High Pressure And High Temperature Conditions Research Articles

A proposal for a constitutive equation fitting methodology for the rheological behavior of drilling fluids at different temperatures and high-pressure conditions

Drilling fluids are complex suspensions of particles with a wide diameter range. While extensive research has explored the rheological behavior of drilling fluids, several limitations still exist. High-pressure and high-temperature (HPHT) conditions encountered in drilling fluids have introduced unique challenges, and only a few studies have attempted to develop a comprehensive equation that addresses both aspects concurrently. This study aims to perform a rheological characterization of a water-based drilling fluid (WBDF) containing xanthan gum under HPHT conditions and propose a constitutive equation to fit rheological data in such conditions. The experiments were conducted using an Anton Paar MCR 702TD rotational rheometer, coupled with a pressure cell. Steady-state flow curves were obtained at three different temperatures (25, 55, and 100 °C) and pressures ranging from 100 to 800 bar. The experimental data were fitted to the power-law model, and the rheological parameters of the model were fitted with variations in temperature and pressure. The fluid exhibited shear-thinning behavior, with the influence of temperature being more predominant than the effect of pressure, however, both variables have a strong relationship. Furthermore, we proposed a methodology to establish an equation capable of predicting the shear stress of the drilling fluid under HPHT conditions. The equation was also compared with different drilling fluids tested on different rheometers. This equation demonstrated excellent predictive accuracy within the fitted range. The insights provided in this study hold substantial implications for the oil and gas industry, as predicting the rheological behavior of drilling fluids under varying temperatures and pressures within the annular region of the well is essential for efficient drilling planning, particularly in offshore fields.

Temperature dependence of growth-sector-dependent Raman spectra of boron-doped diamonds synthesized at high-pressure high-temperature

Single crystals of boron-doped diamond (BDD) were synthesized by the temperature gradient method in high-pressure and high-temperature conditions in the Fe–Al–B–C system, and multisectoral diamond plates were extracted. Temperature-dependent (77–600 K) high-resolution Raman spectroscopic studies have been carried out to investigate the behavior of anharmonic phonon decay in the {001}, {113}, and {111} growth sectors of multisectoral diamond plates with different content of boron impurities (⩽80 ppm) and compare with the data for undoped IIa diamond. Micro-Fourier transform infrared spectroscopy was used to estimate the spatial distribution of uncompensated boron impurity [Na-Nd] in BDD plates by analyzing boron-related absorption peaks. The plates were shown to have non-uniform growth-sector-dependent content of uncompensated boron impurity in the range from 1.1 × 1018 to 1.4 × 1019 cm−3. The effects of anharmonic decay (damping) of optical phonons in BDD are studied by modeling the temperature dependence of phonon frequency and linewidth of the diamond’s F2g and boron-induced vibrational modes. The extrapolated zero-temperature optical phonon linewidth and frequency and the anharmonic nature of their linear relationship are determined as a function of the growth sector and boron doping. The predominant mechanisms and parameters of the anharmonic decay of optical phonons are determined, which is of fundamental importance for the thermal conductivity of semiconductor materials. The anharmonic phonon decay remained the predominant process at higher temperatures, irrespective of the doping level.

Multifunctional tantalum disilicide ceramics sintered at high temperature and high pressure

AbstractSilicide ceramics are attracted significant attention due to their exceptional physical properties. However, their inherent brittleness at room temperature limits their practical applications. Here, we aim to improve the mechanical properties of tantalum disilicide (TaSi2) ceramics by modifying the preparation methods and sintering conditions. We fabricate the dense TaSi2 ceramics using high‐pressure and high‐temperature (HPHT) sintering technology at 5.5 GPa and 800–1300°C. We characterize the microstructures, mechanical, and electronic properties of bulk TaSi2 ceramics at HPHT conditions. Our results indicate an enhancement in the fracture toughness of 11.97 MPa m1/2 for TaSi2 ceramics. More importantly, the electrical conductivity (47.13 × 105 S/m) of TaSi2 ceramic is increased and verified by theoretical calculations. These findings provide crucial insights for future applications of TaSi2 and offer valuable avenues for the design and synthesis of advanced ceramic materials.

