Proppant In Hydraulic Fractures Research Articles

Numerical Calculation Method of Key Performance Parameters of Proppant Based on 2D Computer Simulation

The key performance parameters of proppant are mainly the crushing rate and fracture conductivity, which are usually evaluated using physical experimental methods. However, the testing method for fracture conductivity has limitations, such as its long time-consumption, high testing costs, instability, and even the presence of large errors in testing results under the same conditions. The purpose of this paper is to propose a calculation method that can replace physical experiments. Firstly, we analyze the random and deterministic phenomena in the contact relationship between proppant particles from a microscopic perspective. Subsequently, we develop a physical model of the microscopic arrangement of these particles, enabling us to conduct further computer simulations of their microscopic configuration. Secondly, we conduct a microscopic mechanical analysis of the contact between proppant particles and between particles and boundaries and establish a corresponding mathematical model. Then, utilizing the simulation and mechanical analysis results of the proppant, we calculate the crushing rate. Considering the crushing rate of proppant, we improve the Kozeny–Carmen equation to determine the fracture permeability, and subsequently calculate the fracture conductivity. Finally, the calculated results are compared with the experimental results. The results show that the calculated values for the proppant crushing rate and fracture conductivity matched well with experimental data, and that the model’s calculation values were more accurate. As the number of simulations increased, the accuracy of the calculation results became higher. Research shows that the fracture conductivity is influenced by factors such as the particle size, microstructure, and crushing rate. Numerical calculation methods can replace physical experiments and provide theoretical support for engineering applications of hydraulic fracturing proppant materials.

Numerical simulation study on the ultimate injection concentration and injection strategy of a proppant in hydraulic fracturing

The injection volume and the distribution of a proppant inside a fracture have a direct impact on the stimulation effect of fracturing. In this study, a new proppant transport model was established based on the Euler method. In this model, the proppant plugging element allows fluid to pass through. Furthermore, the proppant plugging process was successfully simulated based on this model. The proppant transport and ultimate injection concentration under different injection modes were discussed. The numerical simulation results indicate that compared with the strategy of constant concentration, the strategy of a stepwise increasing concentration can make the proppant distribution in the fracture more uniform. The strategy of injection with a stepwise increasing concentration and a periodic injection with a stepwise increasing concentration can increase the injection volume of the proppant by 25%. In the fracture network, a 67% increase in the number of branch fractures resulted in a 17% increase in the maximum proppant injection volume. If the branch fracture width is reduced by 50%, the maximum proppant injection volume is reduced by 17%.

Physical Simulation Experiments of Hydraulic Fracture Initiation and Propagation under the Influence of Deep Shale Natural Fractures

Horizontal wells’ multi-section and multi-cluster hydraulic fracturing plays an important role in the efficient development of shale gas. However, the influence of the perforating hole and natural fracture dip angle on the process of hydraulic fracture initiation and propagation has been ignored in the current researches. This paper presents the results related to a tri-axial large-scale hydraulic fracturing experiment under different natural fracture parameters. We discuss the experimental results relating to the near-wellbore tortuosity propagation of hydraulic fractures. Experimental results showed that the triaxial principal stress of the experimental sample was deflected by the natural fracture, which caused significant near-wellbore tortuosity propagation of the hydraulic fractures. The fractures in most rock samples were not perpendicular to the minimum horizontal principal stress after the experiment. As well, the deflection degree of triaxial principal stress direction and the probability of hydraulic fractures near-wellbore tortuosity propagation decreased with the increase of the natural fracture dip angle. After hydraulic fractures’ tortuous propagation, the hydraulic fractures will propagate in the direction controlled by the triaxial stress in the far-wellbore area. For reservoirs with natural fractures, proppant in hydraulic fracturing should be added after the fractures are fully expanded to prevent sand plugging in tortuous fractures. When the permeability of natural fractures is low, the volume of fracturing fluid entering natural fractures is small, and hydraulic fractures are easy to pass through the natural fractures.

