Predicting Fluid Phases and Properties in Shale Gas Settings Using PVT in Basin Modeling

Meuric, Olivier ¹; Dieckmann, Volker ¹; Idiz, Erdem ¹; Senior, William ¹; Keym, Matthias ¹
(1) Shell Global Solutions International, Rijswijk, Netherlands.

Unconventional resources have emerged as an important part of the world's energy supply. While technological advances such as drilling and completion have contributed to the exponential growth of unconventional gas opportunities and their exploitation, a deep understanding of the subsurface geologic controls on source rock and reservoirs characteristics (geochemical and petrophysical) is becoming paramount to identifying sweet-spots and areas of highest resource density.

In this context the properties of first formed petroleum from the source rock kerogen and its PVT behaviour through time and space is amongst the most critical elements for a proper resource estimate. This is particularly relevant for unconventional gas opportunities as many of them are in basins which have experienced significant geological uplift and have thus undergone pressure and temperature changes in the storage space (pore network). This has major impact since mechanisms such as phase separation and/or fluid expansion can dramatically change the volume and properties of the fluids originally stored at the time and conditions of original hydrocarbon charge.

Several of the issues highlighted above were investigated using Shell’s proprietary basin modelling tool. We can now treat a source rock as a reservoir and address not only the generation and expulsion of fluid types in response to maturation and kerogen conversion, but also the phase behaviour of hydrocarbons reservoired within the source rock pore system. This clearly has an impact on fluid types and volumes and has established itself as a powerful methodology to de-risk unconventional petroleum systems.

In this paper we will illustrate how our ShellGenex multi-species, coupled generation & expulsion model was further developed to account for processes occurring within the tight pore system of unconventional gas plays and the PVT changes associated with uplift, commonly occurring in unconventional gas settings. We will show the effect of slow diffusion within and out of the kerogen on fluid composition, its impact on PVT characteristics with increasing levels of maturity (saturation pressure, dew point temperature) and the consequences for phase separation depth, fluid properties (GOR, CGR) and volumes.

This methodology was applied to several plays in North America and Europe and some of the key findings will be illustrated.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.