Well Shear Associated with Conventional and Unconventional Operations: Diagnosis and Mechanisms

2021 ◽  
pp. 1-18
Author(s):  
Russell T. Ewy
Keyword(s):  
Cross Sections ◽  
Slip Surface ◽  
Bedding Plane ◽  
Vertical Stress ◽  
Natural Fracture ◽  
Shear Deformations ◽  
Horizontal Fracture ◽  
Bedding Planes ◽  
Shear Slip ◽  
Fluid Pressurization

Summary Wells are sometimes deformed due to geomechanical shear slip, which occurs on a localized slip surface, such as a bedding plane, fault, or natural fracture. This can occur in the overburden above a conventional reservoir (during production) or within an unconventional reservoir (during completion operations). Shear slip will usually deform the casing into a recognizable shape, with lateral offset and two opposite-trending bends, and ovalized cross sections. Multifinger casing caliper tools have a recognizable response to this shape and are especially useful for diagnosing well shear. Certain other tools can also provide evidence for shear deformation. Shear deformations above a depleting, compacting reservoir are usually due to slip on bedding planes. They usually occur at multiple depths and are driven by overburden bending in response to reservoir differential compaction. Shear deformations in unconventional reservoirs, for the examples studied, have been found to be caused by slip on bedding planes and natural fractures. In both cases, models, field data, and physical reasoning suggest that slip occurs primarily due to fluid pressurization of the interface. In the case of bedding plane slip, fracturing pressure greater than the vertical stress (in regions where the vertical stress is the intermediate stress) could lead to propagation of a horizontal fracture, which then slips in shear.

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 Stress-Dependent Deformation and Permeability of a Fractured Coal Subject to Excavation-Related Loading Paths

2021 ◽  
Author(s):  
Wenzhuo Cao ◽  
Qinghua Lei ◽  
Wu Cai
Keyword(s):  
Coal Mining ◽  
Coalbed Methane ◽  
Axial Stress ◽  
Equilibrium Phase ◽  
Natural Fracture ◽  
Equivalent Permeability ◽  
Coal Matrix ◽  
Bedding Planes ◽  
Fractured Coal ◽  
Stress Dependent

AbstractThe deformation and permeability of coal are largely affected by the presence and distribution of natural fractures such as cleats and bedding planes with orthogonal and abutting characteristics, resulting in distinct hydromechanical responses to stress loading during coal mining processes. In this research, a two-dimensional (2D) fracture network is constructed based on a real coal cleat trace data collected from the Fukang mine area, China. Realistic multi-stage stress loading is designed to sequentially mimic an initial equilibrium phase and a mining-induced perturbation phase involving an increase of axial stress and a decrease of confining stress. The geomechanical and hydrological behaviour of the fractured coal under various stress loading conditions is modelled using a finite element model, which can simulate the deformation of coal matrix, the shearing and dilatancy of coal cleats, the variation of cleat aperture induced by combined effects of closure/opening, and shear and tensile-induced damage. The influence of different excavation stress paths and directions of mining is further investigated. The simulation results illustrate correlated variations among the shear-induced cleat dilation, damage in coal matrix, and equivalent permeability of the fractured coal. Model results are compared with results of previous work based on conventional approaches in which natural fracture networks are not explicitly represented. In particular, the numerical model reproduces the evolution of equivalent permeability under the competing influence of the effective stress perpendicular to cleats and shear-induced cleat dilation and associated damage. Model results also indicate that coal mining at low stress rates is conducive to the stability of surrounding coal seams, and that coal mining in parallel to cleat directions is desirable. The research findings of this paper have important implications for efficient and safe exploitation of coal and coalbed methane resources.

Features and genesis of micro-nanometer-sized grains on shear slip surface of the 2008 Wenchuan earthquake

2014 ◽  
Vol 57 (8) ◽  
pp. 1961-1971 ◽  
Author(s):  
RenMao Yuan ◽  
BingLiang Zhang ◽  
XiWei Xu ◽  
ChuanYong Lin ◽  
LanBing Si ◽  
...  
Keyword(s):  
Wenchuan Earthquake ◽  
Slip Surface ◽  
2008 Wenchuan Earthquake ◽  
The 2008 Wenchuan Earthquake ◽  
Shear Slip

Tectonic ripples and associated minor structures in the Silurian rocks of Denbighshire, North Wales

1970 ◽  
Vol 107 (1) ◽  
pp. 51-60 ◽  
Author(s):  
P. T. Warren ◽  
R. K. Harrison ◽  
H. E. Wilson ◽  
E. G. Smith ◽  
M. J. C. Nutt
Keyword(s):  
Bedding Plane ◽  
Linear Structures ◽  
Regional Stress ◽  
Bedding Planes ◽  
North Wales ◽  
Tectonic Origin

