Donald Sherlock

Seismic imaging of sandbox models.

Analogue sandbox models provide cheap, concise data and allow the evolution of geological structures to be observed under controlled conditions in a laboratory. Seismic physical modelling is used to study the effects of seismic wave propagation in isotropic and anisotropic media, and to improve methods of data acquisition, processing and interpretation. BY combining these two independent modelling techniques, the potential exists to expand the benefits of each method. For seismic modelling, the main advantages are that the seismic data collected from these models contain natural variation that cannot be built into conventional solid models that are machined with predetermined structures, which results in a more realistic image. In addition, the cost and construction time of these models is dramatically reduced. For sandbox modelling, the ability to record seismic images before the model is manually sectioned for conventional interpretation allows far more detailed study of subtle structures than previously possible. It also provides the missing link when comparing structures generated within the models with interpretations from field seismic data.

Time-lapse monitoring of immiscible fluid-flow models

Physical fluid-flow models aid understanding of hydrocarbon movement through water-saturated sediments because they provide real data that do not rely on assumptions and are therefore useful to validate numerical reservoir simulations or to study processes for which the mathematical formulations are not well defined. Such models can have applications in geology for studying mechanisms of secondary oil migration (Thomas and Clouse, 1995), or in reservoir engineering to evaluate enhanced oil recovery methods such as steam injection (Frauenfeld et al., 1994) and carbon dioxide floods (Tuzunoglu and Bagci, 2000).

Observations of seismic reflections from variations in grain packing

Summary Seismic physical modelling experiments with unconsolidated sands have shown that it is possible to record a seismic reflection from a layer boundary where there are only slight changes in material velocity and density. Furthermore, reflections have been recorded from the interface of two sand packages that have different average grain sizes but equal density and velocity. This suggests that it is the combination of the sands at the interface that produces the acoustic impedance contrast required for a reflection, which is a provocative statement and challenges the need for separate layers with different acoustic impedances.

Developing a monitoring and verification plan with reference to the Australian Otway CO2 pilot project

Developing a monitoring and verification plan with reference to the Australian Otway CO 2 pilot project Kevin Dodds*, Tom Daley**, B Friefeld**, Milovan Urosevic***, Anton Kepic***, Sandeep Sharma**** *BP formerly CO2CRC/CSIRO,**LBNL,***CO2CRC/Curtin University,****CO2CRC/Schlumberger Introduction The Australian Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) is currently injecting 100,000 tons of CO 2 in a large scale test of storage technology in a pilot project in South Eastern Australia called the CO2CRC Otway Basin Project (Otway). The Otway Basin with its natural CO 2 accumulations and many depleted gas fields, offers an appropriate site for such a pilot project. An 80% CO 2 stream is produced from a well (Buttress) near to the depleted gas reservoir (Naylor) used for storage. The goal of this pilot project is to demonstrate that CO 2 can be safely transported , stored underground and its behaviour tracked and monitored. The monitoring and verification framework has been developed to monitor for the presence and behaviour of CO 2 in the sub-surface reservoir, near surface and atmosphere. This monitoring framework has been selected to address the areas identified by a rigorous process of risk assessment and subsequently verify conformance to clearly identifiable performance criteria. These criteria have been agreed with the regulatory authorities to manage the project through all phases addressing responsibilities, liabilities and to provide assurance of safe storage to the satisfaction of the public at large. Buttress Naylor-1 Figure 1. Site location showing location of Buttress CO 2 producer 3 km from Naylor-1 observation well Naylor 1, 2-3 km distance away. The Otway field is a gas producing field onshore Otway Basin in South-Eastern Australia. Many aspects of the proposed monitoring will be discussed and this paper will provide an overview of the whole plan, with reference to progress in baseline measurements. An extensive range of established direct and remote sensing technologies deployed on surface and in the borehole are being used for repeat assessments from a reservoir, containment, wellbore integrity, near surface and atmospheric perspective. These involve seismic, microseismic, petrophysical well logs and geochemical sampling including tracer and isotope analysis, plus associated forward modelling. The presence of naturally occurring CO 2 in the Otway area makes it more difficult to identify injected CO 2 . A regional survey of the distribution, type and origin of existing CO 2 will be carried out through soil gas sampling. The areal consequences of CO 2 migration and trapping are being addressed through characterization of the hydrodynamic properties of the region. The connectivity and fluid migration time scales of the potential fresh water reservoirs are being established using all available (and appropriate) well pressure and geological information. The Otway project has been selected as one of the Carbon Sequestration Leadership

Time Lapse VSP Program for Otway Basin CO2 Sequestration Pilot Project

The Australian Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) is currently undertaking the Otway Basin Pilot Project, which involves the injection and storage of 100,000 tonnes of carbon dioxide within the subsurface. The Otway Project is the first of its kind, where CO2 injection will be into a depleted gas reservoir and, therefore, the project will provide important experience for monitoring and verification under these conditions. The overall complexity of the field, its depth, small size and the presence of free and residual gas zones present a serious challenge for 4D seismic monitoring. Accordingly, we adopted a monitoring strategy which combines surface and borehole seismic measurements that optimises our ability to verify CO2 containment. Design of the monitoring program involved numerical modelling and, crucially, pilot field tests. Of particular interest was the application of borehole seismic methods as they can provide better resolution, higher signal to noise ratio and superior repeatability in comparison to surface seismic data. Data recorded from several test VSP surveys and 3D base line VSP survey are analysed for quality, consistency and repeatability.

Seismic physical modelling of immiscible fluid flow

Summary Fluid flow models are designed to aid our understanding of how hydrocarbons move through water saturated sediments, but acoustic monitoring of these models has been limited to 2D pulse-transmission methods. Conventional 3-D seismic physical models have previously employed only solid, nonporous materials. Two models are presented that use scaled seismic surveys to monitor the migration of (1) kerosene, and (2) air through water saturated sand models in threedimensions. Changes in interval travel times are used to map the distribution and saturation of kerosene. Time-lapse seismic difference sections show how a contrasting sand layer affects the migration pathway of air, while amplitude maps clearly reveal the influence that lateral variations in permeability has on the areal distribution.