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Research and Exploration of High Energy Gas Fracturing Stimulation Integrated Technology in Chinese Shale Gas Reservoir
Abstract
The reserves of Chinese shale gas is very rich, but still haven’t ever formed a mature technology. According to Chinese shale gas reservoir characteristics, the development technology situation and the principle of high energy gas fracturing, the research and exploration of HEGF stimulation integrated technology which is suitable for the development of Chinese shale gas reservoir need to be carried out. Through a series of analysis and study, compositing high energy gas fracturing technology achievements, this paper discusses the research idea and feasibility of the integrated technology, formed by the liquid gunpowder fracturing technology, in-fracture deeply explosive fracturing technology in low permeability oil layers, composite perforating technology, the multi-pulse fracturing technology and the hydraulic fracturing, simultaneous fracturing ,which transforms shale gas reservoir and develops shale gas. Launching field application test is suggested, and studying the way to optimize the theory and design method of integrated technology, so as to promote the development of shale gas.
... There have been many studies on waterless fracturing fluids, such as liquefied petroleum gases [12][13][14], supercritical carbon dioxide or liquid carbon dioxide [15][16][17], high energy gas [18,19], nitrogen foam [20,21], and LN 2 [6,11]. These waterless fracturing technologies have been applied. ...
Cryogenic LN2 fracturing is one of the environmentally friendly waterless fracturing technologies that promote the fracture complexity of shale gas reservoir. The water-ice phase transition under freezing condition causes frost heave in saturated shale. The effect of moisture in shale should be taken into account during cryogenic damage process. Therefore, the differences of cracking characteristics between dry and saturated shales were studied in this paper. A laboratory triaxial and high temperature fracturing system was developed for nitrogen fracturing dry and saturated shale after LN2 injection. The influence of moisture on breakdown pressure was studied under different confining pressures (3 MPa, 6 MPa, 9 MPa, and 12 MPa) and bedding directions (parallel bedding and vertical bedding). The experimental results demonstrated that when the confining pressure increased from 3 MPa to 12 MPa, the breakdown pressure of dry parallel bedding after LN2 preconditioning decreased 7.12 MPa, 6.06 MPa, 4.58 MPa, and 3.11 MPa, respectively. Therefore, LN2 preconditioning could damage shale resulting in a lower breakdown pressure, but the effect of cryogenic damage decreased with the confining pressure increasing. The moisture in shale had little impact on nitrogen fracturing without LN2 injection because the breakdown pressure difference between dry and saturated shales was small. However, the breakdown pressure of saturated shale after LN2 preconditioning was always lower than that of dry shale. The breakdown pressure of saturated parallel bedding shale after LN2 injection decreased 8.62 MPa, 7.67 MPa, 6.08 MPa, and 4.63 MPa, respectively, with the confining pressure increasing from 3 MPa to 12 MPa. The breakdown pressure difference between dry and saturated shales was impacted by the migration of unfrozen water and frost heave. In addition, the extent of cryogenic damage varied substantially between different bedding directions. When the confining pressure was 3 MPa, the breakdown pressure of saturated parallel bedding shale reduced by 69.18% after LN2 preconditioning, but that of saturated vertical bedding shale only decreased by 22.49%. The tensile strength of shale had a greater influence on the breakdown pressure. According to the Brazilian disc test results, the tensile strength of matrix was much higher than that of bedding planes. As a result, it is useful to wet the shale in order to reduce the breakdown pressure. The fracturing direction of horizontal drilling should be consistent with the bedding direction for better cryogenic fracturing effect.
... New shale gas development technologies must be explored [1] for wider fracture works. The in-situ combustion-explosion technology is a transformative and disruptive technology in shale gas production [2,3]. It is a complex dynamic process of shale fracturing during in-situ combustion-explosion of methane [4,5]. ...
