Hydraulic Fracturing Method Research Articles

THE FLUID PRESSURE IN A HYDRAULIC FRACTURE PERPENDICULAR TO THE HORIZONTAL WELL

For many decades, the hydraulic fracturing method, due to its efficiency, has been actively used to increase the productivity of wells in the oil and gas industry. This article is devoted to modeling fluid filtration in a fracture obtained by hydraulic fracturing running perpendicular to the wellbore.
 The cases of constant flow rate and constant pressure in the well are considered in the paper. A mathematical model of the «well – fracture – reservoir» system for the case of a hydraulic fracture perpendicular to the well is described. The solution is derived by the sequential change of stationary states method, graphs with the results of test calculations are plotted.

Construction practice of water conveyance tunnel among complex geotechnical conditions: a case study

The construction practice of water conveyance tunnels often encounters various complex geotechnical engineering conditions, which bring huge challenges to the design and construction of water conveyance tunnels. Based on the theory of rock elastic–plastic mechanics and finite element analysis technology, this article carried out investigations of engineering geological features, geological formations and hydrological conditions establishes a calculation model for the 3# water conveyance tunnel of the Fenhe River Diversion Project, and analyzes the variation law of surrounding rock stress and displacement during TBM excavation of the tunnel. The results indicate that the dominant direction of the rock mass principal stress measured by the hydraulic fracturing method is NE84°, and the maximum horizontal principal stress, minimum horizontal principal stress, and vertical stress decrease sequentially, analyzing the characteristics of shield TBM construction technology, it is applied to the construction of water transfer tunnels. The numerical simulation of TBM construction using FLAC3D software shows that as the excavation surface advances, the subsidence value of the tunnel roof first slowly increases, then rapidly increases, and then tends to stabilize. The horizontal displacement of the surrounding rock is increasing. The maximum principal stress of the surrounding rock gradually increases. The final surrounding rock stress is 35 MPa. The TBM shield machine with mud water balance driven by indirectly controlled frequency conversion motor is selected for TBM construction of the tunnel. The study offers statistical information to support tunneling technology for water conveyance in the geotechnical engineering practice.

Experimental and numerical study of measuring in-situ stress in horizontal borehole by hydraulic fracturing method

Horizontal directional investigation is an alternative method different from traditional (vertical) geotechnical investigation, which can effectively reflect geological conditions along the axis and evaluate the engineering characteristics of tunnels in mountainous areas with super long distances and depths. However, the absence of effective methods to measure in-situ stress in horizontal boreholes hinders the promotion of horizontal directional investigation. This paper relies on the thorough horizontal directional drilling geotechnical investigation of the Tianshan Shengli tunnel in China, based on the method of hydraulic fracturing in-situ stress measurement, the relationship between the direction and magnitude of in-situ stresses and the parameters of the hydraulic fracturing was established in a horizontal borehole by enhancing the previous model of inclined boreholes. The interpretation principles of horizontal boreholes by hydraulic fracturing method are further explored through experimental and numerical study. The conclusion of this paper provides theoretical and empirical support for in-situ stress measurement in horizontal boreholes by hydraulic fracturing method.

Prediction of Fracture Initiation Pressure for Slotting-Directional Hydraulic Fracturing Based on the Anisotropy of Coal

Abstract The precise estimation of fracture initiation pressure is crucial for the effective implementation of slotting-directional hydraulic fracturing methods in coal seams. Nonetheless, current models fail to account for the impact of the morphology of the slotted borehole and the anisotropy of coal. To address this issue, a three-dimensional model was created in this study, which simplified the slotted borehole as an elliptical medium and the coal as an orthotropic medium. Laboratory experiments were conducted to validate the model, and the findings regarding the changes in fracture initiation pressure and deflection angle due to various factors were presented. The calculated outcomes of the proposed model align with the observed pattern of the experimental results, and the numerical discrepancy falls within the acceptable range of 7%, showcasing the precision of the proposed model. A rise in the horizontal stress difference and a decrease in the depth of the slots will result in an elevation of the fracture initiation pressure and deflection angle. In addition, the slotting angle will impact the distribution pattern of the fracture initiation pressure and deflection angle, underscoring the significance of these factors in the hydraulic fracturing of slotted boreholes.

