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Channel fracturing technology is designed to form fractures supported by non-uniform pillar proppants. Non-cured adhesive resin-coated proppant gradually becomes viscous after immersion and agglomerates during transportation. The pillars are stable after the fracture is closed. They not only maintain a certain compressive strength but also maintain long-term conductivity. Currently, there are few evaluations of coated proppant migration. Based on CFD-DEM method, a two-phase flow coupling model considering the adhesive contact force of coated proppant particles is established to study the cementation characteristics of coated proppant during transportation. The transportation mechanism of coated proppant are revealed by numerical calculation analysis. The results show that different from the conventional proppant, the migration process of the coated proppant is divided into four stages (1) the softening of the proppant contact; (2) the paving of the proppant agglomeration; (3) proppant pillars growth along fracture height; and (4) proppant pillars growth along fracture length. We have completed a preliminary geometric characteristics evaluation of sand bank formed by coated proppant by evaluating the pore volume ratio (the ratio of void volume between pillars to the sand bank volume) under various parameters. This evaluation offers some theoretical guidance for the optimization of channel fracturing proppant injection parameters. [ABSTRACT FROM AUTHOR]

Oil and gas resources are becoming increasingly difficult to extract owing to long-term exploitation. Therefore, hydraulic pressure technologies, such as fracturing proppants, are needed to stimulate production. In this study, the strength and corrosion resistance of quartz were increased by modifying quartz sand and preparing high-performance coated-sand-based oil-fracturing proppants. Although many resins play crucial roles in the process of preparing fracturing proppants, their performances differ considerably. Chemical structural compositions and microstructures were investigated through infrared spectroscopy and scanning electron microscopy. The modification mechanism of quartz sand and the bonding mechanism between quartz sand and different types of resin proppants were analyzed by systematically investigating the flexural strength, corrosion resistance of the proppants as a function of resin contents, and curing temperature. The results show that the performance of the coated proppants is superior to those of conventional quartz sand and ceramic proppants. The flexural strength of modified quartz sand improved by 5.3%. The best performance was obtained using an 8% polyimide resin film and a curing temperature of 180 °C, achieving a coated sand proppant with a breakage ratio of 2.89% under 55.2 MPa. [ABSTRACT FROM AUTHOR]

The migration law of proppants in slick water during fracturing is of great significance for field fracturing. A large‐scale visualized experimental device was utilized to test sand patterns for varying injection parameter combinations, and sensitivity parameters of proppant settlement are analyzed. Experimental results showed that when the viscosity of fluid is 5 mPa.s, proppants with 70–140 mesh and 8% sand ratio were used, the slick water for fracture initiation had a good sand‐carrying capacity, and there was no sand bank formed at the entrance of the fracture but the spreading of sands in fractures was insufficient. When slick water with a lower viscosity of 10 mPa.s, the proppant of 40–70 mesh and 10% sand ratio were used, massive proppants were filled within the fractures, and a high sand bank was formed in the deep of the fracture, while a poor‐filling effect appeared at the entrance of fracture. When the higher viscosity slick water of 20 mPa.s, proppants with 20–40 mesh and 20% sand ratio were used; with the growth of pump‐in rate, the distance between the sand front and fracture entrance increased, the height of the bank is lower, and the balance height stayed the same for various fracturing fluid and proppant combination. The injection parameters affected the sand bank patterns and made diverse bank shapes, which made it essential to modify the fracturing fluid and proppant combination in the field to improve the conductivity at the entrance of the fracture. [ABSTRACT FROM AUTHOR]

The gas production of deep coalbed methane wells in Linxing-Shenfu block decreases rapidly, the water output is high, the supporting effect is poor, the effective supporting fracture size is limited, and the migration mechanism of proppant in deep coal reservoir is not clear at present. To investigate the migration behavior of proppants in complex fractures during the volume reconstruction of deep coal and rock reservoirs, an optimization test on the conductivity of low-density proppants and simulations of proppant migration in complex fractures of deep coal reservoirs were conducted. The study systematically analyzed the impact of various fracture geometries, proppant types and fracturing fluid viscosities on proppant distribution. Furthermore, the study compared the outcomes of dynamic proppant transport experiments with simulation results. The results show that the numerical simulation is consistent with the results of the proppant dynamic sand-carrying experiment. Under the conditions of low viscosity and large pumping-rate, a high ratio of 40/70 mesh proppant can facilitate the movement of the proppant to the depths of fractures at all levels. The technical goal is to create comprehensive fracture support within intricate trapezoidal fractures in deep coal and rock reservoirs without inducing sand plugging. The sand ratio is controlled at 15%–20%, with a proppant combination ratio of 40/70:30/50:20/40 = 6:3:1. Proppant pumping operations can effectively address the issue of poor support in complex fractures in deep coal formations. The research results have been successfully applied to the development of deep coalbed methane in the Linxing-Shenfu block, Ordos Basin. [ABSTRACT FROM AUTHOR]

Porous proppants are an important type of lightweight proppants, which can be transported to far fractures in hydraulic fracturing. The ideal proppants should have higher strength besides lower density. Usually, as the pores increases, the crushing strength of porous proppants will decrease, resulting in the difficulty propping more fractures. In this study, the three-dimensional finite element model (3D-FEM) was used to study crushing strength of single proppant. The effects of pore distribution, pore size and porosity on proppant crushing strength were analyzed. Weibull theory was used to describe the dispersion of crushing strength. The failure processes of solid proppant and porous proppant were studied. The results show that the solid proppant has obvious brittle fracture, while porous proppant has structural plasticity. With the increase of pore size and decrease of porosity, the distribution of crushing strength is more dispersed. The crushing strength decreases significantly when porosity is less than 7% and then decreases slowly as porosity continues to increase. The crushing strength will increase with the increase of pore size. When the pore size is larger than 0.1 mm (d/D<1/6), the crushing strength has no obvious change. These results can guide the preparation and application of porous proppants. [ABSTRACT FROM AUTHOR]

The present article describes a method for determining the physico-mechanical properties of a synthesized batch of proppants. Industrial waste is one of the sources of anthropogenic impact on the environment on a global scale, being formed in the process of coal and oil extraction as a by-product.With the decrease in stocks of high-quality natural raw materials and the accumulation of man-made products, the problem of waste utilization becomes urgent. [ABSTRACT FROM AUTHOR]

When better fuel-air mixing in the combustion chamber or a reduction in base drag are required in vehicles, rockets, and aeroplanes, the base pressure control is activated. Controlling the base pressure and drag is necessary in both scenarios. In this work, semi-circular ribs with varying diameters (2, 4, and 6 mm) positioned at six distinct positions (0.5D, 1D, 1.5D, 2D, 3D, and 4D) inside a square duct with a side of 15 mm are proposed as an efficient way to apply the passive control technique. In-depth research is done on optimising rib size for various rib sites. According to this study, the base pressure rises as rib height increases. Furthermore, the optimal location for the semi-circular ribs with a diameter of 2 mm is at 0.5D. The 1D location appears to be optimal for the 4 mm size as well. For the 6 mm size, however, the 4D position fills this function. Graphic Abstract [ABSTRACT FROM AUTHOR]

