scholarly journals CO2-Driven Hydraulic Fracturing Trajectories across a Preexisting Fracture

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Qi Zhang ◽  
Jiehao Wang ◽  
Yufeng Gao ◽  
Shengfei Cao ◽  
Jingli Xie ◽  
...  
Keyword(s):  
Hydraulic Fracture ◽  
Damage Evolution ◽  
Stress Ratio ◽  
Bedding Plane ◽  
Hydraulic Fractures ◽  
The Finite Element Method ◽  
Bedding Planes ◽  
Initiation And Propagation ◽  
Gas Seepage ◽  
Simulation Results

Defining the trajectory of hydraulic fractures crossing bedding planes and other fractures is a significant issue in determining the effectiveness of the stimulation. In this work, a damage evolution law is used to describe the initiation and propagation of the fracture. The model couples rock deformation and gas seepage using the finite element method and is validated against classical theoretical analysis. The simulation results define four basic intersection scenarios between the fluid-driven and preexisting fractures: (a) inserting—the hydraulic fracture inserts into a bedding plane and continues to propagate along it; (b) L-shaped crossing—the hydraulic fracture approaches the fracture/bedding plane then branches into the plane without crossing it; (c) T-shaped crossing—the hydraulic fracture approaches the fracture/bedding plane, branches into it, and crosses through it; (d) direct crossing—the hydraulic fracture crosses one or more bedding planes without branching into them. The intersection scenario changes from (a) → (b) → (c) → (d) in specimens with horizontal bedding planes when the stress ratio β ( β = σ y / σ x ) increases from 0.2 to 5. Similarly, the intersection type changes from (d) → (c) → (a) with an increase in the bedding plane angle α (0° → 90°). Stiffness of the bedding planes also exerts a significant influence on the propagation of hydraulic fractures. As the stiffness ratio E 1 ¯ / E 2 ¯ increases from 0.1 to 0.4 and 0.8, the seepage area decreases from 22.2% to 41.8%, and the intersection type changes from a T-shaped crossing to a direct crossing.

scholarly journals Investigation of the Fracturing Effect Induced by the Disturbing Stress of Hydrofracturing Using the Bonded-Particle Model

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-24
Author(s):  
Xin Zhang ◽  
Yuqi Zhang ◽  
Bingxiang Huang
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fracture Zone ◽  
Fracture Propagation ◽  
Bedding Plane ◽  
Particle Model ◽  
Hydraulic Fractures ◽  
Bedding Planes ◽  
Geological Conditions ◽  
Hydraulic Fracture Propagation

Hydraulic fracturing applications have shown a stress disturbance effect during hydraulic fracture propagation, which is often ignored. Using laboratory and discrete element numerical simulation tests, hydraulic fracture propagation under this stress disturbance is systematically studied. The results show that during hydraulic fracturing, the bedding plane is damaged by the stress disturbance, forming a bedding fracture zone (BFZ). The nonlinear fracture characteristics of the formation process of the disturbed fracture zone are revealed, and two indexes (the number of fractures in the disturbed fracture zone and the size of the disturbed fracture zone) are proposed to evaluate the fracturing effect of the stress disturbance. Based on these indexes, multifactor sensitivity tests are conducted under different geological conditions and operational factors. When the principal stress ( σ 1 ) difference is large, the number of hydraulic fractures gradually decreases from many to one, and the direction of the hydraulic fractures gradually approaches the vertical direction of σ 3 , but the change in the in situ stress condition has no obvious effect on the stress disturbance effect. The weaker the bonding strength of the bedding plane, the more significant the stress disturbance effect is, and the easier it is for the fractures to expand along the bedding plane. With increasing injection rate, the stress disturbance effect first increases and then decreases, and the hydraulic fracture propagates from along the bedding plane to cross the bedding plane. With increasing relative distance between the injection hole and bedding plane, the stress disturbance effect presents a linearly increasing trend, and the hydraulic fractures along the bedding planes extend. Based on the experimental results, the relationship between the fracturing effect of the stress disturbance and the extension mode of the hydraulic fracture is determined, and an optimization method for hydraulic fracturing in composite rock reservoirs is given. The research results can provide a theoretical basis for controlling the formation of complex fracture networks in composite rock reservoirs.

scholarly journals Fully three-dimensional propagation model of horizontal borehole hydraulic fractures in strata under the effect of bedding planes

2018 ◽  
Vol 36 (5) ◽  
pp. 1189-1209 ◽  
Author(s):  
Bingxiang Huang ◽  
Jiangwei Liu
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Three Dimensional ◽  
Fracture Morphology ◽  
Bedding Plane ◽  
Propagation Model ◽  
Tensile Failure ◽  
Propagation Mechanism ◽  
Hydraulic Fractures ◽  
Bedding Planes

