Mapping hydrocarbon charge-points in the Wessex Basin using seismic, geochemistry and mineral magnetics

R Abubakar,D Heslop,A Fraser,A.R Muxworthy,M.A Sephton,G.A Paterson,J.S Watson,P Southern

doi:10.1016/j.marpetgeo.2019.08.042

Abstract

Abstract This study reports a multidisciplinary approach to determining hydrocarbon charge-points and migration in the Wessex Basin, southern England. Geochemical analysis of reservoir core material (Bridport Sandstone and Inferior Oolite) using gas chromatography-mass spectrometry (GC-MS), suggests that the oil in the Wessex Basin is from a single source, and that small variations in environmentally sensitive biomarkers are likely due to small differences in maturity or depositional conditions during the formation of the oil over millions of years. Using seismic data, basin modelling revealed two potential hydrocarbon migration pathways from the hanging wall of the Purbeck fault into the Sherwood Sandstone reservoir at Wytch Farm. One of these potential pathways is represented by cores termed Creech and the other Bushey Farm. To try to distinguish between the two potential pathways, cores were studied using mineral magnetic techniques. The magnetic signature was characterised using low-temperature (

Highlights

The Wessex Basin located in Dorset, southern England (Fig. 1), was formed during the Late Permian and evolved throughout subsequent extensional and compressional tectonic events in the Mesozoic and Tertiary (e.g., Butler, 1998; Hawkes et al, 1998; Underhill and Stoneley, 1998)
The reason for the differences in the thicknesses in the model is likely because seismic section B90-32 lies across the Abbotsbury-Ridgeway Fault System, whereas seismic section B90-37 is located on the hanging wall of the fault system making it the most affected by the basin inversion as reported by Hawkes et al (1998)
Geochemical data suggests that the data is from a single source (Table 2), and that small variations in environmentally sensitive biomarkers are probably due to small differences in oil thermal maturity or depositional conditions during the millions of years it took to form the Lias

Summary

Introduction

The Wessex Basin located in Dorset, southern England (Fig. 1), was formed during the Late Permian and evolved throughout subsequent extensional and compressional tectonic events in the Mesozoic and Tertiary (e.g., Butler, 1998; Hawkes et al, 1998; Underhill and Stoneley, 1998). The apparent inconsistency is derived from the reorganisation of the basin during Tertiary inversion and an associated complex hydrocarbon migration history (Hawkes et al, 1998). To resolve these complexities, this study presents burial history reconstructions developed using PetroModTM and incorporating well data and Rock-Eval pyrolysis data from selected wells from the Wessex Basin. Mineral magnetic techniques have an advantage over geochemical ones, as they are relatively fast and inexpensive, allowing us to study many samples. They can, suffer from ambiguity in interpretation

Objectives

Methods

Results

Discussion

Conclusion