High-temperature Fluids Research Articles

Analytical protocol for measuring micro-molar quantities of sulfur volatile species in experimental high pressure and temperature fluids

Validating thermodynamic models is essential in experimental geosciences for exploring increasingly complex systems and developing analytical protocols. However, investigating solid–fluid equilibria in mm3-sized experimental capsules poses several challenges, particularly in sulfur-bearing chemical systems. These include maintaining bulk fluid composition and performing quantitative analysis with extremely low amounts of synthesized fluid. We present an innovative methodology for measuring ultra-low amounts of sulfur volatiles (H2S and SO2) generated during experimental runs at high pressure and temperature conditions of 3 GPa and 700 °C. Using solid sulfides (FeS + FeS2) and water as reactants, we performed redox-controlled syntheses employing a piston cylinder apparatus. We demonstrate that ex-situ measurements of these fluids by quadrupole mass spectrometry ensure accurate and precise analysis, confirming predicted thermodynamic compositions. This methodology allows in-depht investigation of sulfide solid–fluid equilibria, shedding light on sulfur volatiles behavior and geochemical cycles under high P–T conditions characteristic of the Earth’s interior.

Calculation algorithm for a multilayer thermal insulation system of a thermal energy storage device with a high-temperature working fluid

RELEVANCE. Managing the surplus and deficit of electric power generation, which contributes to the stabilization of the energy system and enhances its reliability, is a pressing issue. One of the solutions is the development and implementation of thermal energy storage systems within distributed energy systems. An important task in their development is creating an effective insulation system. THE PURPOSE. To develop an algorithm for the effective design of insulation systems for thermal energy storages with high-temperature working bodies. METHODS. The research is carried out using theoretical methods, including thermal engineering calculation of thermal insulation layers and thermal conductivity analysis. Mathematical modeling methods were used to determine the thickness of the thermal insulation system of a thermal energy storage device. RESULTS. The design of a thermal energy storage device has been developed. Based on the developed algorithm, it was determined that the thickness of the thermal insulation system should be 151 mm (the thickness of the first thermal insulation circuit is 135 mm, the thickness of the second thermal insulation layer made of mineral wool is 16 mm), ensuring minimal heat loss at a temperature of the heat accumulator equal to 2000 °C. It was revealed that the radiant heat flux prevails in the layers closest to graphite, accounting for about 70% of the total flux. CONCLUSION. The study confirmed the effectiveness of the proposed multi-layer insulation system for thermal energy storage. The developed algorithm allows for the calculation of insulation systems of thermal energy storage, taking into account various parameters and operating conditions.

Modified natural polymers as additives in high-temperature drilling fluids: A review.

Drilling fluids are often referred to as the "blood" of the drilling process, as they play a crucial role in determining both the efficiency and safety of drilling operations. Natural polymers, derived from renewable sources, such as cellulose, lignin, chitosan, xanthan gum, and starch, offer inherent advantages such as sustainability, biodegradability, and environmentally-friendliness when used as additives in drilling fluids. However, the inherent properties of natural polymers are adversely affected by thermal degradation due to their low heat resistance under harsh drilling conditions, where temperatures can exceed 150°C. To address these challenges, various modification techniques, including free radical polymerization, esterification, etherification, silanization, hydroxymethylation, and ionic crosslinking, have been employed. This paper provides an overview of recent advances in the application of modified natural polymers as additives in water-based drilling fluids (WBDFs) under high-temperature drilling conditions. It begins by discussing the degradation mechanisms of natural polymers at high temperatures, followed by a review of the techniques used for their modification. Subsequently, the application of modified natural polymers as rheological and fluid loss additives in high-temperature WBDFs is briefly presented. Finally, the challenges, environmental impacts, and future considerations for the use of modified polymers are outlined to guide future development of environmentally friendly, high-performance WBDFs.

