An Efficient Numerical Hybrid Model for Multiphase Flow in Deformable Fractured-Shale Reservoirs

SPE Journal ◽  
2018 ◽  
Vol 23 (04) ◽  
pp. 1412-1437 ◽  
Author(s):  
Xia Yan ◽  
ZhaoQin Huang ◽  
Jun Yao ◽  
Yang Li ◽  
Dongyan Fan ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Hybrid Model ◽  
Hydraulic Fractures ◽  
Fluid Exchange ◽  
Flow Process ◽  
Numerical Examples ◽  
Fracturing Process ◽  
The Matrix ◽  
Shale Reservoirs ◽  
Porosity Model

Summary After hydraulic fracturing, a shale reservoir usually has multiscale fractures and becomes more stress-sensitive. In this work, an adaptive hybrid model is proposed to simulate hydromechanical coupling processes in such fractured-shale reservoirs during the production period (i.e., the hydraulic-fracturing process is not considered and cannot be simulated). In our hybrid model, the single-porosity model is applied in the region outside the stimulated reservoir volume (SRV), and the matrix and natural/induced fractures in the SRV region are modeled using a double-porosity model that can accurately simulate the matrix/fracture fluid exchange during the entire transient period. Meanwhile, the fluid flow in hydraulic fractures is modeled explicitly with the embedded-discrete-fracture model (EDFM), and a stabilized extended-finite-element-method (XFEM) formulation using the polynomial-pressure-projection (PPP) technique is applied to simulate mechanical processes. The developed stabilized XFEM formulation can avoid the displacement oscillation on hydraulic-fracture interfaces. Then a modified fixed-stress sequential-implicit method is applied to solve the hybrid model, in which mixed-space discretization [i.e., finite-volume method (FVM) for flow process and stabilized XFEM for geomechanics] is used. The robustness of the proposed model is demonstrated through several numerical examples. In conclusion, several key factors for gas exploitation are investigated, such as adsorption, Klinkenberg effect, capillary pressure, and fracture deformation. In this study, all the numerical examples are 2D, and the gravity effect is neglected in these simulations. In addition, we assume there is no oil phase in the shale reservoirs, thus the gas/water two-phase model is used to simulate the flow in these reservoirs.

scholarly journals Three-Dimensional Ultrasonic Imaging and Acoustic Emission Monitoring of Hydraulic Fractures in Tight Sandstone

2021 ◽  
Vol 11 (19) ◽  
pp. 9352
Author(s):  
Wei Zhu ◽  
Shangxu Wang ◽  
Xu Chang ◽  
Hongyu Zhai ◽  
Hezhen Wu
Keyword(s):  
Acoustic Emission ◽  
Hydraulic Fracturing ◽  
Rock Mechanics ◽  
Oil And Gas ◽  
Ordos Basin ◽  
Water Injection ◽  
Three Dimensional ◽  
Hydraulic Fractures ◽  
Tight Sandstone ◽  
Fracturing Process

Hydraulic fracturing is an important means for the development of tight oil and gas reservoirs. Laboratory rock mechanics experiments can be used to better understand the mechanism of hydraulic fracture. Therefore, in this study we carried out hydraulic fracturing experiments on Triassic Yanchang Formation tight sandstone from the Ordos Basin, China. Sparse tomography was used to obtain ultrasonic velocity images of the sample during hydraulic fracturing. Then, combining the changes in rock mechanics parameters, acoustic emission activities, and their spatial position, we analyzed the hydraulic fracturing process of tight sandstone under high differential stress in detail. The experimental results illuminate the fracture evolution processes of hydraulic fracturing. The competition between stress-induced dilatancy and fluid flow was observed during water injection. Moreover, the results prove that the “seismic pump” mode occurs in the dry region, while the “dilation hardening” and “seismic pump” modes occur simultaneously in the partially saturated region; that is to say, the hydraulic conditions dominate the failure mode of the rock.

scholarly journals Effect of Joint Geometrical Parameters on Hydraulic Fracture Network Propagation in Naturally Jointed Shale Reservoirs

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-23 ◽  
Author(s):  
Zhaohui Chong ◽  
Qiangling Yao ◽  
Xuehua Li
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Geometrical Parameters ◽  
Breakdown Pressure ◽  
Opening Mode ◽  
Hydraulic Fracture Network ◽  
Shale Reservoirs ◽  
Network Pattern