Simulation of Rock Electrical Properties in Deep Reservoirs Based on Digital Rock Technology

Deep reservoirs are in a high-pressure and high-temperature (HPHT) environment, while the experimental conditions for rock electrical properties that meet the deep reservoir conditions are harsh and costly. Although digital rock technology can simulate the electrical properties of rocks, it is limited to electrical simulation studies under normal temperature and pressure conditions (NPT), which limits their ability to capture the electrical characteristics of deep hydrocarbon reservoirs. This limitation affects the accuracy of saturation prediction based on resistivity logging. To simulate the rock electrical properties under HPHT conditions, we proposed a low-cost and high-efficiency HPHT digital rock electrical simulation workflow. Firstly, samples from deep formations were CT-scanned and used to construct multi-component digital rocks that reflect the real microstructure of the samples. Then, mathematical morphology was used to simulate the overburden correction under high-pressure conditions, and the changes in the conductivity of formation water and clay minerals at different temperatures were used to simulate the conductivity changes of rock components under high-temperature conditions. To carry out the electrical simulation of digital rock in deep reservoirs, a numerical simulation condition for HPHT in deep layers was established, and the finite element method (FEM) was used. Finally, based on the equivalent changes in the conductivity of different components, the effects of clay minerals and formation water under HPHT conditions on rock electrical properties were studied and applied to predict the water saturation based on well logging data. We found that considering the influence of temperature, salinity, and clay type, the saturation index (n) of the rock depends on the ratio of the clay conductivity to the formation water conductivity. The larger the ratio is, the smaller the value of n. In addition, the average relative error between the predicted water saturation under HPHT conditions and the sealed coring analysis was 6.8%, which proved the accuracy of the proposed method. Overall, this method can effectively simulate the pressure and temperature environment of deep formations, reveal the electrical conductivity mechanisms of rocks under formation pressure and temperature conditions, and has promising prospects for the study of rock physical properties and reservoir evaluation in deep formations.

Impact of surface-modified silica nanoparticle and surfactant on the stability and rheology of oil-in-water Pickering and surfactant-stabilized emulsions under high-pressure and high-temperature

Emulsions have a wide range of applications, and with the advancement in the use of nanoparticles to form stable Pickering emulsions, it is important to understand their rheological properties to infer their stability under high-pressure and high-temperature (HPHT) compared to the emulsion formed using conventional surfactants. In oil and gas production strategies, oil often forms an emulsion with brine either within reservoirs or at surface facilities in the presence of natural or artificial surfactants. Nanoparticles are also being explored to increase oil recovery from matured reservoirs. In various instances, stable emulsions are either formed in-situ (within the reservoir) or at surface facilities or injected into the reservoir to mobilize the trapped oil. It is also essential to understand their rheology for efficient oilfield application. This study investigates the impact of surface-modified silica nanoparticles (Ludox CL), NaCl salt, and surfactant on the stability of oil-in-water Pickering and surfactant-stabilized emulsions under high-pressure (0.1–10) MPa and high-temperature (303–363) K conditions. The viscosity of emulsion samples was measured at varying shear rates (0.1–1000) s−1. The viscoelastic behavior (G′, G″, η*, and δ) of the Pickering emulsion and surfactant-stabilized emulsion were also measured. The stability of the emulsions was measured in terms of changes in emulsion viscosity and droplet diameter. Both emulsions showed non-Newtonian shear thinning behavior and an increase in droplet diameter under HPHT conditions. However, the surfactant-stabilized emulsion exhibits a greater degree of change in emulsion viscosity and droplet diameter than the Pickering emulsion. It indicates that the Pickering emulsion showed better stability than the surfactant-stabilized emulsion under HPHT conditions. Hence, Pickering emulsions are an incredibly promising tool that might be employed in HPHT applications, especially for enhanced oil recovery applications, due to their better rheological stability.

Electrostructural and morphological features of etch pits in boron-doped HPHT-diamond single crystals and multisectoral plates