A review: supramolecular polymers used in high-temperature fracturing fluids research status and prospects on the coupling relationship between molecular conformation and temperature resistance mechanism

A review: supramolecular polymers used in high-temperature fracturing fluids research status and prospects on the coupling relationship between molecular conformation and temperature resistance mechanism

Design of compliant thermal actuators using topology optimization involving design-dependent convection and pressure load

This study presents a topology optimization method for thermal actuators that accounts for boundary conditions influenced by variables such as thermal convection and pressure load. Thermal actuators with gripper-like designs are essential for handling hot and brittle materials. The objective of this study is to design actuator shapes that achieve an optimal balance between flexibility and stiffness in high-temperature environments. Unlike previous studies that consider load conditions imposed on fixed boundaries within the design domain, this research introduces a high-temperature fluid as the driving source and employs a novel approach to boundary condition setting by integrating fictitious physical problems. This approach allows for the precise specification of various boundary conditions across multiple domains. A weighted-sum method is applied to optimize three objective functions related to deformability, stiffness, and thermal diffusibility of the actuators. To address the issue of excessively thin structures compromising deformability and the poor convergence of the optimization process, stress constraints based on the optimization history are introduced. The proposed method is validated through numerical examples, demonstrating improvements in structural deformability while controlling deformation on the target surface plane. The numerical results confirm that the objective function decreases and stress is suppressed, verifying the effectiveness of the proposed approach.

Mineral assemblages and the genesis of platinum metal mineralization of the Vuruchuayvench intrusion (Kola Peninsula, Russia)

The layered Vuruchuaivench intrusion is located in the eastern part of the Baltic Shield and is part of the Early Paleoproterozoic Monchegorsk Intrusive Complex. The platinum-metal mineralization of IW is localized within the stratiform platinum-bearing horizon of the reef type with a length of about 2 km and a thickness of 1-3 m, in some boreholes up to 15–20 m. The dissemination of Fe-Cu-Ni sulfides containing the platinum-group minerals, silver and gold is confined to areas of gabbronorites and anorthosites of massive and taxitic texture, with a wide development of fluid-bearing minerals in the intercumulus of cumulative phases. The uniform distribution of petrogenic, rare and rare earth elements in the rocks of the platinum-metal reef (PGE-reef) and its host rocks indicates the formation of gabbronorites during intra-chamber differentiation without additional portions of the melt. The composition and ratios of platinum group minerals (PGMs) with sulfides and silicates suggest a close genetic relationship between PGMs and igneous sulfides. As the temperature decreases, primary PGMs and sulfides are modified under the influence of high-temperature magmatic fluids and hydrothermal solutions, with the formation of a wide range of PGMs. The ores are dominated by palladium arsenides, stibioarsenides, and bismuth tellurides. A special role in the formation of platinum-metal mineralization in the Vuruchuaivench intrusion is played by the separation of an immiscible arsenide melt with the formation of numerous drop-shaped, globular intergrowths predominated by Pd-Ni-arsenides and Pd-stibioarsenides. In some sulfide scattered impregnations, instead of globules consisting of palladium and nickel arsenides, platinum diarsenide (sperrylite) occurs. The formation of specific platinum-metal associations is apparently due to the addition of As, Sb, and other incompatible elements to the magma during extensive assimilation of Archean crustal rocks.

Research Status and Progress on Technologies for Exploration of Dry Hot Rock Resources in China

Abstract Hot Dry Rock (HDR) represents a clean and renewable geothermal energy source, playing a crucial role in global energy transition and climate change mitigation. China possesses abundant HDR resources. However, compared to the international advanced level, domestic exploration technology is still in its early stages. This paper analyzes the distribution of HDR resources in China and the achievements in exploration projects. It delves into the principles, applications, limitations, and development trends of key technologies in the main processes of HDR resource exploration. The paper emphasizes the necessity of improving exploration precision, enhancing high-temperature drilling fluid development, advancing logging technology, and establishing unified evaluation standards. Furthermore, it highlights the potential of artificial intelligence and big data technologies in improving exploration efficiency and reducing development risks, aiming to provide scientific technical guidance and practical references for the exploration and utilization of HDR resources in China.

Research on flow structure and heat transfer mechanism of windward bend lattice frame

The lightweight lattice sandwich structure is considered a promising heat transfer technology with broad application prospects for improving the heat dissipation capacity of thermal management systems. The heat transfer performance needs to be further researched urgently. In this study, the flow resistance and heat transfer characteristics of windward bend lattice frames with heat transfer and mechanical load capacity were investigated by experimental and numerical methods. The flow mechanism and enhanced heat transfer mechanism of windward bend lattice frame was revealed from the point of view of unit structure. The results show that the bending shape alters the flow state of the fluid in the passage within the windward bend lattice frame truss to enhance the mixing effect of high-temperature and low-temperature fluids in the passage. Additionally, as the angle of inclination increases, there is a significant improvement in local flow resistance characteristics and enhanced heat transfer performance due to deflection in movement direction and rotation direction of inverse spiral vortex at rear truss rod. Furthermore, it is observed that at constant pumping power, the changes in Angle of inclination significantly affect heat transfer on different surfaces: lower surface (increasing by 101%), upper surface (increasing by 57%), followed by end wall (increasing by 16%). This work has valuable engineering applications for structures with similar bending characteristics.

