Hydraulic Fracturing Pressure Research Articles

Influences of clean fracturing fluid viscosity and horizontal in-situ stress difference on hydraulic fracture propagation and morphology in coal seam

The viscosity of fracturing fluid and in-situ stress difference are the two important factors that affect the hydraulic fracturing pressure and propagation morphology. In this study, raw coal was used to prepare coal samples for experiments, and clean fracturing fluid samples were prepared using CTAB surfactant. A series of hydraulic fracturing tests were conducted with an in-house developed triaxial hydraulic fracturing simulator and the fracturing process was monitored with an acoustic emission instrument to analyze the influences of fracturing fluid viscosity and horizontal in-situ stress difference on coal fracture propagation. The results show that the number of branched fractures decreased, the fracture pattern became simpler, the fractures width increased obviously, and the distribution of AE event points was concentrated with the increase of the fracturing fluid viscosity or the horizontal in-situ stress difference. The acoustic emission energy decreases with the increase of fracturing fluid viscosity and increases with the increase of horizontal in situ stress difference. The low viscosity clean fracturing fluid has strong elasticity and is easy to be compressed into the tip of fractures, resulting in complex fractures. The high viscosity clean fracturing fluids are the opposite. Our experimental results provide a reference and scientific basis for the design and optimization of field hydraulic fracturing parameters.

SOME ISSUES OF DETERMINING THE HYDRAULIC FRACTURE PRESSURE OF LAYERS IN DRILLING OIL AND GAS WELLS

The determining of the hydraulic fracturing pressure of formations in the drilling of oil and gas wells is considered. It should be noted that determining the hydraulic fracturing pressure is important in choosing the well structure, mainly in determining the length of the conductor and regulating their speed while performing technological processes. Mathematical and statistical analyzes of mining data are given in the article. According to the mentioned method, the value of the hydraulic fracking pressure of the stratigraphic sections and depths was determined for Kursangi, Bahar, Karabaghli, Muradkhanli and other fields. One of the main factors in the method proposed in the article is the study of the exact value of hydraulic fracturing pressure. Until now, the average value of the density of rock is taken empirically in some cases, regardless of the age of the section for the intended deposits. Currently, there are certain complications related to hydraulic fracturing of formations during drilling, which take a lot of time and money to eliminate. In the article, it was proposed to find the hydraulic fracturing pressure of the formation. Keywords: well structure, hydraulic fracturing, hydrodynamic pressures, conductor, formation, drilling fluid.

MODELLING OF DEEP WELL CEMENTING PROCESS

The research aims to simulate Managed Pressure Cementing (MPC) for a deepwater field, focusing on optimizing the cementing process to ensure structural integrity and wellbore stability. The study addresses the challenges associated with conventional cementing methods, providing insights into the pressure dynamics, fluid properties, and pump performance crucial for deep well cementing operations. The methodology involves conducting a simulation to model the cementing process for a deep well with a total length of 9144 meters, where the previous casing's shoe is located at a depth of 6096 meters. Real data is utilized to obtain profiles of reservoir pressure, hydraulic fracturing pressure, and viscosities of essential fluids, including cement, drilling fluid, and buffer fluid. The simulation considers factors such as annular pressure loss, Equivalent Circulating Density (ECD) calculation, and pump performance under varying conditions. Additionally, the density of the cement slurry in the annulus during pumping is established. The study reveals that pump performance under the given conditions is 57 m³/h for drilling and buffer fluids, while for cement solutions, it can vary from 19 m³/h to 38 m³/h. These results offer actionable insights for operational planning and optimization of the cementing process in deep wells. The simulation successfully models the cementing process for a deep well, providing valuable data on equivalent circulation density and cement slurry density in the annulus. The determined pump performance under different conditions is critical for understanding the dynamics of fluid circulation during cementing operations. Practical implications of the research include the optimization of cementing processes, contributing to enhanced structural integrity, reduced wellbore instability, and improved efficiency in deepwater field operations. In conclusion, the study not only contributes to theoretical understanding but also provides practical data for optimizing the cementing process in deep wells, reflecting the industry's commitment to continuous improvement in drilling technologies and ensuring the reliability and efficiency of wellbore operations in challenging environments. Keywords: managed pressure drilling (MPD), wellbore stability, downhole conditions, real-time monitoring, managed pressure cementing (MPC), zonal isolation.

