Hydrate Phase Research Articles

Hydration and microstructure formation of magnesium oxysulfate (MOS) cement regulated by sepiolite with high adsorption ability

Magnesium oxysulfate (MOS) cement is a potential low-carbon cementitious material with its characteristic depending on the reaction between light-burned magnesia (LBM) and MgSO4 solution. This work aimed to elucidate the effect of sepiolite with high adsorption ability on regulating the reaction within MOS cement. Replacement levels of LBM by sepiolite at 2 and 5 wt% were adopted. Hydration kinetics, microstructure, phase composition and compressive strength of MOS cement without and with sepiolite were studied. Results showed that adding sepiolite into MOS cement adjusted the ion distribution at the early hydration stage and promoted the reaction with an early onset of heat flow peaks. The presence of sepiolite refined the morphology of formed needle-like 5 Mg(OH)2·MgSO4·7H2O (517 phase) and strengthened the bond water within its structure. The high adsorption ability of sepiolite enabled the nucleation of 517 phase and amorphous phase onto its surface. Sepiolite also densified the poorly hydrated regions by tightly combining with the incompletely hydrated MgO grains. Consequently, compressive strength of MOS cement under air curing was improved after adding sepiolite.

Sorption experiments as efficient as possible: Mini-column experiments (MCE) using HPLC-ICP-MS coupling with a new data analysis approach to determine sorption parameters

To quantify retention and sorption parameters, diffusion-, batch- or column experiments are common practice. However, these are either not close to nature, extremely time-consuming or material intensive. A promising approach to eliminate these problems is the performance of mini-column experiments (MCE). Due to dynamic retention and realistic solid–liquid ratios, these are close to nature and resource-efficient. The aim of this work is to perform highly controllable MCE using a HPLC (high-performance liquid chromatography) system and HPLC-ICP-MS (inductively coupled plasma mass spectrometry) coupling. With this approach, ultra-fast sorption experiments are possible only using 100–150 mg adsorbent and 160 mL eluent. That means, sorption experiments are even more time- and cost-efficient and also more controllable than with conventional methods. The presented method is based on a newly developed MCE-HPLC-ICP-MS coupling, which was applied to investigate the sorption of Eu(III) on kaolinite and sand in 10 mM NaCl. With that it was possible to carry out dynamic sorption experiments in just 5–15 h and thus determine e.g. maximum loading capacity (qmax) in a very short amount of time. Furthermore, a quantification method for eluates of high ionic strength is presented. Here, the sorption of Cs(I) on calcium silicate hydrate (C-S-H) phases in 10 mM and 100 mM NaCl was investigated. For validation, the sorption distribution ratios (Rd) obtained were compared with those from batch experiments. These agreed very well with each other and with those from the literature. Overall, with MCE more sorption parameters can be determined much faster, more accurately and more efficient than with the conventional methods.

Phase equilibrium data for semiclathrate hydrates formed with n-propyl, tri-n-butylammonium bromide and tri-n-butyl, n-pentylammonium bromide under methane, carbon dioxide and nitrogen gas pressure

Semiclathrate hydrates are water-based materials formed from aqueous solutions of ionic substances. To enhance the gas capture performance of these materials, it is necessary to direct focus on the cation, which is a key part of construction of the hydrogen-bonding framework. In this paper, we focus on the partly-asymmetric cations, i.e., the n-propyl, tri-n-butylammonium bromide (N3444Br) and tri-n‑butyl, n-pentylammonium bromide (N4445Br), which are yet to be subjected to gas hydrate formation. The three phase equilibrium (gas–hydrate–liquid) conditions for the systems of (N3444Br or N4445Br) + H2O + (CH4, CO2 or N2) in the range of the pressure and mass fractions of the aqueous solutions between 1 and 11 MPa and 0.10–0.40, respectively, are reported. In all the systems, the semiclathrate hydrates were successfully formed under gas pressure. It was demonstrated that both the N3444Br and N4445Br salts promoted hydrate formation under these gases, while in the case with lean aqueous solutions N3444Br acted as an inhibitor of methane hydrate formation in pure water system. The present data are compared with the literature data, and the effect of the side chain length on the phase behavior of the semiclathrate hydrate phase is discussed.