Experimental Study for the Effects of Different Factors on the Sand-Carrying Capacity of Slickwater

With the continuous exploration and development of unconventional oil and gas reservoirs, volume fracturing technology becomes one of the necessary measures for developing shale gas and tight sandstone gas reservoirs effectively. Volume fracturing technology usually uses slickwater and drag-reducing agent as the core of the fracturing system. The composition of the fracturing system is the main factor determining its performance. Polyacrylamide has many amide groups in its main chain, high activity, and controllable performance, often in solid powder and liquid emulsion states. Furthermore, polyacrylamide which is the water-soluble drag-reducing agent is most widely used in applying current shale gas slickwater fracturing operations. Due to the low viscosity and poor sand-carrying capacity of slickwater, proppant easily settles at the bottom of hydraulic fractures. This phenomenon influences the stimulation effect of volume fracturing. Therefore, the law of sand carrying and placement of proppant in hydraulic fractures in volume fracturing plays an essential role in determining the success of the stimulation effect of volume fracturing. Through the visualization device of proppant transport in the fracture, the settlement of proppant in the fracture was studied experimentally. And through experimental equipment, the effects of different operation pumping rates, liquid viscosity, proppant type, and proppant pumping schedule on the stimulation effect were studied. The experimental results can provide strong support for volume fracturing into well material optimization and operation parameter optimization for unconventional oil and gas reservoirs.

Insight into thermo-mechanical enhancement of polymer nanocomposites coated microsand proppants for hydraulic fracturing

The present work reports the fabrication of ultra-high strength microsand proppants (100 mesh) through a polymer nanocomposite dual coating approach and gives insight into their thermo-mechanical reinforcements. The dual coating can be of 3D-cross-linked poly(styrene-methyl methacrylate)/divinylbenzene) (PS-PMMA/DVB) porous network and thermally cross-linked epoxy with graphene nanosheets. The inner layer of PS-PMMA/DVB was prepared using bulk polymerization of styrene (S) and methyl methacrylate (MMA) at 70 °C with a free radical initiator azobisisobutyronitrile (AIBN). The outer layer was prepared by mixing epoxy resin, a cross-linker, and commercial graphene (CG) followed by thermally curing the mixture. The dual-coated microsand proppants exhibited enhanced mechanical characteristics of elastic modulus (E) as high as 7.78 GPa, hardness (H) of 0.35 GPa, and fracture toughness (Kc) of 3.19 MPa m1/2 along with largely improved thermal properties. Moreover, the dual-coated microsand proppants exhibit a very high-stress resistance up to 14000 psi, and to the best of our knowledge, this is the highest stress resistance value attained for the modified sand-based proppants so far.

Numerical simulation of multi-cluster proppant distribution in horizontal wells

For the staged multi-cluster fracturing of horizontal wells, the distribution of fracturing proppant inside different perforations directly affects the placement of proppant in the fracture, which in turn affects the fracturing performance. In order to study the distribution law of fracturing proppant among different perforation clusters along the horizontal wellbore with different influencing factors, we simulate the distribution state of fracturing proppant inside the different perforation clusters over the hydraulic fracturing process by using the Euler-Eulerian method-based computational fluid dynamics (CFD) model. We obtain the distribution law of the proppant among the perforation clusters under different conditions. The simulation results show that the proppant concentration in the bottom perforation is higher than that in the top perforation due to the influence of gravity; while the viscosity of fracturing fluid increases from 5 mPa·s to 100 mPa·s, the concentration difference of proppant in different perforation clusters decreases, which promotes the uniform distribution of proppant among clusters; while the flow rate of fracturing fluid increases from 4.3 m/s to 10.6 m/s, the difference of proppant concentration in different perforations increases, but it is beneficial to the uniformity of proppant distribution in the same perforation cluster; when the proppant density is increased from 1.50 × 10³ kg/m³ to 3.00 × 10³ kg/m³ and the proppant particle size is increased from 150 μm to 600 μm, the settling rate of proppant is accelarated, the concentration difference of proppant in different perforation clusters is increased, which affects the uniform distribution of proppant among clusters. The findings of this work can be used to guide the design of hydraulic fracturing proppant addition.