Morphological, structural, and nano-electrical features of the growth defects and sectoral boundaries revealed by selective etching in synthetic boron-doped single crystals of diamond (BDD) and multisectoral plates are characterized by a set of scanning probe microscopy (SPM) methods, confocal micro-Raman, and micro-FTIR spectroscopy. Diamond single crystals were grown under high pressure and high temperature conditions (HPHT) in the FeAlBC system. Morphology of dislocation etch pits and micro-defect related pits/protrusions compared both on the growth facets and multisectoral plates cut parallel to the {110} facet of BDD single crystals. Ex situ AFM observation of the etched surface revealed non-homogeneously distributed pits and protrusions over the growth facets correlated with irregular macroscopic growth defects. There is a center-to-periphery gradient of dislocation density in multisectoral plates. The protrusions are homogeneously distributed over plates; some often decorate dislocation pits. Micro-Raman mapping on dislocation pits (boron-rich regions) decorated by low-boron content regions revealed crystalline imperfections in three dimensions, with apparent compressive/tensile strain. The defects were mainly electrically neutral under surface potential mapping by Kelvin probe force microscopy, opposite to the inter-sectoral boundaries having pronounced surface potential steps. The scanning spreading resistance microscopy shows resistivity variations at etching-reviled surface defects and sectoral boundaries if the appropriate DC bias is applied to the SPM tip.

High pressure and high temperature treatment of chemical vapor deposited polycrystalline diamond: From opaque to transparent

The enhanced optical properties of chemical vapor deposited (CVD) diamond have been pursued in academia and industry for many applications. However, the barrier of CVD technology limits the application field of diamond. Herein, the performance of CVD polycrystalline diamond thick films was improved by high-pressure and high-temperature (HPHT) treatment. The microstructures of CVD polycrystalline diamond films before and after HPHT treatments were thoroughly examined using optical microscope, UV–visible and infrared absorption, Raman spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM). It is found that the transparency of the CVD samples at 10 GPa increases dramatically with processing temperatures, from the original opacity to almost full optical transparency. Through spectroscopic and microstructural analyses, the modification mechanism of CVD polycrystalline diamond under HPHT conditions is proposed. The results show that the HPHT treatment can significantly enhance the optical properties of the starting CVD polycrystalline diamond films.

Recent Progress in Phase Stability and Elastic Anomalies of Group VB Transition Metals

Recently discovered phase transition and elastic anomaly of compression-induced softening and heating-induced hardening (CISHIH) in group VB transition metals at high-pressure and high-temperature (HPHT) conditions are unique and interesting among typical metals. This article reviews recent progress in the understanding of the structural and elastic properties of these important metals under HPHT conditions. Previous investigations unveiled the close connection of the remarkable structural stability and elastic anomalies to the Fermi surface nesting (FSN), Jahn–Teller effect, and electronic topological transition (ETT) in vanadium, niobium, and tantalum. We elaborate that two competing scenarios are emerging from these advancements. The first one focuses on phase transition and phase diagram, in which a soft-mode driven structural transformation of BCC→RH1→RH2→BCC under compression and an RH→BCC reverse transition under heating in vanadium were established by experiments and theories. Similar phase transitions in niobium and tantalum were also proposed. The concomitant elastic anomalies were considered to be due to the phase transition. However, we also showed that there exist some experimental and theoretical facts that are incompatible with this scenario. A second scenario is required to accomplish a physically consistent interpretation. In this alternative scenario, the electronic structure and associated elastic anomaly are fundamental, whereas phase transition is just an outcome of the mechanical instability. We note that this second scenario is promising to reconcile all known discrepancies but caution that the phase transition in group VB metals is elusive and is still an open question. A general consensus on the relationship between the possible phase transitions and the mechanical elasticity (especially the resultant CISHIH dual anomaly, which has a much wider impact), is still unreached.

Interaction mechanism of Ge, Ti, and N in diamond prepared by high pressure and high temperature conditions

In this paper, Ge-doped large single crystal diamond was synthesized under high pressure and high temperature (HPHT) conditions in NiMnCo-C and NiMnCo-Ti-C systems. The effects of Ge additives on the diamond morphology, nitrogen impurity content, and internal inclusions were investigated, and the interaction mechanism among germanium (Ge), nitrogen (N), and titanium (Ti) during the diamond growth process was discussed. The results show that the number of inclusions in diamond increase with increases in Ge addition in both systems. The N content of diamond grown in NiMnCo-C systems decreases with increases in Ge addition. However, Ge can more easily be doped into the diamond in a NiMnCo-Ti-C growth system. The experimental results show that the N can inhibit the amount of Ge entering the diamond lattice under HPHT conditions. When Ti was introduced into the system, it effectively removed N by combining with it, such that more Ge atoms could enter the diamond lattice.

