High-temperature Formation Research Articles

A successful case study of using HCl and viscoelastic diverting acid systems for carbonate matrix acidizing in an oil well with optimized predictive model

The oil and gas industry is continuously seeking advanced methods to optimize reservoir productivity. Among the techniques employed, matrix acidizing, particularly using Viscoelastic Diverting Acid (VDA), has shown significant promise in enhancing permeability and improving well performance. However, the absence of standardized formulations for VDA requires a careful evaluation of commercial additives to ensure their reliability and effectiveness in diverse reservoir conditions. This article presents a comprehensive case study that examining the application of hydrochloric acid (HCl) and VDA systems in a low-permeability carbonate reservoir situated in southern Iran. The study integrates design of experiments (DOE) and multi-objective optimization techniques to assess the impact of various operational parameters on acidizing performance. The research focused on high-temperature formations, employing multi-stage acid injections to evaluate the effectiveness of the acid treatments. The use of DoE and response surface methodology (RSM) provided a structured approach for optimizing key parameters to enhance treatment outcomes. The results of this study demonstrated a substantial increase in both oil production and well pressure following the acidizing process. Specifically, oil production improved by 80%, and well pressure increased by 73%, underscoring the effectiveness of the acid treatment in stimulating the reservoir. The VDA system, combined with the bullheading injection technique, facilitated superior acid placement and distribution within the reservoir, enhancing the overall acidizing efficiency. Furthermore, the optimization of operational parameters such as skin factor and maximum invasion depth through the use of RSM allowed for a significant refinement of the acidizing process. The developed models, with correlation coefficients exceeding 0.96, further validated the accuracy of the optimization process and provided valuable insights into the critical factors influencing acidizing performance. Additionally, the refined acidizing program minimized operational uncertainties, leading to improved treatment efficiency and more consistent results in challenging high-temperature formations.

CO2 Foamed Viscoelastic Gel-Based Seawater Fracturing Fluid for High-Temperature Wells.

This study investigates the development of a novel CO2-foamed viscoelastic gel-based fracturing fluid to address the challenges of high-temperature formations. The influence of various parameters, including surfactant type and concentration, gas fraction, shear rate, water salinity, temperature, and pressure, on foam viscosity was systematically explored. Rheological experiments were conducted using a high-pressure/high-temperature (HPHT) rheometer at 150 °C and pressures ranging from 6.89 to 20.68 MPa. To simulate field conditions, synthetic high-salinity water was employed. The thermal stability of the CO2 foam was evaluated at a constant shear rate of 100 1/s for 180 min. Additionally, foamability and foam stability were assessed using an HPHT foam analyzer at 100 °C. The results demonstrate that liquid phase chemistry, experimental conditions, and gas fraction significantly impact foam viscosity. Viscoelastic surfactants achieved a peak foam viscosity of 0.183 Pa·s at a shear rate of 100 1/s and a 70% foam quality, surpassing previous records. At lower foam qualities (≤50%), pressure had a negligible effect on foam viscosity, whereas at higher qualities, it increased viscosity by over 30%. While a slight increase in viscosity was observed with foam qualities between 40% and 60%, a significant enhancement was noted at 65% foam quality. The addition of polymers did not improve foam viscosity. The generation of viscous and stable foams is crucial for effective proppant transport and fracture induction. However, maintaining the thermal stability of CO2 foams with minimal additives remains a significant challenge in the industry. This laboratory study provides valuable insights into the development of stable CO2 foams for stimulating high-temperature wells.

Microwave Shock Synthesis of Porous 2D Non‐Layered Transition Metal Carbides for Efficient Hydrogen Evolution