The presence of a significant amount of discontinuous joints results in the inhomogeneous nature of the shale reservoirs. The geometrical parameters of these joints exert effects on the propagation of a hydraulic fracture network in the hydraulic fracturing process. Therefore, mechanisms of fluid injection-induced fracture initiation and propagation in jointed reservoirs should be well understood to unleash the full potential of hydraulic fracturing. In this paper, a coupled hydromechanical model based on the discrete element method is developed to explore the effect of the geometrical parameters of the joints on the breakdown pressure, the number and proportion of hydraulic fractures, and the hydraulic fracture network pattern generated in shale reservoirs. The microparameters of the matrix and joint used in the shale reservoir model are calibrated through the physical experiment. The hydraulic parameters used in the model are validated through comparing the breakdown pressure derived from numerical modeling against that calculated from the theoretical equation. Sensitivity analysis is performed on the geometrical parameters of the joints. Results demonstrate that the HFN pattern resulting from hydraulic fracturing can be roughly divided into four types, i.e., crossing mode, tip-to-tip mode, step path mode, and opening mode. As β (joint orientation with respect to horizontal principal stress in plane) increases from 0° to 15° or 30°, the hydraulic fracture network pattern changes from tip-to-tip mode to crossing mode, followed by a gradual decrease in the breakdown pressure and the number of cracks. In this case, the hydraulic fracture network pattern is controlled by both γ (joint step angle) and β. When β is 45° or 60°, the crossing mode gains dominance, and the breakdown pressure and the number of cracks reach the lowest level. In this case, the HFN pattern is essentially dependent on β and d (joint spacing). As β reaches 75° or 90°, the step path mode is ubiquitous in all shale reservoirs, and the breakdown pressure and the number of the cracks both increase. In this case, β has a direct effect on the HFN pattern. In shale reservoirs with the same β, either decrease in k (joint persistency) and e (joint aperture) or increase in d leads to the increase in the breakdown pressure and the number of cracks. It is also found that changes in d and e result in the variation in the proportion of different types of hydraulic fractures. The opening mode of the hydraulic fracture network pattern is observed when e increases to 1.2 × 10−2 m.

scholarly journals Experimental Investigation of the Impacts of Fracturing Fluid on the Evolution of Fluid Composition and Shale Characteristics: A Case Study of the Niutitang Shale in Hunan Province, South China

Energies ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 3320
Author(s):  
Jingqiang Tan ◽  
Guolai Li ◽  
Ruining Hu ◽  
Lei Li ◽  
Qiao Lyu ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Mineral Dissolution ◽  
Hunan Province ◽  
Fluid Composition ◽  
Fracturing Fluid ◽  
Specific Chemical ◽  
Metal Elements ◽  
Fracturing Process ◽  
Geochemical Reactions ◽  
Shale Reservoirs

Hydraulic fracturing is a widely used technique for oil and gas extraction from ultra-low porosity and permeability shale reservoirs. During the hydraulic fracturing process, large amounts of water along with specific chemical additives are injected into the shale reservoirs, causing a series of reactions the influence the fluid composition and shale characteristics. This paper is focused on the investigation of the geochemical reactions between shale and fracturing fluid by conducting comparative experiments on different samples at different time scales. By tracking the temporal changes of fluid composition and shale characteristics, we identify the key geochemical reactions during the experiments. The preliminary results show that the dissolution of the relatively unstable minerals in shale, including feldspar, pyrite and carbonate minerals, occurred quickly. During the process of mineral dissolution, a large number of metal elements, such as U, Pb, Ba, Sr, etc., are released, which makes the fluid highly polluted. The fluid–rock reactions also generate many pores, which are mainly caused by dissolution of feldspar and calcite, and potentially can enhance the extraction of shale gas. However, precipitation of secondary minerals like Fe-(oxy) hydroxides and CaSO4 were also observed in our experiments, which on the one hand can restrict the migration of metal elements by adsorption or co-precipitation and on the other hand can occlude the pores, therefore influencing the recovery of hydrocarbon. The different results between the experiments of different samples revealed that mineralogical texture and composition strongly affect the fluid-rock reactions. Therefore, the identification of the shale mineralogical characteristics is essential to formulate fracturing fluid with the lowest chemical reactivity to avoid the contamination released by flowback waters.

