Near-wellbore fracture initiation and propagation induced by drilling fluid invasion during solid fluidization mining of submarine nature gas hydrate sediments

Summary Deep shale gas reservoirs are characterized by high in-situ stresses, a high horizontal-stress difference (12 MPa), development of bedding seams and natural fractures, and stronger plasticity than shallow shale. All of these factors hinder the extension of hydraulic fractures and the formation of complex fracture networks. Conventional hydraulic-fracturing techniques (that use a single fluid, such as guar fluid or slickwater) do not account for the initiation and propagation of primary fractures and the formation of secondary fractures induced by the primary fractures. For this reason, we proposed an alternating-fluid-injection hydraulic-fracturing treatment. True triaxial hydraulic-fracturing tests were conducted on shale outcrop specimens excavated from the Shallow Silurian Longmaxi Formation to study the initiation and propagation of hydraulic fractures while the specimens were subjected to an alternating fluid injection with guar fluid and slickwater. The initiation and propagation of fractures in the specimens were monitored using an acoustic-emission (AE) system connected to a visual display. The results revealed that the guar fluid and slickwater each played a different role in hydraulic fracturing. At a high in-situ stress difference, the guar fluid tended to open the transverse fractures, whereas the slickwater tended to activate the bedding planes as a result of the temporary blocking effect of the guar fluid. On the basis of the development of fractures around the initiation point, the initiation patterns were classified into three categories: (1) transverse-fracture initiation, (2) bedding-seam initiation, and (3) natural-fracture initiation. Each of these fracture-initiation patterns had a different propagation mode. The alternating-fluid-injection treatment exploited the advantages of the two fracturing fluids to form a large complex fracture network in deep shale gas reservoirs; therefore, we concluded that this method is an efficient way to enhance the stimulated reservoir volume compared with conventional hydraulic-fracturing technologies.

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Fracture Initiation and Propagation in Fatigue Contact Loading of AA6082 Aluminium Alloy

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.324-325.1091 ◽

2006 ◽

Vol 324-325 ◽

pp. 1091-1094

Author(s):

Angela Benedetti ◽

Pier Gabriele Molari ◽

Piero Morelli

Keyword(s):

Aluminium Alloy ◽

Contact Area ◽

Contact Fatigue ◽

Fracture Initiation ◽

Free Edge ◽

Element Analysis ◽

Contact Loading ◽

Linear Finite Element ◽

Initiation And Propagation ◽

Microscopy Analysis

This paper presents the results of an experimental investigation on surface contact fatigue of AA6082 aluminium alloy. After testing, microscopy analysis of the specimen contact area shows plastic deformation at the centre and circumferential cracks at the very edge of the print. Major cracks develop at a certain depth under the border of the contact area and propagate beneath the surface, in the direction of both the centre of contact and the lateral free edge of the specimens. No cracks have been observed at the centre of contact, neither on the surface, nor inside the material. Tensile properties of the alloy have been measured and a non linear finite element analysis has been performed in order to calculate the field of deformation and stress in the contact zone. Finally, stress intensities are correlated with the crack initiation points and an interpretation of the propagation paths, in regard to stress distribution, is given.

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Analysis of hydraulic fracture initiation and propagation in deep shale formation with high horizontal stress difference

Journal of Petroleum Science and Engineering ◽

10.1016/j.petrol.2018.06.060 ◽

2018 ◽

Vol 170 ◽

pp. 231-243 ◽

Cited By ~ 34

Author(s):

Bing Hou ◽

Ruxin Zhang ◽

Yijin Zeng ◽

Weineng Fu ◽

Yeerfulati Muhadasi ◽

...

