جستجوی مقالات مرتبط با کلیدواژه « Hydraulic Fracturing » در نشریات گروه « مهندسی معدن »

Considering the extent of unconventional gas reservoirs and the exigency of optimal production from these resources, the design of hydraulic fracturing operation according to the geomechanical aspects is the most important step in the exploitation of these resources. Oil and gas sources differ from each other in many aspects, such as the shape of source and reservoir rocks, mechanisms of formation, penetration, distribution and occurrence. Unconventional reservoirs are resources that cannot be exploited economically with conventional resource extraction methods.

Methodology and Approaches:

Before drilling, the reservoir is in equilibrium, and no special stress causes the reservoir to collapse, but after the drilling operation, stresses are applied to the reservoir as induced stresses, which cause the loss of balance and instability in the wellbore. In this regard, the greater the distance from the center of the well, the stresses will decrease. Knowing the direction of minimum and maximum horizontal stresses helps engineers to predict the possibility of casing collapse.

Due to the low permeability of the unconventional gas reservoirs to achieve optimal production from these sources, geomechanical parameters are of particular importance. To increase production from these sources, one of the most widely used operations worldwide is a hydraulic fracture. One of the important components in studying the propagation of hydraulic fissures is the difference in horizontal stresses. According to what has been obtained based on geomechanical studies in Roseneath and Murteree formations, for reservoir rocks with low horizontal stress such as sandstone reservoirs, the fracture pressure of the formation is much lower. However, the shale reservoir with more horizontal stress has more failure pressure and the fracture in these reservoirs has less expansion. On the other hand, studies in the Montney Formation indicate that Poisson's ratio and Young's modulus affect the characteristics of shales such as their fragility. In this regard, a formation with a lower Young's modulus is more difficult to fracture and is not considered a suitable option for hydraulic fracturing operations.

According to the results, as the injection duration and the pumping rate increase, the fracture length increases and the maximum length created is about 22 meters by applying a fluid with a viscosity of one centipoise during 5 minutes injection time and the rate of 35 barrels per minute or similarly by the same fluid with 18 minutes injection time and the rate of 10 barrels per minute. 

Hydraulic fracturing if properly implemented can be one of the least costly ways to increase the maximum production of the reservoir. Due to the complexity of the hydraulic fracturing process, various modeling has been performed to find the closest predictions of the actual fracture characteristics. Linear elastic fracture mechanics (LEFM), adhesion zone method, and plastic criteria can be used to evaluate the fracture onset time and its expansion in rock. 

To investigate the effect of injection duration on fracture growth, fluid was injected into the well with a viscosity of 1 cp and an injection rate of 0- 10 barrels per minute for periods of 5, 8, 10, 12, 15, and 18 minutes. This injection is made by drilling a well in the middle part of the reservoir. In the first 5 seconds, the injection rate increases linearly from zero to 0.07 barrels per minute and remains constant until the end of injection time. This distribution of injection rate over time is chosen to avoid sudden pressure. As the injection begins, the fluid pressure within the fracture increases, and as the fracture pressure is reached, fracture occurs. 

The purpose of designing hydraulic fracturing operations is to make some predictions to optimize these operations. There are five important factors to design for a hydraulic fracture: the length, height, and fracture opening that the propane holds, the fracture initiation pressure, and the fracture orientation. Four of these critical parameters are derived from hydraulic fracture modeling, so modeling provides 80% of the required solutions.The main input parameters for modeling hydraulic fractures are surface stresses, pore pressure, Young's modulus, Poisson's coefficient, porosity, permeability, angle of friction, and rock adhesion, and parameters related to rock fracture mechanics such as fracture energy, toughness, and components. As the injection duration and pumping rate increase, the fracture length increases, and the maximum length created for a fluid with a viscosity of one centipede at an injection of 5 min at 35 barrels per minute or 18 min at 10 barrels, is about 3 meters high while its maximum height is about 70 meters. Also, the maximum fracture opening in its opening is about 1 mm. Fluid viscosity affects the fracture width more than its length and also increases with the fracture width viscosity.

Given the high importance of hydraulic failure in the oil and gas industry in order to stimulate and increase the capacity of oil reservoirs, the analysis of crack propagation in these environments during this process is very important. Although the amount of porosity in such reservoirs may be low, but these porosities and cracks, are considered as weaknesses and discontinuities of the environment and a determining factor in the number and propagation path of the cracks. In the present paper, using the linear elastic fracture mechanics, initiation, propagation and spread of cracks in porous samples are modeled by the finite element method (XFEM) developed in Abacus software, based on the criterion of the maximum principle stress and the criterion of independent of the failure. In order to validate the proposed method,, the results were compared with the KGD method and with an error of 0.04% in the maximum crack opening size and 4.87% in the maximum crack length, an acceptable agreement was obtained. The results showed that the use of spring elements as elastic support to simulate the elastic properties of the environment can be useful and effective. The hydraulic fracture modeling process is performed on microscopy-CT scan images of three real sandstone samples and the crack growth path is analyzed. Also, the amount of energy absorbed per unit length in each sample is calculated and the final path of crack propagation with increasing injection pressure is presented. Then, by calculating the percentage of empty space before and after failure in each sample, absolute and relative failures in each case are calculated and the results are compared with each other. The results show that due to compression and reduction of porosity, the absorbed energy per unit length decreases and a lower level of the sample is affected by hydraulic failure.