Research on Hydraulic Fracturing Pressure Relief and Improvement Permeability Technology of the Soft Coal Seam Roof.

Aiming at the characteristics of low permeability and large gas content of deep soft coal seam, hydraulic fracturing pressure relief and improvement permeability technology of the roof are proposed. FLAC3D was used to invert the roof hydraulic fracturing of the soft coal seams. On this basis, the dynamic evolution characteristics of permeability before and after fracturing were given by the COMSOL multiphysics software. Finally, roof hydraulic fracturing technology was applied on the site. The results show that after the hydraulic fracture of the roof, the peak stress on both sides of the roadway is reduced by 1.7 MPa, the peak stress concentration in front of the roadway is reduced by 2.2 MPa, the stress concentration range is reduced, and the stress is effectively transferred to the deep part of the roadway. After fracturing, the permeability of the stress concentration area increased by 2.18 times, the permeability of the original rock stress area increased by 1.84 times, and the gas fluidity improved. After roof hydraulic fracturing, the occurrence of a coal cannon decreases from 2 to 4 times per 1 m driving to 0 to 1 times, and the phenomenon of a coal cannon at the working face decreases significantly. The concentration of the return air flow is reduced from 0.5-0.9% to 0.2-0.4%. The results of this study have a guiding role in taking the corresponding measures for gas disaster prevention and control.

3D numerical analysis of stability and onset of hydraulic fracture in the vertical‐oblique‐horizontal wells under wide range of in situ stresses

AbstractInfluence of the depth and location of perforation, direction and magnitudes of in situ stresses, wellbore angle, and pumping pressure is investigated numerically for the hydraulic fracture. 3D models of rock formation with vertical, inclined or horizontal wells containing semi‐circular crack are analyzed to obtain both KI and the minimum pumping pressure. By computing the magnitude and sign of the T‐stress it is demonstrated that hydraulic fracture path is generally stable except for a very limited situations in which the vertical well is subjected to the lowest in situ stresses. The minimum horizontal in situ stress has the most dominant role in controlling the hydraulic fracture. A direct relationship between KI and T was obtained for different ranges of in situ stresses and some relations were presented for estimating the critical stress intensity factor at the onset of hydraulic fracture and minimum injection pressure in terms of the applied in situ stresses.

Determination of fracturing pressure during drilling analytical method

When drilling, the depth of wells is constantly increasing, and as a result, the likelihood of various complications increases. Complications include: loss of drilling fluid; gas-oil-water manifestations, violation of the stability of the well walls, sticking. Almost all complications, if special measures are not taken to prevent and eliminate them, turn into accidents. One of the complications arising from well drilling is hydraulic fracturing. Fracturing pressure is the pressure at which the integrity of the rock in the walls of the well is broken, and artificial fractures are formed. During the drilling process during hydraulic fracturing, the drilling fluid goes into the surrounding rocks. n the proposed scientific work, using the energy condition of destruction, the hydraulic fracturing pressure is determined depending on the mechanical characteristics of the rock and reservoir pressure.

Mechanical weakening behavior and energy evolution characteristics of shale with different bedding angles after microwave irradiation