The in-situ combustion–explosion fracturing technology in shale reservoirs can promote continuous fracture expansion with a radial detonation wave first converging into a shock wave and then decaying into an elastic wave. The transformation scale of the shale reservoir is determined by the range of wave propagation during combustion–explosion. As wave propagation paths are usually tortuous and fractal, the previous integer wave models are not competent to describe the wave propagation and estimate the impact range of the combustion–explosion fracturing process. This study develops two fractional wave propagation models and seeks analytical solutions. Firstly, a novel fractional wave model of rotation angle is proposed to describe the process of detonation waves converting into shock waves in a bifurcated structure. The radial displacement gradient of the detonation wave is represented by the internal expansion and rotation deformation of the shale. Secondly, another fractional wave propagation model of radial displacement is proposed to show the process of a shock wave decaying into an elastic wave. Thirdly, the proposed models are analytically solved through the fractional variable separation method and variational iteration method, respectively. Analytical solutions for rotation angle and radial displacement with fractal time and space are obtained. Finally, the impacts of the branching parameter of the detonation wave converge bifurcation system, aggregation order of detonation compression wave, and different types of explosives on the rotation angle of the shock wave are investigated. The propagation mechanism of the primary wave (P-wave) with time and space is analyzed. The analytical solutions can well describe the wave propagation process in fractured shales. The proposed fractional wave propagation models can promote the research of wave propagation in the combustion–explosion fracturing process of shale reservoirs.
... At present, the fracturing fluid involved in multistage pulse fracturing is mainly gunpowder, which has certain risks. In order to ensure the safety of multi-direction fracturing and fracturing initiation, the charge rate of multistage pulse fracturing is usually in the following order: first-stage burning rate-high-medium rate gunpowder [38] [39]. ...
Oil and gas reserves in our country are large and widely distributed, and usually fracturing techniques are needed to extract oil and gas. Currently, the more mature hydraulic fracturing technology is difficult to extract coal bed methane. Combined with the research progress of fracturing at home and abroad, this paper summarizes the development of relevant anhydrous fracturing technology, fracturing fluid, fracturing process and other aspects, compares and analyzes the advantages and disadvantages of fracturing technology, and provides some ideas for the development of anhydrous fracturing technology in the future. In order to reduce the cost of anhydrous fracturing, meet the requirements of field application, and accelerate the research progress of anhydrous fracturing, the commonly used fracturing technologies are combined to study new fracturing fluids and carry out composite anhydrous fracturing.
... Pulse fracturing can be implemented with hydraulic fracturing operations or can be utilized as a standalone technique. For instance; when the materials/equipment for injecting fluid are not available on the field (Krilove et al., 2008;Zazovsky, 2004), when to stimulate naturally fractured reservoirs to connect with preexisting fractures (Schatz et al., 1989;Schmidt et al., 1980;Wu et al., 2012;Yang et al., 1992), when to stimulate heavy oil with cold heavy oil production technique (Dusseault M. B. and Spanos, 1999;Haney and Cuthill, 1997), to remove condensate banking nearby wellbore region (Al-Nakhli et al., 2013), and when to avoid formation damage near the vicinity of the wellbore originated due to perforation (Gilliat et al., 1999). The detailed description of pulse fracturing can be found in our previous publication (Al-Nakhli et al., 2019;Tariq et al., 2019cTariq et al., , 2019a. ...
Current global energy demand and supply gap needs the best engineering methods to recover hydrocarbons from the unconventional hydrocarbon formations. Unconventional hydrocarbons normally present in deep formations, where the overburden stresses and formation integrity are very high. When fracturing these types of formations, the hydraulic fracturing job becomes much more challenging, and in some scenarios, pumping reached to the maximum capacity limits without generating any fracture. This reduces the operational gap to optimally placed hydraulic fractures. In the present research study, a novel thermochemical fracturing approach is presented to reduce the breakdown pressure of the high-strength formations. The hydraulic fracturing experiments presented in this study are carried out on ultra-tight cement block samples. The composition of cement blocks is synthesized in this way that it simulates the real rocks. The results showed that the newly proposed thermochemical fracturing approach reduced the breakdown pressure in ultra-tight cement from 1095 psia (reference breakdown pressure recorded from conventional hydraulic fracturing technique) to 705 psia. The post treatment experimental analysis showed that the thermochemical fracturing approach resulted in a deep and long fracture while conventional hydraulic fracturing resulted in a thin fracture. In addition to that, a Finite element analysis using ABAQUS is also presented. The main purpose of the numerical investigation is to confirm the sufficiency of the experimental data for reproducing the same breakdown pressure that included depiction of injection pressure versus time plots, failure loads and cracking patterns.