Change Characteristics of the Advance Stress and Strata Fracture Structure of Spatial Isolated Island Formed by Roof Drainage

Large-energy microseismic events, coal bursts, and other abnormal mine stress are often observed in spatial isolated island areas in the roof water-rich gob-side working face during mining operations. In view of this problem, numerical simulation and on-site microseismic monitoring are employed to study the advance abutment stress and strata fracture structure in the spatial island area formed by ‘roof drainage + goaf’ during mining and the method of eliminating the spatial island area. The results show that the lateral stress is distributed in a step-like pattern, and the drainage area and goaf are superimposed to form a high-stress space island area before the mining of the working face along the goaf. The distribution pattern of the advance abutment stress in the spatial island area changes from ‘C’ type to ‘S’ type during the mining process. The strata structure of the roof water-rich gob-side working face is either a single-peak arch or double-peak arch, and the arch peak corresponds to the boundary of the drainage area. The method of local hydraulic fracturing can eliminate the influence of spatial island areas and improve the safety of roof water-rich gob-side working face mining.

Hydraulic fracturing using high-boiling fraction of oil as a fracturing fluid

Background: In recent years, there has been a trend towards deterioration in the structure of residual reserves at the fields of Kazakhstan. A significant part of the reserves is located in low-permeability reservoirs and in the zones not covered by flooding. The main factor negatively affecting the productivity and efficiency of development is the heterogeneity of oil reservoirs.
 Oil-saturated formations are an alternation of permeable oil-saturated sand or limestone and impermeable clay or dolomite layers, lenses and interlayers. Up to 1020 interlayers can be distinguished within the reservoir, which indicates a strong compartmentalization of the reservoirs. Due to the complexity of the structure of oil deposits, it is very difficult or impossible to ensure complete drainage of the entire volume of the deposit and complete coverage of oil displacement by water into production wells through injection wells.
 Aim: Increasing oil recovery in a cost-effective way.
 Materials and methods: Experimental studies of the processes of impact on the bottomhole formation zone with high-boiling oil components were carried out using a laboratory machine for diamond drilling, an installation for determining the permeability of a rock in terms of liquid and gas, an installation for determining oil viscosity, and an installation for pumping fracturing fluid into the reservoir model.
 Results: As a result of applying the hydraulic fracturing method using high-boiling oil components, it is possible to increase the permeability of low-permeability formations and significantly increase oil recovery.
 Conclusion: Due to the geological structure of multi-layer oilfields, water-based gel fracturing fluids to increase oil flow to wells are considered ineffective due to the adsorption of gels with long molecules in the pores of the formation and swelling of the clay particles of the reservoir when they interact with the water-based fluid.

Enhancing Water Management in Shale Gas Extraction through Rectangular Pulse Hydraulic Fracturing

Although conventional hydraulic fracturing techniques have revolutionized shale gas development, they have raised concerns regarding water management and environmental impacts. This research introduces an innovative step-rectangular pulse hydraulic fracturing method to optimize water usage and reduce environmental hazards in shale gas extraction. The method involves the application of lower-energy fluid in a step-rectangular pulse pattern, which results in higher pressures, more intricate fractures, and improved water management. A comprehensive analysis of the propagation and attenuation characteristics of this technique is conducted using a combination of a two-dimensional pulse transient flow equation with damping, software numerical simulations, and theoretical analysis. The study reveals that the step rectangular pulse hydraulic fracturing method offers superior pressurization and more complex fracture networks in shale reservoirs while lowering water consumption by 20% less than conventional methods and increasing shale gas production by 12%. Through identifying optimal pulse parameters, this research provides valuable guidance for field implementation, promoting efficient water management and environmental sustainability in hydraulic fracturing operations. This novel approach to hydraulic fracturing has the potential to significantly advance the industry’s efforts to address water management challenges and mitigate environmental risks associated with shale gas extraction.

