Numerical Investigation into the Effect of Natural Fracture Density on Hydraulic Fracture Network Propagation

Chong, Zhaohui; Li, Xuehua; Chen, Xiangyu; Zhang, Ji; Lu, Jingzheng

doi:10.3390/en10070914

Cited by 24 publications

(19 citation statements)

References 45 publications

(60 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Through hydraulic fracturing, the high-pressure water is able to penetrate the shale matrix and joint, thus not only releasing the adsorbed gas but also creating a fracture network for gas to transport [10,11]. However, the uncertainty regarding the composition of the shale reservoirs compounded by the complex geological setting makes it extremely difficult to control and predict fracture initiation and propagation in hydraulic fracturing [12].…”

Section: Introductionmentioning

confidence: 99%

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

Chong

Yao

2018

Geofluids

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Introductionmentioning

confidence: 99%

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

Chong

Yao

2018

Geofluids

Self Cite

View full text Add to dashboard Cite

show abstract

“…It is essential to investigate fracture network evolution during the nitrogen fracturing process.Several numerical models have been developed to investigate fracture behaviors during the hydraulic fracturing process. These models include the boundary element method [28], finite element method [29][30][31], and discrete element method [32,33]. Wang et al [29] applied a new mathematical model to investigate fracture network evolution of multi-stranded fractures with pre-existing natural fractures.…”

mentioning

confidence: 99%

Numerical Study of Fracture Network Evolution during Nitrogen Fracturing Processes in Shale Reservoirs

et al. 2018

View full text Add to dashboard Cite

This paper develops a numerical model to study fracture network evolution during the nitrogen fracturing process in shale reservoirs. This model considers the differences of incompressible and compressible fluids, shear and tensile failure modes, shale heterogeneity, and the strength and permeability of both shale matrix and bedding planes through the coupling of mechanical-seepage-damage during fracturing fluid injection. The results show that nitrogen fracturing has a lower breakdown pressure and larger seepage zone than hydraulic fracturing under the same injection pressure. Tensile failure was identified as the major reason for the initiation and propagation of fractures. Ignoring the effect of bedding planes, the fracture initiation pressure, breakdown pressure, and fracturing effectiveness reached their maxima when the stress ratio is 1. Under the same strength ratio, the propagation path of the fractures was controlled by the stronger effect that was casused by the bedding angle and stress ratio. With increasing the strength ratio, the fracture number and shearing of the bedding plane increased significantly and the failure pattern changed from tensile-only mode to tensile-shear mode. These analyses indicated that the fracture network of bedding shale was typically induced by the combined impacts of stress ratio, bedding angle and strength ratio.Energies 2018, 11, 2503 2 of 22 more effective if N 2 is applied for the hydraulic fracturing [22,23]. Different fracturing fluids lead to the different pore pressure distributions during fluid flow due to the various properties such as viscosity and compressibility. According to the principle of effective stress, the difference in pore pressure distribution induces the difference in the stress distribution in rocks, which plays an important role in fracturing behavior during the fracturing process [24][25][26][27]. Lower breakdown pressure, larger seepage zone and more complex fracture network were observed during nitrogen fracturing [24][25][26][27]. However, these studies were performed on simple rock samples and the influence of other factors during nitrogen fracturing has not been well evaluated. It is essential to investigate fracture network evolution during the nitrogen fracturing process.Several numerical models have been developed to investigate fracture behaviors during the hydraulic fracturing process. These models include the boundary element method [28], finite element method [29][30][31], and discrete element method [32,33]. Wang et al. [29] applied a new mathematical model to investigate fracture network evolution of multi-stranded fractures with pre-existing natural fractures. Shalev and Lyakhovsky [31] studied the damage evolution and seismicity phenomenon in hydraulic fracturing using an improved damage model based on the finite element method. However, there are still only a few studies on a numerical model for nitrogen fracturing and the comparison between water fracturing and nitrogen fracturing. On the other hand, shale reservoirs occur at di...

show abstract

“…For water softening/hydraulic fracturing, the hanging roof over the gob area of the adjacent depleted working face can be cut off and the side abutment pressure will be reduced. Afterwards, the roof above the operating working face can be pre-fractured to make the roof timely cave in on the gob area, which aims at reducing the front abutment pressure [24,25]. Meanwhile, the physical and chemical reactions between the rock and the water lead to the degraded mechanical performance of the roofs [26].…”

Section: Introductionmentioning

confidence: 99%

A Case Study of Presplitting Blasting Parameters of Hard and Massive Roof Based on the Interaction between Support and Overlying Strata

Zhang

Chen

2018

Energies

View full text Add to dashboard Cite

Due to the existence of a hard and massive roof (HMR), severe ground pressure behaviors have been observed at the working face, resulting in safety issues and the degradation of production effectiveness. Based on the HMR conditions of the Datong Mining Area, the fracture-related instability of the HMR and its effects on the support selection were investigated by analyzing the interaction between support and overlying strata. Advancefixed-distance presplitting blasting (AFPB) technology was proposed to control the caving interval of HMR, and the influence of the controlled interval on the working load of supports was also analyzed. The working load of the support and the caving interval of the HMR were determined based on the controlled HMR fracture technology, and these were verified by field application tests. The working resistance of the support and the step distance were determined based on controlled roof fracture and were verified by on-site application experiments. The results revealed that cracks emerged after the presplitting blasting, resulting in significantly reduced strata behaviors. Furthermore, the support exhibited good adaptability.

show abstract

Numerical Investigation into the Effect of Natural Fracture Density on Hydraulic Fracture Network Propagation

Cited by 24 publications

References 45 publications

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

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

Numerical Study of Fracture Network Evolution during Nitrogen Fracturing Processes in Shale Reservoirs

A Case Study of Presplitting Blasting Parameters of Hard and Massive Roof Based on the Interaction between Support and Overlying Strata

Contact Info

Product

Resources

About