... Pulse fracturing treatment can be applied as a standalone technique or can be combined with the conventional hydraulic fracturing treatments, and in many cases, the combination is more attractive than the only conventional hydraulic fracturing operation. Some of the examples include but are not limited to water availability on the wellsite [21,22], connecting preexisting fractures with induced fractures in naturally fractured carbonate reservoirs [23][24][25][26], stimulating heavy oil reservoirs [27,28], removing condensate banking near the region of the wellbore [29], and reducing formation damage near the vicinity of the wellbore [30]. A comprehensive review of the pulse fracturing technique and its field implementation can be found in our previous publication [31]. ...
Current oil prices and global financial situations underline the need for the best engineering practices to recover remaining oil from unconventional hydrocarbon reservoirs. These hydrocarbon reservoirs are mostly situated in deep and overpressured formations, with high rock strength and integrity. Breakdown pressure of the rock is a function of their tensile strength and in situ stresses acting on them. Fracturing stimulation techniques become challenging when treating these types of rocks, and many cases approached to the operational limits. This leaves a small operational window to initiate and place hydraulic fractures. In this study, a new methodology to reduce the breakdown pressure of the high stressed rock is presented. The new method enables the fracturing of high stressed rocks more economically and efficiently. Fracturing experiments were carried out on different blocks, and the breakdown pressure was measured by creating a simulated borehole at the center of the block. Thermochemical fluids were injected to create the microfractures. These microfractures improved the permeability and porosity and reduced the elastic strength of the subjected samples prior to the main hydraulic fracturing job. The posttreatment experimental analysis confirmed the presence of microfractures which were originated due to the pressure pulse generated from the thermochemical reaction. The results of this study showed that the newly formulated method of thermochemical fracturing reduced the breakdown pressure by 38% in slim borehole blocks and 60% in large borehole blocks. Results also showed that the breakdown time to initiate the fractures was reduced to 19% in slim borehole blocks and 17% in large borehole blocks. The reduction in breakdown pressure and breakdown time happened due to the creation of microfractures by the pressure rise phenomenon in a new thermochemical fracturing approach.
... The main advantage of pulse fracturing over conventional hydraulic fracturing is that lower injection pressure can be used in pulse fracturing. Furthermore, the generated fractures will propagate deeper in the case of pulse fracturing compared to normal hydraulic fracturing [13,15,16]. A new method of pulse fracturing was developed by Al-Nakhli et al. [17], where the fractures are generated using thermochemical fluids. ...
Unconventional reservoirs have shown tremendous potential for energy supply for long-term applications. However, great challenges are associated with hydrocarbon production from these reservoirs. Recently, injection of thermochemical fluids has been introduced as a new environmentally friendly and cost-effective chemical for improving hydrocarbon production. This research aims to improve gas production from gas condensate reservoirs using environmentally friendly chemicals. Further, the impact of thermochemical treatment on changing the pore size distribution is studied. Several experiments were conducted, including chemical injection, routine core analysis, and nuclear magnetic resonance (NMR) measurements. The impact of thermochemical treatment in sustaining gas production from a tight gas reservoir was quantified. This study demonstrates that thermochemical treatment can create different types of fractures (single or multistaged fractures) based on the injection method. Thermochemical treatment can increase absolute permeability up to 500%, reduce capillary pressure by 57%, remove the accumulated liquids, and improve gas relative permeability by a factor of 1.2. The findings of this study can help to design a better thermochemical treatment for improving gas recovery. This study showed that thermochemical treatment is an effective method for sustaining gas production from tight gas reservoirs.
... Krilove et al. (2008) investigated the capability of this technique by applying it on petrophysical laboratory samples and inside production wells. They concluded that HEGF is an effective and efficient method which can increase the oil production rate by a factor of 2 to 3. It has also been experimentally observed that HEGF is rather suitable for exploratory wells or wells with natural fissures around them (Yang et al. 1992;Wu et al. 2012). In addition, this method has been successfully implemented in other applications such as enhancing the injectivity of gas injection wells (Salazar et al. 2002), prefracturing before hydraulic fracturing to reduce the friction pressure losses near the wellbore (Jaimes et al. 2012), stimulating geothermal wells (Chu et al. 1987), extracting gas from coal seams (Chao et al. 2013), etc. ...