Experimental study and thermodynamic modeling of CO2+CH4 gas mixture hydrate phase equilibria for gas separation efficiency

Gas separation is a critical application of gas hydrates, and accurately predicting separation performance is crucial. In this study, we used thermodynamic calculations to predict the equilibrium phase of gas hydrates for various mole fractions of CO2 + CH4 gas mixtures. We also determined the mole fraction of each gas component trapped within the hydrate clathrate. To predict the equilibrium points, we used the Soave–Redlich–Kwong（(SRK) equation of state for the gas phase, the nonrandom two-liquid (NRTL)model for the liquid phase, and the Chen–Guo model for the hydrate phase. We modified the hydrate fugacity formula and introduced a new function to improve the accuracy of the Chen–Guo model. By incorporating experimental equilibrium results from our study and another study, we developed a correlation based on gas mixture composition and temperature, resulting in highly accurate predictions. The use of this new correlation for hydrate fugacity calculation significantly improved precision, as evidenced by an average absolute deviation percent of calculated pressures (AADP) of 1.34% for pure CO2 and 1.25% for CH4. When considering the 27 data points of different CO2 + CH4 mixtures, the AADP% was 1.98%.To implement the model to predict equilibrium phases, we used the Chen–Guo framework to determine the mole fraction of each gas component in the hydrate mixture. Interestingly, we discovered a linear correlation between the CO2 mole fraction in the hydrate and equilibrium pressure, with a slope of approximately 0.001 and a y-intercept of less than one, for all gas compositions. Therefore, we can conclude that low thermodynamic conditions (temperature and pressure) result in a high CO2 mole fraction in the hydrate phase and great separation efficiency.

Analysis of the effect of citrate on radionuclide retention on portlandite

We analysed how citrate (CIT), a chelating agent potentially present in radioactive waste disposals, affects the mobility of four radionuclides (RN): 63Ni, 233U, 152Eu, 238Pu in portlandite, an important hydrated phase of cement, a commonly used material for waste isolation.Portlandite was synthetized in the laboratory and showed high purity and grain size of few μm. This solid, buffers the pH to 12.5 and shows high adsorption capability for the studied RNs: 152Eu and 238Pu exhibited the highest adsorption (Kd ∼1·105 mL g−1) and 233U the lowest (Kd ∼8·102 mL g−1). CIT adsorption was also experimentally evaluated by batch sorption experiments and electrophoretic (ζ-potential) measurements: a non-lineal sorption behaviour was observed, with Kd values decreasing (from ∼1·103 mL g−1) as CIT concentration increased up to 1·10−2 M, according to portlandite sorption sites saturation.In the presence of CIT, a marginal decrease for 233U adsorption in portlandite was observed, one order of magnitude reduction for 63Ni, while 238Pu and 152Eu adsorption decreased significantly. The calculated sorption reduction factors (SRF) for the four RN in the presence of CIT at a concentration of 5·10−3 M were: 2.4, 9.7, 37 and 50.9 for 233U, 63Ni, 238Pu, and 152Eu, respectively.According to the available thermodynamic databases, low complexation between CIT and RN is predicted at pH = 12.5, thus the RN adsorption decrease in the presence of CIT must be attributed to the organic adsorption on portlandite. However, current thermodynamic are still incomplete for this ligand and this pH range and this limits a precise interpretation of the experimental data.

Development of a mayenite composite pellet towards salinity remediation: Experimental demonstration of passive chloride removal from saline oilfield groundwater

This study investigates newly developed sand/gravel-sized mayenite composite pellets with cellulose-based binders as a chloride (Cl−) remover that is compatible with saline groundwater also impacted by hydrocarbons. The mayenite pellets remove Cl− from impacted oilfield groundwater with 60–90 % efficiency in the range of salinity values found at field sites (< 20,000 mg/L total dissolved solids, TDS) in the presence of hydrocarbons, without agitation. The pellet reactions are driven by hydration, anion exchange, adsorption, and mineral phase reconstruction with increasing intraparticle diffusion and pellet heterogeneity during Cl− removal. Cl− removal is significantly correlated with changes in the quantities of pellet components. Mayenite is a key mineral for Cl− removal, during which hydrocalumite is formed. However, high mayenite purity is not required due to the contributions of non-mayenite pellet components (CaO and Al2O3) to Cl− removal. Drastic morphological transformations of pellet minerals occurred from honeycomb-like to cubic or hexagonal structures. Sand/gravel-sized pellets had a comparable Langmuir qmax of 74.5 mg/g. Mayenite pellets are not affected by hydrocarbons in both aqueous and nonaqueous phases. The removal of hydrocarbons observed was likely associated with porous pellet structures. TDS and competitive anions in impacted groundwater regulate the mayenite pellet reactions for Cl− removal.