The bedding plane effect will occur when hydraulic fractures propagate to the bedding plane in sedimentary strata, resulting in the “≠,” “工,” or “/” shaped fracture morphology. Based on previous physical experiments results, this article analyzed the mecroscopic propagation mechanism of tensile failure and the mechanical conditions for main hydraulic fracture and the bedding plane fracture propagating, proposing the criteria for hydraulic fracture to penetrate through the bedding plane. A fully three-dimensional model of hydraulic fracture morphology in horizontal borehole hydraulic fracturing is established with the vertical water flow, water leak-off, and bedding plane effect taken into consideration. Basic equations of continuity, pressure decline, hydraulic fracture morphology, and others are solved. After that, true triaxial hydraulic fracturing experiments with samples containing bedding planes are conducted to verify the aperture, length, width, and height of hydraulic fractures in this model. The model is proved to be accurate and reliable.

scholarly journals The Investigation on Initiation and Propagation of Hydraulic Fractures in Shale Reservoir

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Xiangjun Liu ◽  
Wei Lei ◽  
Jing Huang ◽  
Yi Ding ◽  
Lixi Liang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Hydraulic Fracture ◽  
Fracture Propagation ◽  
Bedding Plane ◽  
Fracture Network ◽  
Natural Fracture ◽  
Strong Anisotropy ◽  
Bedding Planes ◽  
Initiation And Propagation ◽  
Shale Reservoir

Hydraulic fracturing is a necessary technique for shale gas exploitation. In order to have efficient stimulation treatment, a complex fracture network has to be developed, whereas with rich bedding planes and natural fractures, the mechanism of forming a fracture network is not fully understood and it is so tricky to predict propagation and initiation of hydraulic fracture. Therefore, in this paper, considering the strong anisotropy of shale reservoir, numerical simulation has been conducted to analyze fracture propagation and initiation on the basis of finite element and damage mechanics. Simulation results indicate that hydraulic fracture is not merely controlled by in situ stress due to strong anisotropy in shale. With plenty of bedding planes, hydraulic fracture tends to have initiation and propagation along the bedding plane. In particular, this influence becomes stronger with low strength and high development density of bedding planes. Additionally, in combination with natural fracture and bedding plane, the initiation point is usually on a natural fracture plane, causing relatively small breakdown pressure. In the process of fracture propagation, hydraulic fracture connects with natural fractures and bedding planes, forming dendritic bifurcation and more complicated paths. Numerical simulation proves that bedding plane and natural fracture are vital factors of hydraulic fracture. Compared to natural fracture, the bedding plane has a stronger impact on hydraulic fracture propagation. For the initiation of hydraulic fracture, natural fracture is the major effecting factor. The outcome of this study is able to offer theoretical guidance for hydraulic fracturing in shale.

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.

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 Experimental and Numerical Investigation on Hydraulic Fracture Propagation Law of Composite Rock Materials considering the Disturbing Stress Effect

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Xin Zhang ◽  
Yuqi Zhang ◽  
Tao Zhang
Keyword(s):  
Hydraulic Fracture ◽  
Fracture Zone ◽  
Fracture Propagation ◽  
Bedding Plane ◽  
Propagation Path ◽  
Propagation Mode ◽  
Hydraulic Fractures ◽  
Stress Effect ◽  
Propagation Law ◽  
Hydraulic Fracture Propagation

The stress disturbance effect will significantly affect the propagation path of hydraulic fractures in the composite rock reservoir. To reveal the influence mechanism of stress disturbance effect on the hydraulic fracture propagation, several groups of laboratory tests and simulation tests were carried out. The test results showed that the hydraulic fracture tip formed a disturbing stress field because of the pore water pressure. Before the hydraulic fracture was extended to the bedding plane, the bedding plane had been damaged under stress disturbance, and the disturbed fracture zone was formed. The propagation mode of hydraulic fracture at the bedding plane was highly sensitive to the formation of the disturbed fracture zone. The sensitivity is mainly reflected from two aspects. (1) Under the action of the hydraulic fracture tip disturbance stress, many microfractures are generated and penetrated into the disturbance fracture zone on the bedding plane. This behavior is accompanied by energy dissipation causing the bedding plane material to be significantly softened, and the energy required for hydraulic fracture propagation is reduced dramatically. (2) The formation of the disturbed fracture zone improves the degree of fragmentation of the bedding plane, and the permeability of the local area increases significantly, forming the dominant circulation path. The higher the development of the disturbed fracture zone, the greater the hydraulic fracture propagation tendency along the bedding plane. According to the formation characteristics of the bedding plane disturbed fracture zone, the author proposed a nonlinear fracture model of the bedding plane disturbed fracture zone and established the hydraulic fracture propagation path criterion. This paper further analyzed the influencing factors of the disturbed fracture zone’s formation conditions and found that the bedding plane’s cementation strength was the main factor affecting the development degree of the disturbed fracture zone.