SummaryStructures affecting certain bedding planes, and simulating sedimentary ripples, have been found at a number of horizons in the Wenlock and Ludlow rocks of Denbighshire, North Wales. The megascopic appearance of the ripples, including their association with linear structures and their miscroscopical fabric are described in detail; and it is concluded that they are of tectonic origin, being manifestations of bedding-plane slip. The orientations of the ripples and other minor structures suggest that the stress responsible was the regional stress that produced folding, faulting and cleavage.

scholarly journals Stability estimation of slopes with determined slip surface by the MSTAB-3D method based on sliding body limit equilibrium analysis

2019 ◽  
Vol 262 ◽  
pp. 04004
Author(s):  
Janusz Ukleja
Keyword(s):  
Cross Sections ◽  
Slip Surface ◽  
Limit Equilibrium ◽  
Equilibrium Analysis ◽  
Limit Equilibrium Analysis ◽  
Modified Method ◽  
3D Elements ◽  
Resultant Forces ◽  
The Impact ◽  
Section Analysis

The method developed for this study, established on the premises of the limit equilibrium flat analysis for a spatial solution, is a modification of the STAB-3D method, previously described by the author. It combines the analyses methods of 2D slices of flat cross–sections with the spatial analyses methodology rooted in a specific breakdown of a landslide sliding body into 3D elements assuming some simplifying solution. However, this method is solely applicable in case of a landslide failure with a stipulated slip surface and with a consistent decline of a determined slide direction. Such a method was developed in the article published earlier, which provided then its basic assumptions and the equilibrium formulations. The following publication thereof, presents overall suppositions for this method as well as its modification involving the resultant forces brought to the equilibrium with the generalized slide direction. Apart from that, a comparative analysis was carried out on the impact of this modification applicability of the obtained results with regard to the STAB-3D method. The algorithm was also presented concerning the modified method with its results being compared to a couple of selected methods LEM (limit equilibrium method). The undertaken analysis reveals that the modified MSTAB-3D method determines stability indicators that are very similar to its earlier version. Moreover, the results occur to be also approximating the values obtained in the course of other methods with regard to the flat cross-section analysis.

scholarly journals The Effect of Bedding Structure on Mechanical Property of Coal

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Zetian Zhang ◽  
Ru Zhang ◽  
Guo Li ◽  
Hegui Li ◽  
Jianfeng Liu
Keyword(s):  
Mechanical Property ◽  
Uniaxial Compression ◽  
Peak Stress ◽  
Natural Fracture ◽  
Test Results ◽  
Compression Tests ◽  
Average Amount ◽  
Uniaxial Compression Strength ◽  
Bedding Planes ◽  
Close Relationship

The mechanical property of coal, influencing mining activity considerably, is significantly determined by the natural fracture distributed within coal mass. In order to study the effecting mechanism of bedding structure on mechanical property of coal, a series of uniaxial compression tests and mesoscopic tests have been conducted. The experimental results show that the distribution characteristic of calcite particles, which significantly influences the growth of cracks and the macroscopic mechanical properties of coal, is obviously affected by the bedding structure. Specifically, the uniaxial compression strength of coal sample is mainly controlled by bedding structure, and the average peak stress of specimens with axes perpendicular to the bedding planes is 20.00 MPa, which is 2.88 times the average amount of parallel ones. The test results also show a close relationship between the bedding structure and the whole deformation process under uniaxial loading.

scholarly journals Influence of Bedding Planes on the Mechanical Characteristics and Fracture Pattern of Transversely Isotropic Rocks in Direct Shear Tests

2018 ◽  
Vol 2018 ◽  
pp. 1-14
Author(s):  
Lei Xia ◽  
Yawu Zeng ◽  
Rong Luo ◽  
Wei Liu
Keyword(s):  
Mechanical Characteristics ◽  
Numerical Models ◽  
Transversely Isotropic ◽  
Bedding Plane ◽  
Particle Flow Code ◽  
Fracture Plane ◽  
Direct Shear ◽  
Geometrical Properties ◽  
Bedding Planes ◽  
Fracture Patterns

Bedding planes are the primary control on the anisotropy of mechanical characteristics and fracture patterns in rock. To analyze the influence of the geometrical properties of bedding planes on the direct shear strength characteristics and fracture patterns of transversely isotropic rocks, numerical models were established using an improved modeling method using Particle Flow Code. The results of the numerical model were in good agreement with those of the physical experiments of an artificial rock mass containing a single bedding plane. The results show that the shear fractures with a range of bedding plane geometries can be divided into two patterns. When the inclination angles of the bedding planes were larger or smaller, a thoroughgoing fracture plane was formed near the preexisting shear fracture plane. On the other hand, the intact rock was broken into many parallel sheets.