Hydraulic fracturing based on the use of guar gum water-base fluid with appropriate viscosity has been recognized as a viable solution for extracting oil and natural gas from the reservoir due to its unique benefits such as low cost and proppant carrying capacity. However, the lack of knowledge of reservoirs fractures has challenged field applications. Therefore, the purpose of this study was to investigate the effect of fluid injection rate on fracture pressure and geometry of fractures. To achieve this goal, a series of hydraulic fracturing experiments were performed on limestone rock samples using a guar gum water- base fluid. To investigate the effect of fluid injection rate, CT scan technology was also used to describe the geometric parameters of the fracture. The results of experiments show that with increasing fluid flow rate injected from 1 to 6 ml/min, breakdown pressure and fracture opening increase. As the volume of consumed fluid increases the breakdown time decreases. The findings of this study reveal that low guar gum-flow rates can create a better inter- connected fracture network than higher flow rates.

Hydraulic fracturing defined as a process in which a hydraulic loading caused by fluid injection in a part of wells result fracture propagation in the rock. The main purpose of this research is simulation of hydraulic fracturing based on the concepts of Finite Element Method (FEM) and parameters affecting it. For this goal, ABAQUS software has been used to examine hydraulic fracture initiation pressure in a simulated petroleum reservoir in which the cohesive elements theory with traction-separation law existed. To do so, a cohesive crack model has been introduced, govern equations has been discussed and then the way of building a poroelastic three-dimensional model with cohesive elements is described. The results show that the fracture pressure obtained from FEM model is in agreement with the analytical values. Fluid leak- off rate diagram shows three different time steps that the first two steps represent the expression of leak- off jump and third stage shows dynamic leak- off. Fluid pressure changes along the fracture shows a decreasing trend as the fluid pressure is lower than the initial pore pressure due to the phenomenon of fluid-lag at the fracture tip. Finally, a sensitivity analysis was conducted on a number of parameters on the fracture initiation pressure and results show increasing in all parameters except for Poisson's ratio, led to an increase in fracture initiation pressure. Also, the sensitivity function calculations for each of the parameters show that Young's modulus and leak-off coefficient have the highest and lowest effect on fracture initiation pressure, respectively.

Hydraulic fracturing is one of the most important methods for the propagation of oil and gas reservoirs, which is used to increase the inflow to well bore in low permeability formations. Various parameters such as in-situ stress field, joints and natural fractures of the formation, the fluid rheology, the mechanical properties of the formation, injection fluid flow and perforation affect the hydraulic fracturing pressure. In this research, a triaxial machine was designed and built for experimental investigation of the hydraulic fracturing in conditions close to the field conditions, so that all three of the main stresses in field conditions are applied in laboratory tests. Then, the influence of different perforation parameters such as perforation geometry (including length, diameter and shape), phase of perforation (in both vertical and horizontal wells) and minimum horizontal stress in the presence of perforation, using 38 artificial specimens (plaster + sand) with dimensions of 10×10×10 cm, was considered on the geometry and breakdown pressure, pressure-time diagram, and the development of micro-cracks. The results showed that increasing the perforation diameter, changing the perforation angle to the maximum horizontal stress and increasing the minimum horizontal stress in the case of reverse fault, rises the breakdown pressure. 

Hydraulic fracturing is a stimulation technique used in oil and gas wells to increase the inflow to well bore in low permeability formations. Various parameters such as in-situ stress field, joints and natural fractures of the formation, the fluid rheology, the mechanical properties of the formation, injection fluid flow and perforation affect the hydraulic fracturing pressure. Currently, more than half of the USA oil and gas wells are not able to produce without the use of hydraulic fracturing technology. Many researchers have studied hydraulic fracturing behavior of rocks since decades ago. The researches have showed that hydraulic fracturing operations increase the production of oil wells by up to 30 percent and increase gas wells by 90 percent. 

