unconventional geothermal resources. Extreme downhole temperatures (>150 °C), corrosive brine chemistry, and severe cyclic thermal stresses frequently compromise the integrity of conventional Portland cement sheaths, leading to catastrophic well failure. While existing literature often isolates material chemistry from operational placement, this review spans over two decades of systematic literature review to provide a holistic framework linking microstructural evolution to macro-scale well integrity. Uniquely, this study critically evaluates the "lab-to-field" transition of sustainable alternatives, specifically quantifying the potential of alkali-activated geopolymers and alternative cementitious materials (ACMs). It contrasts their superior acid resistance and low-carbon footprint against the handling difficulties, such as activator sensitivity and rheological control, that currently stall their standardization. Beyond materials, the review dissects the physics of cement placement, demonstrating how advanced techniques like reverse circulation cementing (RCC) and density-optimized displacement strategies can mitigate risks in lost-circulation zones where conventional methods fail. Furthermore, it challenges the validity of static American Petroleum Institute (API) testing protocols, advocating for the integration of machine learning and computational fluid dynamics (CFD) to predict long-term bond durability under realistic downhole conditions. By mapping distinct failure mechanisms, from casing-cement debonding to annular pressure buildup, to targeted mitigation strategies, this work establishes a comprehensive, evidence-based roadmap for engineering resilient, low-carbon geothermal wells capable of withstanding the rigorous demands of next-generation energy production.
Light-and elevated-temperature-induced degradation (LeTID) is one of the important reliability challenges for monocrystalline Si photovoltaics, yet its microscopic origin is unclear. Using electron paramagnetic resonance (EPR) on Ga-doped Czochralski Si, complemented by photoluminescence (PL) imaging to qualitatively track changes due to LeTID, a partially hydrogenated vacancy cluster is postulated as the LeTID-active defect. In the fully degraded state, EPR shows a silicon dangling-bond signal with a g-value of 2.006 and a spin density of similar to 5 & times; 10(12) +/- 10(12) cm(-3). Ab initio simulations were performed using density functional theory (DFT) to obtain g-values and energy levels for a Si dangling bond in different local environments. Consistent with experiments, DFT simulations predict average g-values over the range of similar to 2.006-2.007 with energy levels of similar to 0.2-0.4 eV from the valence band edge. The extent of LeTID was similar to 2 times higher in the wafers obtained from the tail end of the ingot compared to the seed or middle regions, likely due to the differences in the density of intrinsic defects such as vacancies and vacancy clusters. We show that firing creates a shallow precursor state whose concentration rises with the peak firing temperature. The proposed defect model is consistent with dark annealing experiments, based on which we propose the possibility of two competing pathways for recovery in the lifetime: recovery via loss of H from partially hydrogenated vacancy clusters, or permanent regeneration through complete hydrogenation of the defects. The latter pathway offers a possible mitigation strategy. This work advances an atomic-level framework for LeTID, bridging fundamental defect physics with practical approaches for solar cell stabilization.
Gas hydrates are solid compounds that form under high-pressure and low-temperature conditions, posing a major threat to oil and gas operations because of their tendency to agglomerate and block pipelines. One mitigation strategy is to allow hydrates to form under controlled conditions, enabling their transport as a slurry within the liquid phase. However, limited research on how such particles affect key multiphase flow parameters has been conducted. This study investigates the influence of particle concentration on slug flow characteristics, a common flow regime in oil and gas production. Experiments using air-water and air-oil systems with model polyethylene particles mimicking hydrate density were performed in a flow loop. The test section was composed of 50-mm ID, 34-m long horizontal pipe. Four particle concentrations were tested: 0%, 5%, 10% and 20% v/v. Except under flow conditions near the stratified-slug transition line, which lead to long elongated bubbles and low slug frequencies, particles were effectively dispersed and transported in both the film and slug regions. The presence of particles had a weak effect on the slug flow topology - structure lengths, flow frequency, bubble velocity and phase fraction remained almost unchanged. This was attributed to the minimal impact of the particles on the thermophysical properties of the mixture. In contrast, particles significantly increased the pressure drops in the oil system because of a higher mixture density and a particle size comparable to the viscous sublayer, what affects the apparent viscosity. An empirical correlation for pressure drop prediction was proposed, achieving deviations of about 5% compared to experimental data.
New structural mapping and U-Pb sensitive high-resolution ion microprobe-reverse geometry (SHRIMP-RG) zircon analysis on rocks of the WNW-dipping, fault-bounded Nashoba-Putnam terrane in southeastern New England, USA, were used to further constrain its structural and metamorphic history, and test a hypothesis of channel flow and ductile extrusion. The Nashoba-Putnam terrane is an early Paleozoic arc/back-arc complex on the trailing edge of Gondwana-derived Ganderia. It consists of high-grade partially melted rocks between mostly lower-grade rocks in adjacent domains, resembling a ductile extrusion zone.Isoclinal folds are locally refolded by northwest-side-down asymmetric folds throughout the Nashoba-Putnam terrane, and by additional northwest-side-up folds in the southeastern part of the Nashoba terrane and locally in the Putnam terrane to the south. Structures generally dip shallower towards the southern part of the Nashoba terrane and in the Putnam terrane.New SHRIMP-RG data indicate that partial melt occurred at ∼422 Ma in the eastern part of the Nashoba terrane, and at ∼364 Ma in the southern part. Structures and the partial melt history of the southeastern Nashoba terrane are consistent with the center of a previously interpreted Late Silurian–Devonian ductile extrusion zone, of which the top lies in the northwestern part of the terrane. The bottom may lie in an adjacent high-grade metamorphic zone of the Avalon terrane to the southeast or have been removed by a fault. The younging of deformation and metamorphism, and shallowing of structures in the southern Nashoba, and Putnam terranes may be an effect of the Carboniferous–Permian assembly of Pangea.
Abstract A unified effective stress equation for variably saturated frozen soil is proposed, theoretically verified, and experimentally evaluated. Cryostress, capillary suction stress, and adsorptive suction stress coexist when variably saturated soil is subject to freezing and thawing. Cryostress consists of three physically distinct forces at three interfaces: ice–ice bonding, ice–liquid capillary force, and ice–particle adsorptive force. Cryostress is a characteristic function of temperature and water content quantified by the cryostress characteristic curve. A generalized effective stress can be established by applying the principles of mechanical equilibrium and soil water potential equilibrium on the soil–water–ice–air representative element volume. A closed-form equation is developed where effective stress is equal to the total stress minus suction stress and cryostress. The generalized effective stress equation can be reduced to Bishop’s form of effective stress in saturated frozen soil when ice–particle adsorptive stress is neglected, to Lu and Likos’ suction stress-based effective stress in unfrozen unsaturated soil, and to Terzaghi’s effective stress in unfrozen saturated soil. The closed-form equation is experimentally evaluated using published shear strength test results for sandy soil, lean clay, and silty clay. The fitted parameters also show good consistency with independently measured soil water and soil freezing characteristic curves for lean clay. The proposed framework offers a practical and unified approach to describe the strength of variably saturated frozen soils.
