High Pressure And High Temperature Research Articles

Single crystal diamond particles formed by the reaction of carbon black and solid alcohol under high-pressure and high-temperature

The paper presents results of high-pressure and high-temperature (HPHT) experiments on the formation of diamond particles from precursors a mixture consists of carbon black powder and pentaerythritol of a solid alcohol. X-ray diffraction, FE-SEM and TEM methods as well as Raman spectroscopy have been used for characterization of the precursors and formed crystals.The main idea is to avoid any catalyst-based material at HPHT diamond synthesis from carbon materials.The successful formation of cubic structure single crystal diamond particles around 10 μm size during an extremely shorter time (5 s) at 7.5 GPa and 1500 ℃ is demonstrated.

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).

Reusing waste glass powder to improve the strength stability of cement at HTHP

Waste glass powder (WGP), as a kind of silicon-rich material, is used to replace 40 wt% oil well cement to inhibit the strength retrogression of hardened cement pastes (HCPs) at high temperature and high pressure (HTHP). The mechanical properties and microstructure of HCPs containing waste glass powder (WGP) of different particle sizes were studied. The results showed that HCPs modified by WGP exhibited greater compressive strength than those modified by silica flour (SF) at 80 °C × 0.1 MPa, due to the high activity of amorphous SiO2 in WGP. Compared with neat pastes, the incorporation of 325-mesh WGP or 1000-mesh WGP could effectively improve the compressive strength of HCPs at 260 °C × 21 MPa. Microscopic results indicated that the crystalline phases were tobermorite and xonotlite, providing great mechanical properties at HTHP, and xonotlite existed steadily after long-term curing. Mercury intrusion porosimetry results showed that, compared with neat pastes, incorporation of WGP improved the pore structure by stabilizing the total porosity of the cement. Magnesium participated in the transformation of xonotlite phase and change its microstructure. This paper provides a new way to recycle WGP and reduce the carbon dioxide generated in the production of cement.

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.

Effect of diamond additive on the properties of cBN composites with Al–Si as binder by HTHP sintering

In this paper, high thermal conductivity PcBN composites with Al–Si as binder and diamond as additive were prepared by high temperature and high pressure (HTHP) sintering at 5 GPa and 1500 °C. The effects of diamond content on the phase composition, microstructure, density, thermal conductivity, and volume resistivity of PcBN composites were characterized and studied. With the increase of diamond content, the thermal conductivity of PcBN samples increases first and then decreases. When the diamond content is 4 wt%, the thermal conductivity of PcBN composites is the highest, reaching 146.3 W m−1K−1, which is 20.2% higher than the thermal conductivity without diamond. At the same time, the reduction of the residual silicon liquid phase in the sintered body also increases the volume resistivity of the composites. With the increase of diamond content, the volume resistivity of PcBN composites also increases. The volume resistivity of PcBN composite with diamond content of 16 wt% reaches 1.25 * 1010 Ω·cm.

Simulation on influences of Al2O3 nanofluids as coolant for nuclear power plant based on modified empirical formula of nanofluids thermal properties at high temperature and high pressure

ABSTRACT The thermal properties of nanofluids are variable with working temperature and pressure and ignored by the existing empirical formula. In the present work, based on the application of nanofluids in pressurized water reactor (PWR) nuclear power plants, different concentrations of Al2O3/H2O nanofluids are prepared for measuring its thermal properties and then modifying empirical formulas at high temperature and high pressure (HTHP). In addition, the primary heat transfer process of PWR nuclear power plants is simulated by numerical method. The results show that, when volume fraction φ within 2.0%, the heat transfer performance of Al2O3 nanofluid increases with the increase of concentrations; however, it is on the contrary when the volume fraction of nanoparticles is larger than 2%. Comparing with water as the coolant, Al2O3 nanofluids with 2% volume fraction give the largest heat transfer enhancement of 103%. Therefore, Al2O3 nanofluids as the coolant can achieve the goals of heat transfer enhancement and safety limit improvement.