High energy gas fracturing is a simple approach
of applying high pressure gas to stimulate wells by generating several radial cracks without creating any other
damages to the wells. In this paper, a numerical algorithm
is proposed to quantitatively simulate propagation of these
fractures around a pressurized hole as a quasi-static phenomenon. The gas flow through the cracks is assumed as a
one-dimensional transient flow, governed by equations of
conservation of mass and momentum. The fractured
medium is modeled with the extended finite element
method, and the stress intensity factor is calculated by the
simple, though sufficiently accurate, displacement extrapolation method. To evaluate the proposed algorithm,
two field tests are simulated and the unknown parameters
are determined through calibration. Sensitivity analyses are
performed on the main effective parameters. Considering
that the level of uncertainty is very high in these types of
engineering problems, the results show a good agreement
with the experimental data. They are also consistent with
the theory that the final crack length is mainly determined
by the gas pressure rather than the initial crack length
produced by the stress waves.
A multiscale complex fracture and matrix damage coupled productivity prediction model under cyclic percussion of horizontal wells is established, according to the evolution of matrix permeability and the characteristics of complex fracture seepage after cyclic conflagration compression fracturing. The effects of the conflagration loading rate, cyclic percussion times, horizontal in situ stress difference, seepage interference, and wellbore pressure drop on horizontal well productivity are analyzed. The results show that the loading rate and percussion times are positively correlated with the production growth rate, but the growth through percussion has a threshold. Besides that, the length of the branch fracture is closer to that of the main fracture when there is a small stress difference, which results in a higher initial productivity and recovery degree of the gas well. Additionally, section spacing can affect the distribution of the pressure field and flow field around the well. An excessive spacing can lead to bending of flow field around the well, while a too small value is able to aggravate interjoint interference. Therefore, the critical section spacing, which can establish pressure communication between sections, is taken as the optimal section spacing. According to our work, when the fracture half-length is 5, 7, and 9 m, the optimum section spacing is 15, 25, and 30 m, respectively. Under this condition, when the horizontal length exceeds 800, 700, and 500 m, the influence of the wellbore pressure drop on the productivity of horizontal wells should be considered.
The behavior of gas flow in fractures is crucial for evaluating shale gas production. This study focused on the coupling relationships between effective stress, surface roughness, and gas flow behavior in shale fractures. Three fractured shale specimens were generated using Brazilian splitting tests. The fracture surfaces were then scanned using a 3D profilometer to quantify surface roughness in two and three dimensions. Gas flow tests were conducted on the fractured shale specimens under varying effective stresses (1–15 MPa). The results showed that the Spc (arithmetic mean curvature of crest points) had little effect on nonlinear flow at low effective stress (1–5 MPa) but it became more pronounced at high effective stress (10–15 MPa) due to fracture channel narrowing. Then, the inertial force effect regulated by effective stress and roughness was enhanced as the Reynolds number increased. A friction coefficient model based on the nonlinear effect factor and Reynolds number is proposed and it fits the experimental data well. Furthermore, that effective stress plays a dominant role in permeability loss compared to fracture surface roughness and fluid properties, and exponential function better describes fractured shale permeability under effective stress than power function. Finally, during fracture closure under effective stress, Ra (arithmetic mean roughness) correlated positively with the self-supporting effect of fracture surfaces. As Spc increased, fracture surface peaks became sharper and more easily damaged due to excessive extrusion between contact surfaces.