Microwave irradiation, as a novel, clean, and efficient rock-breaking technology, can be employed in shale gas exploitation to address the challenges of low fracture efficiency and environmental pollution. Therefore, it is essential to investigate the physico-mechanical properties of shale under microwave irradiation. Firstly, samples with different bedding angles (0°, 30°, 60°, and 90°) were subjected to microwave irradiation at a power of 1 kW and frequency of 2.45 GHz for durations of 0, 20, 40, 60, and 80 s. Additionally, measurements of mass, P-wave velocity, and porosity were taken before and after microwave irradiation, followed by uniaxial compression testing using acoustic emission (AE). The results demonstrated that with increasing microwave irradiation duration, the P-wave velocity and mass of shale gradually decreased, exhibiting anisotropic behavior for the P-wave velocity. The highest degree of weakening (24.75%) was observed for shale at 0°, while the lowest (7.03%) occurred at 90°. Both uniaxial compressive strength and elastic modulus weakened gradually. Notably, USC displayed more significant weakening at 30° and 60°. The energy evolution pattern revealed increasing dissipated energy and decreasing brittleness index, enhancing anisotropy with duration, particularly at 60°. Moreover, AE captured the transition of failure mode from tensile splitting to tensile-shear failure. The results indicated the significant and anisotropic weakening effect of microwave irradiation on shale. The increase in porosity and permeability also provided preliminary evidence for the enhanced permeability ability of shale, resulting in reduced hydraulic fracturing pressures and decreased environmental pollution. Furthermore, the changes of most parameters revealed threshold effect of microwave irradiation duration, which can be classified as weak or strong depending on whether it occurs before or after 40 s. Therefore, attention should be paid to the threshold conditions of microwave irradiation duration to achieve efficient extraction. This research provided initial theoretical support for microwave-assisted shale gas exploitation.

Asymmetric Damage Mechanisms and Prevention Technology in Large-Section Gob-Side Entry Retaining

Based on the deformation and damage characteristics of the surrounding rock in a large-section gob-side entry retaining and combined with field observations and an analysis of the dominant factors, an overall deformation control plan is formulated. The plan mainly includes a structure of high strength, high stiffness and high ductility for roadside support; the reinforcement of the roadway-in support; and the setup entry hydraulic fracturing pressure release mechanism and advanced long, horizontal borehole “fracturing-jet” pressure relief technology. Industrial field tests were completed taking Tangan coal mine as the engineering background. The research shows that the large-section gob-side entry retaining has the typical “asymmetric” overall deformation and damage characteristics, including top coal sinking along the inner side of the roadside support, the whole roadside support structure skewing, and even splitting damage; floor heaving; and the coal-side bolt support structure basically losing support ability and bulging out from the coal side. The dominant factors of deformation damage are disintegration of the floor mudstone by water and deflection deformation under horizontal stress, splitting damage in the concrete roadside support under asymmetric load, damage and expansion due to the insufficient strength of the coal side support, strong dynamic pressure on the roof, and the mutual influence of support and pressure relief. The industrial test shows that the deformation control scheme optimizes the stress environment of the gob-side entry retaining space, the deformation control effect is remarkable, and the roadside fully meets the reuse requirements.

A study on the excavation face failure of pressurized slurry shield

The Wuhan Metro Line 8 Crossing River Tunnel Project suffered manifest pressure fluctuations when opening the excavation chamber of the slurry shield. In this paper, numerical simulation and air pressure test are both carried out to analyze the causes of the pressure fluctuation. The analysis results show that the air pressure applied on the excavation face during the opening of chamber lies in the safe region, excluding the possibilities of active and/or passive excavation face failures. Then, calculated by empirical formula, the pressure on site is lower than the hydraulic fracture pressure, which means the pressure fluctuation is not related to the hydraulic fracture. At last, by air pressure tests, the break through pressure of the filter cake is found much smaller than the air pressure on site. Therefore, it is concluded in this paper that the quality of the filter cake does not meet the design standard, and the breakdown of the filter cake is the main cause of the observed pressure fluctuations on the excavation face. Furthermore, the mechanism of filter cake breakdown is investigated experimentally.

Experimental Study on Hydraulic Fracturing of Laminated Sandstone Combined with Industrial CT and L-NMR

Hydraulic fracturing in the immediate roof is a suitable method to increase the permeability of soft outburst coal seam. In this work, the propagation law of hydraulic fractures in laminated virgin sandstone and the change of microstructure after hydraulic fracturing were revealed. The results show that the hydraulic fracturing pressure of sandstone with different bedding angles is 15.69~22.17 MPa. In the experiments, the hydraulic fractures extend through the bedding planes when the bedding angle is 45°. When the bedding angle is 0°, 15°, 30°, or 60°, the hydraulic fracture is prone to extend along a bedding plane. The hydraulic fracture in sandstone is jointly determined by the internal fractures and the cementation strengths of the bedding planes. The internal fractures may not necessarily guide the extension of the hydraulic fractures. The hydraulic fracturing pressures of the samples affected by the bedding plane and internal fractures are significantly lower than that of samples with uniform strength. Besides, hydraulic fracturing cannot change the connectivity between pores. The hydraulic fractures are the main channel for gas migration. The results can provide some guidance for the design and application of hydraulic fracturing in the immediate roof of the soft outburst coal seam.