A Review of High-Temperature and High-Pressure Experimental Apparatus Capable of Generating Differential Stress

It has been demonstrated that the matters in the earth’s interior are subjected to isotropic hydrostatic pressure and are also extensively superimposed by the differential stress. The differential stress contributes significantly to the free energy of matters and it is the determining factor controlling the composition, structure, configuration, properties, and interaction processes of the matter system. Hence, the differential stress is one of the most fundamental thermodynamic variables governing the earth’s interior system along with the temperature and the hydrostatic pressure. Nevertheless, due to the limitations of high-temperature and high-pressure (HT-HP) setup and in situ measurement techniques as well as limited understanding of the differential stress, previous HT-HP experiments of the earth’s interior didn’t cover the role of the differential stress except for some special stress-strain mechanics experiments and piezolysis and kinetic metamorphism experiments. This makes many of the knowledge about the earth’s interior obtained from HT-HP experiments generally questionable. Currently, HT-HP experimental apparatus that can be used to simulate the temperature, hydrostatic pressure, and differential stress in the earth’s interior includes the Griggs press, the Paterson rheometer, the D-DIA press, the RDA press, and the torsional diamond anvil cell. The maximum hydrostatic pressure that can be simulated in the Griggs press at high temperatures is only about 2 GPa and there is large uncertainty in the calibration of the differential stress. The Paterson rheometer provides too low confining pressure. The D-DIA press and RDA press can simulate a wide range of temperature and pressure but the D-DIA press can achieve very small strain variables and the RDA press has very heterogeneous sample stresses. The torsional diamond anvil cell can only accept a small sample size and it is difficult to calibrate the differential stress. Also, these existing HT-HP experimental apparatus with the differential stress are not easily interfaced with in situ measurement systems for investigating the physical properties such as electrical, ultrasonic, and thermophysical properties. Hence, scholars need to invest more efforts in the research and development of HT-HP apparatus with the differential stress in the future to properly understand the composition, structure, configuration, properties, and interactions of the matter in the earth’s interior.

Cation effect on bis(trifluoromethylsulfonyl)imide-based ionic liquids with triethylsulfonium, 1,2-dimethyl-3-propylimidazolium, 1-methyl-1-propylpyrrolidinium, and 1-butyl-2,3-dimethylimidazolium density at high pressure

In this work, cation effect on density for four commercial ionic liquids (ILs) based on bis(trifluoromethylsulfonyl) imide ([(CF3SO2)2N]) anion were determined at high pressure and high temperature (HPHT) at P = (0.20 to 100.00) MPa and T = (298.15 to 398.15) K, using the vibrating tube method. Triethylsulfonium ([S222]), 1,2-dimethyl-3-propylimidazolium ([C3C1C1Im]), 1-methyl-1-propylpyrrolidinium ([C3C1pyr]), and 1-butyl-2,3-dimethylimidazolium ([C4C1C1Im]) cations were combined with bis(trifluoromethylsulfonyl) imide ([(CF3SO2)2N]) anion to form four different ionic liquids. Density increases in the following order: [C4C1C1Im][(CF3SO2)2N] < [C3C1pyr][(CF3SO2)2N] < [C3C1C1Im][(CF3SO2)2N] < [S222][(CF3SO2)2N], in accordance to the packing effect. Experimental density data were correlated by using Tammann-Tait-type equation, with an average absolute relative deviation (%AARD) less than 0.0090 % for [S222][(CF3SO2)2N], [C3C1C1Im][(CF3SO2)2N], and [C4C1C1Im][(CF3SO2)2N], and less than 0.0150 % for [C3C1pyr][(CF3SO2)2N]. Furthermore, seven group contribution estimation methods were successfully used to density prediction for these ionic liquids. Finally, isothermal compressibility (κT), isobaric expansivity (αp), thermal pressure coefficient (γv), and internal pressure (Pi) were determined from these experimental data, showing their relationship with anion and cations structural packing effect.

Surface Modification towards Integral Bulk Catalysts of Transition Metal Borides for Hydrogen Evolution Reaction

Transition metal borides (TMBs) are promising catalysts for hydrogen evolution reaction (HER). While the commercially available TMBs indicate poor HER performance due to powder electrode and low activity sites density, optimizing commercial TMBs for better HER performance is urgent. To break through the challenge, a new strategy is proposed to compose integral bulk electrodes with needle surfaces in TMBs. The integral bulk electrodes in TiB2, ZrB2, and HfB2 are formed under high pressure and high temperature (HPHT), and the nanoneedle morphology is constructed by chemical etching. In the three materials, the smallest overpotential is 346 mV at 10 mA cm−2 in the HCl etched bulk TiB2 electrode, which is about 61.9% higher than commercial TiB2 powder. Better performance arises from better conductivity of the integral bulk electrode, and the nano morphology exposes the edge sides of the structure which have high activity site density. This work is significant for developing new kinds of bulk TMBs catalysts.

