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Citation
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HERO ID
8748337
Reference Type
Meetings & Symposia
Title
Origin and potential of unconventional Jurassic oil reservoirs on the Northern Arabian Plate
Author(s)
Goff, J
Year
2005
Publisher
Society of Petroleum Engineers (SPE)
Page Numbers
797-812
Language
English
DOI
10.2523/93505-ms
Abstract
Unconventional oil reservoirs exist in deep, overpressured, fractured carbonate source rocks, and in adjacent dolomitised carbonate platforms, in the Jurassic Gotnia Basin on the northern Arabian Plate. These reservoirs are an important potential future resource for the region once the low risk prospect inventory in conventional plays is drilled out, and production from their reservoirs inevitably reaches a plateau. An estimated 5-10 trillion barrels of oil have been generated in the Jurassic source kitchen; recovery of just 0.5% of this volume would yield substantial oil reserves. A high proportion of the generated oil has probably been retained in secondary porosity within the Jurassic Petroleum System, beneath an evaporite caprock. Pore pressure gradients approaching 1 psi/ft during oil generation (at pore pressures of 10,000 - 20,000 psi), and localized folding in Late Jurassic, Turonian and Late Tertiary time, have created a complex fractured reservoir system within the Jurassic source rocks and interbedded carbonates. Sustained production from the source rock reservoirs may only be possible in areas where oil filled microfractures are able to recharge large connected permeable tectonic fractures during pressure drawdown. Dolomitising fluids and oil have migrated into carbonate platforms underlying, and flanking, the source kitchen. Fluid inclusion studies indicate that dolomitisation occurred at temperatures of 80-140 deg C from pore waters with salinities of 100,000 - 250,000 ppm, locally creating world class oil reservoirs (sealed by tight limestones) seen at outcrop in the Zagros Mountains on the deformed eastern margin of the basin. Successful exploration and development of the Jurassic reservoirs will be challenging - requiring pre drill seismic imaging of fracture systems and of laterally discontinuous porous dolomite units, application of unconventional wells in challenging drilling environments, and careful reservoir management during production to achieve commercial recovery factors. Copyright 2005, Society of Petroleum Engineers Inc.
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