Improvement of strength and microstructure of low-carbon cementitious materials with high volume of calcined coal gangue

The accumulation of coal gangue poses significant environmental challenges due to its massive volume and low reactivity. This study investigates the influence of calcium hydroxide (Ca(OH)₂) and gypsum on the mechanical properties, hydration, and pore structure of low-carbon cementitious materials incorporating high volumes of calcined coal gangue (CCG) and limestone. The results showed that the addition of Ca(OH)₂ significantly increased compressive strength, with a 19 % improvement at 28 days in LCC-40-P mix, which contained 40 % cement and 2.73 % Ca(OH)₂ by weight. The incorporation of 10 % gypsum in the LCC-40-P mix and 20 % gypsum in the LCC-70 mix (containing 70 % cement without Ca(OH)₂) effectively refined the pore structure, reduced overall porosity, and enhanced the material's density and mechanical properties, resulting in compressive strengths of 38.4 MPa (72 % of the strength of Portland cement) and 50.2 MPa (94 % of the strength of Portland cement) at 28 days, respectively. Microstructure and hydration heat tests showed that the addition of Ca(OH)₂ accelerates the hydration reaction and significantly enhanced compressive strength by ensuring sufficient Ca(OH)₂ for pozzolanic reactions, leading to the formation of additional calcium silicate hydrate, calcium aluminate silicate hydrate and carboaluminate phases. Gypsum refined the pore structure by shifting the pore size distribution towards smaller sizes, reducing overall porosity, and increasing the proportion of gel and small capillary pores. These findings highlight the potential of using CCG with optimized additives to develop sustainable, low-carbon construction materials with enhanced performance characteristics.

Predicting three phase (hydrate–liquid–vapour) equilibria of mixed hydrates in guest gas swapping: AI‐based approach versus physical modelling

Predicting three phase (hydrate–liquid–vapour) equilibria of mixed hydrates in guest gas swapping: <scp>AI</scp>‐based approach versus physical modelling

Density Functional Theory Study of the Crystal Structure and Infrared Spectrum of a Synthetized Ettringite Mineral

One of the most important hydration phases of Portland cement is ettringite, a calcium sulfo-aluminate mineral (Ca6Al2(OH)12(SO4)3·26H2O) showing a great capacity of adsorbing radionuclides and other contaminant cationic and anionic species, or incorporating them into its crystal structure. In this work, the X-ray diffraction pattern and infrared spectra of a synthetized ettringite sample are recorded and simulated, employing theoretical methods based on Density Functional Theory. Despite the complexity of this phase, the calculated structure, X-ray diffraction pattern and infrared spectrum are in excellent agreement with their experimental counterparts. Since the calculated and experimental spectra are consistent, the main infrared bands are assigned using a normal coordinate analysis, some of them being completely reassigned with respect to other experimental works. The good agreement found provides strong support for the computational methods employed towards their use for studying the surface adsorption properties and the incorporation of contaminations in its structure. The density of reactive groups at the surfaces of ettringite is reported, and the surface adsorption of water molecules is studied. These surfaces appear to be highly hydrophilic, in agreement with the experimental finding that the ettringite structure may include more water molecules, at least up to 27, one more than in its standard formula.

Experimental Evaluation of Compressive Properties of Early-Age Mortar and Concrete Hollow-Block Masonry Prisms within Construction Stages.