Ultrafine‐grained B6O–diamond composites with superb mechanical properties

AbstractWe report here the high‐pressure and high‐temperature (HPHT) synthesis of well‐sintered B6O–diamond composites from B6O and carbon black nanopowders. The carbon black was transformed into diamond nanograins at HPHT conditions, and simultaneously formed high‐strength B6O–diamond interfaces. The ultrafine B6O and diamond nanograins and the high‐strength B6O–diamond interfaces synergistically construct excellent mechanical properties for the synthesized composites. The B6O–diamond composites possess a hardness (avg. 52 GPa) comparable to that of polycrystalline diamond (40–60 GPa), whereas the fracture toughness (avg. 7.2 MPa m1/2) is increased several times compared to previously synthesized polycrystalline B6O ceramics (1.7–3.1 MPa m1/2) and B6O‐based composites (3–4 MPa m1/2). Fracture behavior analysis demonstrates that the main toughening mechanisms in this B6O–diamond composite are nanotwin toughening, crack deflection, and crack bridging.

Designing Smart drilling fluids using modified nano silica to improve drilling operations in Geothermal wells

High pressure and high temperature (HPHT) conditions in geothermal wells have necessitated the need to develop thermally stable geothermal drilling mud systems to combat potential drilling complications. This is because mud fluids degrade under HPHT conditions due to high temperature effects. This study therefore aims to establish the optimum concentration of a cationic surfactant that would successfully modify the surface of silica nanoparticles and thereafter, evaluate the performance of modified nano silica as a rheological and filtration property enhancer in water-based muds (WBMs). The surface of silica nanoparticle was successfully modified by adding Hexadecyltrimethylammonium bromide (CTAB) to silica solution. Different mud formulations containing modified nano silica with varying zeta potential values, SNP3 -S2, SNP3 -S4, SNP3 -S5, SNP3 -S6, and SNP3 -S7 with -17.7 mV, 20 mV, 28.2 mV, 35.4 mV, and 37.1 mV respectively were investigated. Results showed that modified nano silica with the highest absolute value of zeta potential enhanced drilling mud rheology as temperature increased from 149°C to 232 °C. The optimal amount of CTAB was found to be between 1.0 and 2.0 wt.%. Filtration loss was reduced by 11.4, 17.6, and 29.5% on average for mud samples SNP3-S5, SNP3-S6, and SNP3-S7, respectively, at all temperatures. Mud cake thickness was reduced by 19.9, 11.6, and 28.7% on average by mud samples SNP3-S5, SNP3-S6, and SNP3-S7 respectively at all temperatures.

Rheological Properties of the Water-Based Muds Composed of Silica Nanoparticle Under High Pressure and High Temperature

Summary Research currently has shown two contradicting conclusions about silica nanoparticle (SNP) application in mud fluid. While different studies have concluded that adding SNPs reduces the rheological properties, others have found that this is not the case. Therefore, this work was carried out to add to the literature and research that has already been done by different scholars on the performance of SNPs in water-based muds (WBMs). The synthesis of SNPs was performed by the sol-gel process based on the Stöber method in a mixture of a catalyst ammonium hydroxide containing tetraethyl orthosilicate (TEOS), ethanol, and water. The distribution of particle dispersion, size, and zeta potential of SNP analysis was obtained using the dynamic light scattering analysis. Rheological analysis indicated good rheology at different temperatures with 0.5 wt% and 1.0 wt% silica concentration. Furthermore, viscosity and yield point (YP) were stabilized with nanoparticles (NPs at elevated temperatures (up to 176°C) as well as the reference mud maintained rheology (up to 121°C) and above that temperature, there was a drastic change indicating failure. Aging at temperatures above 121°C for 16 hours showed that NP WBMs remained stable with minor changes in rheology. Using bigger sized SNPs than previously used resulted to enhancement in the rheology of WBMs. Previous studies had used SNPs in sizes of 20–40 nm which negatively affected mud rheology. In this study, SNP of a bigger size resulted in rheological property enhancement. It is believed that particle size with other dynamics and mechanisms that still need to be investigated, for example, zeta potential, repulsive and attractive forces are some of the factors in play that affect nanoparticle performance in mud fluids. The obtained rheological data for different NP muds were matched to the traditional drilling mud rheological models to ascertain the best fit model that would be applied to an efficient design and the data fitted the Herschel-Bulkley model. Filtration tests at high pressure and high temperature (HPHT) conditions also indicated that synthesized SNPs used in the mud fluid resulted in a slightly low permeable thin mudcake and a low API gravity filtration loss which have great advantages when drilling through highly permeable formations. Filtrate loss was reduced by 7.5, 9.1, 15.4, and 6.7% when temperature increased to 100, 121, 149, and 176 °C at 1 wt% silica concentration, respectively. The mudcake was also improved and thickness reduced by 30 and 25% at 0.5 wt% silica concentration when temperatures increased from 149 and 176°C, respectively, compared to the reference mud (R) under HPHT conditions. The research results provide a comprehensive evaluation of an enhanced WBM using SNPs for HPHT applications. The investigated NP has the potential to improve drilling mud properties which may led to less formation damage and efficient drilling operations.