Keyword(s):

Hydraulic Fracture ◽

Fracture Initiation ◽

Horizontal Stress ◽

Stress Difference ◽

Initiation And Propagation ◽

Shale Formation ◽

Horizontal Stress Difference

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An Experimental Evaluation of the Effects of Filtercake in Wellbore Strengthening: Filtercake Rupture Resistance and Fracture Sealing Time

Journal of Energy Resources Technology ◽

10.1115/1.4044802 ◽

2019 ◽

Vol 142 (4) ◽

Cited By ~ 2

Author(s):

Mingzheng Yang ◽

Yuanhang Chen

Keyword(s):

Drilling Fluid ◽

Experimental Tests ◽

Fracture Initiation ◽

Vital Role ◽

Fracture Sealing ◽

Initiation Stage ◽

Induced Fractures ◽

Wellbore Strengthening ◽

New Criterion

Abstract Recent research studies have indicated that filtercakes play a role in preventing fracture initiation, blocking pre-existing narrow fractures, and isolating drilling-induced fractures at the initiation stage. The ability of the filtercakes to effectively strengthen the wellbore expectedly depends on its capability in maintaining its integrity and providing the barrier to isolate pressure and fluid transmission between the wellbore and fractures. In this research, a modified permeability apparatus was used to evaluate the quality of drilling fluid filtercakes. A new criterion defined as filtercake rupture resistance is proposed to characterize the filtercake quality regarding its ability to sustain pressure over an open fracture. Experimental tests were conducted to investigate how filtercake thickness and filtercake yield strength affect the rupture resistance. The mechanism of filtercake in sealing the narrow fractures is explored, and it was observed that solid's plugging/bridging plays the vital role in this mechanism. A thicker and stronger filtercake also contributes to a faster establishment of complete fracture seal. The results of this research can be utilized as a reference that guides the optimization of drilling fluid for continuously strengthening the wellbore.

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In-situ synchrotron characterisation of fracture initiation and propagation in shales during indentation

Energy ◽

10.1016/j.energy.2020.119161 ◽

2021 ◽

Vol 215 ◽

pp. 119161

Author(s):

Lin Ma ◽

Anne-Laure Fauchille ◽

Michael R. Chandler ◽

Patrick Dowey ◽

Kevin G. Taylor ◽

...

Keyword(s):

Fracture Initiation ◽

Initiation And Propagation

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The Rule of Carrying Cuttings in Horizontal Well Drilling of Marine Natural Gas Hydrate

Energies ◽

10.3390/en13051129 ◽

2020 ◽

Vol 13 (5) ◽

pp. 1129 ◽

Cited By ~ 2

Author(s):

Na Wei ◽

Yang Liu ◽

Zhenjun Cui ◽

Lin Jiang ◽

Wantong Sun ◽

...

Keyword(s):

Particle Size ◽

Flow Velocity ◽

Gas Hydrate ◽

Horizontal Well ◽

Drilling Fluid ◽

Test Method ◽

Critical Flow ◽

Fluid Density ◽

Critical Flow Velocity ◽

Orthogonal Test Method

Horizontal well drilling is a highly effective way to develop marine gas hydrate. During the drilling of horizontal wells in the marine gas hydrate layer, hydrate particles and cutting particles will migrate with the drilling fluid in the horizontal annulus. The gravity of cuttings is easy to deposit in the horizontal section, leading to the accumulation of cuttings. Then, a cuttings bed will be formed, which is not beneficial to bring up cuttings and results in the decrease of wellbore purification ability. Then the extended capability of the horizontal well will be restricted and the friction torque of the drilling tool will increase, which may cause blockage of the wellbore in severe cases. Therefore, this paper establishes geometric models of different hole enlargement ways: right-angle expansion, 45-degree angle expansion, and arc expanding. The critical velocity of carrying rock plates are obtained by EDEM and FLUENT coupling simulation in different hydrate abundance, different hydrate-cuttings particle sizes and different drilling fluid density. Then, the effects of hole enlargement way, particle size, hydrate abundance and drilling fluid density on rock carrying capacity are analyzed by utilizing an orthogonal test method. Simulation results show that: the critical flow velocity required for carrying cuttings increases with the increase of the particle size of the hydrate-cuttings particle when the hydrate abundance is constant. The critical flow velocity decreases with the increase of drilling fluid density, the critical flow velocity carrying cuttings decreases with the increase of hydrate abundance when the density of the drilling fluid is constant. Orthogonal test method was used to evaluate the influence of various factors on rock carrying capacity: hydrate-cuttings particle size > hole enlargement way > hydrate abundance > drilling fluid density. This study provides an early technical support for the construction parameter optimization and well safety control of horizontal well exploitation models in a marine natural gas hydrate reservoir.

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