Research on Hydraulic Fracturing Pressure Relief Technology in the Deep High-Stress Roadway for Surrounding Rock Control

With the increase of mining depth in underground engineering, deep ground pressure has an extremely unfavorable impact on safety production and the economic benefits of coal mines and the control of the roadway stability in deep mines are gradually highlighted. In this study, the working face 14203 of the Zaoquan coal mine was taken as the engineering background, the deformation mechanism of surrounding rock in the deep-buried high-stress roadway was analyzed, and the hydraulic fracturing pressure relief technology in the advanced roadway was proposed for surrounding rock control. Finally, the numerical simulation and field tests were used to validate the comprehensive effect of the proposed technology. Without damaging the roadway stability in the working face, the hydraulic fracturing pressure relief technology can optimize the stress environment and stability of the roadway through the artificial control of the roof fracture position. The numerical simulation shows that under the action of hydraulic fracturing, the cutting slot is formed, the deformation and failure mode of the roof are changed, the stress of surrounding rock is reduced, and the development of the plastic zone of surrounding rock is limited. As a result, the stability of surrounding rock in the roadway is effectively protected. The field test shows that after the adoption of hydraulic fracturing pressure relief technology, the roof subsidence, floor separation, bolt stress, and cable stress decrease, and the deformation of surrounding rock is reduced significantly. Therefore, hydraulic fracturing pressure relief technology is verified as an effective method to control the large deformation of the surrounding rock in the deep-buried roadway.

Influence of natural caves on hydraulic fracturing pressure curves: numerical modelling and ANNs

Influence of natural caves on hydraulic fracturing pressure curves: numerical modelling and ANNs

Advances and challenges in hydraulic fracturing of tight reservoirs: A critical review

The hydraulic fracturing technology has been widely utilized to extract tight resources. Hydraulic fracturing involves rock failures, complex fracture generation, proppant transport and fracture closure. All these behaviors affect the productivity of fractured wells. In this work, the advances and challenges in hydraulic fracturing development of tight reservoirs are summarized from following aspects: the hydraulic fracture propagation, the proppant transport and distribution in hydraulic fractures, the calculation of hydraulic fracture conductivity, and productivity and/or pressure analysis model of multi-stages fractured horizontal wells. Current fracture propagation simulation methods generate only limited propagation paths and cannot truly reflect the complexity of the propagation. The current proppant migration and distribution research is mainly focused on indoor experimental studies of proppant migration in a single fracture or branched fracture, and simulation studies on proppant migration and distribution in a small-scale single slab fracture. Whereas fractures formed after hydraulic fracturing in tight reservoirs are generally complicated. There is a lack of models for calculating complex fracture conductivity that take into consideration the effect of proppant placement and proppant distribution in fractures, fracture surface roughness and dissolution, diffusion, deposition, elastic embedding, and creep caused by stress. The productivity models of fractured horizontal wells are mostly conducted based on the original reservoir fluid saturation and pressure distribution. Most of the studies are focused only on one aspect of the fracturing process. Predications of well performance after fracturing based on these studies are often inconsistent with actual field data. The paper also discusses the future research directions of fracturing in tight reservoirs and the results may be used to promote the development of tight reservoirs.