CO2pre-injection during hydraulic fracturing is an important method for the development of medium to deep heavy oil reservoirs. It reduces the interfacial tension and viscosity of crude oil, enhances its flowability, maintains reservoir pressure, and increases reservoir drainage capacity. Taking the Badaowan Formation as an example, in this study a detailed three-dimensional geomechanical model based on static data from well logging interpretations is elaborated, which can take into account both vertical and horizontal geological variations and mechanical characteristics. A comprehensive analysis of the impact of key construction parameters on Pre-CO2based fracturing (such as cluster spacing and injection volume), is therefore conducted. Thereafter, using optimized construction parameters, a non-structured grid for dynamic development prediction is introduced, and the capacity variations of different production scenarios are assessed. On the basis of the simulation results, reasonable fracturing parameters are finally determined, including cluster spacing, fracturing fluid volume, proppant concentration, and well spacing. [ABSTRACT FROM AUTHOR]

This article studies the migration and settlement laws of backflow proppants after fracturing tight sandstone. This paper proposes a fitting method based on a multi-task learning network to address the issue of interference from multiple physical parameters during the transport and settlement processes of proppants. This method can effectively handle multi-dimensional interference factors and fit the mapping logic of multiple engineering parameters to transport patterns through the continuous correction of multi-layer networks. We first introduce the characteristics of tight sandstone reservoirs and their important value in mining, as well as the status of current research on the migration and settlement laws of proppants at home and abroad. Based on this, we then deeply analyze the sedimentation rate model of proppants in tight sandstone backflow and the equilibrium height of proppants under multiple factors of interference while considering the distribution characteristics of proppants. In order to more accurately simulate the transport and settlement laws of proppants, this paper introduces a multi-task learning network. This network can comprehensively consider multi-dimensional parameters, learn the inherent laws of data through training, and achieve accurate fitting of the transport and settlement laws of proppants. This study trained and tested the model using actual production data, and the results showed that the proposed model can fit the input–output relationship well, thus effectively supporting the study of proppant transport and settlement laws. [ABSTRACT FROM AUTHOR]

After hydraulic fracturing, unconventional reservoirs frequently encounter challenges related to limited effective proppant support distance and suboptimal proppant placement. Due to the strong heterogeneity of offshore reservoirs, which causes varying fracture roughnesses depending on different lithologies, a systematic study of the relationship between roughness and proppant transport could optimize operational parameters. This study incorporates the box dimension method for fractal dimension analysis to quantify roughness in auto-correlated Gaussian distributed surfaces created by true triaxial tests. Combined with the numerical analysis of (computational fluid dynamics) CFD-DEM (discrete element method) for bidirectional coupling, the laws of proppant deposition and transport processes within fractures with different roughnesses are obtained through comparative verification simulations. The results show that for rougher fractures of shale, the proppants are transported farther, but at JRC_52, (joint roughness coefficient), where there may be plugging in curved areas, there is a risk of near-well blockages. Compared to the smooth model, fluctuations in JRC_28 (tight sandstone) drastically increase turbulent kinetic energy within the fracture, altering particle transport dynamics. Moreover, smaller proppants (d/w ≤ 0.3) exhibit better transport capacity due to gravity, but the conductivity of the proppant is limited when the particles are too small. A d/w of 0.4 is recommended to guarantee transport capacity and proppant efficiency near the well. Additionally, proppants injected sequentially from small to large in shale fractures offer optimal propping effects, and can take advantage of the better transport capacity of smaller proppants in rough fractures. The large proppant (d/w = 0.8) is primarily deposited by gravity and forms a sloping sand bed, which subsequently ensures the aperture of the fractures. This research provides a fresh perspective on the influence of fracture roughness on proppant transport in offshore unconventional reservoirs and offers valuable considerations for the order of proppant injection. [ABSTRACT FROM AUTHOR]

The influence of cleat permeability and porosity on the cumulative gas produced is studied. The cleat parameters are weighed for producing reserve in the least time and the minimum breakdown pressure requirement to create fractures. The reservoir is stimulated. The breakdown pressure required is more to create fractures at closer spacing than needed to increase the width of new fractures. The non-linear hyperbolic partial differential equations (PDE) are solved by the implicit finite difference method. Cleat permeability has a more significant influence on the gas produced than the porosity. Optimized values of 300 mD and 0.03 porosity sweep more area in a short time. Due to the faster propagation of drainage, the adsorbed gas is not recovered to nearly complete before the entire reservoir/pay zone length is drained. Fracturing a formation can be successful if the same adsorbed gas is spread over a larger area, and length is insufficient to accommodate the gas in place. The pay zone length needs to be larger than the present value. The novel approach of checking both the economic feasibility of fracturing a formation and its relation with the length of the reservoir, is discovered and solved here. [ABSTRACT FROM AUTHOR]

Proppant is one of the key materials for hydraulic fracturing. For special situations, such as middle-deep reservoirs and closure pressures ranging from 40 MPa to 60 MPa, using a single proppant cannot solve the contradiction between performance, which means crushing rate and fracture conductivity, and cost. However, using combined proppants is an economically effective method for hydraulic fracturing of such special reservoirs. Firstly, for different types, particle sizes, and proportions of combined proppants, various contact relationships between proppant particles are considered. The random phenomenon of proppant particle arrangement is described using the Monte Carlo method, and the deterministic phenomenon of proppant particles is processed using an optimization model, achieving computer simulation of the microscopic arrangement of proppant particles. Secondly, a mathematical model for the force analysis of combined proppant particles is established, and an improved singular value decomposition method is used for numerical solution. A computational model for the crushing rate and fracture conductivity of combined proppants is proposed. Thirdly, the numerical calculation results are compared and discussed with the test values, verifying the accuracy of the computational model. Finally, the application of combined proppants is discussed, and a model for optimizing the proportion of combined proppants is proposed. The onsite construction technology is introduced, and the cost and economic benefits of combined proppants are compared with those of all ceramic particles and excessive all-quartz sand. It is proved that combined proppants can balance performance and price, and are an economically effective method for hydraulic fracturing of special reservoirs. The research results can select the optimal proppant material and optimize the combination of different proppant types, which can help achieve cost reduction and efficiency increase in oil and gas development. [ABSTRACT FROM AUTHOR]