Testing the stability of chemical inhibitors at geothermal conditions and their efficiency to prevent galena formation

Multiple inhibitors are commercially available to mitigate the formation of both scaling and corrosion precipitates. However, the conditions in a geothermal installation are often extreme. This includes high temperatures and high pressures besides the presence of a possibly very saline fluid. In the Balmatt geothermal installation of Mol (Belgium) pressure was kept at 45 bar, which is higher than most other geothermal installations. The temperature of the brine in the installation is ∼120 °C before it passes through the heat exchanger. The amount of totally dissolved solids (TDS) in the Balmatt brine is 165 g L-1 and it has a high ionic strength (∼3.5 mol L-1). To evaluate if inhibitors could have possibly caused the precipitation of the amorphous organic phase observed in the filter scales, a series of experiments was performed. Two inhibitors (DETPMP (diethylenetriamine pentamethylene phosphonic acid) and TD1100) were selected for high pressure and high temperature (HP-HT) experimental tests using autoclaves. Both inhibitors were exposed to conditions present in the surface installation of the Balmatt site, i.e. high temperatures (75 °C and 120 °C) and a high pressure of 45 bar to evaluate their stability. They were mixed with synthetic brine and pressurized and heated in separate autoclaves. Both inhibitors showed poor stability at the HP-HT conditions of the surface installation of the Balmatt site. Precipitates on the borders of the Teflon insert pot were observed (mainly iron oxides). In the synthetic brine - DETPMP mixture, additional precipitates besides the precipitation on the borders of the Teflon insert pots, were observed after being exposed to high temperatures and high pressure. The precipitates consisted of an amorphous matrix containing CaCl2, Fe-oxides and some minor Ca-rich BaCl2 minerals. The DETPMP and TD1100 inhibitors are not stable at the conditions present in the Balmatt geothermal installation. In order to investigate the efficiency of inhibitors to prevent the formation of galena scaling in the Balmatt geothermal installation, laboratory experiments with synthesized galena, three different background solutions (synthetic brine, NaCl solution and milliQ water) and three inhibitors were performed. According to the knowledge of the authors, no specific inhibitors to prevent galena formation are commercially available. Based on literature research, the DETPMP, TD1100 and ScaleTrol inhibitors were selected for this research. The DETPMP prevented the formation of galena in synthetic brine but other Pb-rich phases were formed. The TD1100 and ScaleTrol inhibitors did not prevent the formation of galena in synthetic brine. In the NaCl solution, all three inhibitors seemed to work well for galena inhibition. However, other Pb-rich phases were formed. No formation of galena was observed in the milliQ water (with or without inhibitors).

Disproportionation of SO_{2} at High Pressure and Temperature.

Materials once suffered at high-pressure and high-temperature (HPHT) conditions often exhibit exotic phenomena that defy conventional wisdom. The behaviors of sulfur dioxide (SO_{2}), one of the archetypal simple molecules, at HPHT conditions have attracted a great deal of attention due to its relevance to the S cycle between deep Earth and the atmosphere. Here we report the discovery of an unexpected disproportionation of SO_{2} via bond breaking into elemental S and sulfur trioxide (SO_{3}) at HPHT conditions through a jointly experimental and theoretical study. Measured x-ray diffraction and Raman spectroscopy data allow us to solve unambiguously the crystal structure (space group R3[over ¯]c) of the resultant SO_{3} phase that shows an extended framework structure formed by vertex-sharing octahedra SO_{6}. Our findings lead to a significant extension of the phase diagram of SO_{2} and suggest that SO_{2}, despite its abundance in Earth's atmosphere and ubiquity in other giant planets, is not a stable compound at HPHT conditions relevant to planetary interiors, providing important implications for elucidating the S chemistry in deep Earth and other giant planets.