Analysis and Application of Hydraulic Fracturing to Control Hard and Stable Roof in Initial Mining Stage

Previously conducted studies have established that the sudden collapse of large areas of overhanging roofs in longwall working faces can cause shock loads and wind blast. In order to solve the problem of the hard and stable roof (HSR) being difficult to collapse in the initial mining stage, a combination of theoretical analysis and numerical simulation is used, taking Dongqu coal mine as the engineering background. The mechanical model of the initial fracture of the main roof is established, the relationship between the thickness-to-span ratio of main roof, the internal stress of the roof is analyzed, and the relationship between the thickness of the roof and the initial weighting step is revealed. The method of hydraulic fracturing (HF) is proposed to pre-crack the main roof in order to achieve controllability of the roof. The effect of HF on the control of the HSR is analyzed. The main conclusions are as follows: under the condition of a certain span of the rock beam, a smaller thickness of the rock beam makes for a larger tensile stress inside of it, increasing the likelihood that the rock beam will fracture. It is possible to reduce the initial weighting interval of the main roof by decreasing the thickness of the HSR and increasing the thickness of the load layer. The abutment pressure in the initial mining stage is obviously reduced after HF. The technical scheme of HF was proposed and applied in the field, and the field observations show that after HF, the HSR can collapse in time at the initial mining stage, leading to remarkable results being achieved.

INFLUENCE TECHNOLOGICAL PARAMETERS ON HYDRAULIC FRACTURING EFFICIENCY

Link for citation: Khizhniak G.P., Assane Dieng. Influence technological parameters on hydraulic fracturing efficiency. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 6, рр.120-125. In Rus. Relevance. Hydraulic fracturing in production and injection wells is one of the effective method for enhancing oil recovery, involving low-permeability zones and interlayers in the development, a mechanism for a wider coverage of productive zones by waterflooding, which makes it possible to convert part of off-balance reserves into commercial ones. According to experts, the use of hydraulic fracturing can increase the oil and gas recovery factor by 10–15 %. Currently, most of the oil fields in the Perm Territory are at the final stage of development. These fields, as a rule, are characterized by non-draining zones with residual reserves and low well flow rates. Most of the remaining reserves of the fields are concentrated in low-permeability reservoirs with a high degree of heterogeneity and difficult fluid filtration. The increase in the productivity of wells of these production facilities is achieved through the use of various geological and technical measures. The main aim: to develop a methodology for predicting the oil production rate post-frac with parameters that influence more, taking into account geological and technological characteristics of the object. Objects: Kashirskiy and Podolskiy carbonate deposits on one of the Permian fields. Methods: correlation and regression analysis. Results. The hydraulic fracturing method is widely used to increase well productivity. Unfortunately, oil flow rates obtained in practice do not always correspond to preliminary calculations. Using the example of one of the fields in the Perm Territory, a method proposed that allows estimating the initial oil production rate after hydraulic fracturing using the values of the technological parameters of productive deposits and the methods of mathematical statistics. A good agreement between model and experimental results was obtained.

Influence of the combined action of water and axial pressure on the microscopic damage and mechanical properties of limestone

As one of the main methods, hydraulic fracturing method is widely used in underground energy exploitation. Groundwater not only restricts the energy exploitation efficiency, but seriously affects the safety and stability of underground energy storage structure. To study the influence of groundwater and geostress on hydraulic fracture propagation and rock failure mechanism, the water injection tests were performed on limestone under different constant axial loading (0, 1, 2 and 3 MPa). After water injection, the evolution law of the micropore structure in water-injection samples were studied through SEM and mercury-injection tests; Moreover, the mechanical properties of the water-injection samples were studied through laboratory loading crushing tests. During loading process, the acoustic emission (AE) and infrared radiation temperature (IRT) parameters were collected synchronously and nondestructively. The results indicated that the pore size and porosity of limestone considerably increased with increasing axial pressure, and obvious stage characteristics of the stress-strain curve, cumulative AE energy and IRT difference were determined. Furthermore, the strength, cumulative AE energy and cumulative IRT difference decreased continuously with increasing axial pressure. Compared to limestone subjected to only water injection, the cumulative AE energy of the specimens subjected to high-pressure water under 1–3 MPa axial pressure decreased by 11.31%, 24.71% and 25.56%, and the IRT difference decreased by 10.71%, 19.64% and 26.79%, respectively. In addition, the extreme values of both cumulative AE energy and IRT occurred earlier than the peak stress, which can be interpreted as a sign of structural failure in limestone.