Experimental investigation on proppant transport and distribution characteristics in coal hydraulic fractures under true triaxial stresses

Fracturing is one of the key technologies for unconventional oil and gas production. However, the closure stress will cause the hydraulic fractures to close, and proppant is often injected into the fracture to maintain the effective conductivity of the fractures for a long time. The proppant distribution in the fractures is one of the key factors affecting the efficient exploitation of unconventional natural gas. However, there are few studies on the proppant transport and distribution characteristics in the real hydraulic fractures. A self-developed high-pressure sand injection triaxial hydraulic fracturing experimental system was used to study the proppant migration and distribution in hydraulic fractures. The results show that the proppant migration process mainly includes four stages: water filling stage, fracture reopening stage, proppant transport stage, and pressure relief stage. The basic characteristics of proppant transport in horizontal fractures is mainly along slope gradient transport or dispersion, and reverse slope gradient or low valley deposition. The sedimentary areas mainly include peak climbing deposition, ring peak deposition, and convection-diffusion deposition. The surface roughness of horizontal fractures is one of the key factors affecting the proppant transport and distribution. The fracture inlet roughness determines the proppant transport direction, and the overall roughness of the fracture surface determines the proppant distribution form. The proppant deposition is the most in the open hole parallel area, followed by the sealed hole parallel area in vertical fractures. The stress concentration at the hole bottom forms horizontal wing branch fractures, and a little proppant is deposited in the fractures. Generally, the stress required for proppant transport in horizontal fractures is smaller than that in vertical fractures. The findings of this study can help us better understand the migration and distribution of proppant in hydraulic fractures, and provide theoretical guidance for the efficient exploitation of unconventional natural gas.

Characterisation of graphene oxide-coated sand for potential use as proppant in hydraulic fracturing

Characterisation of graphene oxide-coated sand for potential use as proppant in hydraulic fracturing

Investigating the Impacts of Nonuniform Proppant Distribution and Fracture Closure on Well Performance in Shale Gas Reservoirs

The nonuniform distribution of proppant in hydraulic fractures is an essential factor determining the accuracy of well performance evaluation in shale gas reservoirs. In particular, unpropped and propped parts hold distinct closure behavior. To study the impacts of distinct closure behavior between unpropped and propped parts in fracture on gas production, we combine the proppant transport simulation and the 3D hydromechanical coupling simulation. This study quantitatively indicates the significant effects of nonuniform proppant distribution and fracture closure on well performance in shale gas reservoirs. By comparing the well performances with three kinds of typical proppant distribution at the same injection volume, the distribution accumulating near the wellbore is recommended as it can reduce the impact of unpropped fracture and exploit more gas. In addition, the cases with higher natural fracture permeability are found to have less difference in the well performance with different proppant coverages. Therefore, the impacts of nonuniform proppant distribution and fracture closure on well performance in shale gas reservoirs should be investigated comprehensively.

Utilizing Ultrasonic Waves in the Investigation of Contact Stresses, Areas, and Embedment of Spheres in Manufactured Materials Replicating Proppants and Brittle Rocks

In the oil and gas industry, hydraulic fracturing (HF) is a common application to create additional permeability in unconventional reservoirs. Using proppant in HF requires understanding the interactions with rocks such as shale, and the mechanical aspects of their contacts. However, these studies are limited in literature and inconclusive. Therefore, the current research aims to apply a novel method, mainly ultrasound, to investigate the proppant embedment phenomena for different rocks. The study used proppant materials that are susceptible to fractures (glass) and others that are hard and do not break (steel). Additionally, the materials used to represent brittle shale rocks (polycarbonate and phenolic) were based on the ratio of elastic modulus to yield strength (E/Y). A combination of experimental and numerical modeling was used to investigate the contact stresses, deformation, and vertical displacement. The results showed that the relation between the stresses and ultrasound reflection coefficient follows a power-law equation, which validated the method application. From the experiments, plastic deformation was encountered in phenolic surfaces despite the corresponding contacted material. Also, the phenolic stresses showed a difference compared to polycarbonate for both high and low loads, which is explained by the high attenuation coefficient of phenolic that limited the quality of the reflected signal. The extent of vertical displacements surrounding the contact zone was greater for the polycarbonate materials due to the lower E/Y, while the phenolic material was limited to smaller areas not exceeding 50% of polycarbonate for all tested load conditions. Therefore, the study confirms that part of the contact energy in phenolic material was dissipated in the plastic deformation, indicating greater proppant embedment, and leading to a loss in fracture conductivity for rocks of higher E/Y.