ENHANCING PERFORMANCE OF MECHANICALLY OPERATED PACKER

During hydraulic fracturing operations of low-permeability reservoirs, packers are the key component to ensure the success of multistage fracturing. Packers enable sections of the wellbore to be sealed of and separately fractured by hydraulic pressure, one at a time, while the remainder of the wellbore is not afected. However, reliable sealing properties of the packer rubber are required to meet the high-pressure and high-temperature (HPHT) conditions of reservoirs (such as 70 MPa and 170 °C). In this study, the structures of the packer rubber with two diferent materials are optimized numerically by ABAQUS and validated by experiments. The optimization process starts from the packer rubber with a conventional structure, and then, the weakest spots are identifed by ABAQUS and improved by slightly varying its structure. This process is iterative, and the fnal optimized structure of a single rubber barrel with expanding back-up rings is achieved. For the structure of three rubber barrels with metallic protective covers, both HNBR and AFLAS fail under HPHT conditions. For the fnal optimized structure, the packer rubber made of AFLAS can work better under HPHT than that made of HNBR which ruptures after setting. The results show that the optimized structure of a single rubber barrel with expanding back-up rings and the material AFLAS are a good combination for the packer rubber playing an excellent sealing performance in multistage fracturing in horizontal wells. Keywords: packer rubber, sealing property, structure optimization, hydrogenated nitrile–butadiene rubber (HNBR), AFLAS rubber.

Evaluation of Surfactant Mixture for Supercritical Carbon Dioxide Foamed Acid in Carbonate Matrix Acidizing

The effectiveness of matrix acidizing using CO2 foamed acid is dependent on the duration of foam stability. This paper presents a supercritical CO2 foamed acid with a surfactant mixture to improve the foam stability in carbonate matrix acidizing. The experimental apparatus was developed to conduct foam-stability and wormhole-propagation tests under high-pressure and high-temperature (HPHT) conditions. The foam decay times of five types of surfactants were measured under atmospheric conditions. Trimax (blend of cocamidopropyl betaine, disodium cocoamphodiacetate, and amine oxide) and Aromox C/12W (coco bis-(2-hydroxyethyl) amine oxide) had a high foam decay time. The surfactant mixture was prepared using these two surfactants. The foam stability tests of the surfactant mixture were performed according to the HCl concentration, surfactant mixing ratio, and injection rate of HCl under HPHT conditions. As a result, the foam stability could be improved by adding an HCl concentration of 20% to the surfactant mixture. Wormhole-propagation tests were performed using Indiana and Indonesian limestones. Because of the supercritical CO2 foamed acid injection, dominant wormholes were formed in all the core samples; thus, the absolute permeabilities significantly increased. The results of the scanning electron microscopy/energy-dispersive X-ray spectroscopy and thin-section analyses revealed that the number of large pores with pore sizes of ≥0.5 mm increased by the injection of CO2 foamed acid. Therefore, the supercritical CO2 foamed acid with the surfactant mixture exhibited a high efficiency of matrix acidizing in carbonate reservoirs.

Influence of CO2 at HPHT Conditions on the Properties and Failures of an Amine-Cured Epoxy Novolac Coating

Using a three-phase batch reactor with coated steel panels, this investigation studies the influence of carbon dioxide (CO2), present in the gas phase at conditions of high pressure and high temperature (HPHT), on the degradation of an amine-cured epoxy novolac (EN) coating. The combined effect of the gas, hydrocarbon, and seawater phase compromises the coating and leads to underfilm corrosion. Consequently, an understanding of the role of each of the phases is essential for the effective design of superior epoxy-based coatings for HPHT applications in the petroleum and other industries. Upon exposure to the three phases individually, at a low pressure of N2, the EN network remained unaffected and impervious. However, in the hydrocarbon-exposed zone, a combination of para-xylene, representing the hydrocarbon phase, and CO2 at HPHT initiated glass-transition temperature depression with subsequent softening of the EN network. This allowed the dissolved CO2 gas to diffuse into the EN network, thereby generating pinholes at the coating surface. The seawater-exposed zone, in the presence of CO2 at HPHT, suffered from increased seawater ion diffusion, leading to blister formation. Moreover, the most detrimental subzone for the EN network was when CO2, para-xylene, and seawater were synergistically interacting at its hydrocarbon–seawater interface. This combination resulted in an increased chain motion of the EN network, subsequently allowing CO2 and seawater ions to diffuse into the EN network to the steel substrate, imposing underfilm corrosion. In the absence of CO2, blisters were formed at the interface subzone, but no corrosion was detected. The results are of high relevance to the petroleum industry but also for the protection of transport pipelines and process equipment in the next-generation carbon capture and storage technologies.

