CO2 Storage Reservoir Architecture using Palaeoenvironmental Evidence from Petrographic, Palynological and Diagenetic Pathway Study

Daniel, Ric¹; Bunch, Mark¹; Menacherry, Saju²; Golab, Alexandra³; Lawrence, Mark⁴;
¹Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia.
²Chevron Australia Pty Ltd, Perth, WA, Australia.
³Digitalcore Pty Ltd, Canberra, ACT, Australia.
⁴GNS Science, Wellington, New Zealand.

The Late Cretaceous Paaratte Formation is a deep saline succession currently the target for field-scale CO2 injection experiments at the CO2CRC Otway Project. A relatively homogeneous injection interval ~7 m thick was identified towards its base following early analysis of well and core data acquired for a newly-drilled injection well, CRC-2. Core intersecting the injection interval and stratigraphy both above and below, has been sampled extensively for the purposes of an extensive petrological and petrographic study to quantify the effects on CO2 storage of physical and chemical heterogeneities at micrometre-to-millimetre scale.

The injection interval consists of two sections representing distinct but related facies associations of a deltaic depositional environment. They exhibit broadly similar bulk reservoir properties though their bulk mineralogy and fine-scale sedimentary fabric differs. Above the reservoir section a concretionary interval constitutes the overlying seal. The dominant interstitial cement is dolomitic and was formed early in the lithification process. Cementing material was drawn from shell solute generated in a shallow marine environment with fresh water influx. The immediate succession is topped by a mineralogically diverse silt-rich mudstone that is highly bioturbated and therefore relatively isotropic.

Digital core rendering demonstrates the effect on pore throat networks of sporadic clay-rich tidal laminae and discontinuous mud drapes within reservoir sandstone. Mineralogical markers give an indication of proximal-to-distal and lateral position within the deltaic depositional tract. Applying the model to data from successive core samples gives an indication of sequence stratigraphic and autocyclic shifts in the local depositional environment at CRC-2 over time. Low resolution sedimentation rates derived from palynological dating provides information to estimate the spatial scale of delta geo-body elements. Their orientation is calibrated by a continuous record of sediment dispersal interpreted from open-well image logs.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012