The mechanical properties of conventional simulated cement target is very different from coal-bed methane. However, if large size coal rock is directly used for the ground test of multi-pulse fracturing, the coal rock will be completely broken and the formation state of multiple fractures cannot be observed. We studied and designed the simulation test method of CBM coal rock coated with cement target. It mainly includes coal rock coal sample, coated cement layer, multi-pulse test device and test system, etc. The formation state of multiple cracks in coal rock can be obviously observed by firing range test, and P-T curve can be measured. It provides a new experimental method for the study of multi-pulse fracturing mechanism of low permeability coal-bed methane.KeywordsCoal-bed methaneMulti-pulse fracturingSimulation testDesign method
A multi-fracture pressure flow regime coupled productivity prediction model considering shale gas adsorption and desorption, mass transfer and diffusion and cross-scale zoning was established based on cross-scale seepage characterization in unmodified area, interstitial matrix area, main fracture area, branched micro-fracture area and broken damage area formed from by conflagration compression fracturing. Then, geometric similarity, hydropower similarity and coupled iteration were used to build the model and complete the calculation. Finally, the effects of regional cross-scale seepage, number of fractures, production pressure difference, and fracture zone scale on gas well productivity were analyzed. The following results were obtained. First, the seepage flow of shale gas in different fractured areas is a continuous changing process. Among them, the unaffected area is dominated by transition flow and slip flow while continuous flow exists in the microfracture area-wellbore broken area and artificial fracture area. Second, the productivity of gas wells increases with the increase of fracture length and number, but the productivity increase tends to be stable after the fracture length exceeds 2 m. It is worth to mention that the increase of the number of fractures is more conducive to improving the productivity of shale gas under this condition. Third, when the number of high energy gas fractures is 6, its mining capacity is equivalent to that of hydraulic fracturing fractures with a half-fracture length of about 100 m. Fourth, when the production pressure difference exceeds 22 MPa, the free gas production capacity shows a decreasing trend. Therefore, the preferred production pressure difference is about 22 MPa. Fifth, the greater the number of artificial fractures, the greater the contribution of the increase in the diffusion coefficient to productivity, and the existence of wellbore fracture zone is also conducive to the stimulation of gas wells.
Shale gas has become the major source of natural gas. However, shale is rich in clay and easily collapsed by water invasion. This not only causes collapse of the reservoir but also causes the loss of natural gas and can even cause local earthquakes and affect the safety of human beings. This paper describes an investigation of the relationship between hydration and collapse. Shale samples were obtained from a series of wells drilled in the lower Silurian Longmaxi Formation at a depth of 3500 m. The different hydrated shales were simulated to analyze the hydration-collapse relationship. Magnetic resonance analysis and mechanical analysis were combined to analyze the collapse of the hydrated shales. The collapse progression was found to follow an S-shaped growth curve that can be divided into three parts, namely, the potential period, the exciting period, and the mature period. The hydration state and degree of damage were determined from the magnetic resonance of water molecules. This paper proposes a mechanism for shale hydration collapse based on basal and numerical data that can be used to predict shale collapse as a function of hydration.
Fracturing plays, a vital role to achieve the optimal recovery from the unconventional shale gas reservoirs and fracturing fluid is considered as “blood” in the entire operation. There are various fracking technology to frack the shale viz., traditional hydraulic fracturing, nitrogen based fracturing, high-energy gas fracturing (HEGF), supercritical carbon di oxide fracturing (SC-CO2), plasma fracturing, etc. However, SC-CO2 fracking requires less water and is able to generate three-dimensional fractures with its low viscosity. It is also considered as a good option for using as a fracking fluid in unconventional shale or tight gas reservoirs because of its properties of liquid like density, low viscosity, without any capillary force, good miscible characteristics with hydrocarbons. The low viscosity of SC-CO2 can create complex, multi-orthogonal fracture networks in unconventional shale reservoir resulting into high flow rates. Similarly, HEGF is also characterised by less water consumption, it uses propellant to burn the formation around wellbore area and make tailored pressure–time behaviour. This burning is fully controllable from surface and is able to produce multiple fractures in all radial directions at short distance. The present review paper discusses the recent scientific studies on supercritical CO2 fracking and high energy gas fracking in unconventional shale and examine its experimental results, field results, its advantages and disadvantages.Graphical abstract
Shale gas and other unconventional resources such as coal bed methane, gas hydrates, tight oil etc. have gained significant worldwide interest because of their potential to increase the energy supply. Hydro fracking is the common technique to exploit the shale reservoir. However, there are some technical and environmental challenges linked to hydro fracking, which must be addressed in order to optimize resource recovery. Plasma fracturing has emerged as a technological breakthrough that may improve unconventional shale gas recovery which is a sustainable technique preventing the depletion of water resource and also reduces cost, energy use and environmental impacts. This technique utilizes the electrical energy to generate the plasma pulses thus minimizes the formation damage near the wellbore. The present paper reviews research progress on plasma fracturing mechanism and its advantages and associated challenges.