Hydraulic fracturing pressure of concentric double-layered cylinder in cohesive soil

Hydraulic fracturing pressure of concentric double-layered cylinder in cohesive soil

Ultimate pressure determination in hydraulic fracturing of boreholes for different rock failure criteria

The problem on elastoplastic deformation and rock failure around boreholes under the action of internal pressure is considered. The stress state in the intact rock mass is assumed to be hydrostatic. The hydraulic fracturing pressure is conventionally determined by the maximum normal stress criterion. However, the experimental studies described in scientific articles show that this criterion is not consistent with the results obtained in the course of laboratory tests on failure of cylindrical and spherical cavities made in rock samples. It has been known that test results on complex loading for solid samples of various materials are not confirmed by the theory of maximum normal stress both in terms of ultimate load value and direction of failure surface propagation. In this case, for the complex stress state of rocks, it is proposed to determine the ultimate pressure by the experimentally substantiated fracture criteria which are in good agreement with the results of laboratory tests on hydraulic fracturing of boreholes.

Aerodynamics and Heat Transfer of Swirling Natural Gas Flow in a Vortex Heat Exchanger of the Heating System of a Gas Control Point

Purpose of research. To obtain a two-parameter model characterizing the aerodynamic and heat exchange processes occurring in a vortex heat exchanger, giving a better agreement between the calculated and experimental values of the heat transfer coefficient taking into account the curvature of the swirling gas flow in a vortex heat exchanger, in which a controlled gas pressure drop is used as a source of thermal energy. This technical solution will make it possible to abandon the installation of autonomous sources of thermal energy, which will reduce the cost of gas as a fuel in the heating system of the industrial premises of the gas distribution point (GDP), as well as provide more comfortable working conditions for the hydraulic fracturing pressure regulator. Methods. Comprehensive analysis of thermal and hydraulic characteristics in a vortex heat exchanger is based on well-known theoretical positions and equations of motion of a swirling gas flow and heat exchange laws. Results. It is obtained a dependence that characterizes the intensification of heat transfer based on the influence of the axial and rotational speed, as well as the path of motion of the swirling gas flow. This dependence is obtained on the basis of a comprehensive analysis of the aerodynamic and heat exchange characteristics of a vortex heat exchanger, in which a controlled gas pressure drop is used as a source of thermal energy. Conclusion. The obtained two-parameter model gives the best agreement of the calculated values of the heat transfer coefficient with the values obtained experimentally, which were used in the thermal engineering calculation of the design parameters of the vortex heat exchanger.

Data Analysis of Hydraulic Fracturing Pressure in Unconventional Oil and Gas Fields

After the completion of fracturing construction in unconventional oil and gas fields, the phenomenon of water hammer oscillation in the process of pump stopping during fracturing construction will lead to the inaccuracy of reflecting the trend of pressure transformation and increase the difficulty of fracturing effect evaluation in the process of fracturing construction. Therefore, three filtering methods, Savitzky-Golay filter, FFT filter and wavelet transform filter, are used to calibrate the measured pressure in this paper It is found that the method of wavelet transform can achieve the most ideal effect by comparing with the measured data. The field example of well X1 in Ordos Basin proves that the method of wavelet transform can accurately reflect the trend of pressure transformation. This method is of great significance to improve the evaluation of post pressure effect in the process of fracturing construction.

Risk analysis of natural hydraulic fracturing in an overpressured basin with mud diapirs: A case study from the Yinggehai Basin, South China sea

The Yinggehai Basin is a strongly overpressured basin without large-scale faults in the Central Depression Zone. The hydraulic seal capacity of the caprocks over geological history has been the key factor controlling the vertical distribution characteristics of oil and gas. Based on leak-off data, rock mechanics tests and measured pore pressure data, this paper analyses the potential of natural hydraulic fracturing with the fault analysis seal technology (FAST) methodology for caprocks C1 (caprock of the Huangliu Formation) and C2 (caprock of the Meishan Formation) of the diapir belt in the north Central Depression Zone and determines the failure mode and gas sealing capacity of the two caprocks. The results show that gas leakage occurred continuously in both C1 and C2 in the diapir zone (DZ) throughout geological time. However, far from the diapir zone (FDZ), hydraulic leakage occurred only in caprock C2 while no leakage occurred in caprock C1 over geological time. These results are consistent with the gas accumulation that occurred in both the Yinggehai Formation and Huangliu Formation in the DZ but only in the Huangliu Formation in the FDZ. A relatively reasonable explanation is that diapirism promoted natural hydraulic fracture development via the following effects: (i) Diapirism transfers deep overpressure to shallow layers and increases the pressure gradient; (ii) The high-angle fractures associated with diapirism reduce the critical stress condition for the occurrence of natural hydraulic fracturing; and (iii) Diapirism results in the formation of dome structures in shallow layers, causing more shallow burial of caprock in the DZ than the FDZ. Shallowly buried caprocks, which have a relatively lower hydraulic fracture pressure, facilitate gas migration. These effects promoted natural hydraulic fracturing in the DZ, which is the main reason for the difference in the vertical distribution of gas reservoirs between the DZ and FDZ.

