Induced Stress and Interaction of Fractures During Hydraulic Fracturing in Shale Formation

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Desheng Zhou ◽  
Peng Zheng ◽  
Jiao Peng ◽  
Pei He
Keyword(s):  
Hydraulic Fracturing ◽  
Principal Stress ◽  
Hydraulic Fracture ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Single Fracture ◽  
Complex Fracture ◽  
Induced Stress ◽  
Transverse Distance ◽  
Complex Fracture Network

Creating complex fracture network by hydraulic fracturing operation in unconventional reservoir development is the key factor of effective exploitation. The mechanism of creating a fracture network is not clear up to today. Conventional hydraulic fracturing theory is based on tensile failure of a rock, and a hydraulic fracture is widely accepted as propagating along the direction of in situ maximum horizontal principal stress in the industry. Based on rock elastic mechanics and fracture mechanics, considering combined tensile and shear failures, the maximum circumferential strain criterion and boundary element method (BEM), the paper studies the induced stress and its variation during a fracture propagation, the interaction between two or more hydraulic fractures, and the interaction between a hydraulic fracture and a natural crack. The paper shows that a propagating fracture will produce induced stresses on surrounding rock and form a stress shadow. Instead of propagation along the direction of maximum horizontal principal stress as a single fracture, the outside two fractures of two or more hydraulic fractures are exclusive and turning away from each other. A natural crack may be awaked and extend at its both tips by a propagating hydraulic fracture before their intersection, and the hydraulic fracture may deflect toward the natural crack. The interaction between a hydraulic fracture and a natural crack depends on the transverse distance between them and the initial length of the crack. The shorter the transverse distance and the longer the crack length are, the higher the possibility of the crack to be awaked is. The research results are helpful in understanding complex fracture network and may be used in determining hydraulic fracture places to create a complex fracture network.

scholarly journals A New Method to Improve the Fracturing Effect of Coal Seams by Using Preset Slots and Induced Stress Shadows

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Li Li ◽  
Lei Zhou ◽  
Honglian Li ◽  
Binwei Xia ◽  
Junping Zhou
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracturing ◽  
Fracture Network ◽  
Coal Bed ◽  
Hydraulic Fractures ◽  
Large Area ◽  
Multiple Fractures ◽  
Complex Fracture ◽  
Induced Stress ◽  
Complex Fracture Network

Efficient extraction of coal bed methane before coal mining is essential to eliminate the risk of coal-gas outbursts. However, stimulation technologies should be implemented to enhance the conductivity of the coal seam. In this study, we propose a novel method to create a complex fracture network in underground coal mines with the integration of multiple hydraulic slotting and hydraulic fracturing. In this method, hydraulic slots are used to direct hydraulic fractures and initialize branch fractures, while hydraulic fracturing is used to extend the fractures. Given the mutually exclusive and attractive propagation of multiple fractures, a relatively evenly distributed fracture network can be generated. The results show that (1) the dynamically induced stress shadows of hydraulic fractures can cause exclusive and attractive propagation of multiple hydraulic fractures; (2) a preset slot that deviates from the principal stress can direct hydraulic fractures to a certain extent and generate branch fractures; and (3) with a staggered distribution of preset slots, a relatively large volume of the coal seam in both the minimum and maximum horizontal stress directions can be stimulated, creating a complex fracture network including many vertical branch fractures and a large area of horizontally layered directional fractures.

scholarly journals Numerical simulation on the simultaneous stress interference of parallel multiple hydraulic fractures

2021 ◽  
pp. 014459872110019
Author(s):  
Weiyong Lu ◽  
Changchun He
Keyword(s):  
Principal Stress ◽  
Hydraulic Fracture ◽  
Stress Ratio ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Fracture Spacing ◽  
Induced Stress ◽  
Minimum Principal Stress ◽  
Fracturing Process ◽  
Stress Ratios

