Publication Name: The North West Shelf Australia
Authors: G.K. Ellis
Date Published: July 1988
Number of Pages: 24
Reference Type: Book Section
Abstract:
Talisman-1 was drilled in 1984 at the northeastern end of the Dampier Sub-basin in permit WA-191-P. Testing of the Lower Cretaceous reservoir sequence produced a cumulative flow of 11,239 barrels of oil per day from three drill stem tests. The reservoir sequence consists of Berriasian to Tithonian mass-flow sandstones ('B' and 'C' sands) and Hauterivian to Valanginian glauconitic shelf sandstones ('A' Sand) separated by claystone. An understanding of the diagenetic history of the Talisman-1 reservoir sequence has been developed from the integrated evaluation of petrography and petrophysics, with hydrocarbon show, sulphur isotope, formation water and oil compositional data. This has, in turn, provided insight into controls on reservoir quality and the history of oil entrapment.Two pyrite/ferroan dolomite-cemented sandstone intervals, below the present oil/water contact in the Berriasian to Tithonian reservoir sandstones, are interpreted to have developed at palaeo-oil/water contacts in "stacked" oil accumulations during the late Cretaceous to early Tertiary. The pyrite and ferroan dolomite is considered to have developed as a result of anaerobic bacterial reduction of formation water sulphate: H2S and C02 are generated and react with iron derived from dissolution of glauconite. Glauconite dissolution has enhanced the porosity and permeability of the reservoir sandstone.
Miocene tectonism produced minor faulting in the reservoir sequence, causing cross-feed of oil between the
stacked pays, redistributing the oil accumulation to its present configuration. Lighter hydrocarbons preferentially leaked up the fault during this phase of tectonism, with some accumulating in the Hauterivian
to Valanginian reservoir sandstone.