scholarly journals High-Resolution Imaging of the ML 2.9 August 2019 Earthquake in Lancashire, United Kingdom, Induced by Hydraulic Fracturing during Preston New Road PNR-2 Operations

2020 ◽  
Vol 92 (1) ◽  
pp. 151-169 ◽  
Author(s):  
Tom Kettlety ◽  
James P. Verdon ◽  
Antony Butcher ◽  
Matthew Hampson ◽  
Lucy Craddock
Keyword(s):  
United Kingdom ◽  
Stress Field ◽  
Hydraulic Fracturing ◽  
B Value ◽  
In Situ Stress ◽  
Mitigation Strategies ◽  
Hydraulic Fractures ◽  
Rupture Area ◽  
United Kingdom Government ◽  
Downhole Array

Abstract Hydraulic fracturing (HF) at Preston New Road (PNR), Lancashire, United Kingdom, in August 2019, induced a number of felt earthquakes. The largest event (ML 2.9) occurred on 26 August 2019, approximately three days after HF operations at the site had stopped. Following this, in November 2019, the United Kingdom Government announced a moratorium on HF for shale gas in England. Here we provide an analysis of the microseismic observations made during this case of HF-induced fault activation. More than 55,000 microseismic events were detected during operations using a downhole array, the vast majority measuring less than Mw 0. Event locations revealed the growth of hydraulic fractures and their interaction with several preexisting structures. The spatiotemporal distribution of events suggests that a hydraulic pathway was created between the injection points and a nearby northwest–southeast-striking fault, on which the largest events occurred. The aftershocks of the ML 2.9 event clearly delineate the rupture plane, with their spatial distribution forming a halo of activity around the mainshock rupture area. Across clusters of events, the magnitude distributions are distinctly bimodal, with a lower Gutenberg–Richter b-value for events above Mw 0, suggesting a break in scaling between events associated with hydraulic fracture propagation, and events associated with activation of the fault. This poses a challenge for mitigation strategies that rely on extrapolating microseismicity observed during injection to forecast future behavior. The activated fault was well oriented for failure in the regional stress field, significantly more so than the fault activated during previous operations at PNR in 2018. The differing orientations within the stress field likely explain why this PNR-2 fault produced larger events compared with the 2018 sequence, despite receiving a smaller volume of injected fluid. This indicates that fault orientation and in situ stress conditions play a key role in controlling the severity of seismicity induced by HF.

scholarly journals Modeling Simultaneous Multiple Fracturing Using the Combined Finite-Discrete Element Method

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-20 ◽  
Author(s):  
Quansheng Liu ◽  
Lei Sun ◽  
Pingli Liu ◽  
Lei Chen
Keyword(s):  
Hydraulic Fracturing ◽  
Solid Phase ◽  
Horizontal Wells ◽  
In Situ Stress ◽  
Gas Production ◽  
Hydraulic Fractures ◽  
Multiple Fractures ◽  
Fracture Geometry ◽  
Stress Shadow ◽  
Oil Gas

Simultaneous multiple fracturing is a key technology to facilitate the production of shale oil/gas. When multiple hydraulic fractures propagate simultaneously, there is an interaction effect among these propagating hydraulic fractures, known as the stress-shadow effect, which has a significant impact on the fracture geometry. Understanding and controlling the propagation of simultaneous multiple hydraulic fractures and the interaction effects between multiple fractures are critical to optimizing oil/gas production. In this paper, the FDEM simulator and a fluid simulator are linked, named FDEM-Fluid, to handle hydromechanical-fracture coupling problems and investigate the simultaneous multiple hydraulic fracturing mechanism. The fractures propagation and the deformation of solid phase are solved by FDEM; meanwhile the fluid flow in the fractures is modeled using the principle of parallel-plate flow model. Several tests are carried out to validate the application of FDEM-Fluid in hydraulic fracturing simulation. Then, this FDEM-Fluid is used to investigate simultaneous multiple fractures treatment. Fractures repel each other when multiple fractures propagate from a single horizontal well, while the nearby fractures in different horizontal wells attract each other when multiple fractures propagate from multiple parallel horizontal wells. The in situ stress also has a significant impact on the fracture geometry.