ABSTRACTTransition metal carbides (TMCs) serve as efficient catalysts for electrocatalytic hydrogen evolution reactions (HERs), holding significant importance in promoting hydrogen production for carbon neutrality. To optimize interfacial catalytic activity, structurally designing TMCs into two‐dimensional (2D) and porous structures to expose more practical surface areas and enhance electronic configurations is a common and effective strategy. Particularly, porous 2D non‐layered TMCs (2D NL‐TMCs) demonstrate richer active sites distinct from layered interfacial inertness. However, mainstream selective etching and chemical deposition growth mechanisms struggle to prepare highly active porous 2D NL‐TMCs due to constraints posed by their high structural strength and formation temperature. Herein, we successfully synthesized porous 2D W2C (2D p‐W2C) rapidly using a microwave shock method. Mechanistic verification reveals that leveraging transient high temperature and rapid on‐off properties of microwave effectively combines with an oxidation‐induced porosity mechanism, facilitating the evolution of porous 2D structures. These low‐dimensional nanostructures with abundant edge defect sites aid in efficient adsorption reactions of intermediate species in HER. Moreover, the successful preparation of a series of porous 2D NL‐TMCs (Mo2C, NbC, TaC) confirms the universality of this method, with the synthesized 2D p‐W2C exhibiting optimal HER performance. This strategy offers new insights into the topological synthesis of porous 2D NL crystals.

Experimental Evaluation of Lactic Acid for Matrix Acidizing of Carbonates

Summary To improve the efficiency of standard hydrochloric acid (HCl) stimulation treatments, many alternative acid systems have been developed to mitigate corrosion, increase wormhole efficiency, and divert fluids for better acid coverage. However, these alternative systems come at a price compared with HCl, which is cheaper and sufficient in most applications. Lactic acid is an organic acid that is less corrosive and has reduced reactivity compared with HCl. The advantages and application of lactic acid have not been studied extensively like other alternative acids. To evaluate lactic acid as a viable alternative acid system, we conducted a series of linear coreflood matrix acidizing experiments using Indiana limestone rock samples with 40 wt% lactic acid at two temperatures over a range of injection rates. The goal was to characterize the wormholes created by lactic acid and identify the appropriate condition that lactic acid can outperform HCl. Coreflooding tests were also conducted at high temperatures and lower concentrations to observe a change in behavior and performance. Lactic acid performance was analyzed by comparing pore volumes (PVs) to breakthrough (PVbt) with previous HCl experiments. Because HCl exhibits low efficiency when injected below the optimal condition, lactic acid was found to be more efficient than HCl at injection rates below optimum for 40 wt%. At a temperature of 150°F, lactic acid maintained similar PVbt over the range of injection rates. Wormhole geometry from computed tomography (CT) imagery and pressure response data was studied to identify unique characteristics or behaviors of lactic acid. CT images of lactic acid-generated wormholes reveal a geometry vs. injection rate relationship that is contrary to the conventional understanding of wormhole growth patterns. The images show extensive branching in most low injection rate tests. The results are characterized as appearing to have self-diverting behavior. At an elevated temperature of 240°F, precipitation of lactic acid after reacting with calcium carbonate became visible. Pressure differential data across the core showed the pressure drop increased in nearly every experiment. When lower lactic acid concentrations were used, the pressure differential increase was not observed. Precipitation occurred during and immediately after most high-temperature experiments, and when the concentration is above 30 wt%, it is suspected to be plugging permeable channels. The study concludes that at a temperature of 150°F (relatively low compared with 240°F), lactic acid has advantages in wormhole efficiency when compared with HCl. Combined with less corrosiveness to the well tubulars and surface equipment, lactic acid can be a good chemical system for carbonate acidizing. For high-temperature formation, lower concentration lactic acid can be used as long as wormhole efficiency is not compromised. It is recommended that for each specific reservoir formation, the appropriate lactic acid concentration should be identified from laboratory tests to ensure the stimulation efficiency, avoid detrimental precipitation, and save operation costs.

Synthesis and Evaluation of High-Temperature Resistant Polymer Plugging Agent for Water-Based Drilling Fluids.