During horizontal well staged fracturing, there is stress interference between multiple transverse fractures in the same perforation cluster. Theoretical analysis and numerical calculation methods are applied in this study. We analysed the mechanism of induced stress interference in a single fracture under different fracture spacings and principal stress ratios. We also investigated the hydraulic fracture morphology and synchronous expansion process under different fracture spacings and principal stress ratios. The results show that the essence of induced stress is the stress increment in the area around the hydraulic fracture. Induced stress had a dual role in the fracturing process. It created favourable ground stress conditions for the diversion of hydraulic fractures and the formation of complex fracture network systems, inhibited fracture expansion in local areas, stopped hydraulic fractures, and prevented the formation of effective fractures. The curves of the maximum principal stress, minimum principal stress, and induced principal stress difference with distance under different fracture lengths, different fracture spacings, and different principal stress ratios were consistent overall. With a small fracture spacing and a small principal stress ratio, intermediate hydraulic fractures were difficult to initiate or arrest soon after initiation, fractures did not expand easily, and the expansion speed of lateral hydraulic fractures was fast. Moreover, with a smaller fracture spacing and a smaller principal stress ratio, hydraulic fractures were more prone to steering, and even new fractures were produced in the minimum principal stress direction, which was beneficial to the fracture network communication in the reservoir. When the local stress and fracture spacing were appropriate, the intermediate fracture could expand normally, which could effectively increase the reservoir permeability.

Predicting Well Performance in Naturally Fractured Reservoir

2013 ◽  
Author(s):  
Yunsuk Hwang ◽  
Jiajing Lin ◽  
David Schechter ◽  
Ding Zhu
Keyword(s):  
Hydraulic Fracture ◽  
Fracture Network ◽  
Darcy Flow ◽  
Natural Fracture ◽  
Hydraulic Fractures ◽  
Natural Fractures ◽  
Well Performance ◽  
Fracture Networks ◽  
Complex Fracture ◽  
Complex Fracture Network

Multiple hydraulic fracture treatments in reservoirs with natural fractures create complex fracture networks. Predicting well performance in such a complex fracture network system is an extreme challenge. The statistical nature of natural fracture networks changes the flow characteristics from that of a single linear fracture. Simply using single linear fracture models for individual fractures, and then summing the flow from each fracture as the total flow rate for the network could introduce significant error. In this paper we present a semi-analytical model by a source method to estimate well performance in a complex fracture network system. The method simulates complex fracture systems in a more reasonable approach. The natural fracture system we used is fractal discrete fracture network model. We then added multiple dominating hydraulic fractures to the natural fracture system. Each of the hydraulic fractures is connected to the horizontal wellbore, and some of the natural fractures are connected to the hydraulic fractures through the network description. Each fracture, natural or hydraulically induced, is treated as a series of slab sources. The analytical solution of superposed slab sources provides the base of the approach, and the overall flow from each fracture and the effect between the fractures are modeled by applying the superposition principle to all of the fractures. The fluid inside the natural fractures flows into the hydraulic fractures, and the fluid of the hydraulic fracture from both the reservoir and the natural fractures flows to the wellbore. This paper also shows that non-Darcy flow effects have an impact on the performance of fractured horizontal wells. In hydraulic fracture calculation, non-Darcy flow can be treated as the reduction of permeability in the fracture to a considerably smaller effective permeability. The reduction is about 2% to 20%, due to non-Darcy flow that can result in a low rate. The semi-analytical solution presented can be used to efficiently calculate the flow rate of multistage-fractured wells. Examples are used to illustrate the application of the model to evaluate well performance in reservoirs that contain complex fracture networks.

scholarly journals Experimental Investigation on Hydraulic Fractures in the Layered Shale Formation

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Jingyin Wang ◽  
Ying Guo ◽  
Kaixun Zhang ◽  
Guangying Ren ◽  
Jinlong Ni
Keyword(s):  
Acoustic Emission ◽  
Hydraulic Fracturing ◽  
Fracture Network ◽  
Injection Rate ◽  
Vertical Stress ◽  
Hydraulic Fractures ◽  
Stress Difference ◽  
Complex Fracture ◽  
Fracturing Process ◽  
Complex Fracture Network

