Seismic Risk Due to Induced Earthquakes at the Preston New Road (UK) Shale Gas Site

Session: Earthquake Source Parameters: Theory, Observations and Interpretations [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

In this study we present a seismic risk analysis for the Preston New Road (PNR) shale gas site near Blackpool, UK. Hydraulic fracturing of the first shale gas well at PNR in late 2018 marked the end of a seven-year moratorium on fracking in the UK. A strict traffic light system was in place, with the ‘red light’ set at M_L 0.5. Despite this, seismic events up to M_L 1.5 were initially detected. In a second well at the same site, hydraulically fractured 9 months later, events up to M_L 2.9 were induced. Initially, site characterization is carried out, showing that low-velocity sedimentary deposits (V_s30 = 200 – 280 m/s) dominate the region. We then test ground motion prediction equations for applicability to the recorded waveform data. Predicting median and 84^th-percentile peak ground velocity fields for M_L 2.5 to 4.5 events we subsequently determine macroseismic intensity. Median epicentral intensities of EMS III, IV and VI are predicted for M_L 2.5, 3.5 and 4.5, respectively. 84^th percentile PGV predictions show that epicentral intensities may, in limited localities, be as high as EMS V and VII for the M_L 3.5 and 4.5 scenarios, respectively. Nonlinear dynamic analysis is next undertaken to define the fragility curves to be used for risk calculations. A probabilistic analysis of damage is performed on our building inventory using the OpenQuake-engine. Based on these analyses, the onset of cosmetic damage (DS1) in terms of median risk is expected at M_L 3.5. DS2 (minor structural damage) may occur at M_L 4, while DS3 and DS4 (moderate to major structural damage) may occur at M_L 4.5. Finally, structural analysis of the well is undertaken, which shows that integrity is unlikely to be affected by strain due to seismic waves (up to M_L 4.5) or damage due to fault ruptures (with slip up to 17 mm). Additionally, the shear strength of the well itself is found to be in excess of the maximum known fault stresses at reservoir depths.

Presenting Author: Benjamin Edwards

Authors