A Workflow Solving Migration Problems with Combined Structural and Petroleum Systems Modelling - Case Studies from Offshore Brazil and Onshore Trinidad

Jonathan McQuilken
BG Group plc, Thames Valley park Drive, Reading, Berkshire, RG6 1PT, United Kingdom

The IES 2D PetroMod software utilizes the present day structural configuration of a depth section and back-strips it through time to give a series of time steps which are then used for petroleum systems modelling. As such, these time steps are not structurally restored and can have an impact on the modelling outcome, particularly, where structuration and migration are contemporaneous. In addition, complex geometries such as salt or thrust tectonics cannot be modelled. To overcome this inadequacy, BG Group jointly sponsored a Joint Industry Project (JIP) to develop the IES 2D PetroMod TecLink Module which enables a workflow whereby structurally restored depth sections can be directly imported into 2D PetroMod for use as a series of time steps for modelling. This workflow has now been successfully used on a number of structurally restored sections within BG Group: these include a salt tectonics section from the Santos Basin, offshore Brazil and a complex thrust tectonics section from the Central Block area, onshore Trinidad.

For the Santos Basin, BG Brazil were concerned with the role of salt on hydrocarbon migration and supplied ten structurally restored time steps directly exported from the Midland Valley 2DMove software ranging in age from the Top Albian to the present day. Simulation showed that salt windows were not developed through time and that the salt acts as a migration barrier and top seal to all the oil and gas generated from the pre-salt Barremian and Aptian source rocks allowing the generated hydrocarbons to be trapped in the pre-rift succession. Furthermore, the absence of salt windows precludes any further vertical migration through the petroleum system. It is also evident that the traps within the pre-rift succession begin to fill with gas as early as the mid Albian; in addition, there is evidence of oil being displaced by gas. Insignificant gas pools exist in the Albian fractured carbonates and are sourced from the mid Albian post-salt source and have filled by vertical migration through fractures.

BG Trinidad & Tobago were primarily concerned with being able to explain the mix of liquids and dry gases seen in the petroleum system as accumulations in the onshore Central Block area and supplied eight structurally restored time steps from the Midland Valley 2DMove software ranging in age from the Oligocene to the present day. Simulation showed that the working petroleum system in the Central Block area is a combined biogenic and thermogenic system which explains the presence of dry gas in the down-dip extension of the Corosan discovery, the mix of biogenic and thermogenic gas seen in the down-dip extension of the Carapal Field and the liquids and associated thermogenic gas in the Penal-Barrackpore structure.

Overall this workflow is now utilised within the routine workflows at BG Group and highlights how JIPs can be used to overcome problems and significantly improve workflows.

AAPG Search and Discovery Article #90091©2009 AAPG Hedberg Research Conference, May 3-7, 2009 - Napa, California, U.S.A.