The Otway Stage 3 Project will inject 15,000 tonnes of high content CO2 into a saline aquifer (at 1500m) to develop and commercialise subsurface M&V technologies.

Site summary

The Otway Stage 3 Project uses five new injection and monitoring wells in addition to existing wells onsite.

The injection zone is Para Sequence 1 (PS1) in the Paaratte formation and the injection well (CRC-3) is down dip in the reservoir to provide buoyancy for CO2 migration. The location of the wells (one injection well, CRC-3, and 4 monitoring wells, CRC-4 to CRC-7 as well as existing wells, CRC-1 and CRC-2) is shown in Figure 1.

Technology Overview

The Otway Stage 3 Project will evaluate the following monitoring methodologies:

  • Pressure inversion and tomography, based on downhole pressure sensors.
  • Downhole seismic monitoring (VSP vertical seismic profiling) using well-based (DAS distributed acoustic sensors) and permanently deployed seismic sources known as (SOV surface orbital vibrators).

Surface seismic

Surface seismic surveys will be conducted prior, during and after the injection as benchmarks to validate the results of the new technologies being tested.

Downhole seismic

The demonstration of downhole seismic monitoring involves using an array of permanent SOV to create a seismic signal which will be received by the DAS in the monitoring wells and detecting the plume as it grows and migrates during injection.

The development of ancillary monitoring methods such as using the analysis of earth tides and passive seismic will enable future geo-mechanical research to be conducted

Pressure monitoring

Using high resolution pressure gauges, two distinct modalities of pressure monitoring will be investigated.

Pressure inversion locates a pressure source by way of triangulation from pressure measurements in the monitoring wells during and post CO2 injection. The acquired pressure data will be inverted to identify the compressible pressure boundary as the CO2 enters and migrates through the formation.

Pressure tomography denotes a cluster of techniques that rely on interpreting the pressure changes resulting from perturbing the reservoir with water injections at one monitoring well and monitoring pressure at other wells. In a world first, pressure tomography will be demonstrated on a CO2 plume to test the range and sensitivity of the technique to image a plume’s distribution. With downhole pressure gauges set to acquire data continuously, the pressure data obtained for each survey performed will be inverted to produce an image of the CO2 plume in the subsurface.

The quality of tomographic imaging will depend on the signal-to-noise ratio of the pressure measurements, the geometrical arrangement and number of wells, and extent to which variations in permeability affect pressure propagation.

Well design

To meet the requirements of the proposed monitoring techniques, the following well design and equipment specifications were selected.

  • All wells will be cased and perforated at PS1 level.
  • Down hole pressure gauges in each well.
  • DAS external to the casing, and inside the well (on tubing for CRC-2 and CRC-3 wells and on wireline for CRC-4, CRC-5 and CRC-6 as a backup).
  • All monitoring wells will also be used as water injectors.
  • All wells designed and constructed to oil and gas specifications with a maximum surface working pressure of 3,000 psi.
  • DAS external to the casing, and inside selected wells (on tubing for CRC-2 and CRC-3 wells and on wireline for CRC-4).

Downhole seismic monitoring

In 2017, as part of the appraisal program, a pair of (DAS) fibres were deployed behind casing in CRC-3. The performance was tested with both (SOV) and conventional vibroseis-generated seismic sources. The seismic data acquired was excellent in both cases. In the upcoming injection and post injection phases, the data obtained from each well for each of the SOVs will provide single-offset (VSP seismic profiles) that can be used for continuous monitoring.

Algorithms are under development for processing the data on-site in near real time, mitigating the need for large volumes of data to be transported to remote computers and significantly reducing processing time.. The analysis to date indicates that signal-to-noise ratio is more than adequate, so the emphasis is on the geometry of ensuring there are enough transects across the predicted plume in Figure 3.

Resulting Publications

Jenkins, C 2019. Otway Stage 3 – how did we get here?  Oral presentation given at the CO2CRC CCUS Symposium 2019.

Jenkins, C, Dance, T, Ennis-King, J, Glubokovskikh, S, Gurevich, B, La Force, T, Marshall, S, Paterson, L, Pevzner, R, Tenthorey, E and Watson, M, 2016. Validating subsurface monitoring as an alternative option to surface M&V. In: GHGT-13, Lausanne, 114-18 November 2015.

Jenkins, C, 2016. Developments and Opportunities at the CO2CRC Otway Project. Oral presentation given at the International Collaboration in CCS, British Geological Survey, 1-3 March 2015.

Works to date

Reservoir characterisation

Reservoir characterisation works were performed from April 2017 to May 2019 during the Evaluate and Define phases of the project including seismic interpretation, geological studies, static modelling, reservoir engineering data analysis and dynamic modelling.

Different vintages of seismic are available including the regional Curdievale survey and all seismic monitoring performed as part of CO2CRC’s past Otway storage program investigations. Horizon and fault interpretation were performed in Two Way Time (TWT) on the reprocessed Curdievale 3D regional seismic survey. Depth conversion used a new updated velocity model fine-tuned for the Curdievale 3D and using all available data in the areal of interest (AOI). For the Otway Stage 3 Define phase, a new static model structural framework was built based on the updated Curdievale seismic interpretation. It captures most of the faults in the modelled area and includes detailed vertical zonation in PS1. A cell size of 20 x 20m allowed for more realistic fault geometries to be preserved in the model grid compared to previous generations of the model.
Property modelling was performed using well data and variograms based on depositional analogues, and the Curdievale 3D acoustic impedance volume was used by zone and by facies to constrain the distribution of porosity, which in turn guided the permeability distribution.

A thorough reservoir engineering data analysis was performed including well history evaluation, core and fluid analysis as well as formation pressure test evaluation to provide inputs into the dynamic modelling.

The dynamic model was history matched using available historical data in the Otway site to make it more reliable for predicting injection scenarios for Otway Stage 3. The parameters considered include:

  • Single phase water injection test
  • Seismic plume shapes from stage 2C
  • CO2 saturation from Neutron logs
  • In zone and above zone pressure data in CRC-2 during 2C injection
  • Injection interference test between CRC-3 and CRC-2

Fit-for-purpose history matching was achieved by adjusting key subsurface parameters including absolute and relative permeability, saturation end point parameters, ratio of vertical to horizontal permeability, aquifer parameters and splay fault transmissibility.

The Otway Stage 3 base case scenario includes injection of 150 tonnes per day of Buttress gas into the reservoir over 100 days. Based on this modelling, the injected plume is expected to reach the existing Stage 2C plume approximately 70 days after the start of injection.

Dynamic and static uncertainty analysis were performed as part of Otway Stage 3 scenario simulation. The main objective was to understand how a combination of uncertainty parameters affect the plume shape and extent.

For uncertainty analysis, Latin Hypercube sampling was used to stochastically select 60 samples from the influential uncertainty parameters (which were aligned with the adjusting parameters during history matching and including P10, P50 and P90 static models) and run the simulations. The obtained P50 and P90 of the plume boundaries at the end of Otway Stage 3 injection of 15,000 tonnes are shown in Figure 2. The base case plume thickness is also shown in this figure to compare the probabilistic results with the base case scenario.

Stage 3 modelling
Stage 3 modelling

The project will provide on-demand, permanent monitoring solutions, enabling continuous plume data acquisition, transmission and analysis.

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