As part of a seismic survey conducted in 2013 in Uganda’s Murchison Falls National Park, Total showed that the use of cableless technology to record seismic data is an effective solution to conducting onshore operations while addressing HSE concerns. It is a demonstration of both our commitment to reducing Total’s environmental impact in the regions where we operate and our mastery of the very latest technology in the field of seismic operations.
The most widely used technology in onshore seismic data acquisition is cable telemetry, which relies on geophones to capture seismic waves in analog form. The data is then digitized and sent to the recording laboratory via cables, from terminal units positioned at each geographical location in the spread.
However, this practice has a number of drawbacks:
- To improve data quality, you need to increase the number of sensors in the field and, by extension, the number of channels used for each survey. This requires increasingly heavy equipment, more complex logistics and a greater level of expertise.
- Mountains, cities and protected nature reserves are all difficult environments in which to conduct 3D projects with seismic laboratories and the requisite telemetry cables.
- Cabled operations are far from hazard-free. Personnel who handle continuous cable along seismic data acquisition lines are at constant risk of an accident. Substantial heavy vehicle traffic during the survey poses a road risk. Cables can deteriorate or be stolen.
- The process has a major environmental and social impact, notably through the disruption caused to both nearby communities and the flora and fauna in natural areas.
These constraints led to the development in the early 2000s of an alternative, cable-free method that capitalized on recent technological advances in data storage, positioning and power supply. With this system, seismic data is recorded autonomously upon reaching the receiver. The information can then be captured in a number of ways: by collecting the terminal units in the field and downloading the data at the base camp; by transmitting the data in the field to a movable receiver; or through real-time radio relays to the recording laboratory. Each of these solutions eliminates the need for connecting cables between the terminal units.
Wireless Terminal Units For Enhanced Operating Efficiency
The cableless system relies on a combination of three elements:
- Integrated GPS receivers that, using GPS time, can synchronize data recording with trip programming;
- High-capacity memory cards that can store hundreds of shots;
- Long-lasting Li-ion batteries, for capturing recordings over a period of several weeks.
This approach to seismic data acquisition offers a number of advantages. The use of wireless sensors significantly improves operating efficiency, thanks to equipment that is much less unwieldy than a cabled system (it can be transported by car and deployed using fewer personnel). Moreover, the data acquisition process is shorter, and therefore more acceptable to the community. It also has a lower impact on the environment and biodiversity, since some terminal models can be buried and remain out of sight for the entire duration of the project.
An Initial Large-Scale Rollout In a Protected National Park
For this reason, for its maiden application, we chose to deploy the new system in Uganda, where our permits encompass portions of the Murchison Falls National Park. The park features a variety of vegetation, from savannah grasslands to woodland areas and papyrus swamps, depending on the altitude and proximity to water points. Given those environmental factors, in 2013 we decided to use cableless technology for a large-scale seismic survey spanning nearly 400 square kilometers — the first use of the technology in Africa.
The project required intense preparation: Total employees analyzed satellite images, conducted a photographic survey of initial biodiversity conditions and identified steps to preserve health and the environment. In view of the large number of endangered endemic species in the region, our goal was to minimize the risk of any impact on local animal and plant life while maintaining operating efficiency and an acceptable level of data quality.
With that in mind, we chose a terminal unit that incorporated all the necessary components, in order to reduce its visual impact. This was an ambitious move, since the region’s geological characteristics coupled with the shallow nature of the reservoirs entailed an extensive network of source and receiver lines. In terms of the number of channels used, this seismic data acquisition survey is the second largest cableless project in the oil and gas industry to date.
A Success to Be Duplicated On a Wide Scale
The seismic survey conducted in Murchison Falls National Park lasted one year and yielded overall positive results:
- Stakeholders looked favorably on the project: the use of a cableless system was a decisive argument in support of the campaign.
- The project required fewer personnel and relied primarily on cars instead of trucks, thereby reducing its environmental footprint.
- Downtime for cable maintenance was eliminated, and no recording problems were observed.
- All the necessary 3D seismic data for drilling the production wells planned for the region were successfully captured.
- The quality of the data matched that obtained using cable telemetry, thanks to the innovative noise reduction tools we used during data processing (individual receivers are more sensitive to ambient noise than clusters of geophones scattered around a barycentric position).
Based on those results, we now give preference to cableless recording systems for all of our new onshore seismic data acquisition projects, such as that conducted in the Democratic Republic of the Congo in 2016. Our affiliate there performed a 2D seismic data acquisition survey over an area spanning almost 250 kilometers in the East African Rift, using the same type of autonomous sensors.
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