Practical Solutions for Pressure-Transient Responses of Fractured Horizontal Wells in Unconventional Shale Reservoirs

2011 ◽  
Vol 14 (06) ◽  
pp. 663-676 ◽  
Author(s):  
M.. Brown ◽  
E.. Ozkan ◽  
R.. Raghavan ◽  
H.. Kazemi
Keyword(s):  
Horizontal Wells ◽  
Flow Regimes ◽  
Fluid Exchange ◽  
Diagnostic Features ◽  
Pressure Transient ◽  
Flow Solution ◽  
The Matrix ◽  
Computationally Intensive ◽  
Shale Reservoirs ◽  
Fractured Horizontal Wells

Summary This paper presents an analytical trilinear-flow solution to simulate the pressure-transient and production behaviors of fractured horizontal wells in unconventional shale reservoirs (Ozkan et al. 2009). The model is simple, but versatile enough to incorporate the fundamental petrophysical characteristics of shale reservoirs, including the intrinsic properties of the matrix and the natural fractures. Special characteristics of fluid exchange among various reservoir components may also be considered. Computational convenience of the trilinear-flow solution makes it a practical alternative to more rigorous but computationally intensive and time-consuming solutions. Another advantage of the trilinear-flow solution is the convenience in deriving asymptotic approximations that provide insight about potential flow regimes and the conditions leading to these flow regimes. Though linear- and bilinear-flow regimes have been noted for fractured horizontal wells in the literature on the basis of their diagnostic features, they have not been associated with particular reservoir characteristics and flow relationships. The trilinear-flow solution also provides a suitable algorithm for the regression analysis of pressure-transient tests in shale reservoirs.

Poroelastic Dual-Porosity/Dual-Permeability After-Closure Pressure-Curves Analysis in Hydraulic Fracturing

SPE Journal ◽  
2016 ◽  
Vol 22 (01) ◽  
pp. 198-218 ◽  
Author(s):  
Chao Liu ◽  
Amin Mehrabian ◽  
Younane N. Abousleiman
Keyword(s):  
Hydraulic Fracturing ◽  
Field Data ◽  
Transition Period ◽  
Time History ◽  
Natural Fracture ◽  
Dual Porosity ◽  
Fluid Exchange ◽  
Pressure Derivative ◽  
Wellbore Pressure ◽  
The Matrix

Summary The dual-porosity and dual-permeability theory of poroelasticity is used to analyze the wellbore dual-pressure responses of dual-porosity or naturally fractured formations. The pressure decline is analyzed by modeling the dual-pressure regimes of the dual-porosity/dual-permeability medium during the after-closure phase of hydraulic fracturing. The analysis shows that both the matrix and natural-fracture permeability, as well as the developed-fracture length, can be estimated on the basis of the obtained pseudolinear and pseudoradial dual-pressure and dual-flow regimes. The estimations are made by use of the corresponding one-half and −1 slopes in the time-history plots of the wellbore-pressure derivative. The transition period between pseudolinear and pseudoradial regimes is also analyzed. The solution involves three time scales related to the rate of fluid flow through and in between the matrix and fractures network. Findings indicate the possible emergence of an additional −½ slope in the log-log pressure-derivative plot of low-permeability shale formations. It is further shown that the transient-pressure response of the formation could be calibrated by incorporating an appropriate interporosity flow coefficient as a measure of the linear-fluid-exchange capacity between the matrix and fracture porosities. The analytical expressions for the time markers of the upper limit for the pseudolinear regime, lower limit for the pseudoradial regime, and the time at which the dip bases occur in pressure-derivative curves are given to estimate this parameter. The solution is successfully applied to and matched with a published set of field data to provide estimations for the associated reservoir properties. The field-data analysis is elaborated by a corresponding sensitivity analysis, through which the prominent poroelastic parameters of the solution are determined. Last, the definitions of conventional key parameters attributed to solutions of this type, such as formation total compressibility, storage coefficients, and hydraulic diffusivity, are reformulated by use of the presented dual-porosity poroelastic approach to the problem.

scholarly journals Numerical Investigation of the Effect of Partially Propped Fracture Closure on Gas Production in Fractured Shale Reservoirs

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5339 ◽  
Author(s):  
Xia Yan ◽  
Zhaoqin Huang ◽  
Qi Zhang ◽  
Dongyan Fan ◽  
Jun Yao
Keyword(s):  
Gas Production ◽  
Displacement Discontinuity ◽  
Hydraulic Fractures ◽  
Klinkenberg Effect ◽  
Apparent Permeability ◽  
Discrete Fracture Model ◽  
Flow Equations ◽  
Fracture Closure ◽  
Shale Reservoirs ◽  
Porosity Model