In this research, a triaxial machine was designed and built for the experimental study of hydraulic fracturing and to apply in-situ stresses with different values. This machine has the ability to apply anisotropic stresses in laboratory scale. Abaqus software was utilized to design the machine in terms of stability against the applied stresses. Then, using physical modeling, 38 samples with dimensions of 10×10×10 cm including plaster and sand were constructed and the influence of different perforation parameters such as perforation geometry (including length, diameter and shape), phase of perforation (in both vertical and horizontal wells) and minimum horizontal stress in the presence of perforation on hydraulic fracturing operations were investigated. Finally, the breakdown pressure, hydraulic fracturing geometry, pressure-time diagram and the development of micro-cracks were studied. 

The results of this study showed that increasing the perforation diameter, changing the perforation angle to the maximum horizontal stress and increasing the minimum horizontal stress in the case of reverse fault, rises the breakdown pressure. Also, the increase of the perforation length and its geometry have not significant effect on the breakdown pressure. Additionally, the change in the perforation angle and the minimum horizontal stress relative to the change in the perforation geometry, including length, diameter, and shape, have more effect on the breakdown pressure and changing the perforation angle relative to changing the in-situ stress in the horizontal well bore is more effective on the breakdown pressure.

Hydraulic fracturing is used in the oil industry in order to increase the index of production and processing in wells whose efficiencies have been dropped due to long-term harvest or the rocks around the well are low permeable. Since the hydraulic fracturing operation is costly, it is of special importance to determine the pressure required for hydraulic fracturing and the suitable pump for this operation to the project managers. In this research, sandstone specimens of Lushan area were used and investigated the effect of thermal stress on hydraulic fracturing pressure of sandstone. The Hoek triaxial cell was adapted for a laboratory modelling of hydraulic fracturing. The specimens under study are in the shape of thick-walled hollow cylinders with an external diameter of 54.7 mm, an internal diameter of 12 mm, and a height of 108 mm. To study the effect of thermal stress, the tests were conducted on the specimens that heated up to 100 °C in the furnace at heating process and then cooled in water 5, 10 and 15 °C. Results indicated that hydraulic fracturing pressure reduced with decreasing Cooling temperature of samples. In hydraulic fracturing operations, this decreasing fracture pressure causes the pump to be purchased at a lower pressure production capacity, resulting in lower operating costs. Hydraulic fracturing pressure changes in the effect of thermal stress were consistent with the variations of velocity of longitudinal waves, dry unit weight, uniaxial compressive strength and permeability. CT scan images were used to examine micro cracks changes in the effect of thermal stress and the CT value calculated by the images confirms hydraulic fracturing pressure variations.

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.

Due to the increasing demand for more production rates and output from oil reservoirs, the re-activation of oil wells in Iran is a vital task. Oil production reduces overtime because of a decrease in reservoir's pressure and also as a results of the closure of cracks and microscopic holes. Hydraulic fracture, as a method for stimulating oil reservoirs related to various factors, including characteristics of the environment in which the fracture grows. Mechanical properties of layers has been recognized as one of the most effective parameters on the progress of hydraulic fracture and its geometry. In this study, the primary rock was considered as non-cracked. In this research, numerical modeling was done by ABAQUS software in 21 different cases for which the effect of each input parameters on the hydraulic fracture pressure was investigated by performing sensitivity analysis. The input parameters were well's data and included Young's modulus, minimum and maximum horizontal stress, vertical stress, tensile strength, Poisson''s ratio and pore pressure. The required data is obtained from the excavated wells in carbonate rocks in Iran. The results showed minimum horizontal stress has the highest impact on the hydraulic fracture pressure. Finally, using SPSS software and by performing multivariate regression analysis, a formula was made using the numerical modeling data to estimate the hydraulic fracture pressure. The results of statistical analysis corroborate the precision of regression line and consequently the suggested formula. In this formula, the parameters such as minimum horizontal stress, the difference between minimum and maximum horizontal stresses, pore pressure and tensile strength, have the most effect on the hydraulic fracture pressure respectively. Using the presented formula in this study, the hydraulic fracture pressure in carbonate wells with different properties could be obtained. Gaining this pressure will help to determine the proper pump and case to reduce operating costs.

Nowadays, the need to enhance the exploitation of hydrocarbon resources due to importance and increase in the rate of consumption of this material is more crucial than ever. On the other hand, the rock formations with low effective porosity, which are considered as hydrocarbon reservoirs prevented to have a suitable productivity of these reservoirs. Hydraulic fracturing is known as a process of initiation and propagation of fractures caused by fluid injection into the part of the boreholes in rock formations, which has an important role in increasing of the exploitation of hydrocarbon reservoirs with low efficiency. Initiation and propagation fractures have a high dependency to the parameters and properties of reservoir rocks. Among these parameters can mention, such as rock material, rock tensile strength, pore pressure and etc. Importance tensile strength of rock for predicting the breakdown pressure of hydraulic fracturing test is remarkable and this parameter is a function of lithology of reservoir rock. Hence, in this study with sampling at typical section of Asmari formation, evaluation of breakdown pressure parameter as a function of rock tensile strength and lithology parameters has been paid. The ratio of hydraulic fracturing tensile strength to Brazilian test tensile strength and Point load test allows prediction of the tensile strength and is an important parameter for simulation of hydraulic fracturing test results. Comparison of these ratios shows that the tensile strength parameter is dependent on the test method. Rock tensile strength that obtained from hydraulic fracturing test is 20.08 MPa and proportion between tensile strength of hydraulic fracturing test to Brazilian test is equal to 2.35. Slight differences in the distribution of data and regression coefficient 0.9 are due to the small karst cavities, relatively low porosity and intragranular voids because of fossils in the rock structure. All evidences, including the results of physical and mechanical properties reveal the influence of lithology on the results of tensile strength obtained from hydraulic fracturing test.