Low Equivalent Circulating Density Organoclay-Free Invert Emulsion Drilling Fluids

AbstractHigh pressure and high temperature (HPHT) wells especially those with narrow pore/fracture pressure gradient margins present challenges in drilling. Maintaining optimum and low rheology for such wells becomes a challenge where a slight change in the bottom-hole pressure conditions can lead to nonproductive time. However, maintaining low viscosity profile for a drilling fluid can pose a dual challenge in terms of maintaining effective hole-cleaning and barite-sag resistance. This paper describes the formulation of 95pcf medium-density organoclay-free invert emulsion drilling fluids (OCIEF) with a low viscosity profile. The fluids gave lower plastic viscosity (PV), which ensured that the fluid presents low equivalent circulating density (ECD) contribution while drilling/circulating. These fluids were formulated with acid-soluble manganese tetroxide as weighting agent and a specially designed bridging-agent package. The fluids were hot rolled at 300 °F and their filtration and rheological properties were measured. The paper describes the static-aging, contamination, and high pressure/high temperature rheology measurements of the fluids at 300 °F. Particle plugging experiments were performed on the fluids to determine the invasion characteristics and the nondamaging nature of the fluids. These organoclay-free invert emulsion fluids (OCIEFs) were then field-trialed in different wells with good results. Field deployment of the 95pcf organoclay-free invert emulsion fluid helped to maintain the required hole stability in the high temperature and high pressure (HTHP) well. The well was displaced to 95pcf production screen test (PST) fluid and completed with a 4 ½ in. sand screen. The paper demonstrates the superior performance of the developed fluid in achieving the desired lab and field performance.

A Quantitative Evaluation Method of Anti-Sloughing Drilling Fluid Inhibition for Deep Mudstone

Wellbore instability resulting from deep mudstone hydration severely restricts the development of oil and gas resources from deep reservoir in western China. Accurate evaluation of drilling fluid inhibition properties plays an important role in selecting drilling fluid that can control deep mudstone hydration and then sustain wellbore stability. The previous evaluations are conducted by qualitative analysis and cannot consider the influence of complex hydration conditions of deep mudstone (high temperature, high pressure and flushing action). The study proposes a quantitative method to evaluate drilling fluid’s inhibition property for deep mudstone under natural drilling conditions. In this method, the cohesive strength of mudstone after hydration is adopted as the inhibition index of the tested drilling fluid. An experimental platform containing a newly designed HPHT (High pressure and high temperature) hydration experiment apparatus and mechanics characterization of mudstone after hydration based on scratch test is proposed to obtain the current inhibition index of tested drilling fluid under deep well drilling environments. Based on the mechanical–chemical wellbore stability model considering strength weakening characteristics of deep mudstone after hydration, a cross-correlation between drilling fluid density (collapse pressure) and required inhibition index (cohesive strength) for deep mudstone is provided as the quantitative evaluation criterion. Once the density of tested mud is known, one can confirm whether the inhibition property of tested mud is sufficient. In this study, the JDK mudstone of a K block in western China is selected as the application object of the proposed evaluation method. Firstly, the evaluation chart, which can demonstrate the required inhibition indexes of the tested fluids quantitatively with various densities for JDK mudstone, is constructed. Furthermore, the experimental evaluations of inhibition indexes of drilling fluids taken from two wells in K block are conducted under ambient and deep-well drilling conditions, respectively. In order to show the validity and advantage of the proposed method, a comparison between the laboratory evaluation results and field data is made. Results show that the laboratory evaluation results under deep-well drilling conditions are consistent with the field data. However, the evaluation under ambient conditions overestimates the inhibition property of the tested fluid and brings a risk of wellbore instability. The developed quantitative method can be a new way to evaluate and optimize the inhibition property of drilling fluid for deep mudstone.

S0.05Co4Sb11.6Te0.4 skutterudite introduced into graphene at high pressure and high temperature and its thermoelectric performance enhancement

A series of graphene-S0.05Co4Sb11.6Te0.4 (Cx-S0.05Co4Sb11.6Te0.4) composite polycrystalline skutterudite materials with graphene stoichiometric ratio of x = 0, 0.05, 0.10, 0.20 have been successfully prepared by high pressure and high temperature (HPHT) technology. Graphene is a two-dimensional material with large carrier mobility and large specific surface area. Through microscopic observation, it is found that graphene is attached to the grains in the sample. At the same time, with the increase of graphene content, grain growth is inhibited. Graphene addition reduces the thermal conductivity of skutterudite by increasing grain boundaries and achieves the purpose of optimizing its thermoelectric properties. At the same time, there are numerous lattice defects and distortions introduced in skutterudite synthesized by HPHT technology. Finally, the samples were synthesized under the conditions of 1.5 GPa and 900 K. The lattice thermal conductivity of the graphene composite sample Cx-S0.05Co4Sb11.6Te0.4 with x = 0.10 reaches a minimum of 0.99 at 773 K, and the zT value of this sample is 1.25 at 773 K, which is greater than pure S0.05Co4Sb11.6Te0.4, its zT value is 1.00 at 773 K. Compared with the method of synthesizing skutterudite under normal pressure, the HPHT technology can dramatically reduce the reaction time from several days to less than 30 min, while forming a high-pressure airtight reaction environment, which can effectively prevent the volatilization and oxidation of samples during the reaction process, thus providing a convenient method for synthesizing thermoelectric materials quickly and efficiently.