As the exploration and development of deep wells have emerged as a key option to extract more oil and gas resources trapped underneath, high-temperature formations impose stringent requirements on the thermal stability of plugging agents used in water-based drilling fluids. In this work, β-cyclodextrin, with its unique conical toroidal rigid stable structure and internal hydrophobic and external hydrophilic special adsorption capacity, was first grafted with maleic anhydride to prepare a silicone polymer and then copolymerized with dimethyldiallylammonium chloride (DMDAAC) in the presence of coupling agent vinyltriethoxysilane (A151) and cross-linking divinylbenzene (DVD) to finally obtain a high-temperature resistant plugging agent (AMMD). Subsequently, the molecular structure was evidenced and the performance of AMMD was examined in the polysulfonate-base fluid via a series of tests including high-temperature high-pressure filtration loss, sand tray plugging, and drilling fluid displacement, and the results were compared with the counterpart Soltex under the same conditions. The optimal synthesis conditions for the plugging agent were found as total monomer concentration of 25%, initiator mass fraction of 1% (based on the mass of monomers), monomer feed ratio of m (DVD):m(A151):m(DMDAAC):m(MD) of 15:3:2:15, pH value of 10, reaction temperature of 75 °C, and reaction time of 4 h. FT-IR spectra indicated that the monomers used to prepare AMMD were successfully involved in the reaction for the design of the plugging agent structure. TGA showed that AMMD has a total weight loss of about 35.98% in the range of 284 to 453 °C. Moreover, the addition of 3%AMMD into the base fluid produced a 4.38-fold and 3.8-fold filtration loss control over 60 min at 200 °C using 400 and 800 mD sand trays, respectively, which were comparatively higher than the commercially available Soltex (ca. 3.72-fold and 3.14-fold, respectively, using 400 and 800 mD). This then contributed to AMMD's superior plugging performance in drilling fluid based on the drilling fluid displacement experiment, implying that AMMD could find potential use as a plugging agent in polysulfonate drilling fluid under severe geothermal conditions.

Degradation Effects in Li4Ti5O12-Based Cells─Learning from Electrode Potential Profiles.

Li4Ti5O12 (LTO) is a promising negative electrode active material for high-power applications of lithium-ion batteries due to its structural and dimensional stability, high safety properties, and rate capability. However, there are still challenges regarding the cyclic aging behavior of LTO-based cells, especially when it comes to the origin of gas evolution that needs to be resolved in order to enable an optimized cell design and prolonged cycle life. Using a three-electrode setup provides operando insights into the cyclic aging behavior of LiNi1/3Co1/3Mn1/3O2 (NCM111)||LTO cells. The results demonstrated that an initial slight increase in specific capacity followed by an intense decrease after 40 cycles could be attributed to a relative shift of the individual electrode potential profiles caused by loss of lithium inventory and associated electrolyte consumption during cyclic aging. By using higher formation temperatures, the capacity decrease, an associated loss of lithium inventory, and continuous electrolyte consumption were successfully suppressed. Moreover, the results suggested that gas evolution in Li4Ti5O12-based cells majorly originates from the reductive decomposition of moisture residues and the electrolyte at the Li4Ti5O12 electrode surface.

Характер матрикса — индикатор температурных условий формирования зювитов (на примере обломочных импактитов Карского метеоритного кратера)

The paper proposes a new approach for the study of suevites formation features — the analysis of temperature conditions of clastic impactites formation based on the analysis of local matrix sintering using materials science methods. Structural and textural features and substance composition of the suevite matrix of the bottom and ejecta facies of the Kara astrobleme are studied. The petrochemical composition of the clastic impactite matrix reflects the composition of the target rocks, it can be complicated with the suevites post-impact altering. Quartz and albite clusters in the matrix have signs of different sintering stages, indicating a strong variety in local temperature conditions of the suevites formation. In this regard, it makes no sense to conclude about a certain temperature of rock formation as a whole. During lithification the suevites of aerodynamic facies the local temperature could reach 1200 °C. The bottom facies had relatively higher temperature formation where the maximum temperatures locally reached 1700 °C. The sintering nature of the suevite matrix is an indicator of the specifics of the formation conditions and can be used to diagnose facies of detrital impactites and to clarify the parameters and scenario of impact events.

The Effects of Temperature and Fluoroethylene Carbonate Concentration on the Formation of the Graphite SEI and Its Impact on the Full-Cell Performance

