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Derisking of Unconventional Gas and LTO Opportunities: Application of Basin Modelling

Matthias Keym¹, Olaf Podlaha¹, Volker Dieckmann², Olivier Meuric¹, Ozkan Huvaz¹, Elise Leenaarts¹, and Erdem Idiz¹
¹Shell Global Solutions International, Rijswijk, The Netherlands
²Shell International Exploration and Production, Houston, TX, USA

Unconventional Light Tight Oil (LTO) and shale gas (SG) plays are self-charged systems, relying on the indigenous organic matter as the source of hydrocarbons. The fine-grained organic rich sediments or tight layers in their vicinity act with their residual pore space as the reservoirs. Pressure and temperature can significantly increase during burial and even more decrease during erosion and uplift. These changes strongly influence the phase behaviour of the generated and trapped hydrocarbons thereby affecting their flow properties, potential migration routes, retention capacity of the source rock, and predicted volumes initially in place. Shell’s integrated Cauldron Shale Gas Simulator calculates resource density on a regional to basin scale, typically during the opportunity identification and screening phase. Informed decision-making in exploring for such unconventional opportunities relies on integrating all available (i.e., sometimes scarce) data and their associated uncertainties for basin scale physical elements and processes into a working geologic model.

Successful exploitation of shale gas opportunities depends on 1) resources in place, 2) favourable geomechanics, and 3) use of appropriate production technology to optimize rates and ultimate recovery. Unique characteristics of gas storing shales are that they are both source and reservoir at the same time, and require no structural or stratigraphic trapping mechanism to retain the gas. The generated hydrocarbons are stored in the very tight pore network of those rocks in very close vicinity to where they were generated in the first place. In this context and for a proper resource estimate, the properties of initially formed petroleum from the kerogen and its PVT behaviour through time and space are amongst the most critical elements. This is particularly relevant in basins which have experienced significant geological uplift and associated erosion and have thus undergone pressure and temperature changes in the pore network since the hydrocarbon generation. The impact is major since mechanisms such as phase separation and/or fluid expansion can dramatically change the volume and the properties of the originally stored fluids , i.e., at the time and conditions of original hydrocarbon charge.

AAPG Search and Discovery Article #120098©2013 AAPG Hedberg Conference Petroleum Systems: Modeling the Past, Planning the Future, Nice, France, October 1-5, 2012