Rheological and thermal property of KH570-modified nano-SiO2 grafted xanthan gum and its application in drilling fluid system

Xanthan gum (XG), recognized for its environmentally friendly properties and versatile capabilities, has been studied for drilling fluid applications. However, its limited solubility and thermal stability restricts its broader use. In this study, a modified XG derivative, XG-g-KH570 modified SiO2, was synthesized by grafting XG with KH570-modified nano-SiO2. The modified product exhibited lower molecular weights with Mn and Mw of 3.00 × 105 g/mol and 3.77 × 105 g/mol, respectively. Its pyruvate and acetyl contents decreased to 2.72 % and 1.68 %, respectively. Meanwhile, XG-g-KH570 modified SiO2 showed a higher branching degree of 45.3 % based on methylation analysis. In terms of performance, XG-g-KH570 modified SiO2 exhibited improved water solubility. XG-g-KH570 modified SiO2 demonstrated superior high-temperature and high-salinity performance, retaining high viscosity retention and viscoelasticity. Additionally, XG-g-KH570 modified SiO2 exhibited a markedly reduced fluid loss of only 3.4 mL at 150 °C, compatible with conventional desulphonated drilling fluids. Furthermore, its high-temperature thickening and fluid loss control mechanisms was found to be associated with an enhanced cross-linked network structure based on the zeta potential and particle size distribution under high-temperature and salinity conditions. These results represent a promising advancement in the field of biomolecular drilling fluid additives, providing an efficient and eco-friendly solution for the oil and gas industry.

Shock compression of crystalline TeO2 to the high-pressure fluid regime: Insights from ab initio molecular dynamics simulations

The shock response of fully-dense and porous crystalline tellurium dioxide (TeO2) to the high-pressure and high-temperature fluid regime was investigated within the framework of density functional theory with Mermin’s generalization to finite temperatures. The principal and porous shock Hugoniot curves were predicted from canonical ab initio molecular dynamics (AIMD) simulations, with the phase space sampled along isotherms up to 80 000 K, for densities ranging from ρ=3 to 17 g/cm3. The polymorphs investigated are α-TeO2 paratellurite (P41212), TeO2 cotunnite (Pnma), and TeO2 post-cotunnite (P21/m). Based on the discontinuity found in the calculated Us−up slope of TeO2 post-cotunnite at a shock velocity of Us≃8.35 km/s and a particle velocity of up≃3.64 km/s, the shock melting temperature and pressure are predicted to be ≃6500 K and ≃170 GPa. Results from the AIMD simulations are in line with the static compression data of TeO2 paratellurite and cotunnite, and with the recent shock Hugoniot data for single-crystal α-TeO2 for pressures up to 85 GPa, obtained using the inclined-mirror method and the velocity interferometer system for any reflector combined with powder gun and two-stage light-gas gun.

Peculiarities of clay minerals formation in the Pleistocene sediments under specific tectonomagmatic and hydrothermal conditions of the Central Hill (Escanaba Trough, Gorda Ridge, Pacific Ocean). Communication 1. Hole ODP 1038B