Extending the cycle-life of state-of-the-art lithium-ion batteries (LiBs) is, amongst other aspects, predicated on optimizing the properties of the solid electrolyte interphase (SEI), such as its stability and resistance.[1] It is formed at the negative electrode during the first cycles by electrolyte decomposition and acts as a passivating layer between the electrode surface and the electrolyte.[2,3] Since the SEI formation is accompanied by an irreversible loss of cyclable lithium, its stability during cycling is crucial for improving the charge/discharge efficiency of LiBs. Furthermore, the arising resistance associated with the SEI formation, predominantly depending on the SEI thickness, its chemical composition, and its lithium-ion conductivity, all impact the rate performance of the anode.[4] Two of the most crucial factors impacting SEI formation are temperature and electrolyte composition (i.e., using electrolyte additives).[5] Additives are added to the electrolyte to inhibit the predominant reduction of other electrolyte constituents and thereby form an SEI with improved stability during cycling.[1,6,7] One of the most prominent additives for LiBs is fluoroethylene carbonate (FEC), which is preferentially reduced compared to common carbonate solvents (e.g., ethylene carbonate, ethyl methyl carbonate) due to its higher reduction potential.[7] In this study, we investigated the influence of the formation temperature between 10 and 60 °C, as well as the concentration of FEC (2 and 20 %wt in EC:EMC 3:7 wt/wt with 1 M LiPF6, Gotion, USA) on the characteristics of a synthetic graphite (SMG-A5, Resonac, Japan) anode, both in SMG/Li half-cells and in Ni-rich NCM/SMG full cells.We quantified the first-cycle irreversible capacity loss (ICL) in SMG/Li half cells with a lithium reference electrode after two 0.1 C formation cycles and compared the FEC containing electrolytes to the baseline- (LP-57) and an LP-572 (1 M LiPF6 in EC:EMC 3:7 wt/wt + 2 %wt vinylene carbonate (VC), Gotion, USA) electrolyte. Employing electrochemical impedance spectroscopy in an SMG/Li half-cell setup with a µ-reference electrode and a free-standing graphite electrode,[8,9] we could further quantify the intercalation resistance (R Int, representing the sum of the charge-transfer and the SEI resistance) after an identical formation protocol at 40 % SOC. Both quantities, the ICL and R Int, increase with increasing formation temperature and higher FEC content.The impact of an increasing R Int on the rate performance was tested in Ni-rich NCM/SMG full cells with a lithium reference electrode, revealing a decreased rate capability and higher susceptibility for lithium plating for cells that were formed at higher temperatures and contained 20 %wt FEC. Additionally, the cycling stability of Ni-rich NCM/SMG full cells at 25 °C was assessed in coin cells. Despite an increased ICL and R Int after formation, cells that were formed at elevated temperatures and contained 20 %wt FEC showed enhanced cycling stability compared to those that were formed at a lower temperature and contained less FEC.Finally, on-line electrochemical mass spectrometry (OEMS) was employed to quantify the evolved gases during the formation of a Ni-rich NCM/SMG full cell containing either of the FEC-containing electrolytes at different temperatures. In accordance with an increased ICL and R Int, a higher formation temperature, as well as a higher FEC content, gave rise to a more pronounced gas evolution during formation.

High-entropy-perovskite subnanowires for photoelectrocatalytic coupling of methane to acetic acid

The incorporation of multiple immiscible metals in high-entropy oxides can create the unconventional coordination environment of catalytic active sites, while the high formation temperature of high-entropy oxides results in bulk materials with low specific surface areas. Here we develop the high-entropy LaMnO3-type perovskite-polyoxometalate subnanowire heterostructures with periodically aligned high-entropy LaMnO3 oxides and polyoxometalate under a significantly reduced temperature of 100 oC, which is much lower than the temperature required by state-of-the-art calcination methods for synthesizing high-entropy oxides. The high-entropy LaMnO3-polyoxometalate subnanowires exhibit excellent catalytic activity for the photoelectrochemical coupling of methane into acetic acid under mild conditions (1 bar, 25 oC), with a high productivity (up to 4.45 mmol g‒1cat h‒1) and selectivity ( > 99%). Due to the electron delocalization at the subnanometer scale, the contiguous active sites of high-entropy LaMnO3 and polyoxometalate in the heterostructure can efficiently activate C − H bonds and stabilize the resulted *COOH intermediates, which benefits the in situ coupling of *CH3 and *COOH into acetic acid.

