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

Energy ◽  
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

Fracture Initiation and Propagation in a Deep Shale Gas Reservoir Subject to an Alternating-Fluid-Injection Hydraulic-Fracturing Treatment

SPE Journal ◽  
2019 ◽  
Vol 24 (04) ◽  
pp. 1839-1855 ◽  
Author(s):  
Bing Hou ◽  
Zhi Chang ◽  
Weineng Fu ◽  
Yeerfulati Muhadasi ◽  
Mian Chen
Keyword(s):  
Hydraulic Fracturing ◽  
Shale Gas ◽  
Fracture Initiation ◽  
Fluid Injection ◽  
Hydraulic Fractures ◽  
Stress Difference ◽  
Gas Reservoirs ◽  
Complex Fracture ◽  
Initiation And Propagation

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.

scholarly journals Recent comprehensive review for extended finite element method (XFEM) based on hydraulic fracturing models for unconventional hydrocarbon reservoirs

2020 ◽  
Vol 10 (8) ◽  
pp. 3319-3331 ◽  
Author(s):  
Belladonna Maulianda ◽  
Cindy Dhevayani Savitri ◽  
Aruvin Prakasan ◽  
Eziz Atdayev ◽  
Twon Wai Yan ◽  
...  
Keyword(s):  
Finite Element ◽  
Hydraulic Fracturing ◽  
Fracture Initiation ◽  
In Situ Stress ◽  
Extended Finite Element ◽  
Gas Reservoirs ◽  
Initiation And Propagation ◽  
Unconventional Gas Reservoirs ◽  
In Situ Stress Field

Abstract Hydraulic fracturing has been around for several decades since 1860s. It is one of the methods used to recover unconventional gas reservoirs. Hydraulic fracturing design is a challenging task due to the reservoir heterogeneity, complicated geological setting and in situ stress field. Hence, there are plenty of fracture modelling available to simulate the fracture initiation and propagation. The purpose of this paper is to provide a review on hydraulic fracturing modelling based on current hydraulic fracturing literature. Fundamental theory of hydraulic fracturing modelling is elaborated. Effort is made to cover the analytical and numerical modelling, while focusing on eXtended Finite Element Modelling (XFEM).

A Novel Method and its Application to Define Maximum Horizontal Stress and Stress Path

2021 ◽  
Author(s):  
Jianguo Zhang ◽  
Karthik Mahadev ◽  
Stephen Edwards ◽  
Alan Rodgerson
Keyword(s):  
Fracture Initiation ◽  
Stress Path ◽  
Horizontal Stress ◽  
Geomechanical Model ◽  
Breakdown Pressure ◽  
In Situ Stresses ◽  
Fracture Closure ◽  
Minimum Horizontal Stress ◽  
Maximum Horizontal Stress

Abstract Maximum horizontal stress (SH) and stress path (change of SH and minimum horizontal stress with depletion) are the two most difficult parameters to define for an oilfield geomechanical model. Understanding these in-situ stresses is critical to the success of operations and development, especially when production is underway, and the reservoir depletion begins. This paper introduces a method to define them through the analysis of actual minifrac data. Field examples of applications on minifrac failure analysis and operational pressure prediction are also presented. It is commonly accepted that one of the best methods to determine the minimum horizontal stress (Sh) is the use of pressure fall-off analysis of a minifrac test. Unlike Sh, the magnitude of SH cannot be measured directly. Instead it is back calculated by using fracture initiation pressure (FIP) and Sh derived from minifrac data. After non-depleted Sh and SH are defined, their apparent Poisson's Ratios (APR) are calculated using the Eaton equation. These APRs define Sh and SH in virgin sand to encapsulate all other factors that influence in-situ stresses such as tectonic, thermal, osmotic and poro-elastic effects. These values can then be used to estimate stress path through interpretation of additional minifrac data derived from a depleted sand. A geomechanical model is developed based on APRs and stress paths to predict minifrac operation pressures. Three cases are included to show that the margin of error for FIP and fracture closure pressure (FCP) is less than 2%, fracture breakdown pressure (FBP) less than 4%. Two field cases in deep-water wells in the Gulf of Mexico show that the reduction of SH with depletion is lower than that for Sh.

In Situ X-ray Tomography Observations of Initiation and Propagation of Pits During Atmospheric Corrosion of Aluminium Alloy AA2024

2021 ◽  
Author(s):  
Sarah Jane Marie Glanvill ◽  
Andrew Du Plessis ◽  
Steven Richard Street ◽  
Trevor Rayment ◽  
Alison J Davenport
Keyword(s):  
Aluminium Alloy ◽  
Atmospheric Corrosion ◽  
X Ray ◽  
Initiation And Propagation

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

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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