Multi-Scale Characterisation of the Paaratte Formation, Otway Basin, for CO2 Injection and Storage

Bunch, Mark¹; Lawrence, Mark²; Dance, Tess³; Daniel, Ric¹; Menacherry, Saju⁴; Browne, Greg²; Arnot, Malcolm²
¹Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia.
²GNS Science, Wellington, New Zealand.
³Earth Science & Resource Engineering, CSIRO, Perth, WA, Australia.
⁴Chevron Australia Pty Ltd, Perth, WA, Australia.

Stage 1 of the CO2CRC Otway Project demonstrated capture, transport, subsurface storage and monitoring of CO2 in a depleted methane gas field (the Naylor Field). Pressure and tracer time series have been used to refine a working geological storage system model. Stage 2 aims to quantify the contribution to CO2 storage made by residual saturation and dissolution trapping mechanisms. CO2 is injected at a new well, CRC-2, into a deep saline succession stratigraphically younger and structurally less disturbed than for Stage 1. The CO2 storage system will thus be defined by future CO2 plume extent rather than the geometric constraints of a structural closure.

Information defining the Stage 2 storage system was scarce so comprehensive geological characterisation was required. This involved extensive coring and acquisition of a large suite of well logs. With no prior record of reservoir response, only part of the Stage 1 characterisation and simulation workflow is adopted. The greater uncertainty introduced is offset by executing Stage 2 as two experiments of increasing spatial and temporal scale. The first injected ~150 tonnes of CO2 into a stratigraphic interval ~7 m thick. Subsequent production recovered remaining free CO2 before the plume could reach far beyond CRC-2. Geological certainty was judged high at this spatial scale. The experiment permitted accurate calibration of residual CO2 saturation and relative permeability for reservoir material near the well.

The second Stage 2 experiment will inject 10-30 Kt of CO2 into the same ~7 m interval at CRC-2. Predictions for expected plume thickness, extent and concentration are conditioned by results from the first experiment. Experimental design is predicated on representativeness of reservoir property estimates away from the zone calibrated around CRC-2. Other wells with data are ~164 m away at CRC-1 (injection well for Stage 1) or ~326 m away at Naylor-1 (the original gas production well). These distances are thought greater than the lateral dimension of a representative elementary volume for the injection interval. Geological certainty between wells must be improved to accurately characterise the Stage 2 storage system. A multi-scale study (microscopic; core; well log; geo-body; stratigraphic) has sought to describe the stratigraphic architecture and diagenetic pathway of the deep saline succession at the Otway Project site. This produced a most probable geological storage system concept.

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