Prediction of the settling velocity of the rod-shaped proppant in vertical fracture using artificial neural network

As a new technology proppant, rod-shaped proppant is receiving more and more attention because it can greatly improve the performance of hydraulic fracturing. With special shape, the rod-shaped proppant is subject to greater flow resistance, resulting in complex migration in fractures. Accurate prediction of the settling velocity of rod proppant in fracture is important for predicting the transport distance and bed height of rod proppant in hydraulic fractures to improve the fracture performance. In this study, high-speed photography and transparent parallel plates were used to simulate and record the settling process of proppant in vertical fractures. A total of 588 effective tests were conducted to reveal the influence of proppant shape, fracturing fluid properties, and the wall effect of fracture on the settling characteristics involving the range of proppant aspect ratio and Reynolds number are 1.5–5.0 and 0.001–172.54, respectively. It was found that the rod proppant settled vertically at the low Reynolds number and horizontally at the high Reynolds number. First, an artificial neural network model of settling orientation with the prediction accuracy of 100% is established as the basis for predicting settlement velocity. The topological structure of the neural network is further extended to establish the prediction model of settling velocity with mean relative error of 1.21%. The relative importance of each input factor to the settling velocity was analyzed by the connection weights algorithm, and the weight and bias of the neural network are provided for the application and generalization of the model. Finally, the neural network model is evaluated objectively by comparing with the mathematical model. This study is a successful exploration of artificial intelligence in particle migration and will provide guidance for improving the performance of rod proppant in hydraulic fracturing.

Parameters affecting the distribution of pulsed proppant in hydraulic fractures

Intermittent proppant injection into hydraulic fractures is a newly-developing technology in well stimulation. It is designed to form voids inside proppant packs which serve as highly conductive channels for oil and gas transport. However, it remains unclear the extent to which this non-homogeneous, pulse-like proppant concentration persists over the extent of the fracture. This paper models proppant transport in a PKN (Perkins–Kern–Nordgren) fracture in which the proppant-laden and proppant-free fluids are pumped intermittently. Simulations are performed to investigate proppant transport and final distribution under the influence of various factors. It can be observed that several parameters such as Young's modulus and fluid injection rate have significant influence on proppant transport, particularly the spatial period and attenuation of the resulting waves of proppant concentration as they move into the growing fracture. In contrast, when fluid viscosity is high, some parameters such as density difference, particle size do not strongly affect spatial period and attenuation of the proppant waves. The simulations show when the proppant is injected intermittently using high viscosity fracturing fluid, proppant concentration inside a hydraulic fracture from wellbore bottom hole to fracture tip is non-uniform and appears like a damped wave. An equation which is similar to damped wave solution is used to describe this proppant concentration characteristic, thus enabling a dimensional analysis to identify the key parameters affecting proppant distribution and specifically the attenuation of the concentration waves. Two characteristic lengths can be associated with attenuation of these proppant waves prior to severe screen-out and settlement– one for cases with leakoff and one for cases without leakoff. After scaling the horizontal coordinate by the appropriate characteristic length, the relationship between concentration amplitude and dimensionless distance for all cases can be depicted in a uniform way.

Quantifying the Economic Impact of Hydraulic Fracturing Proppant Selection in Light of Occupational Exposure Risk and Functional Requirements.