As a crucial exploration technique for unconventional reservoirs, hydraulic fracturing enables the formation of complex fracture networks, thereby facilitating the flow of oil and gas. The closure of natural fractures decreases stimulation performance. Microparticle proppants are used to fill natural fractures and effectively increase the stimulation area. The 100-mesh proppant conventionally used in field operations may be insufficiently small to effectively access natural fractures. In order to effectively overcome natural fractures closure, microparticle proppants (i.e., proppants with a diameter of 75 µm (200-mesh) or less) are required. The particle size threshold test of microparticle proppants placement is conducted to determine the size threshold of proppants flowing into natural fractures. The microparticle proppants placement experiment in multi-branch fractures is conducted to investigate the volume difference of proppants in different fractures. Numerical simulations are performed to model proppant transport within fractures of actual dimensions to facilitating the optimization of stimulation parameters. The main conclusions are as follows: (1) Effective inflow of microparticle proppants requires a size threshold of proppants. For the 200-mesh proppants, the size should be less than half of natural fractures width when microparticle proppants effectively flow into natural fractures. (2) Sand concentration affects the size threshold of microparticle proppants. The size threshold should appropriately increase to ensure the inflow of proppant. (3) Difference of multi-branch fracture width has a significant effect on volume of microparticle proppants inside fractures. When the width ratio of multi-branch fractures exceeds 2, this effect becomes obvious. (4) Particle size has an effect on proppant placement. 200-mesh proppants can obtain uniform distribution of proppants among natural fractures. 140-mesh proppants can obtain maximum proppant volume among natural fractures. Sand concentration significantly affects proppant placement performance. The optimal sand concentration is 60kg/m³. The pumping rate for a single cluster fracture should not be excessively low. The pumping rate should be larger than 0.5m³/min and the optimal pumping rate 2m³/min. In this paper, the particle size and concentration of particulate proppant are optimized and the geometric characteristics of fractures are considered. These conclusions provide important practical guidance and scientific basis for the optimization and application of hydraulic fracturing technology. [ABSTRACT FROM AUTHOR]

Understanding the behavior of dispersed particles in subsurface porous media is essential for studying many transport phenomena in geo-energy exploration. Relevant phenomena include fluid transport through rock matrices, undesirable production of formation sands, colloid migration, circulation of drilling cuttings, and displacement of proppants in hydraulic fractures. The discrete element method (DEM), when coupled with the lattice Boltzmann method (LBM) and computational fluid dynamics (CFD), represents a useful numerical approach to studying these microscopic processes. This integrated approach allows for detailed modeling of particle–fluid and particle–particle interactions, which is particularly useful in dealing with particles with non-spherical shapes. This review focuses on recent advancements in DEM implementations for such particles and their coupling schemes with LBM and CFD numerical tools. It aims to assist scholars and practitioners in selecting the most effective LBM/CFD-DEM strategy for studying particle transport and packing in geo-energy scenarios. Although tailored for geophysical flows, the methodologies and analytical frameworks presented here also apply to fundamental investigations of particle-laden flows. [ABSTRACT FROM AUTHOR]

This study aimed to assess the feasibility of manufacturing fracturing proppants by microwave sintering and using low‐grade bauxite as raw material. The effects of microwave hotspot SiC and sintering additive MnO2 content on the performance of the mullite‐based structural materials were studied, respectively. The optimum sintering condition was determined by single‐factor experiments. The sintering process and mechanism were explored based on the analysis of physicochemical properties, phase transitions, and microstructure. The results showed that (1) mullite ceramic composites could be successfully prepared only with SiC added and with poor interparticle bonding microstructure. (2) With the addition of MnO2 and CaO, the granular‐shaped mullite crystals transformed into rod‐like mullite crystals, forming a net structure. (3) As the input power increased, the overfast sintering rate would reduce proppants' mechanical properties, and it was also necessary to select a reasonable sintering time to avoid overburning. (4) When the mass ratio of MnO2:CaO:SiC:bauxite was 2:1.5:12:84.5 and under the sintering condition of 1000 W, 2 h, the performance (breakage ratio of 8.5% under 28 MPa closed pressure, apparent density of 2.58 g/cm3, turbidity of 52 FTU, and acid solubility of 6.77%) could meet the requirements of the Chinese Petroleum and Gas Industry Standard (SY/T 5108–2014). This study provides a powerful way for reducing the fracturing cost, which not only improves the low‐grade bauxite utilization scale within the ceramic industry, but also expands the application of microwave sintering technology in mullite structural materials for the petroleum and gas industry. [ABSTRACT FROM AUTHOR]

The conductivity of propped fractures following hydraulic fracturing is crucial in determining the success of the fracturing process. Understanding the primary factors affecting fracture conductivity and uncovering their impact patterns are essential for guiding the selection of fracturing engineering parameters. We conducted experiments to test fracture conductivity and analyzed the effects of proppant particle size, closure pressure, and fracture surface properties on conductivity. Using the orthogonal experimental method, we clarified the primary and secondary relationships of the influencing factors on conductivity. The results indicate that proppant particle size, formation closure pressure, and fracture surface properties significantly affect fracture conductivity, with the order of influence being closure pressure > fracture surface properties > proppant particle size. Using large-particle-size proppants effectively increases interparticle porosity and enhances fracture conductivity. However, large-particle-size proppants reduce the number of contact points between particles, increasing the pressure on individual particles and making them more prone to crushing, which decreases fracture conductivity. Proppants become compacted under closure pressure, leading to a reduction in fracture conductivity. Proppant particles can embed into the fracture surface under closure pressure, further impacting fracture conductivity. Compared to non-laminated fracture surfaces, proppant particles are more likely to embed into laminated fracture surfaces under closure pressure, resulting in a greater embedding depth and reduced conductivity. [ABSTRACT FROM AUTHOR]

As a crucial exploration technique for unconventional reservoirs, hydraulic fracturing enables the formation of complex fracture networks, thereby facilitating the flow of oil and gas. The closure of natural fractures decreases stimulation performance. Microparticle proppants are used to fill natural fractures and effectively increase the stimulation area. The 100-mesh proppant conventionally used in field operations may be insufficiently small to effectively access natural fractures. In order to effectively overcome natural fractures closure, microparticle proppants (i.e., proppants with a diameter of 75 ^m (200mesh) or less) are required. The particle size threshold test of microparticle proppants placement is conducted to determine the size threshold of proppants flowing into natural fractures. The microparticle proppants placement experiment in multi-branch fractures is conducted to investigate the volume difference of proppants in different fractures. Numerical simulations are performed to model proppant transport within fractures of actual dimensions to facilitating the optimization of stimulation parameters. The main conclusions are as follows: (1) Effective inflow of microparticle proppants requires a size threshold of proppants. For the 200-mesh proppants, the size should be less than half of natural fractures width when microparticle proppants effectively flow into natural fractures. (2) Sand concentration affects the size threshold of microparticle proppants. The size threshold should appropriately increase to ensure the inflow of proppant. (3) Difference of multi-branch fracture width has a significant effect on volume of microparticle proppants inside fractures. When the width ratio of multi-branch fractures exceeds 2, this effect becomes obvious. (4) Particle size has an effect on proppant placement. 200-mesh proppants can obtain uniform distribution of proppants among natural fractures. 140-mesh proppants can obtain maximum proppant volume among natural fractures. Sand concentration significantly affects proppant placement performance. The optimal sand concentration is 60kg/m3. The pumping rate for a single cluster fracture should not be excessively low. The pumping rate should be larger than 0.5m3/min and the optimal pumping rate 2m3/min. In this paper, the particle size and concentration of particulate proppant are optimized and the geometric characteristics of fractures are considered. These conclusions provide important practical guidance and scientific basis for the optimization and application of hydraulic fracturing technology. [ABSTRACT FROM AUTHOR]