WITHDRAWN: Evaluation of Surfactant Mixture for Supercritical Carbon Dioxide Foamed Acid in Carbonate Matrix Acidizing

Abstract The effectiveness of matrix acidizing using CO2 foamed acid is dependent on the duration of foam stability. This paper presents a supercritical CO2 foamed acid with a surfactant mixture to improve the foam stability in carbonate matrix acidizing. The experimental apparatus was developed to conduct foam stability and wormhole propagation tests under high-pressure and high-temperature (HPHT) conditions. The foam decay times of five types of surfactants were measured under atmospheric conditions. Trimax (blend of cocamidopropyl betaine, disodium cocoamphodiacetate, and amine oxide) and Aromox C/12 W (coco bis-(2-hydroxyethyl) amine oxide) have a high foam decay time. The surfactant mixture was prepared using these two surfactants. The foam stability tests of the surfactant mixture were performed according to the HCl concentration, surfactant mixing ratio, and injection rate of HCl under HPHT conditions. As a result, the foam stability could be improved by adding an HCl concentration of 20% to the surfactant mixture. Wormhole propagation tests were performed using Indiana and Indonesian limestones. Because of the supercritical CO2 foamed acid injection, dominant wormholes were formed in all the core samples; thus, the absolute permeabilities significantly increased. The results of the scanning electron microscopy/energy-dispersive x-ray spectroscopy and thin-section analyses revealed that the number of large pores with pore sizes of ≥0.5 mm increased by the injection of CO2 foamed acid. Therefore, the supercritical CO2 foamed acid with the surfactant mixture exhibited a high efficiency of matrix acidizing in carbonate reservoirs.

Rapid preparation and characterization of pyrite materials under HPHT: A new method

This paper reports the synthesis of bulk pyrite (FeS2) polycrystals at high pressure and high temperature (HPHT) for the first time. The HPHT method markedly improves the speed of synthesis, reducing the time for synthesizing bulk pyrite from several hundred hours to several hours. A unique honeycomb-type structure was introduced into the system by the primary reaction to refine the size of the reactants. On this basis, the sulfur-deficient contamination phase Fe7S8 was effectively eliminated by secondary synthesis. Using Raman spectroscopy and X-ray diffraction (XRD), the crystalline phase of the product was confirmed to be the cubic pyrite phase. The crystal structure and initial crystal parameters of pyrite crystals synthesized under HPHT conditions were obtained for the first time by Rietveld refinement with GASA software. In combination with a scanning electron microscope (SEM) assay, the reaction process was traced, and the significance of secondary synthesis for HPHT was analyzed. Seebeck data showed that as the temperature increased, the sample changed from p-type to an n-type semiconductor and the conductivity increased monotonically, revealing the typical semiconductor characteristics of pyrite. UV reflectance spectra and VSM tests revealed the bandgap width and magnetic properties of pyrite.

A Parametric Study for Radial Cracking in Cement Under Different Loading Events Based on the Stress Intensity Factor

AbstractCement is one of the primary barriers in a wellbore and critical to well integrity. Radial cracking is a pervasive failure mode in cement due to the temperature and pressure variation during drilling, completion, or production. This work presents a comprehensive analysis of radial cracking in cement under various loading events. The proposed model estimates the stress intensity factor and fracture surface displacement as indicators for crack propagation and opening, respectively, through a distributed dislocation technique. Three types of radial cracks, divided by their tips terminating at the casing–cement interface, inside cement, or at the cement–formation interface, are considered. Based on this model, we conduct a parametric study for radial cracking under typical loading events such as steam injection, CO2 injection, and high-pressure and high-temperature (HPHT) drilling. Results indicate that the crack near the casing–cement interface has an increased risk for steam injection and HPHT drilling, while all three types of radial cracks are destructive during CO2 injection. The thermal expansion coefficient of cement is a significant parameter for steam and CO2 injection wells. The fluid pressure and the cement’s thickness are crucial to radial cracking under HPHT conditions. Stiffer cement could promote crack opening for steam injection but prohibit the crack deformation for CO2 injection or HPHT wells. Thicker cement would accelerate radial cracking under the three loading events. These findings are helpful in designing cement to maintain long-term integrity.