Early-age masonry structures require temporary support until they achieve full strength. Nevertheless, there is a limited understanding of the properties of freshly laid masonry and the design of newly constructed, unsupported masonry walls. This situation has led to numerous instances of structural damage and injuries to workers, prompting conservative construction bracing techniques. This paper presents comprehensive experimental studies on early-age mortar cubes and masonry prisms to assess the effects of curing time on the compressive properties of masonry assemblies, which is necessary for the design of temporary bracing. The change in modulus of elasticity and compressive strength of masonry prisms and mortar with curing time has been experimentally assessed. The results indicate that the compressive strength of freshly cast mortar cubes is relatively insignificant until approximately 24 h after construction, when it was observed to increase logarithmically. Regarding the performance perspective, the compressive strength of early-age masonry prisms is inconsiderable, less than 15% of full strength during the first day after construction. By contrast, regarding the life safety perspective, the compressive properties of a mortar joint within a masonry assembly (which is of more practical interest) appear to have no effect on the failure strength of concrete masonry prisms over the range of ages tested. The failure modes of the early-age mortar cubes and early-age masonry prism samples depend on the curing time, and different failure modes occurred before and after the start of the primary hydration phase, which is 20.8 h after construction. It is anticipated that the proposed research will provide valuable material properties leading to efficient design of control devices (e.g., temporary bracing) and improved guidelines for concrete-block masonry construction.

Dissociation line and driving force for nucleation of the nitrogen hydrate from computer simulation. II. Effect of multiple occupancy.

In this work, we determine the dissociation line of the nitrogen (N2) hydrate by computer simulation using the TIP4P/Ice model for water and the TraPPE force field for N2. This work is the natural extension of Paper I, in which the dissociation temperature of the N2 hydrate has been obtained at 500, 1000, and 1500bar [Algaba et al., J. Chem. Phys. 159, 224707 (2023)] using the solubility method and assuming single occupancy. We extend our previous study and determine the dissociation temperature of the N2 hydrate at different pressures, from 500 to 4500bar, taking into account the single and double occupancy of the N2 molecules in the hydrate structure. We calculate the solubility of N2 in the aqueous solution as a function of temperature when it is in contact with a N2-rich liquid phase and when in contact with the hydrate phase with single and double occupancy via planar interfaces. Both curves intersect at a certain temperature that determines the dissociation temperature at a given pressure. We observe a negligible effect of occupancy on the dissociation temperature. Our findings are in very good agreement with the experimental data taken from the literature. We have also obtained the driving force for the nucleation of the hydrate as a function of temperature and occupancy at several pressures. As in the case of the dissociation line, the effect of occupancy on the driving force for nucleation is negligible. To the best of our knowledge, this is the first time that the effect of the occupancy on the driving force for nucleation of a hydrate that exhibits sII crystallographic structure is studied from computer simulation.

Pore-scale behaviors of CO2 hydrate formation and dissociation in the presence of swelling clay: Implication for geologic carbon sequestration

Hydrate-based CO2 sequestration (HBCS) under seafloor with huge storage capacity and long-term mechanical stability is attractive for large-scale carbon reduction. However, as representative geochemical constituents of marine sediments, swelling clay minerals still play ambiguous roles in hydrate phase transition and sedimentary structure stability. In this study, pore-scale behaviors of hydrate deposition and reservoir structure evolution in the presence of montmorillonite (MMT), a representative swelling clay, was investigated using low-field nuclear magnetic resonance (LNMR) technique. Total inter-particle interaction energy of 195.4 KbT ensured the dispersion of clay in 0.5 wt% MMT system, which facilitated homogeneous hydrate formation by providing nucleation sites and surface electric fields, improving hydrate conversion from 78.2 % to 89.6 %. Weak water activity caused by strong water absorption of swelling clay resulted in a 14.4 % reduction in CO2 storage capacity of high-concentration (10.0 wt%) MMT reservoir. Hydrate phase transition accompanied by the migration of MMT particles and liquid water synergistically contributed to sedimentary structure evolution. Migration of MMT-rich fluid with high viscosity could cause irreversible geologic damages by exacerbating sedimentary skeleton deformation. This work reveals the interaction between swelling clay and CO2 hydrate at microscopic scale, providing new perspectives for effective implementation of CO2 geologic sequestration in marine sediments.

The morphology of liquid CO2 hydrate films at different temperatures under saturation pressure