Lightweight ceramic proppants are prepared using coal gangue, fly ash, and bauxite as raw materials, and a mixture of manganese dioxide and magnesium oxide is used as composite additives. The total content of the coal gangue and fly ash in the raw materials reaches up to 70 wt%. The effects of coal gangue and fly ash precalcination, sintering temperature, and composite additive content on the phase compositions, microstructures, and performances of the resulting ceramic proppants are studied in detail. The ceramic proppant prepared at 1285 °C using 1 wt% of the composite additive is composed of quartz, corundum, and mullite. It also presents the desired sphericity, roundness, and microstructure. The apparent density, bulk density, and breakage ratio of the ceramic proppant described above are 2.55 ± 0.06 g/cm3, 1.03 ± 0.02 g/cm3, and 8.30 ± 0.68% at 35 MPa, respectively. This ceramic proppant belongs to lightweight ceramic proppants and meets the requirement of the 5K grade in the standards of SY/T 5108-2014 and API STD 19C-2018. [ABSTRACT FROM AUTHOR]

A three-dimensional reconstruction of rough fracture surfaces of hydraulically fractured rock outcrops is carried out by casting process, a large-scale experimental setup for visualizing rough fractures is built to perform proppant transport experiments. The typical characteristics of proppant transport and placement in rough fractures and its intrinsic mechanisms are investigated, and the influences of fracture inclination, fracture width and fracturing fluid viscosity on proppant transport and placement in rough fractures are analyzed. The results show that the rough fractures cause variations in the shape of the flow channel and the fluid flow pattern, resulting in the bridging buildup during proppant transport to form unfilled zone, the emergence of multiple complex flow patterns such as channeling, reverse flow and bypassing of sand-carrying fluid, and the influence on the stability of the sand dune. The proppant has a higher placement rate in inclined rough fractures, with a maximum increase of 22.16 percentage points in the experiments compared to vertical fractures, but exhibits poor stability of the sand dune. Reduced fracture width aggravates the bridging of proppant and induces higher pumping pressure. Increasing the viscosity of the fracturing fluid can weaken the proppant bridging phenomenon caused by the rough fractures. [ABSTRACT FROM AUTHOR]

The deployment of proppant to fracture shear is a promising approach to stimulating hydraulic permeability in fractured reservoirs. However, the interactive effects of proppant and surface roughness have not been clearly revealed. To better understand this concern, direct shear tests (DSTs) are implemented on 2D rough fractures with a joint roughness coefficient (JRC) varying from 4 to 6 and 18 to 20 under propped conditions. The results show that peak shear strength is positively proportional to asperity amplitude. The highest peak shear strength is determined with a JRC of 14–16 due to it having the highest asperity of 6.34 mm. The peak shear load was decreased significantly by deploying the proppant. Shear damage only occurs in the localized zone where the upper–lower asperities contact. The shear dilatancy was attributed to both the "shear climbing" effects and the shear damage that caused the frictional slip. The proppants weaken the climbing effect but also prevent the shear damage that in turn promotes shear dilatancy. [ABSTRACT FROM AUTHOR]

In treatments that involve multiple stages and clusters, one of the most important challenges is ensuring that the proppant is evenly distributed across all clusters. It is crucial to distribute the proppant equally to ensure that all perforation clusters are contributing to production. To forecast the proppant distribution between perforation clusters, an experimental correlation was established using data from the literature on horizontal wellbores. A dimensional analysis was performed using the Buckingham Pi-theorem to develop the correlation. Data from different independent variables, such as completion designs and orientations, were incorporated. In this study, an improved novel experimental correlation is proposed to accurately forecast the proppant distribution using various perforation configurations and orientations. The correlation can predict the proppant distribution with a low percentage difference of less than 20%. This correlation may be upscaled to predict the distribution of proppants across multiple clusters in a single-stage hydraulic fracturing stimulation. The developed correlation illustrates that injecting more proppant at a higher rate may help to allocate the proppant more evenly across perforation clusters. However, a nonuniform proppant distribution is obtained by increasing the proppant median diameter. [ABSTRACT FROM AUTHOR]

Oil-based drilling cutting pyrolysis residues (ODCPRs), bauxite, and sintering additives were applied to manufacture ceramic proppants with low density and high strength in this work. The effect of ODCPRs ratio, sintering temperature, holding time, and the content of additives on the performance of the proppants was comprehensively investigated, respectively. And the sintering mechanism of proppants was also discussed according to the phase, microstructure, and thermal behavior analyses. The results revealed that at the best sintering condition (1280 °C, holding for 60 min), and a mass ratio (ODCPRs: bauxite: MnO2 at 3:7:0.1), the well-developed granular corundum and acicular mullite formed inside the proppants and interspersed with each other to form a dense structure. The proppants presented low density and high strength as the bulk density of 1.48 g/cm3, the apparent density of 2.94 g/cm3, a breakage ratio of 5.25% under 52 MPa closed pressure, and the acid solubility of 4.80%, which could well meet the requirement of the standards of SY/T 5108-2014. This work provided a new pathway for recycling ODCPRs and the fabrication of high-performance proppants. [ABSTRACT FROM AUTHOR]