Well bore stability analysis is a procedure with the view to economically improving the drilling operation. Identification of diverse types of rupture in the well bore is crucial in stability analysis. Due to reduction I reservoir pressure and index of per، hydraulic fracturing well be performed in order to increase the permeability and production from well. During the aforementioned procedure، fluid is injected inside the well to induce the fracture in the walls. Hydraulic fracturing has received much recognition as a reliable method for the stimulation of oil reservoir. In this study، conducted on 400 m of limestone in fahlyian reservoir in darkhovein oil field، pressure of shear and compressional failure is determined by virtue of parameters including rock mechanic and information on well logging as well as in situ stress of vertical and maximum and minimum horizontal. Safety mud window was defined between 0. 84 and 4. 2. The minimum allowable mud pressure for preventing the shear failure was between 33. 51 and 52. 89 and the maximum range was determined between 47. 4 and 97. 55. Furthermore، minimal required mud pressure for inducing compressional rupture and hydraulic fracturing was estimated between 108. 87 and 151. 38.

Hydraulic Fracturing method was developed to increase the productivity of low permeability reservoirs. In this method، it is very important to predict the hydraulic fracturing geometry to ensure a safe and optimum design. Hydraulic fracture propagation is affected from natural discontinuities (fault، joint…) in fractured reservoirs. In this study، the interaction of hydraulic fracture with natural fractures and consequently the fracture propagation and variation of fluid pressure inside the hydraulic fracture is studied numerically. The numerical program (2DFPM) was developed based on combination of boundary element method (displacement discontinuity method (DDM)) and finite difference method (FDM). The validity of the numerical program was verified by KGD model. Different conditions of hydraulic and natural fracture interaction are modeled and the effect of natural fracture on distribution of fluid pressure profile along the hydraulic fracture length is studied. The results show that the interaction condition and injection parameters of fluid have more influence on the hydraulic fracturing method.

Hydraulic fracturing as a method for reservoir stimulation depends on the properties of the media that fracture propagates in it. The elastic properties of layers greatly affect the geometry and propagation of hydraulic fractures. In this research study، the hydraulic fracturing propagation in multi-layered media (stiff and soft) with different elastic properties is investigated. Therefore، boundary element method based on the displacement discontinuity formulation is presented to solve general problems of hydraulic fracturing propagation in layered formations. The crack tip element and a higher order boundary displacement collocation technique are used to increase the accuracy of the method (2DFPM) in modeling of non-homogenous media. The stress intensity factor and tensile stress near the crack tip under different elastic modulus are evaluated to study the hydraulic fracture propagation. Related to the position of the fracture with interface (vertical، intersect and parallel) these factors have different values and finally، they control the fracture propagation. In comparison between the width of fractures in soft and stiff layers، the study displays that the fracture width in soft layers is greater than width of fracture in stiff layers.

The hydraulic fracturing is a suitable operational method for stimulating and increasing the productivity of oil and gas wells. In this method, a liquid is pumped to the wellbore until creation and then propagation of a fracture in the wall of wellbore. The aim of this paper is to determine the minimum pressure required for developing a hydraulic fracture from an initial perforation in the wall of well. The evaluation of the minimum pumping pressure is an important task for performing an optimum and successful hydraulic fracture operation. Since the hydraulic fracturing is essentially a process of crack growth in the wellbores and in the reservoir formations, it is preferred to investigate this method using the concepts of rock fracture mechanics. In this paper, the minimum pumping pressure diagrams have been presented for different conditions of a wellbore during the hydraulic fracturing process. In order to obtain the diagrams, several 3D finite element models of the well having an initial semi circular perforation were analyzed under different loading conditions and the influence of affecting parameters such as the in-situ stresses, the depth of initial perforation and the wellbore inclination angle on the minimum pumping pressure were investigated numerically. It is shown that the minimum horizontal in-situ stress is the most affecting parameter on the required pumping pressure at great depths. The pumping pressure increases by increasing the minimum in-situ stress. Meanwhile, inclined wells require smaller pumping pressures in comparison with the vertical wellbores.