Molecular Simulation of Adsorption in Deep Marine Shale Gas Reservoirs

Deep marine shale gas reservoirs are extremely rich in the Sichuan basin in China. However, due to the in situ conditions with high temperature and high pressure (HTHP), in particular reservoir pressure being usually much higher than the test pressure, it is difficult to accurately clarify the adsorption behavior, as seepage theory plays an important role in shale gas reserves evaluation. Therefore, three kinds of sorbent, including illite, quartz and kerogen, and two simulation methods, containing the grand canonical ensemble Monte Carlo method and molecular dynamics method, are synthetically used to determine the methane adsorption behavior under HTHP. The results show that both absolute adsorption and excess adsorption decrease with the increase of temperature. When the pressure increases, the absolute adsorption increases quickly and then slowly, and the excess adsorption first increases and then decreases. The superposition of wall potential energy is strongest in a circular hole, second in a square hole, and weakest in a narrow slit. The effect of pore size increases with the decrease of the pore diameter. Under HTHP, multi-layer adsorption can occur in shale, but the timing and number of layers are related to the sorbent type.

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.

Reaction mechanism of metal and pyrite under high-pressure and high-temperature conditions and improvement of the properties

Pyrite tailings are the main cause of acid mine wastewater. We propose an idea to more effectively use pyrite, and it is modified by exploiting the reducibility of metal represented by Al under high-pressure and high-temperature (HPHT) conditions. Upon increasing the Al addition, the conductivity of pyrite is effectively improved, which is nearly 734 times higher than that of unmodified pyrite at room temperature. First-principles calculations are used to determine the influence of a high pressure on the pyrite lattice. The high pressure increases the thermal stability of pyrite, reduces pyrite to high-conductivity Fe7S8 (pyrrhotite) by Al. Through hardness and density tests the influence of Al addition on the hardness and toughness of samples is explored. Finally we discuss the possibility of using other metal-reducing agents to improve the properties of pyrite.

Evaluation of viscoelastic surfactant‐based diverting agent during the chemical treatment of sandstone reservoirs

AbstractThe challenges of diversion during the stimulations of carbonate formations have been widely studied for decades. It has been shown that viscoelastic surfactants (VES) are among the effective diverting solutions which can be used during the stimulation of carbonate formations. These chemicals benefit from the reaction products between the acid and the calcite to increase the viscosity of the acid, therefore reducing, temporarily, the permeability of the first invaded rock layer, which holds the highest permeability. This temporary blockage steers the remaining acid to the layers with lower permeability that need treatment. This is usually called self‐diverting acidizing treatment. However, the same approach may not necessarily be applied for sandstone formations that are not calcite rich. In such cases, combining acid stages with batches of diverting agents is still feasible. For this approach, VES is also a suitable, non‐damaging solution that is often overlooked. In this study, the application of VES as a diverting agent was investigated during the chemical treatment operations in sandstone formations. Several dual core‐flooding experiments were performed at high pressure and high temperature (HPHT) conditions using sandstone core samples with high permeability contrast.

Ilmenite Inclusion: A Solution towards Solid Sagging for Hematite-Based Invert Emulsion Mud

The sagging tendency of hematite in drilling mud is a common challenge occurring at high-pressure and high-temperature (HP/HT) applications. This work studies the performance of hematite-based invert emulsion mud for HP/HT conditions and provides a solution to prevent the hematite settlement using a combination of ilmenite with hematite. Practical mud formulation was utilized over a range of ilmenite/hematite ratios (0/100, 20/80, 40/60, and 50/50%) to study sagging behaviour. From the sag tests, the optimum combination proportion was determined. Thereafter, the density, emulsion stability, rheological and viscoelastic properties, and filtration conduct for the formulated mud were evaluated. The experiments were conditioned as per the standards of the American Petroleum Institute. The obtained results of sagging experiments indicated that including 50% of ilmenite mitigated the hematite settling and reduced the sag tendency towards the safe range. A slight drop (4%) in mud weight was noticed upon adding the ilmenite, whereas the emulsion stability was enhanced from 551 to 574 volts with the 50% ilmenite content. The rheology and viscoelasticity measurements showed that 50/50% combination improved the yield point (YP) by 50% with a trivial 1 cP increment on plastic viscosity (PV), hence enhancing the YP/PV ratio by 46%. Also, the gelling strength was enhanced resulting in flat rheology and better gel structure. The filtration behaviour of 50% ilmenite mud was improved compared to blank hematite as it resulted in 21, 15, and 17% reduction on the filtrated volume, filter cake weight, and thickness, respectively. This study provides a solution for hematite sagging issue at HP/HT using combined weighting agents, which contributes to enhancing the mud stability and avoiding several well control issues and related operational and technical challenges that eventually will economize the drilling cost and time.