Determination of geo-stress in deep strata incorporating borehole diametral deformation measurement and overcoring

In deep energy engineering such as coal mining, oil & gas extraction, underground hydropower projects and deep buried water tunnels, rock failure and large deformation hazards often occur due to the complicated geological conditions and high geo-stress. Knowledge of the geo-stress state is an essential content in deep rock engineering. The complex environment of high temperature and high hydraulic pressure in deep rock mass makes geo-stress measurement more difficult than shallow strata. In this study, a novel method for geo-stress measurement based on the cross-sectional borehole diametral deformation is proposed. A borehole diametral deformation gage (BDD gage) is developed based on the measurement method. The scheme design of multi-contacts and micro-optical imaging avoid the influence of the high temperature and high hydraulic pressure environment. The results of the calibration experiment show that the measurement accuracy of BDD gage reaches 3 μm. Incorporating with the wireline coring tool for rapid overcoring, geo-stress measurement in deep vertical borehole via stress relief is realized. Field test procedure is summarized and application is carried out in a deep borehole of limestone stratum in Guizhou Province, China. Measurement process is verified to be rapid and simple. Measurement results including magnitude and direction of principal stresses are consistent with the results from hydraulic fracturing method. Special discussions were conducted on the measurement error of BDD gage and the improvement design of wireline coring tools. This article provides new ideas for geo-stress measurement in deep borehole.

FOAM ACID FRACTURE AS AN ALTERNATIVE TO STANDARD FRACKING AND LIQUID-LESS METHODS OF ROCKS LIQUIDATION

The article discusses the issue of the resource potential of tight terrigenous gas-saturated reservoirs, which lie at significant depths within the central part of the Dnipro-Donetsk oil and gas-bearing region, and ways to solve problems related to the methods of development of these deposits, since they are non-convective and cannot be extracted by the classical method. Within the scope of this issue, the article considers the method of hydraulic fracturing as one of the most effective ways of causing the inflow of hydrocarbons from the productive horizon and intensifying the development of hard-to-extract deposits. An overview of fracturing substances used for the process of densification of rocks, in particular, liquids based on water, hydrocarbon, acid bases, liquid-free methods and foam systems, was performed. The compositions of the reagents, the features of their use, and their main disadvantages are listed. Examples of world experience in the use of well-known fracturing fluids and fluid-free methods of reservoir densification are given.In this work, attention is focused on increasing the permeability of rocks through the use of foam acid systems, since, as experience shows, they are highly effective in conditions of tightand heterogeneous reservoirs due to their selectivity, they can be adapted to rocks of various lithological and mineralogical composition and a wide range thermo-baric conditions, they have satisfactory transport properties and the ability to cause self-cleaning of the well.The main reasons for popularizing the use of methods of loosening rocks with a minimum liquid content in the composition of explosive substances for unconventional gas deposits of Ukraine are highlighted. It is recommended to carry out work on the creation of more effective, ecological and economically profitable new or improvement of existing disintegrants, especially foam systems.

Early estimation method of rockburst and large deformation of surrounding rock based on the deep borehole test

In geotechnical engineering, several major catastrophic accidents occur frequently in areas of high in-situ stress. To study the influence of high in-situ stress on deep mining, the in-situ stress was tested using the hydraulic fracturing method in the mine. Based on the measured data of the initial stress, a comprehensive evaluation of the stress field of the deep surrounding rocks was carried out. Combining the physical and mechanical indexes of the surrounding rocks, field measurements, and theoretical analysis, the Russenes criterion and Turchaninov criterion were applied to evaluate the propensity of rockbursts of hard rocks in the mine area. In addition, the large deformation of the soft rock in the mine was predicted based on the large deformation classification criteria. The results demonstrate that the vertical stress is linearly related to the depth. The horizontal principal stress values tested in all holes except boreholes G and I are approximately linearly distributed with depth. The greater the depth, the greater the propensity for rockburst. For obvious deviation from the maximum horizontal main stress direction of the mining tunnel, the tendency of rockburst during construction is greater. Slight deformation occurs when the tunnel surrounding rock is shallow than 660 m; larger deformation occurs when the burial depth exceeds 660 m. Level-Ⅱ or level-Ⅲ deformations may occur near the bottom of holes F, G, and I due to the lower uniaxial compressive strength of the phyllites of these holes.