Using a complex of analytical methods, clay minerals were studied in Pleistocene sediments from Hole ODP 1038B, 120.50 m deep, drilled on the northwestern edge of the Central Hill, located in the Escanaba Trough (Gorda Ridge) near a hydrothermal source with a temperature of 108°C, as well as in Pleistocene background terrigenous sediments from reference Hole ODP 1037B, drilled in the Escanaba Trough, 5 km south of Central Hill. The association of terrigenous clay minerals in sediments from Hole 1037B consists of mixed-layer smectite-illites, smectite, chlorite, illite, and kaolinite. In sediments from Hole 1038B in the interval from the bottom surface to a depth of 5–7 m, clay minerals are terrigenous. In the rest of the sedimentary section, clay minerals are represented by newly formed biotite, chlorite, and dioctahedral smectite. Their formation occurred under the conditions that arose during the intrusion of basaltic melt into the Escanaba trough with the formation of a laccolith and the subsequent rapid cooling of its flank; the intrusion was accompanied by the ascent of high-temperature hydrothermal fluid in the central discharge channel, interacting with the adjacent sediments. As a result, at the high-temperature stage of this interaction, finely dispersed biotite was formed in the sediments due to the original terrigenous clay minerals, K-feldspar and amphiboles. Then, at the rapid cooling of the hydrothermal fluid to a temperature presumably 270–330°C, partial replacement of biotite by chlorite. With further rapid cooling of the hydrothermal fluid to a temperature of 200°C and below and its mixing with sea water seeping into the sediments of the Central Hill, smectite was formed.

Causes of Multi-Mechanism Abnormal Formation Pressure in Offshore Oil and Gas Wells

This study thoroughly investigates the complex origins of abnormal formation pressure in offshore oil and gas wells, taking the Rio del Rey Basin in Cameroon as a case study. Renowned for its abundant oil and gas resources, the area faces unique challenges in predicting overpressure due to its high-temperature and high-pressure reservoir characteristics. By quantitatively analyzing the main mechanisms such as undercompaction, high-temperature fluid expansion, and mud diapirism, the study addresses the complexities of overpressure prediction. This paper introduces an innovative analytical framework that combines hierarchical clustering algorithms with the LightGBM model. Further refined by the application of Bayesian optimization, the model intelligently adjusts hyperparameters to enhance predictive accuracy. Utilizing well logging data and applying machine learning techniques, the paper classifies and identifies different mechanisms causing abnormal pressures, achieving a model prediction accuracy of 0.942. The research findings highlight the predominant role of the undercompaction mechanism, accounting for approximately 70% of the abnormal high-pressure events in the study area. Fluid expansion and shale diapirism contribute smaller but significant proportions of 10% and 20%, respectively. These quantitative insights into the pressure mechanisms are vital for optimizing drilling operations and reducing risks in oil and gas exploration. The study’s hybrid approach, integrating geophysical analysis with advanced computational techniques, sets a precedent for future research. It provides new avenues for applying machine learning to understand complex geological phenomena in similar geological environments and makes a significant contribution to the strategic planning of hydrocarbon exploration and production activities.

Distribution of Co, Te, Se in porphyry copper systems: A case study of the Tonglvshan deposit, Eastern China

Porphyry copper systems contain porphyry Cu, skarn, carbonate-replacement and epithermal deposits, and presently supply nearly all the Te and Se, and have the potential to produce Co as by-product in the future. However, few studies have investigated the distribution of Co, Te, and Se in the specific porphyry-skarn deposit. Detailed mineralogical and geochemical analyses were conducted to investigate the distribution of Co, Te, and Se across porphyry, skarn, and carbonate-replacement ore types in the Tonglvshan porphyry-skarn Cu-Fe-Au deposit, Eastern China. The early sulfide stage in three ore types is characterized by Co-bearing pyrite (Py1a, Co up to 1.3 wt%) + droplet-like tetradymite ± hessite ± cattierite. The texture transition from coarse-grained, pore-free to porous Py1a in porphyry and skarn type ores suggests a shift from stable physico-chemical conditions to gentle fluid boiling, resulting in the precipitation of Co- and Te-bearing minerals. In contrast, fine-grained euhedral Py1a in carbonate-replacement type ores implies rapid cooling from high-temperature fluid interaction with marble.The late sulfide stage, which only occurs in skarn and carbonate-replacement type ores, is characterized by Co-rich pyrite (Py2) + carrollite + hessite + Bi-sulfosalts. In skarn type ores, tetradymite-kawazulite solid solution (TKSS) + hessite + native Te + naumannite reflects intense boiling, leading to an increase in fO2 and pH that precipitates Py2b (Co up to 19.2 wt%) and carrollite, while Te and Se may precipitate through vapor phase condensation. Conversely, the presence of fine-grained carrollite, zoned Py2a, sphalerite, and galena in carbonate-replacement type ore suggests that rapid cooling and increasing pH, resulting from fluid mixing, played a significant role in the precipitation Co and Te. Furthermore, the porous texture resulting from coupled dissolution-reprecipitation (CDR) during the late sulfide stage also provided favorable conditions for the formation of micro-nano sized critical metal particles.

