The most effective method for improving seismic survey efficiency

This article forms part of our 'The most important equipment considerations for reliable, efficient, and cost-effective land seismic acquisition' blog post series. 

In our last blog, we introduced the concept of ultra-dense land seismic data recording using receiver nodes. 

The objective? To generate a high-definition subsurface image for hydrocarbon exploration, mining, civil engineering, or for alternative energy such as geothermal. The project we discussed in our last blog covers 3000 km² and generates over 1 billion traces per km² with over 230,000 traces per shot. If that sounds like a lot of data…   it is!!! That is roughly 10,000 times the amount of data collected with conventional recording equipment.

Clearly, this is outside the realm of conventional seismic recording. In this set of articles, we will be exploring what it would take to accomplish such a task with the most modern technologies, with adequate human and mechanical support.

Traditionally, land seismic recording is very expensive, time-consuming, and plagued with operational issues - from weather to terrain and cultural obstacles. These, plus variable near-surface conditions, topography, and access have led to limited channel counts and relatively low trace densities which has a tremendous effect on the quality of the subsurface image produced. 

So, where do opportunities for seismic survey efficiency exist? 

A seismic recording operation has 4 major components:

1. Sources and related equipment
2. Human labor and efficiency 
3. Recording instrumentation
4. Receivers and related equipment

Among these, Receivers and related equipment provide the most exciting opportunities for efficiency improvements. Innovations in receiver technology will improve both image quality and operational efficiency by better enabling simultaneous source recording, using larger live spreads made possible by rapid node charging and data download, even with reduced crew size.

• Sources and related equipment

In recent years, there have been significant improvements in productivity on the source side. These are mostly related to the concepts of simultaneous sweeping, where multiple sources are operating at the same time. Each source is recorded in different areas of the project to reduce interference. This adds operational complexity because multiple full spreads of receivers need to be laid out simultaneously. Having multiple sources operate independently and concurrently helps reduce “dead time” in the acquisition operation by allowing some sources to operate while others are moving from one shot position to the next. You can only have as many sources operating as you have receiver spreads laid out for. 

Without increased efficiency in getting the spreads laid out, source efficiency improvements will stagnate.

• Human labor and efficiency

Human labor has always been very expensive. Therefore, seismic acquisition contractors always strive to seek out opportunities to enable each worker to be more efficient and productive. Recording operations need to be able to layout the multiple spreads and cycle through the receivers without needing to manage an army of people. 

Improving the receiver management per person ratio is therefore critical for unlocking efficiency gains and cost reduction opportunities, and will in turn minimize vehicular usage, the number of people required to execute the survey, reduce exposure to HSE risk and environmental footprint. 

• Recording instrumentation 

Conventional cabled recording systems record discrete shots.  A centralized recording system activates the source and starts recording the traces at the specified receivers to generate “shot records”. When using vibratory sources, the traces are generally correlated with the sweep and summed by the recording instruments in the field yielding one shot-record for each source location.

Nodal systems record continuously into memory in the node. The traces from each node are reconstructed by taking time segments from the continuous record that coincide with the timing of the shots that contribute to that node. When vibratory sources are used, this generates “uncorrelated and unstacked receiver records”. Each segment is assigned to its respective source. When utilizing vibratory sources, correlation with the sweep and stacking is then performed in the processing center. 

To be able to retrieve the nodes, download the data from the nodes, and generate the receiver records for those nodes, an entire cycle of deploying, recording, retrieving, harvesting, recharging, and re-deploying the nodes is required. 

Therefore, improving data harvesting and data management technology to accelerate acquisition speed is a critical success factor for unlocking operational efficiencies. 

• Receivers and related equipment

The remaining variable is the receiver and related equipment. How can recording be: 

• More efficient
• More appropriate for simultaneous sweeps
• Manage increased channel count
• Reduce the overall cost of the survey

All the while, generating data that can be more readily processed for noise removal and signal enhancement to generate superior final image results? 

The solution? The “nimble node” ….

How the nimble node will help seismic operations be more efficient, cost-effective, and low risk 

The design and development of the “nimble node” was targeted to help: 

• Increase the number of nodes that a person can handle
• Accelerate acquisition speed 
• Reduce survey operational costs 
• Minimize exposure to HSE risk 
• Reduce environmental footprint  

Other design aspects are related to increasing the efficiency of cleaning the nodes, harvesting the data, and recharging the nodes. Considerations have also been made to reduce the need to physically cut receiver lines in some areas. Acquisition personnel need to readily traverse in challenging terrain, while carrying a significant number of nodes for deployment without the need for heavy transportation equipment. 

The main objectives are to deploy, collect and redeploy the nodes faster.

The more you can carry, the more you can deploy and retrieve. The lighter and smaller they are, the more you can carry. The more you can carry, the more can be recycled.

The table below examines the vehicle requirements to move equipment from basecamp or staging area to deployment/retrieval line locations. Light vehicles, typically a 4x4 pickup truck or equivalent, were considered for nodal systems, with a payload of 1000Kg and between 1.2 to 1.9 cubic meters of loading space.

Table 1: Vehicle requirements for a 1 million node system (70 000 nodes a day). Numbers exclude vehicles required for source operations, project management, survey, etc. and are limited to line crew and receiver equipment

Heavy vehicles, typically a 6x6 truck, were considered for cabled system. Transportation of line crews was considered with heavy vehicles on all systems. It becomes apparent that, for an example survey, using nimble node systems results approximately 5 times fewer light vehicles per km driven, resulting in significantly reduced emissions, when compared to medium node systems, and similarly 5 times fewer heavy vehicles than cabled systems.

So, where is the best opportunity for improvement to achieve unrivaled seismic survey efficiencies? 

Receiver technology presents, by far, the best opportunity for unlocking efficiency gains during seismic acquisition. 

Nimble nodes are the result of the most innovative technological research and development and are being utilized by progressive companies as a preferred technology of choice for land surveys across the globe – giving them a competitive advantage.  

Not only do nimble nodes allow the acquisition personnel to deploy and redeploy enough nodes to support higher levels of simultaneous source recording while retaining a manageable number of human resources to perform the work, but they are also proven to: 

• Reduce equipment and survey logistical costs 
• Minimize exposure to HSE risk 
• Lower environmental footprint 
• Reduce manpower requirements