Selection of an effective and economic proppant material for hydraulic fracturing is an important design choice to optimize the production of oil and natural gas. Proppants are made of silica (quartz sand), alumina, resin-coated silica, ceramics, and others. These materials can be toxic to varying degrees and lead to health problems in the employees handling them primarily due to inhalation exposure. Proppants are selected based on grain size, shape, strength, and cost. Current use is dominated by crystalline silica-the proppant that also has the greatest hazard as an inhalation toxin. Existing research describes the effect of silica on human health, but little research has been done to determine the risk-reduction and social-cost-effectiveness associated with using alternative proppants in light of the health risks. This study quantifies the relative risks or benefits to human health by the use of these proppants through an economic analysis considering the health-related economic impact and its technical attributes. Results show that the use of each ton of silica proppant results in $123 of external costs from fatalities and nonfatal illness arising due to exposure to silica for a crew handing 60,000 tons of proppants. If these health-related externalities were incorporated into the cost, silica proppant could be economically replaced by less harmful, more expensive alternatives for hydraulic fracturing crews handling less than 60,000 tons of proppant each year.

Experimental study on the wall factor for spherical particles settling in parallel plates filled with power-law fluids

Hydraulic fracturing is a widespread stimulation technology in the petroleum industry. The retardation due to the fracture wall existence impacts the efficient placement of the proppant in fractures. Accurate prediction of the wall factor for proppant settling in fractures filled with Power-law fluids is important in predicting the transport distance and bed height of proppant in hydraulic fractures. However, few studies were conducted to analyze the wall factor of fracture on the settling proppant. In this study, a set of transparent parallel plates and a high-speed camera were used to record the settling behaviors of the proppant in the fracture. A total of 756 tests were carried out to analyze the effects of fluid properties, the dimensionless diameter, particle size, particle density, and the particle Reynolds number on the wall factor, involving the ranges of the dimensionless diameter and the particle Reynolds number are 0.04–0.9 and 0.0001–144.25, respectively. Results indicate that the wall factor is a function of both the dimensionless diameter and the particle Reynolds number. And a new model with 1.23% relative error was developed to predict the wall factor of the parallel plates on the spherical particles settling in the Power-law fluid. Finally, it was found that the wall effect vanishes when the dimensionless diameter is smaller than 0.057. The results of this study could help field engineers optimize proppant size and fracturing parameters.

Fabrication of Low-density Heat-Resistance Polystyrene/Carbon Black Composite Microspheres Used as Hydraulic Fracturing Proppant

Fabrication of Low-density Heat-Resistance Polystyrene/Carbon Black Composite Microspheres Used as Hydraulic Fracturing Proppant

Characteristic and Erosion Study of Uncoated Sand Proppant Using Impingement Test

The characterization and properties of sand from beaches in Malaysia that has potential to be used as proppant in hydraulic fracturing was investigated through impingement tests. Eight sand samples were obtained from eight different locations in Malaysia; three samples from West Coastal beaches (Selangor) and five from East Coastal beaches (Kelantan). These impingement tests were conducted by varying several parameters i.e. size ranges of sand, type of targeted metal and distance of nozzle standoff from target. In these tests, air was fed through an acrylic pipe with inner diameter of 8 mm and 4 m length at gas velocity of 100 m/s and flow rate of 200 l/min. 250 g of sand samples were fed in compressed air stream and the samples were projected toward targeted metal i.e. mild steel and aluminium with a 90° of impingement angle. These tests were conducted at different separation distance of 0.5, 2.5 and 5.0 inches of nozzle and target. The results were analysed by measuring the mass loss of the metals after impingement and the images of the impinged metals were captured using camera. The highest metal loss was obtained when the targeted metal was impacted with the largest size range of sand samples. The mass loss of mild steel ranged from 0.03 to 0.16 g and 0.10 to 0.22 g for aluminium, at a variable distance between the nozzle and metal target due to higher hardness of mild steel than aluminium. The mass loss reduced when the distance between nozzle and metal target increased due to energy loss because of the inter particle collision.