The research topic deals with one of the important problems that the oil and gas sector suffers from, which is represented by corrosion, as the corrosion of metals annually causes large losses in production as a result of stimulating oil wells using hot HCl solutions, which causes the occurrence of corrosion phenomenon in the well bottom tools, pipes and casing. In addition, a group of organic and inorganic acids and surfactants are used in well stimulation processes. In order to reduce the violent attack of the acid solution on the N80 mild steel casing materials and pipes, during the pickling process inhibitors are added to the acid medium, and to avoid the complexity of the inhibition process in the oil and gas fields, which requires organic inhibitors within the green chemistry depending on the nature of the work field such as pipelines and equipment, recovery wells, refineries, etc. Organic acids and acidic gases such as carbon dioxide and hydrogen sulfide complicate the well inhibition problem. Corrosion problems in the oil industry must be dealt with by considering various factors. Acids used in stimulation, the nature and type of reservoir rocks, and oil well equipment, whose operating conditions include casings and tubes, and these form part of the factors affecting corrosion. Thus, it needs to study each case as it is before determining the final opinion regarding the alternative materials. No suitable material can be found to survive the attack of corrosion. The designers and operators of the oil industry must take into account many serious economic and technical problems, the most important and most dangerous of which is the phenomenon of corrosion that is characteristic of the oil industry that deals with highly volatile and sometimes toxic materials and transported by pipelines over long distances and stored in huge warehouses in addition to because it requires a complex operational process that requires high heat and pressure, so if this equipment is so worn out that it is unable to withstand these harsh conditions, then there is no doubt that explosions may occur, which may be accompanied by fires, and sometimes their effect reaches the neighboring equipment and sometimes the entire production unit. [ABSTRACT FROM AUTHOR]

The polymer ultra‐low‐density proppants are critical to the development of slick‐water fracture technology, but which were prone to obvious deformation under high pressure in the fractures. To increase the stiffness of the styrene‐divinylbenzene copolymer (SDB) and obtain desired ultra‐low‐density (ULD) proppants, carbon dots (CDs) were introduced in‐situ considering their characteristics as the zero‐dimensional carbon nanomaterial. Taking the compressive strength and axial deflection, and so forth into consideration, the synthesis conditions of CDs modified SDB microspheres (CDs‐SDBs) were optimized. Taking the graphite modified SDBs (MG‐SDBs) as a reference, the density of CDs‐SDBs did keep almost constant at about 1.1800 ~ 1.1899 g·cm−3 with the increase of CDs amount. The CDs‐SDBs not only possess high‐peak pressure (41.5 N) but also minute axial deflection (0.090 mm). The advantages of CDs‐SDBs over MG‐SDBs become even more pronounced under higher pressure, which can withstand closure pressure of 80 MPa with a small crush ratio of 4.47%. CDs‐SDBs exhibit significant photoluminescence performances with maximum excitation and emission wavelengths of 634 nm and 554 nm. Highlights: CDs‐SDBs as ULD proppants with high strength and anti‐deformation were developed.Advantages of CDs‐SDBs become more pronounced under high‐closure pressure.With increasing of CDs amount, apparent density of CDs‐SDBs keep almost constant.Axial deflection of CDs‐SDBs is only 0.09 mm under 41.5 N.The crush ratio is only 4.47% under 80 MPa closure pressure. [ABSTRACT FROM AUTHOR]

The article describes the studies on permeability of coal cores with a through drainage fracture with and without a monolayer of a proppant. The experimental procedure is descried. The parameters of the jointed structure of test long-flame coal are given. The efficiency of wedging drainage fractures by a sparse proppant monolayer in building up permeability of deep-seated coal is demonstrated. [ABSTRACT FROM AUTHOR]

The small-sized proppant is widely used in the traditional hydraulic fracturing reservoir stimulation, but the theoretical research shows that the large-sized proppant can greatly improve the fracture permeability. Although many scholars have proposed the method of using large-sized proppant, the characteristics of the pressure field change and gas drainage rate during reservoir development are still unclear after pumping large-sized proppant. In this article, to study the change regularity of the reservoir pressure field, two representative proppants are selected: the small-sized proppant and large-sized proppants. First, the Navier–Stokes equations are solved using the numerical simulation method, and the characteristics of the reservoir pressure field are finely reproduced. Then, the production rate is discussed to reveal the huge potential of large-sized proppant for the natural gas development. The results show that under the same conditions, if the particle size of the proppant increases by 5 times, then the reservoir permeability will increase by 27 times approximately, and the single well production efficiency will increase by 17~19 times in the first 3000 days. In addition, a new quantitative model is proposed to evaluate the permeability magnification of the fracture and reservoir when adopting the large-sized proppant. This study further confirms that the method of large-sized proppant proposed by the author in the earlier stage has great potential. This study is helpful for the researchers and engineers to better understand the evolution regularity of the reservoir pressure field and gas production rate in the process of oil and gas exploitation after using the large-sized proppant. [ABSTRACT FROM AUTHOR]

This study investigates a new type of high-performance coated sand as a petroleum fracturing proppant material. Modified quartz sand was coated with a layer of low-density resin to reduce the overall density of the proppant, thereby improving the suspension of the proppant in the fracturing fluid. Resins play an important role in the preparation of coated sand fracturing proppants. The mechanism of sand formation was studied by examining the phase composition and microstructure of the coated sand proppant. The results demonstrate that when the polyimide resin content is 6% and the curing temperature is 180 °C, the proppant exhibited the best performance with an apparent density of 1.592 g/cm3 and a breakage ratio of only 3.22% under 55.2 MPa. Compared with the widely used epoxy resin-coated support agent and phenolic resin-coated support agent in the early stage, their crushing rate decreased by 5% and their acid solubility decreased by 2%. Hence, this study is worthy of attention. [ABSTRACT FROM AUTHOR]

Objective In view of the large amount of solid waste in the process of oil and gas development and the single way of resource utilization, the ceramic proppant for hydraulic fracturing was prepared by drilling cuttings and secondary aluminum ash, which can effectively broaden the way of resource utilization of drilling cuttings and reduce the production cost of oil and gas development. Methods The low density and high strength ceramic proppant for fracturing was prepared mainly by secondary bauxite, adding 20 wt% drilling cuttings, 10 wt% secondary aluminum ash and methylcellulose as binder at different sintering temperatures. The effects of sintering temperature on the structure, crystal phase composition and product properties of proppant were studied. Results The drilling cuttings need to be pretreated to reduce the effect of organic matter in the drilling cuttings on the subsequent raw embryo sintering. When the sintering temperature was 1 300 ℃, its primary crystalline phase was corundum and secondary crystalline phase was barium feldspar, the bulk density of the proppant was 1.45 g/cm3 and the crushing rate was 5.26% under 52 MPa closure pressure, which could meet the quality requirements of 0.38 mm/0.25 mm proppant under SY/T 5108-2014 Measurement of properties of proppants used in hydraulic fracturing and gravel-packing operations. Conclusions Sintering temperature is a critical control parameter for preparing ceramics proppant. With the increase of sintering temperature, the liquid phase produced inside the proppant gradually increase, which is conducive to accelerate the diffusion and the mass transfer rate, and promote the densification of the proppant. But excessive liquid phase will lead to the expansion and deformation of the proppant and adversely affect the crushing ability. The suitable sintering temperature is recommended to be 1 260-1 300 ℃ when using drilling chips, aluminum ash and bauxite as raw materials. [ABSTRACT FROM AUTHOR]

