Max Watson

MSc Student



Telephone: +61 8 8303 4304

Facsimile: +61 8 8303 4345
E-mail: mwatson@ncpgg.adelaide.edu.au


PhD Project:

Natural Accumulations of Carbon Dioxide in Reservoir Rock as Analogues for Carbon Dioxide Sequestration.

Commenced: 2001

Supervisor: Dr Nick Lemon

Project support: APCRC - GEODISC Program

Scholarship support: GEODISC

The Cretaceous to Tertiary Otway Basin in southeastern South Australia and western Victoria contains a number of natural accumulations of CO2 associated with natural gas discoveries with gas varying from 0% CO2 (100% methane) to 100% CO2. While the methane has largely been derived from the thermal maturation of Cretaceous source rocks, the CO2 has come from degassing of Pleistocene to Recent basic volcanics. The source of the CO2 is proven by its juvenile isotope signature and the ratio of the accompanying He3 and He4. Two stratigraphic units act as reservoirs for the gas accumulations and in some cases the same unit can contain elevated CO2 values in one well while another about one kilometre away may have none. This local variation in CO2 provides an excellent natural laboratory to study the effects of CO2 on reservoir rocks. In addition to studies of the effects of CO2 on mineral composition, knowledge of the onset of CO2-entrapment in this natural system permits constraints to be placed on the likely reaction rates.

Work to Date
A study was completed in 2000 on the mineralogical changes brought about by raised concentrations of CO2 in feldspathic and lithic fluvial sandstone, the Cretaceous Pretty Hill Formation (Watson 2000). Eleven rock samples were collected from core intervals in two adjacent gas fields, the Ladbroke Grove field and the Katnook field. Pure methane is produced from the Katnook field for sales gas to the public while methane with up to 54% CO2 is produced from the Ladbroke Grove field as feedstock for a small electric power station. Detailed petrographic studies involving thin section analysis, cathodoluminescence (CL), X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that the sodium-rich feldspars and lithic fragments in the sandstone have reacted with CO2 to produce kaolin together with sodium ions, which remain in solution.

The completion of formation water analyses from hydrocarbon wells in the Otway Basin in both South Australia and Victoria formed a large part of the completed study. Comparison of the water analyses by the use of Stiff diagrams and by calculation of theoretical precipitates from the waters showed that all wells with elevated CO2 values have an excess of sodium cations that is balanced by bicarbonate (and minor carbonate) anions. These observations are in agreement with the feldspar reactions seen in the reservoir rocks.


Figure: Ladbroke Grove / Katnook Analogue, displaying varying degree of feldspar alteration. (Watson, 2000)

Two other samples were collected from the wells Caroline 1 and Kalangadoo 1. Caroline is currently a commercial producer of pure CO2 for the production and delivery of carbonated soft drink and beer. The reservoir is in this case is the Waarre Sandstone, a quartz-rich Cretaceous mid marginal marine unit. The Waarre Sandstone is the main methane reservoir unit in most gas accumulations in western Victoria. Kalangadoo 1 recorded pure CO2 from fractured metamorphic basement unconformably below the Otway Basin.


Biography:

Max completed a BSc. in Geology at James Cook University, Queensland in 1998. He worked with BHP Minerals as a geologist at the Cannington Silver Lead Zinc Mine in West Queensland in 1999. He then completed a BSc. (Hons) in Petroleum Geology at the NCPGG in 2000. Max is currently studying towards an MSc at the NCPGG researching mineralogical and physical changes in reservoir systems due to carbon dioxide infiltration.