Kevin Dodds

CO2 sequestration monitoring and verification technologies applied at Krechba, Algeria

The In Salah project in Algeria is an industrial-scale CO2 storage project that has been in operation since 2004. CO2 from several gas fields, which have a CO2 content of 5–10%, is removed from the production stream to meet the sales gas-export specification of 0.3% CO2 . Rather than vent that separated CO2 to the atmosphere (as was normal industry practice for such gas plants), BP and its joint venture (JV) partner, Sonatrach, invested an incremental US

1D inversion and resolution analysis of marine CSEM data

100 million in a project to compress, dehydrate, transport, and inject that CO2 into a deep saline formation downdip of the producing gas horizon. Statoil then joined the JV at production start-up in August 2004.

Interval probability process mapping as a tool for drilling decisions analysis—the R&D perspective

We present results from an investigation into 1D inversion of controlled-source electromagnetic (CSEM) data. Based on inspection of a data set, we formulate a simple empirical noise model described by a few pragmatically determined parameters. We also investigate the effects of transmitter height above the seafloor and include the data uncertainty resulting from varying transmitter height in our noise model. Based on the noise model and assumptions about the available data, we analyze model parameter uncertainty estimates derived from the a posteriori model covariance matrix for a resistive layer buried at depth. We find that the layer parameters uncertainty primarily depends on the depth of burial and the thickness of the layer. We then formulate quantitative bounds for these parameters, within which we have a small uncertainty of the parameters of the resistive layer. The depth of burial and the transverse resistance of the layer become better determined the higher its resistance. We invert a field data...

Application of geophysical monitoring within the Otway Project S.E. Australia

The uncertainty arising from the poor predictability of overpressure and its impact on drilling costs and prospect evaluation is a global problem facing all explorationists. There exists no industry consistent methodology for assessing these uncertainties and associated risks. This paper illustrates such a decision and risk analysis methodology through reference to the application of the process to a specific exploration prospect with a perceived high risk of overpressure. Although the case history was assessed prior to drilling, the process has the potential to be developed into a robust framework within which real-time decisions can be made. The risk analysis technique used is interval probability analysis and provides a framework for the incorporation of geologic and geophysical studies along with the well construction, safety and planning decisions prior to selecting a well for drilling. This framework is also able to record the circumstances related to people, timing, resources, as well as absence of...

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

The Australian Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) is currently injecting 100,000 tons of CO2 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 CO2 accumulations and many depleted gas fields, offers an appropriate site for such a pilot project. An 80% CO2 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 CO2 can be safely transported, stored underground and its behavior tracked and monitored. The monitoring and verification framework has been developed to monitor for the presence and behavior of CO2 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.

A simple approach to assessment of seismic expression of abnormal geo‐pressure

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

An Early Look at a Time-Lapse 3D VSP

Drilling uncertainties related to abnormal geo-pressure are common in the Barrow and Dampier Sub-Basins of the North West Shelf. These uncertainties contribute to increased drilling risk and costs. In this study we analyse seismic response to over-pressure in WA-25-P (P25) in the Barrow Sub-Basin. The analysis includes 3D surface seismic and VSP data, well logs, mud weight and pressure data from the wells. The results of a mineralogical analysis conducted on core samples were also incorporated into the study. Initially we analyse the response of sonic velocity to variations in the effective stress. In addition to the well data, the study included response of various seismic attributes to changes in the effective stress. This extended the information available in an area with sparse data sets and was complementary to the velocity data. We used VSP data recorded in a highly overpressured well to compute various seismic attributes from down-going energy and analysed their variations with depth and effective stress. Attributes, which displayed satisfactory degree of correlation, were selected and compared to the same or “equivalent” attributes computed from up-going waves. We then related these attributes to those computed in the 3D data set at the well location. Finally we compute attribute cubes, mapping an area within the volume with a high correlation with overpressure. This VSP data based pore pressure prediction approach, while at present qualitative, is still highly efficient and suitable for newly explored areas.

ANALOG RESERVOIR MODELLING OF CHANNEL SANDS

In 2007 Australian Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) started a project to evaluate the available technology for monitoring the movement of CO2 in an underground reservoir. In stage one of this project CO2 and methane are being produced in a nearby well, then the CO2/CH4 is being injected back down a second well into a depleted gas sand. The movement of the CO2 up-dip needs to be remotely monitored. One of the technologies being evaluated to monitor the movement of the CO2 is 3D VSP. The CRC-1 injector well is instrumented with 10 3C downhole accelerometers. A baseline 3D VSP survey was shot around this well in late 2007 and was followed by a repeat survey in 2010. We hope to monitor the movement of CO2 around the CRC-1 well by observing changes in the time-lapse signature.

Seismic Attribute Analysis of Experimentally Recorded Waveforms

This paper outlines the results of analog modelling of a sandy deepwater channel reservoir to gain insight into issues of uncertainty in reservoir simulations and their seismic expression. The project is unique in that it integrates seismic and reservoir engineering research in a controlled laboratory environment. Unlike numerical modelling investigations, this laboratory-based modelling study provides real data that does not rely on assumptions and is, therefore, a useful case study for comparing the actual production and seismic response against numerical predictions. The 1 m2 model comprised two intersecting synthetic sandstone channels within a transparent acrylic matrix. The model was initially oil-saturated with irreducible water and was produced through waterflooding of the upper channel. Careful attention was paid to scaling of both the fluid dynamics and the seismic properties to ensure that the response of the model was representative of the field-scale environment. Scaled time-lapse seismic data was recorded before and after production and data such as water cuts, recovery rates and pressure drop between injector and producers were also recorded. Analog reservoir modelling (ARM) provides a new tool that allows seismic attributes to be evaluated against ground truth results and the performance of seismic inversion schemes to be critically assessed.

Some Modern Developments in 3D EM Modeling and Inversion for Surface, Marine, and Borehole Applications

Summary A number of ultrasonic experiments simulating normal compaction, disequilibrium compaction, fluid expansion and tectonic mechanisms of overpressure were performed on reservoir sandstone and shale core samples. The velocity changes and the effects of different stress paths on transmitted ultrasonic pulses were investigated through changes of instantaneous waveform attributes. In all measurements the dependence between seismic velocities and differential stresses coincide well with EberhartPhillips empirical relationship. A positive relationship between differential pressure and several instantaneous seismic attributes has been established for the first time in these experiments. Results obtained proved that wellknown empirical relationships between differential pressure and seismic velocity are also applicable for a number of seismic attributes. This enables the prediction of differential stresses by using seismic attribute and seismic velocity changes. Similarly, based on the combined X-ray CT images and ultrasonic measurements conducted on core samples, the sensitivity of instantaneous seismic attributes to various degree of fluid saturation has been analyzed. It was found that several seismic attributes exhibit similar relationships as the known theoretical models established between seismic velocities as well as fluid saturation. These results indicate that seismic attributes can be used as an alternative approach for discrimination between changes caused by increased pore pressure and fluid saturation.