Brownfields and depleting conventional resources of fossil fuel energy are not enough to fulfill the tremendously increasing energy demands around the globe. Unconventional oil and gas resources are creating a huge impact on the enhancement of the global economy. Tight rocks are usually located in deep and high-strength formations. In this study, numerical simulation results on a new thermochemical fracturing approach is presented. The new fracturing approach was implemented to reduce the breakdown pressure of the unconventional tight formations. The hydraulic fracturing experiments presented in this study were carried out on ultra-tight cement block samples. The permeability of the block samples was less than 0.005mD. Thermochemical fracturing was carried out by a thermochemical fluids that caused a rapid exothermic reaction which resulted in the instantaneous generation of heat and pressure. Different salts of nitrogen such as sodium nitrite and ammonium chloride were used as a thermochemical fluid. The instantaneous generation of the heat and pressure caused the creation of micro-cracks. The fracturing results revealed that the novel thermochemical fracturing was able to reduce the breakdown pressure in ultra-tight cement from 1095 psi to 705 psi. The reference breakdown pressure was recorded from the conventional fracturing technique. A finite element (FEM) analysis was conducted using commercial software ABAQUS. In FEM, two approaches were used to model the thermochemical fractures namely, cohesive zone modeling (CZM) and concrete damage plasticity models (CDP). The sensitivity analysis of peak pressure and time to reach the peak pressure is also presented in this study. The sensitivity analysis can help in better designing thermochemical fluids that could lead to the maximum generation of micro-cracks and multiple fractures.
High Energy Gas Fracturing (HEGF) technology can produce self-supporting crack network in rocks of oil and gas reservoirs under a large number of high temperature and high pressure explosive shock wave caused by explosive detonation. It is expected that the reservoir conductivity will be improved by generating the new crack channels for oil and gas flow, so as to achieve the goal of increasing oil and gas production. However, the numerical study on the crack initiation, extension and propagation of rock under blast loading is still insufficient, which plays a vital role in better understanding the mechanical performance of rocks in the HEGF process. In the present study, taking the typical shale gas demonstration area in Sichuan province as an example, the shale crack model is established, the mechanical properties of shale rock with cracks under explosive loading are studied, the evolution laws of crack propagation are analyzed, and the damage characteristics of crack tip are considered.
The enormous resources of hydrocarbons hold by unconventional reservoirs across the world along with the growing oil demand make their contributions to be most imperative to the world economy. However, one of the major challenges faced by oil companies to produce from the unconventional reservoirs is to ensure economical production of oil. Unconventional reservoirs need extensive fracturing treatments to produce commercially viable hydrocarbons. One way to produce from these reservoirs is by drilling horizontal well and conduct multistage fracturing to increase stimulated reservoir volume (SRV), but this method of increasing SRV is involved with higher equipment, material, and operating costs.
To overcome operational and technical challenges involved in horizontal wells multistage fracturing, the alternative way to increase SRV is by creating multiple radial fractures by performing pulse fracturing. Pulse fracturing is a relatively new technique, can serve as an alternative to conventional hydraulic fracturing in many cases such as to stimulate naturally fractured reservoirs to connect with pre-existing fractures, to stimulate heavy oil with cold heavy oil production technique, to remove condensate banking nearby wellbore region, and when to avoid formation damage near the vicinity of the wellbore originated due to perforation. Pulse fracturing is not involved with injecting pressurized fluids into the reservoir, so it is also a relatively cheaper technique.
The purpose of this paper is to present a general overview of the pulse fracturing treatment. This paper will give general idea of the different techniques and mechanisms involved in the application of pulse fracturing technique. The focus of this review will be on the comparison of different fracturing techniques implemented normally in the industry. This study also covers the models developed and applied to the simulation of complex fractures originated due to pulse fracturing.
In order to solve the difficulty of low-permeability reservoir development, the study on the mechanism and the test of the explosion technique in low-permeability oil layer are carried, and the liquid explosive used for the technique in microscopic critical size is developed. The liquid explosive can stably explode in formation fracture and produce a new fracture network. The mechanism and the main performance parameters such as critical size of the technique are introduced. The field test in horizontal wells proves the safety reliability and the field operability of the technique, which lays a foundation for the further study on the technology, the matching techniques and the field tests of the explosion technique.
in: A key factor promoting rapid development of shale gas in America, Technical progress, Natural Gas Industry
- Yuzhen Huang
- Jinliang Huang
Study and Application of Liquid Powder High Energy Gas Fracturing Technology in Horizontal Well, Drilling & Production Technology, In Chinese
- Jinjun Wu
- Hongwei Liao
- Jie Zhang