In this work, we used a grain-based numerical model based on the concept of lattice. The modelling was done to simulate the lab experiments carried out on the mortar samples. Also the analytical solutions corresponding to the viscosity-dominated regime were used to estimate the Fracture length and width, and the results obtained were compared with the numerical simulations. As the analytical solutions are proposed for a penny-shaped Fracture with no presence of any obstacle such as natural interfaces, in this work, we presented the results of lattice simulations for Hydraulic fracturing in the cement sample, similar to the lab, but with no natural Fractures, and compared the results obtained with analytical solutions. The results indicated that in the case of a continuous medium, the analytical solutions may present a reasonable estimation of the Fracture geometry. Also the viscosity-dominated leak-off model showed a better match between the analytical solutions and the numerical simulation results, confirmed by observing fluid loss into the sample in the lab post-experiment. In the case of assuming leak-off, the results indicated that the Fracture width and length would reduce. However, it should be noted that in real cases, rock formations exhibit Fractures and inhomogeneity at different scales so that the applications of the analytical solutions are limited.

According to increasing demand of the country for more production rates and output from oil reservoirs, it's necessary to re-activate the oil wells in Iran. Oil production in overtime Reduces, The reason of this event is decreased reservoir's Pressure and Closure the cracks and microscopic holes. Hydraulic Fracture as a method for stimulating oil reservoirs related to various factors including the characteristics of the environment which the Fracture grows. Mechanical properties of the layers recognized as the one of the most effective parameters on the progress of Hydraulic Fracture and its geometry. In this study, we try to indagate the various factors involved in Hydraulic Fracture and the effect of each of them on Hydraulic Fracture until reduce both operation costs and better and more efficient failure. In this research, numerical modeling was done by ABAQUS software in 10 different cases and then, the effect of the each input parameters on the Hydraulic Fracture pressure was investigated by performing sensitivity analysis. Actually these input parameters are well's data and including Young's modulus, minimum and maximum horizontal stress, vertical stress, tensile strength, poison’ s ratio and pore pressure. Required information is obtained from excavated wells in carbonate rocks in Iran. The results show's minimum horizontal stress has the most effect on the Hydraulic Fracture pressure and parameters such as vertical stress and Young's modulus are not effective in determination of Hydraulic Fracture pressure.

The effectiveness of Hydraulic fracturing fluid injection is influenced by numerous factors, including pre-existing discontinuities such as discrete Fracture networks (DFNs). Among the geometric characteristics of DFNs, Fracture density is a critical factor. In deep reservoirs, which often consist of hot dry rock (HDR), thermal conduction through the rock and fluid, as well as advection and convective heat transfer within the fluid, can significantly impact fluid–rock interactions. This study examines the influence of DFN density on Hydraulic Fracture ((HF)) propagation in HDR, with a particular focus on the thermo-hydro-mechanical (THM) behavior of HDR using the combined finite-discrete element method (FDEM). Key controlling factors, such as flow rate, fluid kinematic viscosity, in-situ stress magnitude, pre-existing Fracture aperture, and working fluid temperature, are analyzed. The findings highlight the significant role of DFN density in determining the pattern and extent of (HF) propagation under varying conditions. Additionally, the interaction between the working fluid and DFNs is shown to vary considerably with changes in these controlling factors. However, the study reveals that variations in DFN density or the values of the controlling factors have minimal impact on the temperature field. This is attributed to the rapid heat exchange between the cold fluid and the HDR, which quickly raises the fluid temperature, resulting in negligible temperature variations.

Fluid flow in a jointed rock mass with an impermeable matrix is often controlled by joint properties, including aperture, orientation, spacing, persistence, etc. On the other hand, since the rock mass is made of heterogeneous and anisotropic natural materials, the geometric properties of joints may possess dispersed values. One of the most powerful methods for simulation of the stochastic nature of joins geometric characteristics is three dimensional stochastic discrete Fracture network (DFN) modelling. The main goal of this research is development of a method and an instrument for Hydraulic analyses of complicated DFN. For this purpose, DFN-FRAC3D program – which has been proposed for mechanical analyses – was developed to construct a Hydraulic DFN. The joint aperture parameter was added to other geometric features of the model and to increase the accuracy, the correlation between the joint aperture and the length was considered. In addition, the program was developed for detecting the connected joint networks. In the next step, the connected joint networks were converted to equivalent pipe networks. Finally to study the fluid flow within this network, WaterGEMS, a Numerical software for flow modeling, was used that had the capability to make complex pipes and to receive other Hydraulic information. In order to test the performance of the provided program, a 3D Hydraulic model was presented for Fractured networks of the rock mass in the Mazino region. It can be concluded that in the case of executing the Underground Coal Gasification panels in the Mazino coalmine of Central Iran, the resulting gases will not leak to the ground.

