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>

Analysis of hydraulic fracture initiation and vertical propagation behavior in laminated shale formation

Fuel ◽  
2017 ◽  
Vol 206 ◽  
pp. 482-493 ◽  
Author(s):  
Peng Tan ◽  
Yan Jin ◽  
Ke Han ◽  
Bing Hou ◽  
Mian Chen ◽  
...  
Keyword(s):  
Hydraulic Fracture ◽  
Fracture Initiation ◽  
Propagation Behavior ◽  
Vertical Propagation ◽  
Shale Formation

Near-Wellbore Hydraulic Fracture Non-Planar Propagation and Torturous Morphology in Tight Sandstone Formation

2021 ◽  
Author(s):  
Ruxin Zhang ◽  
Qinglin Shan ◽  
Wan Cheng
Keyword(s):  
Stress Distribution ◽  
Fracture Initiation ◽  
Damage Mechanism ◽  
Fracture Morphology ◽  
Propagation Model ◽  
Hydraulic Fractures ◽  
Tight Sandstone ◽  
Propagation Behavior ◽  
Stress Shadow ◽  
Sandstone Formation

Abstract In this paper, a 3D near-wellbore fracture propagation model is established, integrating five parts: formation stress balance, drilling, casing and cementing, perforating, and fracturing, in order to investigate fracture initiation characteristics, near-wellbore fracture non-planar propagation behavior, and torturous hydraulic fracture morphology for cased and perforated horizontal wellbores in tight sandstone formation. The method is based on the combination of finite element method and post-failure damage mechanism. Finite element method is used to determine the coupling behavior between the pore fluid seepage and rock stress distribution. Post-failure damage mechanism is adopted to test the evolution of hydraulic fractures through simulating rock damage process. Moreover, a user subroutine is introduced to establish the relation between rock strength, permeability, and damage, in order to solve the model. This model could simulate the interaction between fractures during their propagation process because of the stress shadow. The simulation results indicate that each operation could cause redistribution and reorientation of near-wellbore stress. Therefore, it is important to know the real near-wellbore stress distribution that affects near-wellbore fracture initiation and propagation. Initially, hydraulic fractures initiate independently from each perforation and propagate along the direction of maximum horizontal stress. However, hydraulic fractures divert from original direction gradually to interconnect and overlap with each other, because of stress shadow, resulting in non-planar propagation behavior. Individual fractures coalesce into a spiral-shaped fracture morphology. In addition, a longitudinal fracture could be observed because of wellbore effect, which is a result of weak cementing strength or near-wellbore weak plane. Finally, the complex and torturous fracture morphologies are created near the wellbore, incorporating Multi-spiral shaped fracture and horizontal-vertical crossing shaped fracture. However, the propagation behavior of fracture far away from wellbore is controlled by in-situ stress, forming a planar fracture. The highlights of this 3D near-wellbore fracture propagation model are following: 1) it considers near-wellbore stress change caused by each construction to ensure the accuracy of near-wellbore stress distribution; 2) it achieves 3D simulation of fracture initiation and near-wellbore propagation from perforations; 3) the interaction between fractures is involved, resulting in complex and torturous morphology. This model provides the theoretical basis for fracture initiation and propagation, which also could be applied into heterogenous formations considering the effect of discontinuities.

Time-Dependent Initiation of Multiple Hydraulic Fractures in a Formation With Varying Stresses and Strength

SPE Journal ◽  
2015 ◽  
Vol 20 (06) ◽  
pp. 1317-1325 ◽  
Author(s):  
Andrew P. Bunger ◽  
Guanyi Lu
Keyword(s):  
Tensile Strength ◽  
Hydraulic Fracture ◽  
Fracture Initiation ◽  
Time Frame ◽  
Hydraulic Fractures ◽  
Static Fatigue ◽  
Breakdown Pressure ◽  
Initiation Point ◽  
Delayed Failure ◽  
Wellbore Pressure