The placement of proppant within fractures is critical to the effectiveness of hydraulic fracturing. To elucidate the migration and placement patterns of proppant within multi-branched fractures during hydraulic fracturing, we conducted simulation experiments under both single-fracture and multi-branched-fracture conditions, varying injection rates and proppant sizes. The results of the research indicate that increasing the injection rate effectively increases the magnitude of vortex formation at the leading edge of sandbars and the drag forces acting on the proppant particles, resulting in increased particle migration distances. However, effective proppant packing near the wellbore entrance is not achieved at higher injection rates, leaving the fractures susceptible to closure under in situ stress, thereby reducing overall fracture conductivity. In addition, increasing the proppant size results in higher settling velocities and weakens the vortex's ability to entrain the proppant particles. This results in shorter proppant placement distances, and the proppant cannot effectively reach the distant branched fractures. In addition, the diversionary effect of the branched fractures gradually reduces the flow rate in the distant branches, resulting in poorer proppant placement efficiency. Based on these findings, we recommend an approach that initially increases injection rates while reducing proppant size to ensure proppant placement in distant wellbore fractures and branched fracture networks. Subsequently, larger proppants can be used to effectively fill fractures close to the wellbore. [ABSTRACT FROM AUTHOR]

Copyright of Petroleum Geology & Oilfield Development in Daqing is the property of Editorial Department of Petroleum Geology & Oilfield Development in Daqing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ceramic proppants are preferred in hydraulic fracturing because of their high strength, good sphericity, and excellent acid corrosion resistance. Bauxite is the main raw material of ceramic proppants, but with the increasing depletion of bauxite resources, substitutes for bauxite need to be sought. Coal gangue is a solid waste that is rich in SiO2 and Al2O3, making it a potential substitute for the preparation of ceramic proppants. The use of coal gangue to prepare ceramic proppants can reduce the cost of ceramic proppants and benefit environmental protection. Studies on using coal gangue to prepare ceramic proppants have been conducted and achieved progress, but further improvement can still be obtained. Here, the basic principle, progress, and prospects of coal gangue ceramic proppants are reviewed. First, coal gangue ceramic proppants are divided into two categories, namely, proppants prepared using coal gangue as an auxiliary material and proppants prepared using coal gangue as the main material. Second, the progress of research of coal gangue ceramic proppants is summarized from the perspective of additives, and the influence of different kinds of additives on the sintering temperature and performance of proppants is discussed. Lastly, the future prospects of coal gangue ceramic proppants are presented. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing (HF) is a commonly used technique to stimulate low permeability formations such as shale plays and tight formations. However, this method of well stimulation has also been used in high permeable unconsolidated sandstone formations to bypass near-wellbore formation damage and prevent sand production at some distance apart from the wellbore wall. The treatment is called frac-pack completion, where a short length but wide width fracture is formed by injecting aggressive concentrations of proppant into the fracture plane. This operation is known as tip screen-out (TSO). Detailed design of fluid and proppant, including an optimal pump schedule, is required to achieve satisfactory TSO. In this study, we first assess the lattice-based numerical method's capabilities for simulating hydraulic fracturing propagation in elastoplastic formation. The results will be compared with the same case simulation results using a pseudo 3D (P3D) model and analytical model. Second, we explore the Nolte (1986) design for frac-pack and TSO treatment using lattice-based software and the P3D model. The results showed that both models could simulate the hydraulic fracturing propagation in soft formation and TSO operation, while some differences were observed in generated geometry, the tip screenout time and net pressure profiles. The results are presented. It was noted that fracture propagation regime (viscosity/toughness), nonlocality and nonlinearity had an influence on the different geometries. The advantages of each model will be discussed. [ABSTRACT FROM AUTHOR]

Natural gas hydrate (GH) is a significant potential energy source due to its large reserves, wide distribution, high energy density and low pollution. However, the gas production rate of past gas hydrate production tests is much lower than the requirement of commercial gas production. Reservoir stimulation technologies like hydraulic fracture provide one potential approach to enhance gas production from GH. The reservoir reformation behaviour of the hydrate-bearing sediments (HBS), particularly sediments with a high clay content, is a complex process during a hydraulic fracturing operation, which has been poorly understood and thus hardly predictable. This paper presents an experimental facility that was developed to analyze the hydraulic fracture mechanism in synthesized HBS. This facility can be used to form GH in sediments, conduct visual observation of hydraulic fracturing experiments, and measure the permeability of HBS under high pressure (up to 30 MPa) and low-temperature conditions (from 253.15 K to 323.15K). It is mainly composed of a pressure control and injection unit, a low temperature and cooling unit, a cavitation unit, a visual sapphire reactor, and a data acquisition and measurement unit. The hydraulic fracture module is consisting of a gas cylinder, fracturing pump, hopper, proppants warehouse and valves. The sapphire reservoir chamber is applied to observe and measure the fracture of HBS during hydraulic fracturing. The permeability test module is composed of a constant-flux pump and pressure sensors, which can evaluate the permeability performance before and after hydraulic fracture in HBS. The fundamental principles of this apparatus are discussed. Some tests were performed to verify hydraulic fracture tests and permeability tests could be practically applied in the HBS exploitation. [ABSTRACT FROM AUTHOR]

Natural gas hydrate (GH) is a significant potential energy source due to its large reserves, wide distribution, high energy density and low pollution. However, the gas production rate of past gas hydrate production tests is much lower than the requirement of commercial gas production. Reservoir stimulation technologies like hydraulic fracture provide one potential approach to enhance gas production from GH. The reservoir reformation behaviour of the hydrate-bearing sediments (HBS), particularly sediments with a high clay content, is a complex process during a hydraulic fracturing operation, which has been poorly understood and thus hardly predictable. This paper presents an experimental facility that was developed to analyze the hydraulic fracture mechanism in synthesized HBS. This facility can be used to form GH in sediments, conduct visual observation of hydraulic fracturing experiments, and measure the permeability of HBS under high pressure (up to 30 MPa) and low-temperature conditions (from 253.15 K to 323.15 K). It is mainly composed of a pressure control and injection unit, a low temperature and cooling unit, a cavitation unit, a visual sapphire reactor, and a data acquisition and measurement unit. The hydraulic fracture module is consisting of a gas cylinder, fracturing pump, hopper, proppants warehouse and valves. The sapphire reservoir chamber is applied to observe and measure the fracture of HBS during hydraulic fracturing. The permeability test module is composed of a constant-flux pump and pressure sensors, which can evaluate the permeability performance before and after hydraulic fracture in HBS. The fundamental principles of this apparatus are discussed. Some tests were performed to verify hydraulic fracture tests and permeability tests could be practically applied in the HBS exploitation. [ABSTRACT FROM AUTHOR]