Experimental study on tensile strength of warm frozen soil based on hydraulic fracturing method

Tensile strength is one of the important parameters of frozen soil mechanics, which is widely used in engineering design of frozen soil and theoretical research of frost heave. At present, the research on tensile strength of frozen soil mainly focuses on low-temperature frozen soil, while that of warm frozen soil is less studied, thus limiting scientific evaluation of the tensile strength characteristics of warm frozen soil. In order to enrich the knowledge of tensile strength of warm frozen soil, the tensile strength experiments of silt clay from the Tibetan Plateau are carried out under various temperatures higher than −2 °C using the hydraulic fracturing method (HFM). Our results show that HFM can enable a reliable evaluation of the tensile strength of warm frozen soil, and the relationship between the tensile strength of warm frozen soil and negative temperature can be described by a power function. Compared with the results of uniaxial tension method (UTM) and radial splitting method (RSM), the feasibility of HFM can be regarded as an indirect tensile method in determining the tensile strength of frozen soil, and the suggestion for correcting the test results of indirect tensile method is given. In addition, the mechanism behind the influence of initial water content and temperature on tensile strength of warm frozen soil is analysed. Our results provide a new approach for researchers to analyse the tensile strength of warm frozen soil, thus can benefit the development of frost heave theory, and can reveal the influence of initial water content and temperature on the tensile strength of warm frozen soil.

Application and discussion of the borehole radial deformation method in deep borehole geostress measurement

Geostress is an important parameter in rock-related fields, such as civil engineering, mining engineering, and energy engineering. There are kinds of methods for geostress measurement; however, many methods still have some limitations, especially when facing deep vertical boreholes. In this paper, we studied the characteristics of borehole radial deformation under the action of geostress. First, the rule of borehole radial deformation under the action of a two-dimensional geostress was studied, and the shape of the borehole radial changes to an ellipse under the action of geostress was proved. We derived the relationship between the magnitude of principal stresses and the parameters of the borehole ellipse, revealing the rule that the principal axis direction of the borehole ellipse is the direction of principal stress, which is the theoretical basis for the geostress calculation method based on borehole radial deformation measurement. Furthermore, we developed an apparatus that can simultaneously measure the changes in borehole diameters in multi-directions. The apparatus was designed with a multi-contact equidistant arrangement, micro-optical imaging measurement, electronic compass azimuth measurement, etc. It can adapt to the complex testing environment of deep boreholes and realize real-time monitoring of the borehole deformation process. Indoor tests were carried out to verify the working performance of the apparatus. The results showed that the measuring accuracy of the apparatus can reach 6.987 μm, meeting the requirement of geostress measurement. Also, the results are well consistent with the loading force and direction of the testing machine. A field test was carried out in a deep borehole, and the borehole radial deformation data were obtained in the process of stress relief. The feasibility of the instrument and method was verified by comparison with the hydraulic fracturing method. This paper provides a new idea and method for geostress measurement, especially in deep vertical boreholes.

Increasing Gas Production of Continuous Freeze-Thaw Hydrate Deposits Based on Local Reservoir Reconstruction

The fracturing technology for increasing gas production based on hydrate reservoir reconstruction has been proven to have the application prospect of hydrate production. The main content of this work is to study the influence mechanism between multiple production wells after fracturing the reservoirs around horizontal wells. Simulation results indicated that the gas production rates and cumulative volume of released gas by using hydraulic fracturing were both higher than that by using the traditional depressurization method. The average gas-to-water ratio in this work has broken through the technical bottleneck of exploiting hydrate only by the traditional depressurization method. After the rock matrix around the horizontal well was fractured, the permeability of the reservoir in the fracturing area would be increased; thus, the propagation distance of pressure drop would be promoted. In addition, the penetration of the hydrate decomposition area between horizontal production wells was conducive to promoting the flow of decomposed gas and water to production wells. Besides, the hydraulic fracturing method to increase the permeability of the reservoir around the production well is very effective for the gas production of low-permeability natural hydrate deposits. The best distance between production wells was recommended to be 45~60 m, and it was recommended to provide appropriate heat in the area between the two wells to accelerate the decomposition of hydrate.