Hydraulic fracturing is one of the most well-known methods in stimulation and enhanced recovery in oil and gas reservoirs. Determination of propagation path of Hydraulic Fractures ((HF)s) and created Fracture network have a dominant role in increasing permeability of the reservoir. Reservoirs contain many natural Fractures (NFs). Understanding the interaction behavior of the (HF) and NFs controls the Fracture network created by the (HF) propagation. In this paper, a higher order displacement discontinuity method is uaed, the numerical model is verified by several analytical well-known problems in Fracture mechanics. Three main behaviors may be named for the interaction of (HF) and NFs i.e. arrest, crossing, and opening. Two well-known interaction criteria are introduced. Then an algorithm is introduced to determine interaction of (HF) and NF. The algorithm and its implementation in a numerical model were tested against experimental results. Using higher order displacement discontinuity method the interaction of (HF) and NFs is investigated in various conditions. Results showed that the possibility of crossing for higher angle of intersection is higher. Also the (HF) energy reduces after each NF crossing. It means that (HF) has lower chance for crossing NFs after previous crosses.

Statement of Problem: In a previous study it was reported that a durable resin-ceramic tensile bond could be obtained by an appropriate silane application without the need for (HF) acid etching the ceramic surface. Evaluation of the appropriate application of silane by other test methods seems to be necessary.Purpose: The purpose of this study was to compare the interfacial Fracture toughness of smooth and roughened ceramic surfaces bonded with a luting resin.Materials and Methods: Ceramic discs of 10 mm in diameter and 2 mm in thickness were prepared.Four different surface preparations (n=10) were carried out consisting of (1) ceramic surface polished to a 1µm finish, (2) gritblasted with 50µm alumina, (3) etched with 10% (HF) for 2 min, and (4) gritblasted and etched. The ceramic discs were then embedded in PMMA resin. For the adhesive area, the discs were masked with Teflon tapes. A circular hole with diameter of 3 mm and chevron-shaped with a 90° angle was punched into a piece of Teflon tape. The exposed ceramic surfaces were treated by an optimised silane treatment followed by an unfilled resin and then a luting resin cylinder of 4mm in diameter and 11 mm in length was built. Specimens were stored in two different storage conditions: (A): Distilled water at 37°C for 24 hours and (B): Distilled water at 37°C for 30 days. The interfacial Fracture toughness (GIC) was measured at a cross-head speed of 1 mm/min. The mode of failure was examined under a stereo-zoom microscope and Fracture surfaces were examined under Scanning Electron Microscope.Results: The mean interfacial Fracture toughness values were; Group A: 1) 317.1±114.8, 2) 304.5±109.2, 3) 364.5±169.8, and 4) 379.4±127.8 J/m2±SD. Group B: 1) 255.6±134.4, 2) 648.0±185.1, 3) 629.3±182.6 and 4) 639.9 ±489.0 J/m2±SD. One way Analysis of Variance showed that there was no statistically significant difference in the mean interfacial Fracture toughness for groups A1-A4 (P>0.05). However, the mean interfacial Fracture toughness for group B1 was significantly different from that for groups B2, B3 and B4 (P<0.05). Independent-ٍٍٍSamples T-Test results showed that there was a significant increase in the GIC mean value for groups B2 and B3 after 30 days water storage (P<0.05). The modes of failure were predominantly interfacial or cohesive within the resin.Conclusions: The Fracture toughness test method used in this study would be appropriate for analysis of the adhesive zone of resin-ceramic systems. From the results, it can be concluded that micro-mechanical retention by gritblasting the ceramic surfaces could be sufficient with no need for (HF) acid etching the ceramic surfaces when an appropriate silane application procedure is used.

In this study, a series of laboratory tests using a real Tri-axial Hydraulic Fracture System were performed to investigate the mechanism of Fracture initiation and propagation on the cement blocks in different reservoirs in normal and tectonic stress regimes. The influences of crustal stress field, confining pressure, and natural Fractures on the Fracture initiation and propagation were discussed. Experimental results demonstrate that stress concentration around the hole would significantly increase the Fracture pressure of the rock. At the same time, natural Fractures in the borehole wall would eliminate the stress concentration, which leads to a decrease about two thirds in the Fracture initiation pressure. Two interaction types between induced Fractures with pre-Fracture were observed including crossing and opening the pre-existing Fracture. In a normal stress regime, Hydraulic Fracture crossed the pre-Fracture. But in tectonically stressed or shallow reservoirs, due to high interaction between Hydraulic and natural Fractures, Hydraulic Fracture was arrested by opening of the pre-Fracture.