MINERAL PARAGENESIS OF EARLY BIOTITE VEINS AT THE KUH-E JANJA Cu-Au PORPHYRY DEPOSIT, SOUTHEASTERN IRAN: IMPORTANCE OF MICROTEXTURAL OBSERVATIONS IN STUDIES CONSTRAINING THE RELATIVE TIMING OF HYPOGENE Cu MINERALIZATION

Abstract Veins consisting primarily of biotite are the earliest stockwork vein type recognized at the Kuh-e Janja Cu-Au porphyry deposit in southeastern Iran. These early biotite veins may contain quartz and minor amounts of sulfide minerals such as chalcopyrite and pyrite. Observations at the hand-specimen scale do not provide reliable constraints on the paragenetic relationships, as the early biotite veins have been repeatedly overprinted during the evolution of the magmatic-hydrothermal system. Microscopic investigations show that the sulfide minerals in the early biotite veins are texturally late, providing evidence that sulfide deposition did not occur at the high temperatures of biotite formation and potassic alteration of the host rocks. Chalcopyrite primarily occurs along hairline fractures that crosscut or refracture the earlier biotite veins. Biotite in contact with the chalcopyrite can be apparently unaltered or is replaced by chlorite, depending on the degree of wall-rock buffering of the magmatic-hydrothermal fluids that caused hypogene Cu mineralization. The findings add to the growing body of evidence that Cu mineralization in this deposit type occurs at temperatures close to the transition from ductile to brittle conditions (<450°C) following a drop in the pressure regime from lithostatic to hydrostatic conditions.

Influence of raw material temperature on the properties of silicate-modified polyurethane grouting materials

Silicate-modified polyurethane (PU/WG) is an effective organic–inorganic hybrid-grouting material that blocks water and reinforces weak formations. In deep high-temperature formations, owing to environmental impacts, PU/WG raw materials are heated before grouting. To elucidate the basic characteristics of PU/WG grouting materials in deep, high-temperature environments, we investigated the effects of raw material temperature on the curing time and strength of PU/WG by considering different mass ratios during the curing time test. Furthermore, the influence of raw material temperature on the micro-structure of PU/WG was analysed from a microscopic perspective using scanning electron microscopy. Energy-dispersive X-ray spectroscopy revealed the composition and curing mechanism of PU/WG. The results indicated that as the raw material temperature increased from 24 to 60°C, the peak strength decreased from 41.65 to 14.51 MPa, and the peak strain decreased from 27.03 % to 8.83 %. Based on the experimental results of the curing time testing and strength test, we established a PU/WG curing time-variation model considering the coupling of raw material temperature and mass ratio and provided an optimisation scheme for the PU/WG strength, which provides effective guidance for grouting time design in high-temperature environments.

Multiple hydraulic fracture propagation simulation in deep shale gas reservoir considering thermal effects

Deep and ultra-deep shale gas will gradually become the focus of unconventional oil and gas resources in the petroleum industry. In the development of shallow shale reservoirs, the multi-cluster hydraulic fracturing of horizontal wells is the commonly applied technique to create a network of fractures and achieve reservoir stimulation. However, for deep shale reservoirs, the behavior of multiple hydraulic fracture propagation is affected by stress interference between fractures. On the other hand, it is also influenced by the temperature disturbances caused by the injection of low-temperature fracturing fluids into high-temperature formations and the resulting thermal effects. Currently, most research on multiple hydraulic fracture propagation in shale only considers the interaction between fluids and solids while neglecting thermal effects. Therefore, based on the displacement discontinuity method, finite volume method, and finite difference method, this study established a numerical model for the non-planar propagation of multi-cluster hydraulic fractures in deep shale, considering the thermal effects. And the model was validated through numerical solutions of the temperature field and double-fracture propagation. Moreover, the number of fracture clusters, pumping rate, and formation temperature were selected as influencing factors, and the differences in multiple hydraulic fracture propagation with and without considering thermal effects were analyzed. The results show that as the formation temperature increases, the thermal effects become more significant, leading to greater differences in the morphology of multi-cluster fractures. Moreover, the thermal effects are more significant when the formation temperature exceeds 90 °C. Additionally, appropriately reducing the number of fracture clusters or increasing the pumping rate can to some extent mitigate stress interference between fractures and promote uniform fracture propagation. The findings of this study contribute to understanding the influence of thermal effects on multiple hydraulic fracture propagation and provide theoretical basis for the efficient development of deep shale gas.