Multistage fracturing of horizontal wells to form a complex fracture network is an essential technology in the exploitation of shale gas. Different from the conventional reservoirs, the mechanical characteristics of shale rock have significant heterogeneity due to the existence of beddings, which makes it difficult to predict the fracture geometry in the shale reservoir. Based on the laboratory experiments, the factors that affect fracture propagation were analyzed. The experimental results revealed that the hydraulic fracture would cross the beddings under the high vertical stress difference, while it would propagate along with the bedding under the low vertical stress difference; besides, the low injection rate and viscosity of the fracturing fluid were beneficial to generate a complex fracture network. Under the high injection rate and viscosity, a planar fracture was created, while a nonplanar fracture was observed under the low injection rate and viscosity, and branch fracture was created. According to the acoustic emission events, the shear events were the main events that occurred during the hydraulic fracturing process, and the acoustic emission events could be adopted to describe the fracture network. Lastly, the supercritical carbon dioxide fracturing was more effective compared with the hydraulic fracturing because the fracture network was more complex.

A Peridynamics Model for the Propagation of Hydraulic Fractures in Heterogeneous, Naturally Fractured Reservoirs

2015 ◽  
Author(s):  
Hisanao Ouchi ◽  
Amit Katiyar ◽  
John T. Foster ◽  
Mukul M. Sharma
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fracture Propagation ◽  
Two Dimensions ◽  
Natural Fracture ◽  
Hydraulic Fractures ◽  
Natural Fractures ◽  
Fracture Networks ◽  
Complex Fracture ◽  
Nonlocal Continuum Theory

Abstract A novel fully coupled hydraulic fracturing model based on a nonlocal continuum theory of peridynamics is presented and applied to the fracture propagation problem. It is shown that this modeling approach provides an alternative to finite element and finite volume methods for solving poroelastic and fracture propagation problems and offers some clear advantages. In this paper we specifically investigate the interaction between a hydraulic fracture and natural fractures. Current hydraulic fracturing models remain limited in their ability to simulate the formation of non-planar, complex fracture networks. The peridynamics model presented here overcomes most of the limitations of existing models and provides a novel approach to simulate and understand the interaction between hydraulic fractures and natural fractures. The model predictions in two-dimensions have been validated by reproducing published experimental results where the interaction between a hydraulic fracture and a natural fracture is controlled by the principal stress contrast and the approach angle. A detailed parametric study involving poroelasticity and mechanical properties of the rock is performed to understand why a hydraulic fracture gets arrested or crosses a natural fracture. This analysis reveals that the poroelasticity, resulting from high fracture fluid leak-off, has a dominant influence on the interaction between a hydraulic fracture and a natural fracture. In addition, the fracture toughness of the rock, the toughness of the natural fracture, and the shear strength of the natural fracture also affect the interaction between a hydraulic fracture and a natural fracture. Finally, we investigate the interaction of multiple completing fractures with natural fractures in two-dimensions and demonstrate the applicability of the approach to simulate complex fracture networks on a field scale.

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 A multi-perforation staged fracturing experimental study on hydraulic fracture initiation and propagation

2020 ◽  
Vol 38 (6) ◽  
pp. 2466-2484
Author(s):  
Jianguang Wei ◽  
Saipeng Huang ◽  
Guangwei Hao ◽  
Jiangtao Li ◽  
Xiaofeng Zhou ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Oil And Gas ◽  
Fracture Initiation ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Breakdown Pressure ◽  
Tight Sandstone ◽  
Heterogeneous Samples ◽  
Initiation And Propagation

Hydraulic fracture initiation and propagation are extremely important on deciding the production capacity and are crucial for oil and gas exploration and development. Based on a self-designed system, multi-perforation cluster-staged fracturing in thick tight sandstone reservoir was simulated in the laboratory. Moreover, the technology of staged fracturing during casing completion was achieved by using a preformed perforated wellbore. Three hydraulic fracturing methods, including single-perforation cluster fracturing, multi-perforation cluster conventional fracturing and multi-perforation cluster staged fracturing, were applied and studied, respectively. The results clearly indicate that the hydraulic fractures resulting from single-perforation cluster fracturing are relatively simple, which is difficult to form fracture network. In contrast, multi-perforation cluster-staged fracturing has more probability to produce complex fractures including major fracture and its branched fractures, especially in heterogeneous samples. Furthermore, the propagation direction of hydraulic fractures tends to change in heterogeneous samples, which is more likely to form a multi-directional hydraulic fracture network. The fracture area is greatly increased when the perforation cluster density increases in multi-perforation cluster conventional fracturing and multi-perforation cluster-staged fracturing. Moreover, higher perforation cluster densities and larger stage numbers are beneficial to hydraulic fracture initiation. The breakdown pressure in homogeneous samples is much higher than that in heterogeneous samples during hydraulic fracturing. In addition, the time of first fracture initiation has the trend that the shorter the initiation time is, the higher the breakdown pressure is. The results of this study provide meaningful suggestions for enhancing the production mechanism of multi-perforation cluster staged fracturing.