Unusual mineralization in basaltic andesite of submarine volcano Esmeralda (Mariana Island Arc)

The results of studies of a basaltic andesite sample complicated by a mineralized crack and voids, with a crack and gas voids filled with secondary mineralization dredged on the Esmeralda underwater volcano, are presented. A detailed comparative study of the mineral composition of the substance lining the crack, the space around the crack, and the part of basaltic andesite unaffected by secondary changes made it possible for the first time for the underwater Esmeralda volcano to establish the presence of an association of minerals that is not characteristic of unaltered volcanic rocks. In the intracrack space and adjacent zones of basaltic andesite, wide ranges of plagioclase composition were determined, isomorphism in the Fe-Ca-pyroxene series was studied, REE oxides, hydroxides and fluorohydroxides were studied, and variability in the composition of minerals in the magnetite-hematite series was shown. It is assumed that tectonic movements led to the emergence of permeable zones in the previously formed basaltic andesites through which new portions of the melt leaked. In a limited space, high fluid gas saturation, temperature and pressure made it possible to extract metal compounds from the melt and host rocks.

Entropy generation analysis and thermal performance of absorber tube in parabolic trough solar collector inserted with eccentric structure insert

To address the issue of uneven heat transfer in parabolic trough solar collectors, this study introduces an innovative insert (composed of vortex generators) layout. The vortex generators are strategically placed in areas with high heat flux density, while their number is reduced in regions with low heat flux density. By adjusting the position of the central rod, the inserts are defined as three different layout strategies (central structure, low eccentric structure, and upper eccentric structure), and their thermal performance is analyzed. The differences in fluid flow and heat transfer induced by different structures are also compared. The results show that the upper eccentric structure can induce unevenly distributed high-intensity mixing vortices, and through the ejection and sweeping movements of these vortices, the high-temperature fluid in areas with high heat flux density is transported to positions with low geothermal flow. Among all the studied configurations, the upper eccentric structure achieves a Nusselt number increase ranging from 1.16 to 2.34 times and a friction number value increase between 1.47 and 5.38 times. In terms of heat transfer performance, the highest value is 1.43 when the number of vortex generators is 6 and Reynold number is 13,750. Additionally, the thermal performance of the inserted tubes is analyzed using the field synergy principle and entropy generation method.

Developing a machine learning-based methodology for optimal hyperparameter determination—A mathematical modeling of high-pressure and high-temperature drilling fluid behavior

Drilling fluids exhibit complex rheological behavior due to a non-linear response to shear rate variations and high sensitivity to changes in temperature, time, and pressure conditions. The prediction of drilling fluid rheological behavior is crucial for the success of oil well drilling, and it directly impacts the fluid's performance. The dataset used in this study was obtained from extensive rheometric tests of water-based and olefin-based drilling fluids in steady-state flow curves. The optimal hyperparameters were guided by performance metrics and compared with alternative models such as Power-law and Herschel-Bulkley rheological models. Different configurations with different hidden layers, using neuron sequences of 16, 32, and 64, learning rates of 0.001 and 0.01, and the ReLU activation function were used to improve the model's performance. Additionally, the paper delved into the impact of the number of training epochs on the accuracy of shear stress predictions. Finding this equilibrium was identified as a crucial factor in achieving precise results. The neural network model demonstrated remarkable accuracy when using the ML-C3 configuration, with MAE values of 0.535 and R2 of 0.987 in predicting the steady-state flow curves of drilling fluids, establishing itself as a powerful tool for forecasting the rheological behavior of these fluids under diverse operational conditions. The present research significantly contributes to the field of drilling fluid rheology and provides valuable insights for optimizing drilling operations in HPHT environments.