Locomotion and feeding traces in Champlain Sea subaqueous outwash deposits near Ottawa, Canada

1990 ◽  
Vol 27 (11) ◽  
pp. 1495-1503 ◽  
Author(s):  
Dana L. Naldrett
Keyword(s):  
Depositional Environment ◽  
Close Association ◽  
Circular Cross Section ◽  
Fine Sand ◽  
Bedding Plane ◽  
Life Forms ◽  
Silty Clay ◽  
Bedding Planes ◽  
Algae And Bacteria ◽  
Medium Silt

Locomotion and feeding traces (repichnia and fodichnia) observed on bedding planes of rhythmically bedded subaqueous outwash deposits in the Brazeau sand pit, Nepean, Ontario, Canada, are the first bedding-plane traces described in detail from the western Champlain Sea. The Planolites–Palaeophycus-like and Taenidium-like traces are cylindrical with circular cross section, smooth sided, unlined, sinuous, sometimes branching, and sometimes meniscate. Organisms producing the traces are tentatively identified as errant polychaetes or nemerteans. The enclosing sediments are rhythmic couplets of alternating fine sand and silt layers overlain by silty clay and fine–medium silt layers. The occurrence of traces within the uppermost portion of the coarse unit, and within the coarser, upper portion of the overlying fine unit, and the rhythmic alternation of coarse and fine layers suggest these deposits may be varves. The traces formed during the more biologically suitable summer months but were preserved only during the latter portion of the summer. Traces are distributed on bedding planes in close association with bedforms and show a high correlation with the substrate and possibly the hydrodynamic regime. This is interpreted as indicating a strong preference in feeding behaviour. The presence of traces in the subaqueous outwash environment necessitates rethinking of the depositional environment to include the presence of errant polychaetes, nemerteans or similar organisms, and the lower life-forms such as epontic algae and bacteria on which they live.

Burrowed Phacops rana from the Moscow Formation of New York

1988 ◽  
Vol 62 (2) ◽  
pp. 311-312 ◽  
Author(s):  
Paul D. Zell
Keyword(s):  
New York ◽  
Visual Field ◽  
Bedding Plane ◽  
Sediment Surface ◽  
Bedding Planes

The trilobite Phacops rana has previously been documented in two life positions: horizontally outstretched and enrolled (Hall and Clarke, 1888). A specimen of Phacops rana was recovered in an unusual life position from the Windom Member of the Moscow Formation (Figure 1). It was collected from a borrow pit along Castle Hill Road, 1 km east of Earlville in Chenango County, New York. The trilobite appears to have burrowed tail first into the substrate, with only part of the cephalon and one or two thoracic segments exposed above the sediment surface. The orientation of the eyes indicate that the visual field was horizontal. The thorax angled into the substrate at an angle of approximately 50° from the horizontal, with the pygidium tilted dorsally relative to the thorax. Compaction effects appear to be slight. Because the specimen was found in situ, no doubt exists as to its orientation with respect to bedding. It is also evident from bedding plane surfaces that this trilobite had burrowed, and was not simply draped over an uneven substrate, as it intersects three bedding planes. There is no evidence of any object over which it could have been draped. No burrow trace, lining, or scratch marks are preserved. No other specimens of Phacops in this position have been reported.

scholarly journals Experimental study on the cracking process of layered shale using X-ray microCT

2017 ◽  
Vol 36 (2) ◽  
pp. 297-313 ◽  
Author(s):  
Shengxin Liu ◽  
Zongxiu Wang ◽  
Linyan Zhang
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Compressive Loading ◽  
Bedding Plane ◽  
Fracture Networks ◽  
Microscopy Imaging ◽  
X Ray ◽  
Bedding Planes ◽  
Cracking Process ◽  
Scanning Electron

The cracking process in Longmaxi formation shale was experimentally studied during uniaxial compressive loading. Both the evolution of the three-dimensional fracture network and the micromechanics of failure in the layered shale were examined as a function of the inclination angle of the bedding plane. To visualize the cracking process, the test devices presented here used an industrial X-ray CT scanner that enabled scanning during the uniaxial compressive loading. Scanning electron microscopy and environmental scanning electron microscopy imaging techniques were used to observe the microscopic characteristics of fractured surfaces of failed specimens. The combination of these observations clearly illustrated the micromechanics of the failure process in the anisotropic shale. The experimental results suggest that the cracking process could be divided into two stages under uniaxial loading, and the microstructures and bedding planes of the shale played an important role in the cracking process of layered shale. In the first stage of deformation, the cracking mainly occurred as smaller microcracks (such as intergranular, microcracks), and the propagation of the newly formed microcracks was controlled by the bedding plane of the shale specimen. The microscopic imaging study showed that the microscopic damage was mainly dominated by microtensile fractures under uniaxial compression. In the second stage, with the increase in loading, the extensive development and coalescence of the microcracks led to the formation of complex fracture networks. The complexity of the fracture networks was related to the microstructure of the sample. The coalescence of the microcracks could be divided into three levels in the spatial scale, and the coalescence patterns included both tensile and shear patterns.

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