The Success of Fabrication of Pure SmFe2 Phase Film with Outstanding Perpendicular Magnetic Anisotropy.

This study used DC magnetron sputtering technology to fabricate Sm-Fe films and systematically investigated the phase transition behavior of Sm-Fe films with different Fe ratios. It was found that at higher Fe content, the films consisted of Sm2Fe17 or SmFe7 phases; as Fe content decreased, the films were mainly composed of SmFe3 or SmFe2 phases; at higher Sm content, the films primarily consisted of Sm phase. Sm is prone to volatilization at high temperatures, so Ta was used as a capping layer to effectively suppress Sm volatilization, successfully synthesizing pure SmFe2 phase films at a nearly 1:2 ratio. The magnetic properties and magnetostrictive behavior of the SmFe2 films were investigated, revealing that pure-phase SmFe2 films exhibit good perpendicular magnetic anisotropy and magnetostriction properties. The larger stress along the perpendicular-to-film direction, resulting from the absence of substrate-induced constraints, contributes to the excellent perpendicular magnetic anisotropy of the films. This study successfully synthesized pure-phase SmFe2 films and discovered a new method for fabricating perpendicularly anisotropic films. The research findings are of great significance for the efficient synthesis of desired films with high phase formation temperatures containing volatile elements.

The Origin of Mesozoic A‐type Granitoids, Fujian Province, Southeast China: Insights from Geochronology, Mineralogy and Geochemistry

AbstractThe magma sources, origins and precise forming ages of the miarolite from Qishan and Kuiqi intrusions are still uncertain. New results reveal that, miarolites from the Qishan and Kuiqi intrusions yield crystallization ages of ∼101 and ∼98 Ma, and they have a high formation temperature (∼910°C) and low oxygen fugacity value, indicating crystallization condition at low pressure in the upper crust with temperature of 678°C. The Qishan and Kuiqi miarolites are characterized by enrichment in SiO2 and high‐K alkali, depletion in Ca and Mg, and belong to the high‐K weak peraluminous rock series. The samples are enriched in HFSEs (i.e., Ta, Zr and Hf) and LILEs (i.e., Ba, P and Sr), depleted in Ba and Sr with the negative anomaly of Eu. In the primitive mantle normalized trace element spider diagram, the samples show a right‐inclined ‘seagull‐type’ pattern, combined the ratios of (La/Yb)N, 10000 × Al/Ga, Rb/Nb and Nb/Ta etc., they were proved to be alkaline A‐type granite. Combined the characterize of the trace elements, they were derived from clay‐rich source accompanied pelite melting, and subjected to K‐feldspar crystallization fractional. The values of εHf(t) and tDM2 are distributed in the range of –2.8 to 3.3 with ∼1.2 Ga, and –6.0 to 4.0 with ∼1.2 Ga, revealing that they were generated from the Mesoproterozoic Cathaysia basement rocks. The comprehensive research reveals the Kuiqi and Qishan intrusions derived from crust‐mantle mixing and partial melting of the crust, respectively, resulting from lithospheric extension generated by the Paleo‐Pacific Plate subducted into the European–Asian Plate.

Occurrence Mechanism of the Abnormal Gelation Phenomenon of High Temperature Cementing Slurry Induced by a Polycarboxylic Retarder.

The class G oil well cement is a type of special cement that can be subjected to a high temperature formation environment. It was found that the class G cement tail slurry with a low polycarboxylic retarder dosage (usually ≤1% by weight of cement) was more prone to cause the abnormal gelation phenomenon (AGP) than the lead slurry with a high retarder dosage at a high temperature (usually when T ≥ 120 °C). This study aimed at the occurrence mechanism of this unfavorable phenomenon that seriously endangers the cementing security. Results showed that the abnormal gelatinous region underwent premature hydration; namely, the calcium hydroxide and calcium silicate hydrate (C-S-H) content were all higher than the nongelatinous region, while the copolymer content was the opposite. Correspondingly, the theory of "premature hydration and crystal nucleation" was proposed to explain the abnormal gelation mechanism of a cementing tail slurry with an insufficient retarder dosage. Furthermore, a novel functionalized copolymer retarder "PAIANS" was synthesized to alleviate the AGP.