scholarly journals PARAMETER PREDICTION OF HYDRAULIC FRACTURE FOR TIGHT RESERVOIR BASED ON MICRO-SEISMIC AND HISTORY MATCHING

Fractals ◽  
2018 ◽  
Vol 26 (02) ◽  
pp. 1840009 ◽  
Author(s):  
KAI ZHANG ◽  
XIAOPENG MA ◽  
YANLAI LI ◽  
HAIYANG WU ◽  
CHENYU CUI ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
History Matching ◽  
Seismic Source ◽  
Fracture Network ◽  
Distribution Area ◽  
Hydraulic Fractures ◽  
Discrete Fracture Model ◽  
Tight Reservoir ◽  
Seismic Source Location

Hydraulic fracturing is an important measure for the development of tight reservoirs. In order to describe the distribution of hydraulic fractures, micro-seismic diagnostic was introduced into petroleum fields. Micro-seismic events may reveal important information about static characteristics of hydraulic fracturing. However, this method is limited to reflect the distribution area of the hydraulic fractures and fails to provide specific parameters. Therefore, micro-seismic technology is integrated with history matching to predict the hydraulic fracture parameters in this paper. Micro-seismic source location is used to describe the basic shape of hydraulic fractures. After that, secondary modeling is considered to calibrate the parameters information of hydraulic fractures by using DFM (discrete fracture model) and history matching method. In consideration of fractal feature of hydraulic fracture, fractal fracture network model is established to evaluate this method in numerical experiment. The results clearly show the effectiveness of the proposed approach to estimate the parameters of hydraulic fractures.

Numerical Simulation of Shale Gas Development Based on Complex Fracture Network Growth

2014 ◽  
Author(s):  
D.. Ye ◽  
C.. Yin ◽  
Y.. Li ◽  
S.. Wang ◽  
G.. Qin ◽  
...  
Keyword(s):  
Shale Gas ◽  
Hydraulic Fracture ◽  
Large Scale ◽  
Fracture Network ◽  
Production Performance ◽  
Network Growth ◽  
Stimulated Reservoir Volume ◽  
Well Production ◽  
Complex Fracture ◽  
Complex Fracture Network

Abstract Micro-seismic result has shown that compared to conventional reservoir, more complex fracture network will be generated in shale gas reservoirs after hydraulic fracturing stimulations, which provides key channels for shale gas to flow in economic rate. It is vitally important to recognize complex fracture network and model such complex system to better understand gas develop process, optimize hydraulic fracturing design, and determine development plans of shale gas reservoirs. Our proposed model enable realistic modeling of complex fracture network growth even with some uncertainty (SPE 157411), but it is possible to represent large-scale fracture network distribution in reservoir modeling and numerical simulation of shale gas development. In this paper, we used this proposed model to generate hydraulic fracture network distribution in shale formation, taking into account interaction between hydraulic fracture and actual large-scale natural fractures. Integrating hydraulic fracture network results and natural fractures in non-stimulated area, highly constrained unstructured gridding and a connection list are constructed, using the Discrete Fracturing Modeling (DFM) method. This model can effectively predict production performance. With real-world well data, the simulation system calibration is done, and the simulated well production performance has good agreement with real-world producing data. Using this simulation system, effective stimulated reservoir volume (ESRV) is also predicted. The proposed approach is capable of modeling complex fracture network propagation and predicting well producing rate, if information data on multi-scale pre-existing natural fracture is available. This approach provide one opportunity to predict well production performance and effective stimulated reservoir volume (ESRV), which is also significant for shale gas development plan.

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