Nonuniform proppant distribution is fairly common in hydraulic fractures, and different closure behaviors of the propped and unpropped fractures have been observed in lots of physical experiments. However, the modeling of partially propped fracture closure is rarely performed, and its effect on gas production is not well understood as a result of previous studies. In this paper, a fully coupled fluid flow and geomechanics model is developed to simulate partially propped fracture closure, and to examine its effect on gas production in fractured shale reservoirs. Specifically, an efficient hybrid model, which consists of a single porosity model, a multiple porosity model and the embedded discrete fracture model (EDFM), is adopted to model the hydro-mechanical coupling process in fractured shale reservoirs. In flow equations, the Klinkenberg effect is considered in gas apparent permeability, and adsorption/desorption is treated as an additional source term. In the geomechanical domain, the closure behaviors of propped and unpropped fractures are described through two different constitutive models. Then, a stabilized extended finite element method (XFEM) iterative formulation, which is based on the polynomial pressure projection (PPP) technique, is developed to simulate a partially propped fracture closure with the consideration of displacement discontinuity at the fracture interfaces. After that, the sequential implicit method is applied to solve the coupled problem, in which the finite volume method (FVM) and stabilized XFEM are applied to discretize the flow and geomechanics equations, respectively. Finally, the proposed method is validated through some numerical examples, and then it is further used to study the effect of partially propped fracture closures on gas production in 3D fractured shale reservoir simulation models. This work will contribute to a better understanding of the dynamic behaviors of fractured shale reservoirs during gas production, and will provide more realistic production forecasts.

scholarly journals The Role of Rock Matrix Permeability in Controlling Hydraulic Fracturing in Sandstones

2021 ◽  
Author(s):  
Marco Fazio ◽  
Peter Ibemesi ◽  
Philip Benson ◽  
Diego Bedoya-González ◽  
Martin Sauter
Keyword(s):  
Hydraulic Fracturing ◽  
Pore Space ◽  
Hydraulic Fractures ◽  
Low Permeability ◽  
Fluid Viscosity ◽  
Rock Matrix ◽  
Porous Rock ◽  
Sleeve Fracture ◽  
Matrix Permeability ◽  
Fracturing Process

AbstractA concomitant effect of a hydraulic fracturing experimenting is frequently fluid permeation into the rock matrix, with the injected fluid permeating through the porous rock matrix (leak-off) rather than contributing to the buildup of borehole pressure, thereby slowing down or impeding the hydro-fracturing process. Different parameters, such as low fluid viscosity, low injection rate and high rock permeability, contribute to fluid permeation. This effect is particularly prominent in highly permeable materials, therefore, making sleeve fracturing tests (where an internal jacket separates the injected fluid in the borehole from the porous rock matrix) necessary to generate hydraulic fractures. The side effect, however, is an increase in pressure breakdown, which results in higher volume of injected fluid and in higher seismic activity. To better understand this phenomenon, we report data from a new comparative study from a suite of micro-hydraulic fracturing experiments on highly permeable and on low-permeability rock samples. Experiments were conducted in both sleeve fracture and direct fluid fracture modes using two different injection rates. Consistent with previous studies, our results show that hydraulic fracturing occurred only with low permeation, either due to the intrinsic low permeability or due to the presence of an inner silicon rubber sleeve. In particular, due to the presence of quasi-impermeable inner sleeve or borehole skin in the sleeve fracturing experiment, fracturing occurs, with the breakdown pressure supporting the linear elastic approach considering poroelastic effects, therefore, with low stress drop and consequently low microseismicity. Rock matrix permeability also controls the presence of precursory Acoustic Emission activity, as this is linked to the infiltration of fluids and consequent expansion of the pore space. Finally, permeability is shown to mainly control fracturing speed, because the permeation of fluid into the newly created fracture via the highly permeable rock matrix slows down its full development. The application of these results to the field may help to reduce induced seismicity and to conduct well stimulation in a more efficient way.

Feasibility of monitoring hydraulic fracturing using time-lapse audio-magnetotellurics

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. WB119-WB126 ◽  
Author(s):  
Lanfang He ◽  
Xiumian Hu ◽  
Ligui Xu ◽  
Zhanxiang He ◽  
Weili Li
Keyword(s):  
Hydraulic Fracturing ◽  
Case History ◽  
Oil And Gas ◽  
Signal To Noise Ratio ◽  
Time Lapse ◽  
Microseismic Monitoring ◽  
High Signal ◽  
Hydraulic Fractures ◽  
Industry Waste ◽  
Fracturing Process