A Review in Polymers for Fluid Loss Control in Drilling Operations

AbstractThe ever‐increasing consumption of fossil energy highlights the urgent need to develop technologies to ensure the efficient drilling and exploration of oil and gas resources mainly distributed in deep layers. The complex geological conditions in deep formations with the feature of high temperature, high pressure, and high salinity result in high requirements for the performance of drilling fluids. Various additives are demonstrated to decide the physicochemical properties and functional characteristics of water‐based drilling fluids. As one of the most widely used additives in water‐based drilling fluids, various polymeric filtrate reducers play an important role in minimizing fluid loss, maintaining wellbore stability, ensuring drilling safety and efficiency as well as avoiding formation damage. Herein the design, preparation, and applications of polymer‐based filtrate reducers for fluid loss control in drilling operation are comprehensively summarized. The spotlight is centered on the design strategies and structure–property–performance relationships of polymeric filtrate reducers to minimize fluid loss under high temperature, high pressure, and high salinity conditions. Future perspectives for achieving excellent comprehensive performance are also discussed to motivate new strategies and technologies to design and develop high‐performance drilling fluids with optimal rheological and filtration properties.

Thermal stability of thick α- and γ-Al2O3 coatings deposited by high-speed PVD

α- and γ-Al2O3 coatings, are often used for high temperature applications T ≥ 800 °C. While stable α-Al2O3 is typically synthesized by chemical vapor deposition (CVD) due to its high formation temperature T ≥ 1000 °C, conventional physical vapor deposition (PVD) is limited to T ≈ 600 °C. Nevertheless, this method may result in metastable or amorphous Al2O3 phases, which limits their thermal stability and application at higher temperatures. Previous studies showed that High-Speed PVD can synthesize thick α- and γ-Al2O3 coatings at T ≈ 780 °C. This study investigates the thermal stability of these coatings deposited by HS-PVD. High-temperature X-ray diffraction (HT-XRD) measurements show no phase transformations of coatings up to T = 1200 °C in a vacuum or atmosphere. The coating morphology remained unchanged, and no cracks were detected by scanning electron microscopy (SEM) after annealing during HT-XRD. In situ, HT nanoindentation (HT-NI) revealed a reduction in indentation hardness of X ≈ 33 % and Y ≈ 40 % at THT-NI = 650 °C and THT-NI = 750 °C, respectively. However, hardness values remained similar to the as-deposited state after annealing in HT-XRD. These findings reveal a high thermal stability of crystalline Al2O3 coatings deposited by HS-PVD up to T = 1200 °C, which can extend the application of these coatings to higher temperatures.

Challenges of formation damage control technology for ultra-deep tight gas reservoirs: A case study from Tarim Basin

Formation damage mechanisms and the corresponding control technology for the tight gas reservoirs have been reported, whereas few studies have discussed ultra-deep fractured tight gas reservoirs. Ultra-deep fractured tight gas reservoirs were susceptible to be damaged owing to geological conditions and engineering status. Taking the ultra-deep fractured tight gas reservoirs located in the Tarim Basin as an example, ultra-tight, high-pressure, high temperature (HPHT), and high-salinity formation water, ultra-low water saturation and fracture networks were identified as special geological characteristics. High-density oil-based drill-in fluids and serious lost circulation were the special engineering status. Challenges in laboratory experiments to evaluate formation damage include rigorous experimental conditions and unsuitable experimental methods. In addition, improving the formation protection ability of working fluids and minimizing the formation damage induced by the sequential use of different types of working fluids were the main challenges associated with using working fluids. Challenges in lost circulation control include the failure of plugging zone due to the degradation of lost circulation materials and repeated lost circulation due to the strength reduction of the plugging zone soaked in diesel oil. Recommendations for key technologies to improve targeted formation damage control technology have been proposed. The comprehensive analysis of these issues provides a road-map for researching formation damage control technologies.