Experimental Investigation on Failure Mechanism of Hot Dry Rock under Microwave Irradiation

Hot dry rock (HDR) geothermal energy is clean energy that can meet people’s demand for low carbon. The traditional hydraulic fracturing method is challenging to break HDR dominated by granite, mainly because of HDR’s high temperature and hard characteristics. Microwave irradiation is considered a proven approach to breaking granite. This study investigates the failure mechanism of HDR at 500°C–800°C under microwave irradiation. The experiments cover preheating, uniaxial compression, granulometric analysis, binocular vision monitoring (BVM) technique, and X-ray powder diffraction. The result shows that the uniaxial compression strength of granite decreases the most at 500°C–600°C, which is 62.77% on average. The failure form is from the brittle failure (untreated) to ductile failure (800 °C) with the rise of the microwave irradiation temperature. The microwave makes a particle size in the range of 0.6–2.36 mm the most apparent particle size of granite after uniaxial compression. The BVM technique reconstructs the surface deformation with a 0.7% error. Microwaves cause heat accumulation near the rock near the magnetron, resulting in the formation of crack networks and a molten cavity. The possibility of microwave-assisted fracturing of HDR is discussed at the end of the article.

Research Status and Prospect of Hydraulic Fracturing Technology in Coal Mine

Hydraulic fracturing is one of the most effective methods to improve the permeability of coal seams at present. In order to promote the development of hydraulic fracturing technology in coal mines, the current development of hydraulic fracturing technology in coal mines is summarized from three aspects of hydraulic fracturing influencing factors, hydraulic fracturing methods and processes, and hydraulic fracturing effect evaluation. It is believed that the mechanism of hydraulic fracturing influencing factors, intelligent fracturing equipment, and systematic fracturing effect evaluation methods need further in-depth study.

Formation of accounting policies of a mining enterprise in accordance with International Financial Reporting Standards

Failure to take into account the perceived impacts of climate change threatens business continuity, for example, in agriculture, food production, the transport sector, and the extractive industry. Building a sustainable development strategy at mining enterprises requires the establishment of scientifically based goals. This will allow them to be specified in operational plans, budgets, and forecasts as part of the strategy. The development of a formalized plan should be based on data from the accounting system, the disclosure of which depends on the adopted accounting policy of the enterprise. Despite the existing methodological and methodical developments regarding the reflection of information in the financial statements of the mining enterprise, there are still debatable issues regarding the attribution to capitalization or expenses of the current period of accruals for individual stages of exploration and evaluation, regarding the accounting of geological information, seismic operations, exploration drilling, depreciation by the production method, accounting and evaluation of hydraulic fracturing and other issues. The complexity of developing an accounting methodology is associated with problems of terminology; unclear formulation of the nature of the asset arising from mining activities; the level of aggregation of information; unclear understanding of the types of mining activities; differentiation of the processes of exploration and evaluation of natural resources at mining enterprises from research activities; recognition of an individual asset «work in progress»; subjectivity associated with assumptions about fair value measurement and other issues. The article proposes disclosure of certain provisions of the accounting policy, in particular, on investment real estate, reserves, employee benefits, capitalized costs for overburden, overburden costs, exploration and evaluation costs of minerals, quarry development costs, intangible assets, reserve for quarry reclamation, borrowing costs, income recognition.

Discrete element modeling for the multistage hydraulic stimulation of a horizontal well in hot dry rock

Hydraulic fracturing aimed at building a network of fractures in hot dry rock (HDR) often induces strong seismic risks. However, few studies have focused on seismic risks, and methods for increasing the stimulated reservoir volume (SRV) while reducing seismic risks have not been adequately studied. Therefore, based on the full hydro-mechanical coupling, a seismic-fracturing model with a discrete fracture network (DFN) was developed, and the methods for increasing the SRV while reducing the seismic risk of horizontal wells at the FORGE site in Utah were discussed. The results showed that the fluid channeling effect between each segment is the main reason for the uneven fracture growth in the horizontal well. Additionally, the spatiotemporal evolution of fracturing-induced seismicity shows that the two ends (L1 and L3) of the horizontal well tend to form high stress concentrations and induce larger seismic events than the middle (L2). To solve these problems, a novel hydraulic fracturing method with a differentiated-stage, variable-injection volume suitable for the multi-fracturing of horizontal wells in HDR was proposed. With the application of the method, the SRV of the horizontal well was improved effectively, and the average magnitude induced by hydraulic fracturing was also decreased by 15.4%.