Hydraulic fracturing is widely used for initiating and subsequently propagating fractures in reservoir strata by means of a pressurized fluid to release oil and gas or to store industry waste. Downhole or surface microseismic monitoring is commonly used to characterize the hydraulically induced fractures. However, in some cases, downhole microseismic monitoring can be difficult due to the limitation imposed by boreholes. Surface microseismic monitoring often faces difficulties acquiring high signal-to-noise ratio data because of the on-site noise from hydraulic fracturing process. Research and field observations indicate that injecting conductive slurry or water into a strata may generate distinct time-lapse electromagnetic anomalies between pre- and posthydraulic fracturing. These anomalies provide a means for characterizing the hydraulic fracturing using time-lapse electromagnetic methods. We examined the time-lapse variation over an hour, one day, one month, and two years of observed audio-magnetotellurics (AMT) resistivity and the 1D and 3D AMT modeling result of the variation pre- and posthydraulic fracturing. There is also a successful case history of applying the time-lapse AMT to map hydraulic fractures. Observed data indicate that the variation of AMT resistivity is normally less than 6% apart from the data of the dead band and some noisy data. Modeling results show the variation pre- and posthydraulic fracturing is larger than 30% at the frequency point lower than 100 Hz. The case history indicates that time-lapse magnetotelluric monitoring may form a new way to characterize the hydraulic fracture.

scholarly journals The Impact of Oriented Perforations on Fracture Propagation and Complexity in Hydraulic Fracturing

Processes ◽  
2018 ◽  
Vol 6 (11) ◽  
pp. 213 ◽  
Author(s):  
Liyuan Liu ◽  
Lianchong Li ◽  
Derek Elsworth ◽  
Sheng Zhi ◽  
Yongjun Yu
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fracture Propagation ◽  
Hydraulic Fractures ◽  
Fracturing Fluid ◽  
Stress Criterion ◽  
Damage And Fracture ◽  
Fracturing Process ◽  
Heterogeneous Rock ◽  
The Impact

To better understand the interaction between hydraulic fracture and oriented perforation, a fully coupled finite element method (FEM)-based hydraulic-geomechanical fracture model accommodating gas sorption and damage has been developed. Damage conforms to a maximum stress criterion in tension and to Mohr–Coulomb limits in shear with heterogeneity represented by a Weibull distribution. Fracturing fluid flow, rock deformation and damage, and fracture propagation are collectively represented to study the complexity of hydraulic fracture initiation with perforations present in the near-wellbore region. The model is rigorously validated against experimental observations replicating failure stresses and styles during uniaxial compression and then hydraulic fracturing. The influences of perforation angle, in situ stress state, initial pore pressure, and properties of the fracturing fluid are fully explored. The numerical results show good agreement with experimental observations and the main features of the hydraulic fracturing process in heterogeneous rock are successfully captured. A larger perforation azimuth (angle) from the direction of the maximum principal stress induces a relatively larger curvature of the fracture during hydraulic fracture reorientation. Hydraulic fractures do not always initiate at the oriented perforations and the fractures induced in hydraulic fracturing are not always even and regular. Hydraulic fractures would initiate both around the wellbore and the oriented perforations when the perforation angle is >75°. For the liquid-based hydraulic fracturing, the critical perforation angle increases from 70° to 80°, with an increase in liquid viscosity from 10−3 Pa·s to 1 Pa·s. While for the gas fracturing, the critical perforation angle remains 62° to 63°. This study is of great significance in further understanding the near-wellbore impacts on hydraulic fracture propagation and complexity.

Near-borehole characteristics of hydraulic fractures and fracturing-induced sonic-wave attenuation

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. D81-D87
Author(s):  
Sheng-Qing Lee ◽  
Huan-Ran Li ◽  
Xi-Hao Gu ◽  
Xiao-Ming Tang
Keyword(s):  
Fractal Dimension ◽  
Hydraulic Fracturing ◽  
Wave Attenuation ◽  
Hydraulic Fractures ◽  
Median Frequency ◽  
Fracture Density ◽  
High Concentration ◽  
Fracturing Process ◽  
Sonic Wave ◽  
Fracture Distribution

The downhole hydraulic fracturing process, besides fracturing formation rocks, generates small, secondary fractures around the borehole, allowing evaluation of the result of fracturing using borehole sonic measurements. We analyzed the near-borehole fracture network from an existing laboratory hydraulic fracturing experiment to study the fracture distribution around the borehole. The result indicates that the fracture distribution exhibits fractal characteristics. The fractal dimension is high in the near-borehole region and decreases away from borehole. Because the fractal dimension increases with fracture density, this indicates that fracturing produces a high fracture-density zone in the near-borehole region. The high concentration of the hydraulic fractures in turn can causes significant attenuation in the sonic-logging waveforms acquired after fracturing. The fracturing-induced sonic attenuation, averaged over the sonic frequency band, can be estimated using a median frequency shift method. Comparison of the attenuation of the fracturing interval with that of an unfractured interval, or with that of the same interval before fracturing allows for evaluating the result of fracturing and the fracture extension along the borehole. The application of the method is demonstrated with field-data examples and validated by comparing results from existing borehole techniques, thus offering a useful technique for evaluating the result of hydraulic fracturing using the borehole sonic-wave attenuation.

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