This study presents the feasibility of preparing ceramic proppants (CPs) using drilling cuttings (DCs) and coal fly ash (CFA) via high-temperature sintering. The reaction behavior of barite in ceramic proppant precursors originating from DCs during the sintering process was investigated. The breakage ratio of the CPs (optimal group S3) met the requirements of Chinese standard SY/T 5108-2014 (2 K grade). The primary chemical reactions (7–8 in Table 4) between the barite and silica/alumina components resulted in a reduction of the eutectic point of the mixtures and the formation of aluminosilicates containing barium. However, these interactions also released gases (SO 2 and O 2), which created pores and weakened the CPs strength. The ideal temperature range for sintering is between 1170 and 1200 °C, during which there should be a gradual weight loss and minimal gas generation. This range will also ensure that the appropriate amount of liquid phase is present, which will have a moderate viscosity and aid in the densification of the ceramic proppants, as well as the formation of a dense enamel layer. The composite reactions of barite in the S3 sample follow a one-and-a-half-order chemical reaction mechanism within the temperature range of 950–1200 °C. The average activation energy and pre-exponential factor were 583.304 kJ mol−1 and 5.81 × 1020 min−1, respectively. The kinetic and reaction rate equations for the composite reactions were (1 − α)−1/2–1 = (5.81 × 1020 × e−5.83 × 10^5/RT) × t and d α /d t = (2(1 − α)3/2) × (5.81 × 1020 × e−(5.83 × 10^5)/RT)), respectively. This study provides a theoretical basis and guidelines for large-scale production of CPs using DCs and CFA. [ABSTRACT FROM AUTHOR]

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hydraulic fracture is crucial for assuring well production from unconventional reservoirs. For the optimization of hydraulic fracture geometry and the ensuing production of an interlayered reservoir, vertical hydraulic fracture propagation path has been analyzed. However, an effective fluid channel cannot be formed if the proppant is unable to reach the area where the fracture propagates. This paper presents a numerical model using the lattice-based method to investigate the hydraulic fracture propagation and proppant transport mechanism in interlayered reservoirs. The hydraulic fracture propagation model was simulated under different geological and fracturing engineering factors. The results indicate that interlayer Young's modulus and horizontal stress anisotropy are positively correlated with longitudinal propagation and proppant carrying ability in interlayered formations. The fracturing injection rate has an optimal solution for fracture propagation and proppant carrying since a too low injection rate is unfavorable for fracture penetration of the interlayer, while a too high injection rate increases fracture width instead of further fracture penetration. In conclusion, attention is drawn to fine particle size proppants used in multi-layer reservoirs for fracturing fluid to carry proppants as far as possible to obtain maximum propped area. [ABSTRACT FROM AUTHOR]

Coalbed methane reservoirs exhibit a low strength and high heterogeneity, rendering them susceptible to coal fines generation during hydraulic fracturing operations. The detrimental impact of coal fines on the conductivity of the propped fracture has been overlooked, leading to a substantial negative effect on the later-stage recovery of coalbed methane reservoirs. Moreover, the particle size distribution of the composite proppant also affects the conductivity of the propped fracture. To mitigate the damage caused by coal fines to the conductivity of the proppant pack in CBM reservoirs, this study conducted conductivity tests on actual coal rock fractures. The aim was to assess the effect of various particle size ratios in composite proppant blends on the conductivity of complex fractures in CBM reservoirs. The ultimate goal was to identify an optimized proppant blending approach that is suitable for hydraulic fracturing in coal seams. The results indicated that, in terms of the short-term conductivity of coalbed methane reservoirs, the conductivity of composite proppants is primarily influenced by the proportion of large or small particles. A higher proportion of large particles corresponds to a stronger conductivity (e.g., the conductivity is highest at a particle ratio of 5:1:1 for large, medium, and small particles). On the other hand, a higher proportion of small particles leads to a poorer conductivity (the conductivity is lowest when the particle ratio is 1:1:5). In the long-term conductivity of coalbed methane reservoirs, the fluid flushing of the fracture surfaces generates coal fines, and small particles can fill the gaps between larger particles, hindering the infiltration of coal fines. Therefore, it is important to control the particle size ratio of composite proppants, with a predominant proportion of larger particles. This approach can maintain long-term conductivity and prevent the excessive infiltration of coal fines, thereby avoiding fracture blockage (e.g., the conductivity is highest at a particle ratio of 5:1:5, followed by a ratio of 3:1:3). Furthermore, considering the influence of proppant placement methods and the support effect on near-wellbore opening fractures and far-end sliding fractures, segmented placement is utilized to fully fill the fractures for short-term conductivity, whereas mixed placement is employed for long-term conductivity to achieve a balance in particle gaps and hinder the infiltration of coal fines. The findings of this study contribute to the understanding of proppant selection and placement strategies for efficient hydraulic fracturing in coalbed methane reservoirs. [ABSTRACT FROM AUTHOR]

Copyright of Petroleum Geology & Recovery Efficiency is the property of Petroleum Geology & Recovery Efficiency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To enhance the extraction of methane gas from coal beds, hydraulic fracturing technology is used. However, stimulation operations in soft rocks, such as coal beds, are associated with technical problems related mainly to the embedment phenomenon. Therefore, the concept of a novel coke-based proppant was introduced. The purpose of the study was to identify the source coke material for further processing to obtain a proppant. Twenty coke materials differing in type, grain size, and production method from five coking plants were tested. The values of the following parameters were determined for the initial coke: micum index 40; micum index 10; coke reactivity index; coke strength after reaction; and ash content. The coke was modified by crushing and mechanical classification, and the 3–1 mm class was obtained. This was enriched in heavy liquid with a density of 1.35 g/cm3. The crush resistance index and Roga index, which were selected as key strength parameters, and the ash content were determined for the lighter fraction. The most promising modified coke materials with the best strength properties were obtained from the coarse-grained (fraction 25–80 mm and greater) blast furnace and foundry coke. They had crush resistance index and Roga index values of at least 44% and at least 96%, respectively, and contained less than 9% ash. After assessing the suitability of coke material for proppants in the hydraulic fracturing of coal, further research will be needed to develop a technology to produce proppants with parameters compliant with the PN-EN ISO 13503-2:2010 standard. [ABSTRACT FROM AUTHOR]

The in situ mining technology is applied to the exploitation of medium- and low-maturity shale oil, which can use heaters to warm up the oil shale formations and pyrolyze the kerogen. Due to the low thermal conductivity of oil shale, electric heaters need extra equipment to improve heat transfer efficiency. In this study, a thermally conductive proppant is fabricated by coating epoxy-resin and graphite on ceramic proppants for the first time, which could support the fracturing crack and transfer heat. The thermal conduction property of epoxy-resin and graphite coated proppants (EGPs) is 245% higher than that of uncoated proppants, which can transfer more heat to the oil shale formation and accelerate the conversion of kerogen. The adhesive property of EGPs is improved by 47.9% under the load force of 1500 nN, which prolongs the time for the fracture to close. In summary, this novel proppant is expected to assist in-situ mining technology in the production of medium and low-maturity shale oil. [ABSTRACT FROM AUTHOR]

