CO2 Well Monitoring

//CO2 Well Monitoring
CO2 Well Monitoring 2017-07-21T09:08:03+00:00

Many of the in-well iDAS™ and DTS applications targeted at the upstream oil and gas industry are also a natural fit for CO2 well monitoring. Silixa have played an active part in the installation of fibre optic enabled monitoring systems for carbon capture and storage projects and continue to acquire data on several of these projects for a variety of reasons.

With a permanent fibre optic cable installed in a CO2 disposal or observation well the user has access to on-demand, and time lapse, borehole seismic data which can help to describe the growth of the CO2 plume within the reservoir.
Concerns over the integrity of the cap rock, or indeed the wellbore, can be addressed by passively monitoring for potential micro-seismic events, an area that is developing quickly as the iDAS sensitivity improves through system development and signal processing.

Temperature offers a traditional method of continuously monitoring the injection of CO2 so that early detection of leaks or gas migration can be facilitated. As a result many CO2 projects elect to routinely instrument wells with a permanent DTS system coupled to a realtime monitoring system.

The iDAS can complement this measurement by adding acoustic detection for gas migration and leaks; retrofitting an iDAS to an existing monitoring system is generally simple for Silixa but the unique ability of the iDAS to operate on either single-mode or multi-mode fibre without the introduction of any additional apparatus and without any appreciable difference in data quality means that iDAS can also be fitted to installations originally intended only for DTS where only multimode fibres are available.

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The image above shows the installation at a well site in Spain, Europe.

Case Study: High-resolution, far-offset VSP survey with Carina® Sensing System for permanent CO2 storage monitoring in Otway, Australia

Project

CO2CRC’s Otway research facility is Australia’s first demonstration of the deep geological storage of carbon dioxide (CO2), the most common greenhouse gas. CO2CRC’s Otway Stage 3 Project aims to develop and deploy a sophisticated monitoring system in the subsurface through up to five new wells. The monitoring system should deliver a permanently deployed solution that is reliable, cost-effective and with high-resolution. It should provide on-demand seismic data for high quality 4D imaging of the CO2 plume migration.

Challenge

The benefits of DAS as a seismic acquisition tool are proven and well-suited to this application. High-resolution measurements with full wellbore coverage for every shot provide unique levels of detail. However, with most VSP type measurements, the imaging aperture is limited, meaning only a small area of the reservoir around the wellbore is imaged. Using far-offset source locations can widen this aperture but often the signal-to-noise ratio is not sufficiently high to extend the seismic image, even when using conventional wireline geophone sensors.

Solution

The advanced Carina Sensing System, developed by Silixa, provides a further 20dB (100 times) improvement in the signal-to-noise performance of DAS measurements, and offers capabilities beyond conventional geophones in many seismic applications. This step-change improvement in performance was confirmed during a baseline VSP acquisition at the Otway research site.

Results

The figures below show a comparison between shot gather data for both a conventional wireline geophone tool and the Carina Sensing System at two different shot locations. Figure 1 shows data from a 700m offset, Figure 2 shows data from a 1800m offset. The source was a single 26,000lbs vibroseis truck using a 6-150Hz, 24sec sweep.

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Silixa’s Carina Sensing System not only ensures high resolution measurements with full borehole coverage, but it saves a considerable amount of time for the operator. Acquiring data with Carina Sensing System took only 4 minutes, whilst acquiring the same amount of data with traditional technology, geophones, took 11 hours.


It can clearly be seen in both figures that the Carina data shows more detail and stronger upgoing reflection energy than the geophone data with the same number of stacked shots. The Carina Sensing System provides high-resolution data with high signal-to-noise ratio.
Figure 2, at the farthest offset source location of 1800m from the wellhead, shows clear coherent reflected energy even at receiver positions towards the bottom of the well. This level of source offset is not typically included in the post-processing imaging for VSP measurements as the signal-to-noise ratio is not sufficiently high with conventional geophones. The Carina Sensing System provides a new level of performance to change this methodology and could therefore provide wider aperture, finer resolution subsurface images with one-shot™.

*Data and images courtesy of CO2CRC Ltd

Download the case study here.