Research on hydraulic fracture initiation and vertical propagation behavior in laminated tight formation

2020 ◽  
Author(s):  
anan wu
Keyword(s):  
Hydraulic Fracture ◽  
Vertical Plane ◽  
Fracture Initiation ◽  
Bedding Plane ◽  
Vertical Stress ◽  
Hydraulic Fractures ◽  
Research Knowledge ◽  
Propagation Behavior ◽  
Vertical Propagation ◽  
Tight Formation

<p>Research on hydraulic fracture initiation and vertical propagation</p><p>behavior in laminated tight formation</p><p>Anan Wu<sup>1</sup>, Bing Hou<sup>*1</sup>, Fei Gao<sup>2</sup>，Yifan Dai<sup>1</sup>，Mian Chen<sup>1</sup></p><ul><li>(1. State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum-Beijing, Beijing, China No.1 Cementing Company, Bohai Drilling Engineering Company Limited, CNPC, China. Renqiu,062550)</li> </ul><p> </p><p><strong>Abstract: </strong>The extent of hydraulic fracture vertical propagation extent is important in evaluating simulated reservoir volume for laminated tight reservoirs. Given that it is affected by the discontinuities (beddings, natural fractures, and other factors), fracture geometry is complex in the vertical plane and is different from a simple fracture in a homogeneous formation. Because the tight formation bedding is very developed, hydraulic fracture is difficult to spread vertically. Now,the propagation mechanism of hydraulic fracture in the vertical plane has not been well understood. To clarify this mechanism, several groups of large-scale tri-axial tests were deployed in this study to investigate the fracture initiation and vertical propagation behavior in laminated tight formation. The influences of multiple factors on fracture vertical propagation were studied.</p><p>we carried out the indoor hadraulic fracturing physical simulation experiments of the bedding-developed rocks. Tight cores obtained from the core well were wrapped with cement into 30 cm cubes, and samples were drilled and cemented. Before the experiment ,three-dimensional axial stress was applied to simulate the stratigraphic environment. When the stress was balanced, a certain flowing rate was set for hadraulic fracturing. After the fracturing work was completed, the cement block was opened to observe the hydraulic fracture propagation pattern.</p><p>The results showed that the ultimate fracture geometries could be classified into three categories: simple bedding fracture, slight turning fracture, stair-like fracture, and multilateral fishbone-like fracture network. Here comes some research knowledge:(1)When the difference between the vertical stress and the minimum horizontal principal stress is less than 12Mpa, the hydraulic fracture will only expand along the rock bedding plane Furthermore. (2)when the vertical stress difference is close to 14 MPa, hydraulic fractures will generate vertical fractures that will communicate multiple beddings of the rock. (3)Increasing flowing rate will cause a slight turning or jumping fractures and improve the complexity of fractures to a certain extent. (4)because of the influence of beddings and lithology,the fracture pressure is usually high.</p><p><strong>Key words:</strong> Hydraulic fracturing, tight reversior Bedding plane, fracture morphology.</p>

Simulation of Stress Changes of Shale Reservoirs during Hydraulic Fracturing to Create Fracture Networks

2013 ◽  
Vol 419 ◽  
pp. 10-16
Author(s):  
G.M. Zhang ◽  
J.D. Liu ◽  
C.M. Xiong ◽  
H. Liu ◽  
J. Jin
Keyword(s):  
Pore Pressure ◽  
Hydraulic Fracture ◽  
Theoretical Data ◽  
Element Model ◽  
Hydraulic Fractures ◽  
Theoretical Studies ◽  
Fracture Networks ◽  
Stress Anisotropy ◽  
Stress Changes ◽  
Simulation Results

Theoretical studies have shown that the generation of hydraulic fractures reduces or even reverses the stress anisotropy between the fractures and results in increasing the complexity of fractures. A finite element model was established in which the pore pressure element was used to simulate the behavior of porous media and the pore pressure cohesive element was adopted to catch the characters of hydraulic fracture. A special fracturing manner was adopted to create complicated fracture networks by reducing or even reversing the stress anisotropy between fractures. The geometries of hydraulic fractures, strains, stresses, pore pressure distributions and fluid pressures within the fractures are obtained. The results of the model are fit well with the corresponding theoretical data. The simulation results show that the stress anisotropy is reduced resulting from the generation of the hydraulic fracture, multiple parallel transverse fractures of horizontal well further reduce or even reverse the stress anisotropy in some place of the reservoir. The simulation results validate the feasibility of the theoretical studies and the expected complex network fractures could be created by adopting the special fracturing manner.