Consequences of rock layers and interfaces on hydraulic fracturing and well production of unconventional reservoirs

Geophysics ◽  
2018 ◽  
Vol 83 (6) ◽  
pp. MR333-MR344
Author(s):  
Seounghyun Rho ◽  
Roberto Suarez-Rivera ◽  
Samuel Noynaert
Keyword(s):  
Hydraulic Fracturing ◽  
Surface Area ◽  
Homogeneous Model ◽  
In Situ Stress ◽  
Unconventional Reservoirs ◽  
Rock Properties ◽  
Hydraulic Fractures ◽  
Shear Stresses ◽  
Principal Stresses ◽  
Well Production

Hydraulic fracturing is a fundamental condition for economic production of hydrocarbons from unconventional reservoirs. Hydrocarbon production is proportional to the propped surface area that is in contact with the reservoir and remains connected to the wellbore. Yet, the propped surface area controlling production appears to be considerably smaller than the surface area created during pumping. Somehow hydraulic fractures are disconnected, truncated, and reduced during production. One important mechanism causing this segmentation is the shear displacement of weak interfaces between rock layers. Shear stresses are generated in response to abrupt changes in material properties and changes in bed orientation, in relation to the orientation of the existing principal stresses. If the layered rocks are strongly laterally heterogeneous, they provide a high potential for shear failures and fracture segmentation along the interfaces between layers. The induced shear stress and shear slip also depend on the current geologic structure and following in situ stress loading, the stress alteration and fluid leakoff during hydraulic fracturing, and the existence of wells. We conducted numerical simulations using the finite-element method on layered and discontinuous rocks, and specifically in organic-rich mudstones and carbonate sequences. Our work was part of a field study. Three different layered rock models were simulated and compared: laterally homogeneous, laterally heterogeneous, and strongly laterally heterogeneous. For the latter, the heterogeneity was introduced by randomly varying the elastic rock properties of each layer. Our results indicate that localized shear stresses develop along interfaces between materials with contrasting properties and along the wellbore walls. This includes the generation of localized shear in planes that were principal in the homogeneous model. It was also seen that rock shear and slip, along interfaces between layers, may occur when the planes of weakness are pressurized (e.g., during hydraulic fracturing).

Study on Hydraulic Fracturing Method for In Situ Stress Measurement in Deep Boreholes

2015 ◽  
Vol 741 ◽  
pp. 567-571
Author(s):  
Yan Xin Zhang ◽  
Chang Sheng Song ◽  
Jian Hui Zhao
Keyword(s):  
Stress Field ◽  
Hydraulic Fracturing ◽  
Stress Measurement ◽  
Stress Test ◽  
In Situ Stress ◽  
Time Curve ◽  
Pressure Time ◽  
Deep Boreholes ◽  
In Situ Stress Field

Information of in situ stress field is crucial for predicting the response of rock masses to the disturbance associated with underground constructions. Hydraulic fracturing is an efficient method for determining the stress field and is suitable at the early stages of projects when no underground access exists. For this, a series of new improved techniques and equipments are developed for the deep boreholes to increase the reliability of system. For a better understanding of the stress test, the ideal HF pressure-time curve is given and the fracturing procedure is analyzed. Based on the theory of HF stress calculation, two implicit inequations are deduced.

scholarly journals Experimental and Numerical Investigation on Basic Law of Dense Linear Multihole Directional Hydraulic Fracturing

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Xin Zhang ◽  
Yuqi Zhang
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Large Scale ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
In Situ Stress ◽  
Hydraulic Fractures ◽  
Directional Hydraulic Fracturing ◽  
Basic Law

Using the dense linear multihole to control the directional hydraulic fracturing is a significant technical method to realize roof control in mining engineering. By combining the large-scale true triaxial directional hydraulic fracturing experiment with the discrete element numerical simulation experiment, the basic law of dense linear holes controlling directional hydraulic fracturing was studied. The results show the following: (1) Using the dense linear holes to control directional hydraulic fracturing can effectively form directional hydraulic fractures extending along the borehole line. (2) The hydraulic fracturing simulation program is very suitable for studying the basic law of directional hydraulic fracturing. (3) The reason why the hydraulic fracture can be controlled and oriented is that firstly, due to the mutual compression between the dense holes, the maximum effective tangential tensile stress appears on the connecting line of the drilling hole, where the hydraulic fracture is easy to be initiated. Secondly, due to the effect of pore water pressure, the disturbed stress zone appears at the tip of the hydraulic fracture, and the stress concentration zone overlaps with each other to form the stress guiding strip, which controls the propagation and formation of directional hydraulic fractures. (4) The angle between the drilling line and the direction of the maximum principal stress, the in situ stress, and the hole spacing has significant effects on the directional hydraulic fracturing effect. The smaller the angle, the difference of the in situ stress, and the hole spacing, the better the directional hydraulic fracturing effect. (5) The directional effect of synchronous hydraulic fracturing is better than that of sequential hydraulic fracturing. (6) According to the multihole linear codirectional hydraulic fracturing experiments, five typical directional hydraulic fracture propagation modes are summarized.