Numerical modeling of porous ceramics microstructure

The presented research is directed to the porous ceramics microstructural behaviour assessment with the use of numerical methods. Such new material can be used for thermal insulation, filters, bio-scaffolds for tissue engineering, and preforms for composite fabrication. One of the newest and most interesting applications, considered in this work, is a usage of those materials for production of proppants for hydraulic fracturing of shale rocks. The hydraulic fracturing is a method of gas recovery from unconventional reservoirs. A large amount of fracturing fluid mixed with proppant (small particles of sand or ceramics) is pumped into the wellbore and its pressure causes the rock cracking and gas release. After fracturing the fluid is removed from the developed cracks leaving the proppant supporting the fracture. In the paper the grain porous ceramics which is used for proppant particles preparation was studied. The influence of grains distribution on the porous ceramics mechanical behaviour during compression was simulated with the use of finite element method.

Modeling of Low-Frequency Downhole Electrical Measurements for Mapping Proppant Distribution in Hydraulic Fractures in Casedhole Wells

Summary A tool concept using downhole electrical measurements for mapping electrically conductive proppant in hydraulic fractures is presented in this paper. The method relies on direct excitation of the casing, which is expected to overcome the severe limitations of induction tools in casedhole wells. An array of insulating gaps is installed and cemented in place as a permanent part of the casing string. The envisioned electrical measurements are performed by imposing a voltage across each insulating gap, one at a time, before and after hydraulic-fracture operations. The voltages across other insulating gaps near the transmitter gap are recorded. The proposed tool's response to the geometry of a single fracture was modeled by solving for the electrical potential with a finite-volume method. Previous simulation results have shown that the electrically conductive proppant alters the path of the electrical current in the formation, and this is recorded as differential signals by the string of insulating gaps surrounding the source gap. The simulated differential signals are highly sensitive to a fracture's location, length, and orientation, and less sensitive to the fracture's aspect ratio. However, to enable the implementation of such a practical system, various aspects of the tool concept must be investigated further through simulations. Following our previous work, this paper focuses on the forward modeling of the tool's response to multiple fractures, which demonstrates the influence of these fractures on the signals, and provides important guidance for inverse modeling. Parametric inversion of fractures from synthetic data, generated by exciting various insulating gaps, is solved with very fast simulated annealing (VFSA). Simulation results show that, when multiple hydraulic fractures are present, the voltages measured at the receiver gaps are determined primarily by the fracture that is in direct contact with the excited section of casing. When two fractures touch the same casing section, they induce voltages very similar to those from a single fracture with the same conductivity and volume. Preliminary inversion results that use synthetic data computed from circular fractures indicate that the proposed VFSA can solve for the multiple fractures’ widths and radii at the same time, without requiring numerous forward simulations. Even with noisy synthetic data, VFSA can make good estimates of the fractures’ parameters. This indicates that the VFSA technique is a proper and robust inversion technique for the measured voltages at various receiver gaps.

Experimental characterization of a new high-strength ultra-lightweight composite proppant derived from renewable resources

Significant improvement in strength in ultra-lightweight (ULW) proppants without sacrificing the specific weight means conductivity endurance in Hydraulic Fracturing (HF). This paper includes a study on experimental characterization of a new Chemically Modified and Reinforced Composite Proppant (CMRCP), which derived from renewable resources. The CMRCP is basically comprised of an organic substrate such as coconut shell or any other nutshells that reinforced with a natural fiber and outer coated with resin or phenolic. For characterization purpose, Microscopic Characterization (FESEM and SEM) and XRD were used to investigate the microstructure and the elements of the CMRCP, and Thermo Gravimetric Analysis (TGA) to determine the range of temperature degradation. Other characteristics envisaged are roundness and sphericity, specific gravity, bulk density, turbidity, crush resistance and fracture conductivity. The developed CMRCP shows promising results and meet the established API/ISO standards. The low specific gravity, high values of roundness and sphericity, low bulk density, low acid solubility, high crush resistance, and low turbidity of the CMRCP have qualified it for possible use as ULW proppant in HF. The results of physical tests are compared with other proppants and fracture conductivity is compared to the commonly known walnut hull-based proppant (i.e., ULW-1.25). Results show that the tolerable pressure of the CMRCP are much higher than its counterpart product.

Preparation of a Ceramic Proppants for Hydraulic Fracturing Using F – Type Fly Ash

Preparation of a Ceramic Proppants for Hydraulic Fracturing Using F – Type Fly Ash