Hydraulic-Fracture Geomechanics and Microseismic-Source Mechanisms

SPE Journal ◽  
2013 ◽  
Vol 18 (04) ◽  
pp. 766-780 ◽  
Author(s):  
N.R.. R. Warpinski ◽  
M.J.. J. Mayerhofer ◽  
K.. Agarwal ◽  
J.. Du
Keyword(s):  
Shear Stress ◽  
Hydraulic Fracture ◽  
Hydraulic Fractures ◽  
Natural Fractures ◽  
Total Stress ◽  
Multiple Fractures ◽  
Significant Information ◽  
Bedding Planes ◽  
Fracturing Process ◽  
Source Mechanisms

Summary Interpretation of microseismic results and attempts to link microseismic-source mechanisms to fracture behavior require an understanding of the geomechanics of the fracturing process. Stress calculations around fractures show that the area normal to the fracture surface is stabilized by a pressurized fracture as a result of increased total stress and decreased shear stress. In this area, microseisms can occur only if leakoff pressurizes natural fractures, bedding planes, or other weakness features, and source mechanisms are thus likely to show a volumetric component that has either opening or closing movement in addition to shear slippage. Conversely, the tip tensile region is destabilized by a reduction in total stress and an increase in shear stress, with the likelihood that microseisms would be generated in this region because of these changes. Such microseisms would not yet be invaded by the fracturing fluid, and events that are mostly shear would be expected. Systems with multiple fractures, such as those that are potentially created in multiperforation-cluster stages, are much more complex, but similar elements can be outlined for those as well. Source mechanisms can help delineate these different types of microseismic behaviors, but the evaluation of such mechanisms reveals that they provide no significant information about the hydraulic fracture. Whereas it would be valuable if source mechanisms could provide information about the mechanics of the hydraulic fracture (e.g., opening, closing, and proppant), calculations show that both the energy and volume associated with microseismicity are an insignificant fraction of the total energy and volume input into the stimulation. Thus, hydraulic fractures are almost entirely aseismic. The analysis of source mechanisms should concentrate on what those data reveal about the reservoir (e.g., natural fractures and faults). Integrated diagnostic studies provide more value in understanding both the microseismicity and interpretation of the microseismic results.

Further testing of the bedding-plane-slip model for hydraulic-fracture opening using moment-tensor inversions

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. KS159-KS168 ◽  
Author(s):  
Yunhui Tan ◽  
Terry Engelder
Keyword(s):  
Hydraulic Fracture ◽  
Moment Tensor ◽  
P Wave ◽  
Hydraulic Fractures ◽  
Washington County ◽  
Gas Shale ◽  
Nodal Plane ◽  
Moment Tensors ◽  
Bedding Planes ◽  
Microseismic Events

Moment tensors are calculated by using the P-wave first motion peak amplitudes of 59 microseismic events with high signal-to-noise ratio. These events are from a surface microseismic data set gathered during hydraulic-fracture stimulation of the Marcellus gas shale in Washington County, Pennsylvania, USA. The majority of these 59 events have a horizontal nodal plane ([Formula: see text] a few degrees) characteristic of a dip-slip/horizontal-slip moment tensor. If the horizontal nodal plane is an auxiliary, the vertical nodal plane has a pure dip-slip motion, which is inconsistent with the opening motion for vertical hydraulic fractures that enables proppant loading. This points to slip on horizontal nodal planes with the auxiliary vertical nodal planes aligned with the local maximum horizontal stress orientation as indicated by drilling-induced fractures in nearby vertical wells. These 59 microseismic events are caused by slip on horizontal mechanical discontinuities such as bedding planes during the opening of vertical hydraulic fractures, a model first proposed by research teams headed by Rutledge and Eisner, respectively. During several stimulation stages in the Washington County Marcellus gas shale, a pattern of opposite slip direction develops within “double lineaments” of microseismic clouds. This suggests that fracking fluid is not only able to move in the direction of fracture propagation, but it can also spread sideways into previously unstimulated rock. A secondary microseismic cloud consistently initiates at approximately 133 m (400 ft) from the position opposite the central perforation toward the unstimulated heel of the horizontal wells. From these moment tensors, we have concluded that microseismic focal mechanisms with horizontal nodal planes are direct evidence of the presence of treatment fluid in open hydraulic fractures.

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