The Reservoir Characterisation and Fault Investigation of the Bowland Shale Formation: The Applications of Seismic Attributes and Inversion to Identify Reactivated Faults and Sweet Spots

Abstract

Unconventional explorations of gas-bearing shales have become an important resource as conventional gas fields have declined. The Bowland Shale Formation is among the most promising unconventional resources in the UK, with its high organic content and brittleness. However, the recent hydraulic fracturing of the Bowland Shale generated problematic felt seismicity. The first objective of this study is to examine the faults that caused felt seismicity at the Preston New Road (PNR) site in 2018 and 2019 using seismic attributes. The second goal is to identify sweet spots, the most promising drilling targets, in the Bowland Shale using seismic inversion.
Firstly, I investigated whether the faults responsible for the induced seismicity could be seen in the reflection seismic data acquired from Lancashire, UK. While many faults were visible on the 3D seismic data, the responsible faults were not. I compound seismic attributes, revealing potential evidence of the causative faults. Nonetheless, these observations were ambiguous since any anomalies were not significantly above background noise levels. This might be because they are subtle strike-slip faults, according to the recorded focal mechanisms, which do not cause vertical offsets. Secondly, I characterised the spatial variability of physical properties within the Bowland Shale. Statistical analysis of well logs from two wells indicates that vertical variations are dominated by changes in the natural gamma ray log. I applied a seismic inversion algorithm to the 3D seismic data, yielding Acoustic Impedance (AI), Shear Impedance (SI), and λρ and μρ volumes. Sweet spots are indicated by low λρ and μρ values. Many sweet spots identified by our analysis have already been targeted by existing wells, except spots between the Preese Hall-1 (PH-1) and Preston New Road (PNR) and between PH-1 and Thistleton-1 (TH-1) wells. These areas have more ductile shale content, which might be promising prospective locations in the future since they are less likely to generate induced seismicity, but may still have potential for high production.

Date of Award	28 Sept 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	James P Verdon (Supervisor) & Joachim Gottsmann (Supervisor)