In many cases some barriers like low permeability, secondary porosity and decreasing in formation permeability due to damages casued by drilling, asphaltene and other problems confine oil production rate in unacceptable region and These problems reduce percentage of oil recovery from these reservoirs, These problems can be solved by utilizing Hydraulic Fracture method. A new model based on cohesive zone method coupling stress-seepage damage filed is developed to simulate the interaction between Hydraulic Fracture and natural Fracture with using ABAQUS software. The effect of differential stress and approaching angle on the intersection between Hydraulic Fracture and natural Fracture, as well as the effect of natural Fracture cementing strength on the geometry of  Hydraulic Fracture propagation, have been investigated. While the Hydraulic Fracture initiates, propagates, and intersects with the natural Fracture, it can either deflect into it or cross it by severing the natural Fracture. The greater the approaching angle and differential stress , the easier it is for the Hydraulic Fracture to cross the natural Fracture.The behavior of Hydraulic Fracture changes from deflection to crossing as the natural Fracture cementing strength is increased.

Hydraulic fracturing is a new and widely used method for extracting reserves and energy resources in the depths of the earth. In the near future, due to increase in energy consumption on the one hand and depletion of energy reserves on the other, using of this method will become a necessity. One of the most important and effective parameters in this process is the pressure and how it is applied in order to create Fractures and Fracture progression in rock layers. Another important parameter is the interaction between pre-existing natural Fractures with different angles and Hydraulic Fracture.  Due to the high costs of this process, the purpose of this study is to achieve the optimal state for the maximum progress of Hydraulic Fracture and the lowest amount of breakdown pressure at the same time. Numerical modeling was performed in two dimensions by Particle Flow Code ( PFC ) software from Itasca company on samples of Pocheon granite rocks with brittle behavior using distinct element method. PFC software uses circular disks in two dimensions to construct and make the sample using distinct element method. These particles are in contact with each other through bonds. In this program there are walls that interact with these disks to apply load on the sample. The flat joint model is used in order to create contacts between particles, and discrete Fracture network is uded to to create pre-existing natural Fractures for interacting with Hydraulic Fracture. Given that in the distinct element method (PFC software) our sample consists of a large number of particles in two dimensions that the general characteristics of the sample are formed based on the interaction between these particles, so we need parameters as input data to our software, existing disks and the link between them, to finally obtain the specifications of the same laboratory sample after modeling. These specifications and input data are referred to as micro parameters, and the final specifications, which are the same as our mechanical parameters in the laboratory, are referred to as macro parameters. To find the micro parameters of the sample we use the trial and error method. Here, our modeling is based on Brazilian and uniaxial compression experiments and … performed by Zhuang et al. laboratory investigations. Due to the limitations of PFC software for fluid flow modeling and limitations for using of CFD relationships, pressure equals to fluid pressure can be used as a new solution. In this way, by modeling a number of walls that form a complete circle with overlapping each other, and by considering the servo control mechanism, we move them in the opposite direction of their normal vectors and off-center, creating a comprehensive pressure Which is actually same as the fluid pressure. From the obtained results, it was found that with increasing the loading rate, the sample reaches the breakdown pressure and breaks in less time, but the amount of breakdown pressure increases. Also, by increasing the natural Fracture angle relative to the horizon (clockwise), the specimen breaks at a lower breakdown pressure. Finally, by increasing the natural Fracture distance from the center of the sample, the effect of the presence of the joint in the sample decreases and the breakdown pressure approaches the seamless state.

In the process of Hydraulic Fracture, various physical parameters such as; viscosity, inertia of fluid and toughness of rock do not influence the Fracture propagation identically, and it is probable that one or more of the parameters be more pronounced. Therefore, it may persuade one special regime which is named base on dissipation of energy. In an impermeable rock, the two limiting regimes can be identified with the dominance of one or the other of the two energy dissipation mechanisms corresponding to extending the Fracture in the rock and to flow of viscous fluid in the Fracture, respectively. In the viscosity-dominated regime, dissipation in extending the Fracture in the rock is negligible compared to the dissipation in the viscous fluid flow, and in the toughness-dominated regime, the opposite holds. Here, it is supposed that the flow of incompressible fluid in the Fracture is unidirectional and laminar. Besides, the Fracture is fully fluid-filled at all times and Fracture propagation is described in the framework of linear elastic Fracture mechanics (LEFM). In this paper, a new semi-analytical method has been introduced for solving the plane-strain fluid-driven Fracture propagating in an impermeable medium in viscosity-toughness dominated (the MK-edge solution). Standard methods of analysis and improvement of diverging series have been applied on the expansion series method to gain the more convergence for the viscosity series diverge due to a nearest (non-physical) singularity on the negative real axis of the viscosity parameter for larger viscosity. For more explanation, Euler transformations have been suggested in terms of small parameter which is a function of viscosity parameter. Compared to the other analytical solution (e. g. Garagash, 2006), the new M-K edge solution represents a significant improvement in term of convergence. In addition to, the results have been compared to the numerical solution (e. g. Adachi, 2000) and it is shown good agreement in the light of quantity and quality. Contrary to numerical methods, the new proposed method can pragmatically be used for the range of M-K edge.