Stability Characteristics of Natural Gas Hydrate Wellbores Based on Thermo-Hydro-Mech Modeling

During drilling operations, drilling fluids undergo heat exchange with hydrate-bearing formations. The intrusion of drilling fluids affects hydrate stability, leading to variations in stress fields around a wellbore and complex scenarios such as borehole collapse, significantly hindering the efficient development of natural gas hydrate resources. This study establishes a thermo-hydro-mech model for hydrate-bearing inclined wells based on linear thermoelastic porous media theory and an appropriately high inhibitive drilling fluid temperature. This research reveals that drilling should follow directions of minimum horizontal stress or perpendicular to maximum horizontal stress during drilling operations to control wellbore stability. Hydrate decomposition due to factors like drilling fluid pressure and temperature can rapidly reduce the strength of low-saturation formations, significantly increasing the risk of wellbore instability. Therefore, selecting appropriate highly inhibitive and low-temperature drilling fluids during drilling operations helps control hydrate decomposition and reduce fluid intrusion, thereby mitigating risks associated with wellbore instability.

An Investigation of the Factors Influencing the High Temperature Rheology of Polymers

Introduction: Nowadays, polymers, as an important application material in drilling engineering, have obvious advantages in solving the rock-carrying problem at the bottom of deep wells, and improving the drilling speed due to their excellent viscosity enhancement effect. Method: In this study, the effects of polymer type, concentration, shear time, electrolyte, and clay on the rheological properties of polymer solutions at high temperature and high pressure were investigated using a Fann 50SL rheometer. The experimental results showed that, except for the polymer additive amount and clay, the increase in shear time and the amount of salt both led to a decrease in the viscosity of the polymer solution, with 190°C as the critical temperature above which the viscosity decreased significantly. Results: The polymer solution containing formate showed higher viscosity retention during heating and then cooling compared to chlorides. The presence of clay enhances the reticulation of polymer molecules in the blend, which facilitates the carrying of rock cuttings at high temperatures. In addition, regression analyses showed that the increase in temperature resulted in an enhanced tendency for the polymer solution to evolve from a pseudoplastic to a Newtonian type. Conclusion: This research provides theoretical basis and data support for developing high-temperature polymers and formulating high-temperature drilling fluid systems.

Titanite from the NYF-type pegmatites of Szklarska Poręba Huta quarry, Karkonosze granite massif, SW Poland

Titanite, an accessory mineral of pegmatite related to aplogranite, was identified in the Szklarska Poręba Huta quarry within the Karkonosze granite massif in Lower Silesia, Poland. It formed during pegmatitic to hydrothermal stages. Besides the isovalent substitution Sn → Ti, the chemical composition of the mineral is characterized by three coupled substitutions: (1) (Al, Fe, Sc)3+ + (OH, F)- → YTi + ZO, (2) XREE3+ + Y(Al, Fe, Sc)3+ →X)Ca2+ + YTi4+, and (3) (Al, Fe, Sc)3+ + (Nb, Ta)5+ → 2YTi. These substitutions are strongly dependent on the composition of the magma in terms of its Al2O3/TiO2 activity ratio, with the first one also influenced by the H2O/HF fugacity ratio. Fluorine, which induced the most common substitution (1), had its source in high-temperature F-bearing fluids released from rocks of the metamorphic envelope adjacent to the intruding granite. These fluids mobilized and transported various rock components (Sc, REE, Nb, Ta, etc.) among others in the form of fluoride complexes, enriching the aplogranite magma with some metallic elements. The substitution of Sn for Ti developed with decreasing temperature to the extent that in thin ore-mineralized quartz veins cutting aplogranite, titanite reaches Sn-bearing compositions up to the prevalence of Sn corresponding to malayaite.

Detection of High-Temperature Gas Leaks in Pipelines Using Schlieren Visualization

This paper investigates the application of Schlieren flow visualization for detecting leaks in pipelines carrying high-temperature fluids. Two experimental setups were constructed: one with a 25 mm PTFE tube featuring a 2 mm diameter perforation, and another with a 100 mm diameter pipe insulated with an aluminum jacket and featuring a 12 mm leak gap. A single-mirror-off-axis Schlieren system, employing a 150 mm diameter parabolic mirror, was used to visualize the leaks. The temperature of the leaking air varied between 20 and 100 °C, while the ambient temperature was maintained at 14 °C. To quantify the leaks, the coefficient of variation for pixel intensity within the leak region was calculated. Results showed that for the PTFE tube, leaks became detectable when the temperature difference exceeded 34 °C, with the coefficient of variation surpassing 0.1. However, in the insulated pipe, detecting clear leak patterns was challenging. This research demonstrates the potential of Schlieren visualization as a valuable tool in enhancing pipeline leak detection.