Data-driven models with some evolutionary optimization algorithms, such as particle swarm optimization (PSO) and ant colony optimization (ACO) for hydraulic fracturing of shale reservoirs, have in recent times been validated as one of the best-performing machine learning algorithms. Log data from well-logging tools and physics-driven models is difficult to collate and model to enhance decision-making processes. The study sought to train, test, and validate synthetic data emanating from CMG's numerically propped fracture morphology modeling to support and enhance productive hydrocarbon production and recovery. This data-driven numerical model was investigated for efficient hydraulic-induced fracturing by using machine learning, gradient descent, and adaptive optimizers. While satiating research curiosities, the online predictive analysis was conducted using the Google TensorFlow tool with the Tensor Processing Unit (TPU), focusing on linear and non-linear neural network regressions. A multi-structured dense layer with 1000, 100, and 1 neurons was compiled with mean absolute error (MAE) as loss functions and evaluation metrics concentrating on stochastic gradient descent (SGD), Adam, and RMSprop optimizers at a learning rate of 0.01. However, the emerging algorithm with the best overall optimization process was found to be Adam, whose error margin was 101.22 and whose accuracy was 80.24% for the entire set of 2000 synthetic data it trained and tested. Based on fracture conductivity, the data indicates that there was a higher chance of hydrocarbon production recovery using this method. [ABSTRACT FROM AUTHOR]

The results of an investigation of the influence of the chemical composition, material structure, crystallization features, and isomorphic substitutions in pyroxene solid solutions of the augite type on the mechanical characteristics of glass ceramics are presented. The mechanism of structure formation is demonstrated, which consists in the crystallization of chromium spinel and subsequent growth on its surface of crystals of a pyroxene solid solution of the augite type in the form of spherical intergrowths, which effects high mechanical strength of glass-ceramic proppants. It was found that on isomorphic substitutions occurring in the diopside-augite series the mechanical strength of glass-ceramic proppants increases, which is correlated with a reduction of bond lengths and an increase in their number as well as compaction of the unit cell. [ABSTRACT FROM AUTHOR]

Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Nowadays, volcanic reservoirs show great development potential. However, the stimulation mechanism of volcanic reservoir is yet unclear. In this article, hydraulic fracturing, acid fracturing, and proppant-carrying acid fracturing of volcanic rock were analyzed by the laboratory tests. The average acid etching and proppant-embedded depths were assessed. The effect of different proppant sizes and acid types on fracture conductivity was studied. The results indicate that acid fracturing is failed to produce high-conductivity fractures. Large-sized proppants had larger embedded depths. For the hydraulic fracturing, the average depth of the 30/50 mesh proppant (5 kg/m2, 60 MPa) embedded in the volcanic rock is 33 μm, and the conductivity is 45.27 D·cm, which is 1.5 times that of the 40/70 mesh proppant. Embedded depth of proppant in the proppant-carrying acid fracturing (347 μm) was ten times larger than that in hydraulic fracturing (33 μm), but in terms of conductivity, hydraulic fracturing is only 20% better than proppant-carrying acid fracturing. This study is helpful to elucidate the mechanism of different stimulation methods and provide scientific means for the efficient development of volcanic reservoirs. In this article, experimental study is made on the stimulation mode of volcanic reservoir. There are few studies on volcanic. This study is helpful to elucidate the mechanism of different stimulation methods and provide scientific means for the efficient development of volcanic reservoirs. Based on the three-dimensional (3D) surface data of the rock, the average acid etching depth and the average embedding depth of proppant are accurately calculated by a new method. The experimental results can provide a good basis for the selection of volcanic reservoir stimulation. The embedded depth and etching depth have an intuitive image display. [ABSTRACT FROM AUTHOR]

Proppant is often used to enhance reservoir stimulations, such as hydraulic fracturing and hydraulic shearing; however, the influence of proppant on the shear deformation of fractures and the potential consequent-induced earthquakes are rarely explored. We explore the systematics of frictional behavior, deformability and dilatancy of proppant-filled fractures to define the complex response to different fracture roughness and proppant mass loadings. Shear experiments on rough granite fractures show that proppant reduces cohesion and internal friction, reduces the shear stiffness, delays the shear displacement to a diminished peak strength, reduces the magnitude of shear dilation, and promotes ductile shear failure that is analogous to aseismic creep. A systematic transition in shear behavior occurs from fracture-roughness-dominant to proppant-dominant with increased proppant mass loading that is augmented by increased grain size. Long-wavelength fracture undulations may engage at large shear displacements, causing increased frictional resistance—identifying an intrinsic-scale effect. The presence of proppant reduces the shear dilation. Thus, the convolved interactions between proppant and fracture roughness require careful assessment in their impact on creating and sustaining permeability and modes of aseismic versus seismic ruptures. Highlights: Frictional behavior systematically transitions from fracture-dominated to proppant-dominated response as proppant mass loading increases. Proppants promote ductile shear failure that is exacerbated by increased proppant mass loading and increased grain size. The transition of frictional behavior caused by proppant could impact permeability and stability of the stimulated fractures. [ABSTRACT FROM AUTHOR]

Proppant transport is critical in hydraulic fractures and enhanced geothermal systems. Proppant transport is essentially a dense granular flow in narrow slots, and the Euler–Euler methods are commonly used to study the principle of proppant transport at the field scale. However, the simulated results cannot reproduce the laboratory observations well because some closure equations are not suitable for describing the quasi-static state of proppants after settlement, and only monodisperse granular flow is considered in simulations, which neglects the interaction between large and small particles. To improve the applicability of the numerical simulation of proppant transport in hydraulic fracturing treatment, binary-size proppant transport numerical simulations using the Eulerian multifluid method (EMM) are performed in this study. First, the motion characteristics of the suspended and settled proppants were analyzed using the kinetic theory of granular flow (KTGF) and the frictional theory of viscous particles. Thereafter, the solid–liquid momentum exchange considering the wall retardation effect and the solid–solid momentum exchange considering the endurable contact among the particles are discussed. Finally, the numerical results are qualitatively and quantitatively verified using proppant transport experiments and particle image velocimetry tests. The combination of traditional KTGF models and frictional models exhibits better performance than the modified KTGF models when considering the inertia flow regime in the proppant transport simulation, and the contribution of viscous-particle cohesion to friction must be considered. Notably, the simulated results are close to the experimental results for the development process of sand banks and the velocity distribution of particles. This verified method is efficient in computing and it will provide new insights into the pumping procedure design for hydraulic fracturing. [ABSTRACT FROM AUTHOR]