ЧИСЛЕННОЕ РЕШЕНИЕ ЗАДАЧ ГЕОМЕХАНИКИ (НА ПРИМЕРЕ МЕСТОРОЖДЕНИЯ ШЕЛЬФА БАЛТИЙСКОГО МОРЯ)

Geomechanical modeling aims at solving problems associated with ensuring accident-free well drilling. The paper deals with building a numerical 3D geomechanical model for a studied field with a further production well stability computation. The region of operations is located in the Baltic Sea shelf. Apart from the field summary, the study contains results of acquisition and audit of initial data for modeling. The method is discussed for unidimensional geomechanical modeling on key wells, including determination of dynamic and static elasticity and strength of the rock varieties, computations of pore pressure, vertical and horizontal stresses. Well stability computations have been obtained and analyzed on the basis of the findings of 1D geomechanical modeling. A further analysis deals with the results of 3D geomechanical modeling, i.e. determination of boundaries and building a structural framework of the model, geometry testing, filling the grid with mechanical properties, and computation of complete stress tensor using the finite element method (FEM). Results of the 1D- and 3D-modeling have been compared. Thus, a numerical 3D geomechanical model has been built for the field under study. The following stage of works was focused on the wellbore stability computation for the planned wells. Additionally, computation was performed for drilling mud absorption pressure gradient cubes, caving pressure, and rock hydraulic fracturing pressure at different inclination angles and drilling azimuths. Recommendations were developed for accident-free construction of wells in the field under study, including upkeep and update of the geomechanical model in real time during drilling of wells. The obtained results and techniques can be used in design and construction of wells in other fields though taking into account regional specifics.

An integrated petrophysical and geomechanical characterization of Sembar Shale in the Lower Indus Basin, Pakistan, using well logs and seismic data

Shale gas reservoirs are generally exploited through horizontal drilling and hydraulic fracturing. Petrophysical and geomechanical parameters help to determine horizontal well orientation, to select drilling mud densities for stable drilling operations, to assess the suitability of specific zones in a formation for hydraulic fracturing, and to assess required hydraulic fracturing pressures. The primary objective of this work was to characterize a shale interval in the Early Cretaceous-age Sembar Formation in the Lower Indus Basin of Pakistan, using only readily available data. A workflow was developed for the estimation and mapping of geomechanical properties using logs from multiple wells and relevant post-stack seismic reflection data. Mineralogy data from well cuttings, core testing results for elastic properties and hydraulic fracturing test data (mostly obtained from one key well) were utilized to constrain the values of the properties estimated from geophysical data. The following results obtained at the well-scale suggest that the Sembar Shale is favorable for development: high gas saturation, good porosity (up to 10%), moderate quantity of thermally mature organic matter (2%–4% TOC), a number of brittle intervals separated by thicker intervals that fall slightly below the brittle-ductile threshold, and a strike-slip stress regime. At the scale of the study area, robust statistical techniques were used to invert seismic stacks and develop a 3D mechanical earth model. This model shows a trend of increasing shale brittleness towards the northeastern portion of the study area, hence suggesting that this area might be most prospective for initial shale gas development. The results of sensitivity analyses are presented, which illustrate the potential errors in the estimated geomechanical properties. Future work to improve confidence in the shale gas potential of the Sembar Formation is given, including extensive coring and laboratory testing, in-situ stress and natural fracture characterization, and better delineation of shale thickness.