The inhibited response of accessory minerals during high‐temperature reworking

AbstractU–Pb zircon and monazite geochronology are considered to be among the most efficient and reliable methods for constraining the timing of high‐temperature (HT) metamorphic events. However, the reliability of these chronometers is coupled to their ability to participate in reactions. A case study examining the responsiveness of zircon and monazite has been conducted using granulite facies metapelitic and metamafic lithologies in the Warumpi Province, central Australia. In some instances, metapelitic granulites from this locality are polymetamorphic, with an early M1 assemblage containing orthopyroxene, cordierite, biotite, quartz, ilmenite and magnetite, and an M2 assemblage represented by garnet, sillimanite, orthopyroxene, cordierite, biotite, sapphirine, ilmenite and magnetite. M2 metamorphism is linked to HT peak conditions of 8–10 kbar and 850–915°C. Detrital and metamorphic zircon and monazite from these rocks dominantly record U–Pb dates of 1670–1610 Ma and have trace element compositions suggesting they grew prior to peak M2 garnet in the rock. Lu–Hf geochronology from M2 garnet gives ages of c. 1150 Ma. Zircon and monazite are therefore suggested to have remained largely inert during HT metamorphism. We attribute the relatively minor response of zircon and monazite during high‐temperature Mesoproterozoic metamorphism to the localized development of refractory bulk compositions at c. 1630 Ma during M1 metamorphism. This created refractory Mg–Al‐rich bulk compositions that were unable to undergo significant partial melting, despite experiencing subsequent temperatures of ~900°C at c. 1150 Ma. In contrast, metapelitic and metamafic rocks in the area that did not develop refractory bulk compositions during M1 metamorphism were able to partially melt and record c. 1150 Ma accessory mineral U–Pb ages. These results contribute to a small, but growing number of case studies investigating the systematics of the U–Pb system in zircon and monazite in polymetamorphic HT terranes and their apparent resistance to isotopic resetting. Where disequilibrium is apparent, garnet Lu–Hf geochronology can form an important tool to interrogate the significance of accessory U–Pb ages. In the Warumpi Province in central Australia, c. 1640 Ma zircon U–Pb ages had previously been interpreted to reflect the formation of HT garnet‐bearing granulites during a collisional event. Instead, the garnet‐bearing assemblages formed at c. 1150 Ma during the Mesoproterozoic, calling into question the existence of a late Palaeoproterozoic collisional system in central Australia.

Experimental investigation of the impacts of supercritical carbon dioxide on acid-etching fracture morphology and conductivity in tight carbonate reservoir

Carbon dioxide (CO2) as energized fluid has been used for acid-fracturing in tight carbonate reservoir. CO2 is often pumped into the wellbore in liquid phase with acid systems, and transited into supercritical state under the high-temperature formation. While the effect of supercritical CO2 (SC-CO2) on acid-etched fracture morphology and conductivity have rarely been investigated. The acid-etching and conductivity experiments were conducted on the outcrops of the Ma5 sub-member of the Ordo Basin in China. The mixed phase reaction simulation device was developed firstly. These experiments involved the mixing of SC-CO2 with various fluids, including formation water and viscoelastic surfactant (VES) acid, as well as different SC-CO2 concentrations with VES acid. The results show that 100 % SC-CO2 is easy to activate natural fractures without dissolution. After 20%SC-CO2 mixed with formation water, the dissolution ability of the mixed solution and conductivity is only 11.8 % and 1 ∼ 2 % of VES acid respectively. Roughness of the morphology created by the mixture of SC-CO2 with VES acid, exhibits a reduction compared to VES acid-etching, accompanied by the presence of wormholes. Additionally, there is a decrease in conductivity and increase in its retention rate. With the increase of SC-CO2 concentration, the roughness of acid-etching fracture decrease and the injection pressure curve becomes more stable. While the reaction rate is also retarded nearly linearly as the SC-CO2 concentration increases. Especially, when the SC-CO2 concentration is up to 40 %, the acid-rock reaction rate reaches only 55 % of that of VES acid. The conductivity of mixed-acid-etched fracture exhibits a segmented characteristic. During the low-medium closure pressure stage, the acid-etched fracture by VES acid generates high conductivity, specifically when it is below 34.5 MPa. While the higher the SC-CO2 concentration in the mixed acid is, the greater the conductivity and retention rate are at pressures above 34.5 MPa during high closure pressure stage. The conductivity of SC-CO2 acid-fracturing fracture depends on the non-uniform etching of the acid solution. The increase in SC-CO2 concentration of the mixed acid not only enhances conductivity and retention rate under high closure pressure, but also reduces the acid volume required for acid-fracturing.