CO2 hydrate film formed on the surface of water droplets in liquid CO2 was studied via digital microscope system and in situ Raman spectrometer. Temperature significantly affects the initial morphology and lateral growth rate of hydrate film. In the temperature range of 273.15–279.15 K under corresponding saturation pressure of liquid CO2, the growth and development process is primarily separated into three stages, that is, rapid lateral growth, rapid thickening, and slow development. However, in the temperature range of 280.15–282.15 K, the growth and evolution of hydrated film is dominated by rapid lateral growth and slow development processes, while the rapid thickening disappears on our experimental scale, caused by the decrease in the driving force. Each of these two temperature ranges has unique characteristics and interesting discoveries during the hydrate film formation and development. For hydrate film formed at 283.15 K, the formation of hydrate is very difficult. It needs to nucleate inside the droplet with the assistance of the hydrate crystal seeds remaining in the water droplet after decomposition, so that the small hydrate crystals can grow in the water phase, and as the crystals get larger, they will eventually emerge on the droplet’s surface and produce a complete hydrate film. Combining the experimental phenomena during the growth and development of hydrate films at various temperatures, the further growth of the hydrate phase during the generation process mainly depends on the mass transfer process of water molecules through the hydrate film. This work provides valuable information on the mechanism of nucleation, growth and decomposition of liquid CO2 hydrate crystals, which is of great significance for applications in seafloor CO2 gas sequestration.

Calculated Aqueous Reduction Potentials of Neutral and Anionic Halogen Diatomic Molecules.

The free energy of hydration, aqueous, and gas phase electron affinity and aqueous reduction potentials of F2, Cl2, Br2, I2, ClF, BrF, IF, BrCl, ICl, IBr, and their corresponding anions were calculated using an electronic structure approach previously developed for these properties for X• and XO•, where X is a halogen which yielded excellent results. The gas phase electron affinities were calculated at the Feller-Peterson-Dixon level based on complete basis set extrapolation of CCSD(T) results with additional corrections. The agreement with the available experimental data is excellent, and the calculations provide a complete set of reliable electron affinities for these diatomic halogens. The hybrid solvation approach uses single point implicit solvation calculations on gas phase optimized clusters with explicit solvent molecules. The gas phase energy calculations were performed using MP2 and CCSD(T)-F12b for tetramer clusters (four explicit waters) and MP2 for octamer clusters (eight explicit waters). The final redox potentials were obtained at the MP2/aug-cc-pVTZ (aT) with a self-consistent reaction field (SMD) level using the octamer clusters. The aqueous reduction potentials of the neutral diatomic halogens are predicted within 0.06 V of the experiment for diatomic neutrals. The same agreement of 0.06 V is predicted for the redox potential resulting from dissociation electron attachment of the diatomic halogen anions. The current work extends reduction potentials for multiple redox couples for which no experimental data is available, for example, those containing iodine and the interhalogen anions. F2•- is predicted to dissociate for its lowest energy structure in both the tetramer and octamer clusters to form solvated F-, HF, and OH•.

Effects of magnetic field on CO2 hydrate phase equilibrium

Effects of magnetic field on CO2 hydrate phase equilibrium

Development of 3D-printed magnesium silicate hydrate cement mixes involving metakaolin as a substitute for silica source

ABSTRACT The printability of MgO-SiO2 cement pastes involving the use of microsilica (MS) and metakaolin (MK) as a SiO2 source was thoroughly investigated. Fresh properties, including rheology and early-age strength, mechanical properties and microstructures of pastes incorporating different contents of MK were presented and analyzed. Amongst samples studied, those containing 5% MK as a substitute for MS exhibited the highest static yield stress, and fastest re-flocculation and structuration rates, resulting in the best buildability. Although the inclusion of 10% MK resulted in enhanced paste strength at 7 and 28 days, increased MK content impeded paste printability due to diminished formation of hydrate phases. Use of 5% MK led to higher M-S-H generation compared to other samples at 28 days, contributing to subsequent strength development. Results demonstrated that optimisation of the MK content in MgO-SiO2 pastes can yield satisfactory mechanical strengths without compromising printability.

The influence of low calcium sulfate contents on early calcium aluminate cement–calcite hydration kinetics and pore solution chemistry

A binder mix consisting of CAC, calcite and H2O was investigated to clarify the influence of the addition of low amounts of calcium sulfate in the form of gypsum, hemihydrate or anhydrite on the hydration at 23 °C. Based on experimental data, a model for the hydration of CAC + calcite in the presence of sulfate ions could be developed. Using heat flow calorimetry at 23 °C, it was shown that hydration is accelerated depending on the solubility rates of the different sulfates. In addition, early hydration is characterized by a sequential reaction in which the calcium sulfate must be consumed completely from the pore solution by the precipitation of ettringite before the already known course of CAC + Cc hydration can occur. Monocarbonate and AH3 precipitate as the stable dominant hydrate phases during the main reaction, but conversion-sensitive hydrate phases such as CAH10 are not stable.