Summary The premise of classical hydraulic-fracture-breakdown models is that hydraulic-fracture growth can only start when the wellbore pressure reaches a critical value that is sufficient to overcome the tensile strength of the rock. However, rocks are well-known to exhibit static fatigue; that is, delayed failure at stresses less than the tensile strength. In this paper, we explore the consequences of delayed failure on axially oriented initiation of multiple hydraulic fractures. Specifically, given a certain breakdown pressure, we investigate the conditions under which subsequent hydraulic fracture(s) can begin within the time frame of a stimulation treatment in regions of higher stress and/or strength because of delayed-failure mechanisms. The results show that wells completed in shallower formations are more sensitive to variations in strength, whereas wells completed in deeper formations are more sensitive to variations in stress. Furthermore, cases in which all hydraulic fractures break down according to the same pressurization regime—that is, all are “fast” (nonfluid-penetrating) pressurization or else all are “slow” (uniformly pressurized fluid-penetrating) pressurization cases—are highly sensitive to small stress/strength variability. On the other hand, if the first hydraulic-fracture initiation is in the “fast”-pressurization regime and subsequent fracture(s) are in the “slow”-pressurization regime, then the system is robust to a much-higher degree of variability in stress/strength. Practically, this work implies that methods aimed at moderately reducing the variability in stress/strength among the possible initiation points (i.e., perforation clusters) within a particular stage can have a strong effect on whether multiple hydraulic fractures will begin. In addition, this analysis implies that pumping strategies that encourage “fast,” nonpenetrative breakdown of the first initiation point followed by the opportunity for fluid-penetrating, “slow” breakdown of subsequent initiation points could be effective at encouraging multiple-hydraulic-fracture initiation.

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.

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.

Hydraulic fracture-height containment by permeable weak bedding interfaces

Geophysics ◽  
2018 ◽  
Vol 83 (3) ◽  
pp. MR137-MR152 ◽  
Author(s):  
Xiaowei Weng ◽  
Dimitry Chuprakov ◽  
Olga Kresse ◽  
Romain Prioul ◽  
Haotian Wang
Keyword(s):  
Coefficient Of Friction ◽  
Hydraulic Fracture ◽  
Shear Failure ◽  
Mechanistic Model ◽  
Bedding Plane ◽  
Horizontal Stress ◽  
Height Growth ◽  
Vertical Stress ◽  
Weak Interface ◽  
Minimum Horizontal Stress

In laminated formations, the vertical height growth of a hydraulic fracture can be strongly influenced by the interaction of the fracture tip with the bedding interfaces it crosses. A weak interface may fail in shear and then slip, depending on the strength and frictional properties, the effective vertical stress at the interface, and the net pressure. Shear failure and slippage at the interface can retard the height growth or even stop it completely. A 2D analytical model called the FracT model has been developed that examines the shear slippage along the bedding interface adjacent to the fracture tip and the resulting blunting of the fracture tip at the interface, as well as the stress condition on the face opposite from the hydraulic fracture tip for possible fracture nucleation that leads to fracture crossing. The growth of the shear slippage along the interface with time is coupled with the fluid flow into the permeable interface. A parametric study has been carried out to investigate the key formation parameters that influence the crossing/arrest of the fracture at the bedding interface and the shear slippage and depth of fluid penetration into the interface. The study suggests that the interfacial coefficient of friction and the ratio of the vertical to minimum horizontal stress are two of the most influential parameters governing fracture arrest by a weak interface. For the fracture tip to be arrested at the interface, the vertical stress acting on the interface must be close to the minimum horizontal stress or the interfacial coefficient of friction must be very small. The FracT model has also been integrated into a pseudo-3D-based complex hydraulic fracture model. This quantitative mechanistic model that incorporates a bedding-plane slip-driven mechanism is a necessary step to understand and bridge the characterization (sonic) and monitoring (microseismic) observations.

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.

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