Effect of pressure on elemental diffusion in sulfur–iron reaction

The reaction between sulfur and iron under high pressure and high temperature (HPHT) was studied. Sulfur–iron reaction models under different pressure levels were constructed. The morphology and formation mechanism of the reactants were comprehensively analyzed by scanning electron microscopy, energy-dispersive spectroscopy–line scanning, metallographic microscopy, and Raman spectroscopy. The results indicated that the pressure of the reaction could significantly affect the diffusion behavior of sulfur and iron during the reaction. With an increase in pressure, the diffusion of iron in the system was inhibited, whereas that of sulfur was enhanced. The pressure distribution gradient at the reaction interface was simulated by finite element calculation. The effect of pressure gradient as the driving force of the reaction on the diffusion behavior of elements was evaluated by thermodynamics combined with experimental results. Based on the experimental results, finite element simulation, and formula derivation, a new standpoint was proposed: the diffusion of substances in the HPHT system was affected by the pressure gradient at the interface.

Effect of high temperature and high pressure on the biodegradability and biotoxicity of typical additives in drilling fluid

Under the high-temperature and high-pressure (HTHP) conditions in the ground, the environmental features of drilling fluid additives may change to some extent. But the relevant information of the influence of HTHP environment on drilling fluid additives is very limited. Four typical additives, namely, sulfonate asphalt (SEB), potassium polyacrylamide (KPAM), potassium humate (KHm) and xanthan gum (XG), were treated for 40 min under two typical bottom hole conditions of 7 MPa, 90 °C and 11 MPa, 120 °C. The biodegradability and biotoxicity of these additives before and after treatments were determined. The structures of the four additives were also analyzed by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA) and gas chromatography-mass spectrometry (GC-MS). The results revealed no remarkable difference in biotoxicity and biodegradability of each sample between the two conditions. SEB became nontoxic from microtoxic after being treated with HTHP, with the value of EC50 notably increased from 2463 to 33,398 mg L−1, which might be due to the relative increase of light components observed by GC-MS. Original XG was nontoxic (EC50 = 21,000 mg L−1) and easily biodegraded (BC ratio = 0.469), but HTHP treatments increased the toxicity (EC50 = 5701 mg L−1) and decreased the biodegradability (BC ratio = 0.02), which could be attributed to the reduce of the C–OH/C–O–C bonds observed by FT-IR and XPS spectra. Both KPAM and KHm were midtoxic and had low degradability, and only KPAM became highly toxic (EC50 < 100 mg L−1) after HTHP treatments, which might result from the slight increase in the relative peak area of the amide group. The results could provide preliminary insights into the mechanism of how the HTHP conditions impacted the pollution properties of the additives and pave a new and facile route for the screening of environmentally friendly additives, and consequently mitigate the pollution from the source in the oil and gas exploitation industry.

Determination of the Cement Sheath Interface and the Causes of Failure in the Completion Stage of Gas Wells

The bonding quality of the cement sheath interface decreases during well completion because of the change in the casing pressure. To explore the root cause of such phenomena, experiments on the mechanical properties and interface bonding strength of a cement sheath have been carried out taking the LS25-1 high-temperature and high-pressure (HTHP) gas field as an example. Moreover, a constitutive model of the cement sheath has been defined and verified both by means of a full-scale HTHP cement sheath sealing integrity evaluation experiment and three-dimensional finite element simulations. The results show that the low initial cementing surface strength is the root cause of cement sheath interface bonding failure. When the pressure in the casing exceeds a certain limit, the stress caused by the change in the internal pressure in the casing is transmitted to the cement sheath, resulting in the degradation of the interface stiffness of the cement sheath. However, with an increase in the casing wall thickness, the stress transmission capacity decreases. Therefore, it is concluded that improving the interfacial cementing strength, appropriately increasing the casing wall thickness and increasing the initial stress of the cement sheath are the keys to ensuring the sealing integrity of the cement sheath in high-temperature and high-pressure gas wells.