Effects of different admixtures on the working performance and mechanical properties of phosphogypsum slag-based composite cementitious materials

Phosphogypsum slag-based composite cementitious materials were prepared by using phosphogypsum and slag powder as the main raw materials, adding quicklime, lithium slag, steel slag and other admixtures, and adding NaOH, NaHCO3 and triethanolamine (TEA). The effects of different admixtures on the fluidity, setting time and compressive strength of the composite cementitious materials were studied. Finally, XRD, MIP, TG-DTG, and SEM microscopic tests were used to analyze the reasons for the performance changes caused by the admixture from the aspects of phase composition, pore distribution, and hydration product morphology. The results show that the addition of NaOH, NaHCO3 and TEA reduces the fluidity and strength of the material and improves the setting time. The paste with 1 % NaOH and 0.03 % TEA can balance the working performance and mechanical properties.

A new thermodynamic model for predicting the 3-D phase equilibrium surface of gas hydrates considering the effect of salt concentration

An accurate understanding of the thermodynamic stability of gas hydrates in salt-bearing systems is of great significance for predicting the extent of hydrate accumulation and determining the hydrate decomposition domain. Therefore, this study proposes a thermodynamic model for predicting the temperature–pressure-salt concentration three-dimensional phase-equilibrium surface. The model considered the interaction of the electrolyte in a mixed salt solution system and non-spherical shaped hydrate crystal cavity. The modified van der Waals-Platteeuw (vdW-P) model and Benedict-Webb-Rubin-Starling (BWRS) equation of state were used to describe the hydrate phase. The Pitzer-Debye-Hückel equation and nonelectrolyte non random two liquid non random factor (N-NRTL-NRF) activity coefficient model were used to describe the fluid phase. The prediction results of the model agreed with the experimental data, and the absolute average relative deviation in temperature (AARD-T) under pure water conditions was only 0.08, and the AARD-T under electrolyte conditions did not exceed 0.15, which proved the accuracy and reliability of the model. The calculation results showed that when the mole fraction of chloride salt was greater than 0.02 and the pressure was higher than 20 MPa, chemical factors caused the p-T curves to translate. When the pressure was low, the temperature gradient along the direction of the salt concentration changed drastically, and the p-T curves no longer had translation characteristics. In comparison, under the same mole fraction, AlCl3 had a stronger inhibitory effect on the CH4 hydrate than the other chloride salts. The lnp-X-1/T three-dimensional surface of the CH4 hydrate exhibited good Clausius-Clapeyron linear behavior locally, and the surface had certain nonlinear characteristics. The degree of nonlinearity of the lnp-X-1/T three-dimensional surfaces of different types of chloride salts was different. A better inhibitory effect of the chloride salt electrolyte on the CH4 hydrate was associated with stronger nonlinearity between 1/T and lnp.

Submarine slope stability during the exploitation of natural gas hydrate from horizontal wells

Horizontal wells have the advantages of high production, considerable access to reserves, and effective sand production control; thus, they are potential well types for hydrate exploitation. In the process of hydrate mining, the decomposition of hydrate will cause the deterioration of the mechanical properties of the reservoir, which may induce submarine landslides, especially in the case of multiple horizontal wells, and the risk of submarine landslides is further increased. Therefore, it is necessary to study the influence of the horizontal well pattern adopted for hydrate mining on the stability of submarine slopes. First, a triaxial mechanical experiment of gas hydrate-containing sediments was carried out, and the mechanical parameters of the hydrate-containing sediments were obtained. Second, a thermal-fluid-solid multifield coupling model considering the hydrate phase transition during the production process was established. Finally, on the basis of the finite element strength reduction method, a slope stability evaluation model for hydrate extraction from a horizontal well pattern was established, and the influence of hydrate extraction from horizontal wells on the stability of submarine slope was analyzed. The results show that the peak strength, elastic modulus and cohesion of gas hydrate-containing sediments increase with increasing hydrate saturation. In the process of hydrate exploitation via horizontal wells, with the reduction in well spacing and the increase in the number of production wells, the risk of slope instability increases. Wells positioned along the slope strike are more conducive to slope stability than those positioned perpendicular to the slope strike. The slope stability increases gradually as the slope dip decreases. When the number of wells is the same, the slope stability increases gradually with increasing well spacing and production pressure.