Mark Bunch

Multi-scale characterisation of the Paaratte Formation, Otway Basin, for CO2 injection and storage

Bunch, Mark; Lawrence, Mark; Dance, Tess; Daniel, Ric; Menacherry, Saju; Browne, Greg; Arnot, Malcolm

Rock typing and facies identification using fractal theory and conventional petrophysical logs

Rock typing or subdivision of a reservoir either vertically or laterally is an important task in reservoir characterisation and production prediction. Different depositional environments and diagenetic effects create rocks with different grain size distribution and grain sorting. Rock typing and zonation is usually made by analysing log data and core data (mercury injection capillary pressure and permeability measurement). In this paper, we introduce a new technique (approach) for rock typing using fractal theory in which resistivity logs are the only required data. Since resistivity logs are sensitive to rock texture, in this study, deep conventional resistivity logs are used from eight different wells. Fractal theory is applied to our log data to seek any meaningful relationship between the variability of resistivity logs and complexity of rock fabric. Fractal theory has been previously used in many stochastic processes which have common features on multiple scales. The fractal property of a system is usually characterised by a fractal dimension. Therefore, the fractal dimension of all the resistivity logs is obtained. The results of our case studies in the Cooper Basin of Australia show that the fractal dimension of resistivity logs increases from 1.14 to 1.29 for clean to shaly sand respectively, indicating that the fractal dimension increases with complexity of rock texture. The fractal dimension of resistivity logs is indicative of the complexity of pore fabric, and therefore can be used to define rock types.

CO2 storage capacity estimation for a deep saline formation by static reservoir modelling: the Cretaceous Paaratte Formation, offshore Otway Basin, Victoria

The APPEA Journal is multidisciplinary technical journal documents peer-reviewed papers presented at APPEA’s Annual Conference. From 2008 onward the APPEA Journal is available in DVD format only.

Feasibility of Storing Carbon Dioxide on a Tectonically Active Margin: New Zealand

Screening of New Zealands sedimentary basins indicates several gigatonnes of carbon dioxide storage capacity might be available. However, carbon dioxide storage is currently untested in New Zealand, and it is likely that most theoretical storage capacity will be discounted once detailed assessments are made. New Zealands position on an active Neogene plate boundary raises additional key factors that will affect final site selection. Issues specific to New Zealands setting include: 1. rapid facies changes, syndeposition and post-depositional structural events, particularly in regions close to the plate boundary; 2. rapid subsidence and high sedimentation rates leading to overpressured reservoirs and strong water drive in some structures, which will potentially result in injectivity issues, particularly in depleted fields; 3. mineralogically immature reservoir rocks requiring assessment of injected gas-rock reactions; 4. common occurrence of faults of various scales, requiring assessments of their sealing capacity and present stress fields; and 5. distinguishing induced seismicity from common natural seismicity. Some of these risk factors will also influence the relationship between social acceptance and the design of regulations. Despite the risks, hydrocarbon-producing fields in Taranaki indicate that viable reservoir-seal pairs are likely to be present. Additionally, injection of small volumes of produced water and significant natural gas storage at the depleted Ahuroa Field have not led to noticeable induced seismicity, though large volumes expected from a carbon dioxide injection project would likely require careful site assessment for seismic risk in some areas. Natural analogue and laboratory fluid-rock experiments are investigating the effects of carbon dioxide injection on reservoir mineralogy, and some effects can now be anticipated. Currently produced gas from New Zealand locally contains significant carbon dioxide (up to 44% carbon dioxide in the Taranaki region and up to 30% in the Canterbury Basin) and if new discoveries also have a high carbon dioxide content, they may require processing before use, with disposal of carbon dioxide. Such a large gas discovery anywhere in New Zealand could, therefore, stimulate rapid deployment of CCS. It is highly likely viable storage sites exist, particularly away from the current plate boundary, though the site-specific nature of site assessment is particularly important in New Zealands geological context.

Gauging geological characterisation for CO2 storage: the Australasian experience so far…

The techno-economic resource–reserve pyramid for CO2 storage is a concept for expressing the reduction in uncertainty in predicting realisable geological capacity for storing CO2 with diminishing spatial and temporal scales of study. A similar concept is implied regarding reduction in certain storage capacity with increasing density and resolution of usable data. In general, these are determined by the collective scope of characterisation objectives, which dictate the characterisation/modelling tools employed. The relationship between the uncertainty scale (the height) of the techno-economic resource–reserve pyramid and the characterisation requirements for real CO2 storage systems is defined by an increasing number of modelling studies in Australasia and elsewhere. Together, these studies represent a range of both spatial and temporal scales, and resolutions of study, and a range of starting-points in terms of an initial information base. This paper summarises a number of these studies to provide examples that elaborate the nature of different levels of the pyramid and its suitability as a metaphor for scale of study and storage capacity estimation certainty. These examples conclude with the first Australian demonstration of geological storage of CO2, the Otway Project, which sits notionally at the top level of the pyramid despite the absence of full requisite economic conditions. A discussion of the merits and shortcomings to the pyramid analogy follows, revealing some important aspects of the characterisation and modelling process that are not represented properly or conveyed effectively. It is concluded that the traditional techno-economic resource–reserve pyramid should be thought of as an idealised first-order conceptual analogy that has inherent limitations.