Application of Magnetic Techniques to Lateral Hydrocarbon Migration – Lower Tertiary Reservoir Systems, UK North Sea

Abstract

Pyrolysis experiments show that magnetic minerals can be produced inorganically during oil formation in the ‘oil-kitchen’. Here we use this observation to identify a magnetic proxy that can be used to trace hydrocarbon migration pathways by determining the morphology, abundance, mineralogy and size of the magnetic minerals present in reservoirs. We address this by examining the Tay formation in the Western Central Graben in the North Sea.

Basin modelling has been carried out in a system in the North Sea well constrained by borehole and 3D seismic data. This allows us to clearly demonstrate vertical migration from a mature Jurassic (Kimmeridge Clay) source in the Central Graben to the East into overlying Tertiary sandstones of the Tay formation. Lateral migration to the west through the Tay channel system is also predicted by the model. Increasing oil gravity along the fill spill chain appears consistent with this interpretation. Importantly, the Jurassic source rock is shown to be immature over the majority of west and central study area, requiring lateral migration as the charge mechanism for the existing Tertiary fields.

The magnetic properties of core samples from the study area were determined using room-temperature measurements on a Vibrating Sample Magnetometer (VSM), low-temperature (0-300K) measurements on a Magnetic Property Measurement System (MPMS) and high-temperature (300-973K) measurements on a Kappabridge susceptibility meter. We identified magnetite, pyrrhotite, pyrite and siderite in the samples. An increasing presence of ferrimagnetic iron sulphides is noticed along the known hydrocarbon migration pathway.

Our initial results suggest mineralogy coupled with changes in grain size are possible proxies for hydrocarbon migration and importantly show trends matching the petroleum systems model

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018