Analysis of Stress-Field Variations Expected on Subsurface Faults and Discontinuities in the Vicinity of Hydraulic Fracturing

2015 ◽  
Vol 19 (01) ◽  
pp. 054-069 ◽  
Author(s):  
Qian Gao ◽  
Yueming Cheng ◽  
Ebrahim Fathi ◽  
Samuel Ameri
Keyword(s):  
Stress Field ◽  
Analytical Solutions ◽  
Numerical Models ◽  
In Situ Stress ◽  
Strike Slip ◽  
Stress Fields ◽  
Hydraulic Fractures ◽  
Slip Tendency ◽  
The Stability

Summary In this study, a local stability evaluation method, slip-tendency analysis, is proposed on the basis of the Coulomb criterion to investigate the effects of hydraulic fracturing on stress-field variations and possibility of fault reactivation. The effects of net pressure and in-situ stress fields on the stability of faults are investigated in two typical faulting environments (i.e., normal and strike-slip faults). A 3D numerical model developed on the basis of the finite-element method (FEM) is also adopted to better understand the stability states around pressurized hydraulic fractures. The orientation and relative magnitudes of in-situ stress fields differ under different faulting environments, which, in turn, control the direction of fracture propagation and its geometry. It is found that the general patterns of slip-tendency distributions around pressurized hydraulic fractures are similar under different in-situ stress fields. Providing the normal and strike-slip faults with a same initial slip-tendency, the normal faulting environment demonstrates larger variations in slip-tendency than the strike-slip faulting environment. The comparison between analytical and numerical solutions indicates an excellent agreement was achieved, which certifies the validity of the proposed numerical models in complex situations. Numerical models and analytical solutions confirm the presence of both unstable and stable regions around the pressurized fractures. Fault stability during hydraulic operation depends on the position of faults with respect to the hydraulic fractures. The critical angle and distance between fault and hydraulic fracture in analytical solutions are identified when a region transits from stable to unstable status. For faults and discontinuities with an angle larger than 40° (i.e., with respect to horizontal direction) and distances less than 2.5 times the height of the fracture (i.e., from the center of pressurized fracture), the slip-tendency is greater than the initial value, indicating that the discontinuities within this zone are unstable and have the potential to slip. The developed model predicts that the unstable regions extend from fracture tips in both lateral and vertical directions. This generates relatively planar-distributed microseismic events, which are well-demonstrated in monitored field events. It was shown that the slippage of underground faults and other discontinuities could improve the fluid flow and transport by increasing the apparent permeability of the reservoir, such that the unstable regions could be recognized as permeability-improved zones.

Disposing of John Lindley's library and herbarium: the offer to Australia

2008 ◽  
Vol 35 (1) ◽  
pp. 15-70 ◽  
Author(s):  
A. M. LUCAS
Keyword(s):  
United Kingdom ◽  
Botanic Gardens ◽  
Final Disposal ◽  
The United Kingdom ◽  
Royal Horticultural Society ◽  
Royal Botanic Gardens ◽  
United Kingdom Government ◽  
The University ◽  
Joseph Hooker

Shortly before he died, John Lindley decided to dispose of his herbarium and botanical library. He sold his orchid herbarium to the United Kingdom government for deposit at the Royal Botanic Gardens, Kew, and then offered his library and the remainder of his herbarium to Ferdinand Mueller in Melbourne. On his behalf, Joseph Hooker had earlier unsuccessfully offered the library and remnant herbarium to the University of Sydney, using the good offices of Sir Charles Nicholson. Although neither the University of Sydney nor Mueller was able to raise the necessary funds to purchase either collection, the correspondence allows a reconstruction of a catalogue of Lindley's library, and poses some questions about Joseph Hooker's motives in attempting to dispose of Lindley's material outside the United Kingdom. The final disposal of the herbarium to Cambridge and previous analyses of the purchase of his Library for the Royal Horticultural Society are discussed. A list of the works from Lindley's library offered for sale to Australia is appended.

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