How to master the art of survey design for high-density land seismic acquisition

by STRYDE
Jan 31, 2023 1:20:18 PM

Land seismic experts, Chris EinchcombJohn Naranjo, and Brendon Mitchell, from STRYDEbp and OceaniaGeo recently hosted an interactive and informative webinar on “Mastering the art of survey design for high-density seismic acquisition”.

Over 150 seismic experts and geophysicists from over 50 countries across the globe tuned in to learn more about the common challenges associated with high-density seismic acquisition and to learn how seismic survey design could be optimised to overcome these challenges.   

The acquisition of high-density data is essential for many industries as it allows for the creation of clear and accurate subsurface images that show the location of buried features, utilities, structures, anomalies, and potential subsurface risks, delivering the information required to make informed investment decisions.  

Over time there has been a significant increase in exploration success and production efficiency in marine seismic with the advances that marine cable and nodal seismic technology has gone through to deliver high-resolution imaging of the subsurface. By making crews more compact, using less bulky equipment, and being more environmentally friendly, not only can better imaging results be achieved by the land seismic industry, but there will be reduced project costs and turnaround. 

 

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This blog will summarise the challenges associated with land seismic acquisition and provide insights into the useful tactics discussed during the webinar, to help improve investment decisions, optimise early project lifecycle, and elevate performance management for land seismic.  

 

Common challenges associated with land seismic acquisition

 

During the webinar, it was discussed that land seismic is often restricted by 5 common factors: 

  1. Volume of equipment – incurring compromises in sampling geometries and spatial coverage 
  2. Budget constraints – resulting in sparse data acquisition 
  3. Timing – large crews on the ground for long periods of time managing complex equipment resulting in higher costs, increased exposure to HSE risk, and more environmental disruption and impact  
  4. Access and infrastructure – causing large data gaps, and reduced fold 
  5. Data volumes – complex processing algorithms, local contractor capabilities, and capacity challenges in being able to manage and process large data volumes typically acquired onshore 

Chris Einchcomb, Geophysical Advisor at STRYDE commented on this,Traditionally, big crews, the number of large vehicles required, complex logistics (in remote locations), and HSSE risk were all factors leading to low operational efficiency and increased environmental challenges when acquiring land seismic. However, I believe if we can make land seismic crews more compact, using less bulky equipment, the results of seismic data acquisition that we see offshore can be achieved on land, and not only will we reduce project costs and turnaround, but we will also see better subsurface image results. 

Brendon Mitchell, Geophysical Consultant from OceaniaGeo agreed: “We've seen the advances that marine cable and nodal seismic technology have gone through to deliver amazing imaging, which has driven a significant increase in exploration success and production efficiency in the industry. Bridging the gap between marine and land seismic technology is the biggest driver for change. It would be beneficial if land seismic had the capabilities to put larger denser surveys out there and make use of the advancements in the technology available on the market today.” 

 It was agreed that for high-density to be achieved in an efficient and viable manner, there needs to be improved S/N, increased lateral sampling, wider azimuths, and longer offsets and one of the key enablers to this is the technology advances and miniaturisation in seismic acquisition equipment. 

 

Tactics for optimising early project life-cycle land seismic acquisition 

 

How companies can get more for less, whilst reducing project uncertainty in the early stages of the lifecycle was discussed during the session. Some tactics for achieving this were covered and included:   

  1. Dense RP / long offset 2D – including deep structural definition, basin modelling, efficient inline deployment improving density but not cost;  
  1. 2D swaths – where multiple receiver lines are acquired with a single shot line – coverage, azimuth, efficiency;   
  2. Reconnaissance 3Ds – how this can overcome access / environmental restrictions, structural and reservoir definition, improved risk quantification, cost optimisation; 

Utilising these tactics to acquire seismic for early project life-cycle decision-making will:  

  1. Improve crew flexibility – less equipment, logistics, and infrastructure, especially with node crews 
  1. Reduce HSE exposure – fewer crew hours, vehicle movements, helicopter time, lighter equipment and will significantly reduce vegetation clearance and overall environmental impact  
  1. Reduce community and landowner impact – in turn, improving timelines for project approvals  
  1. Reduce costs and data delivery – to accelerate decision making  

Chris elaborates,We've seen clients using STRYDE Nodes™ in both 2D and 3D projects, in 2D projects, we've seen some innovative design tactics to achieve longer offsets with dense inline spacing to improve their structural imaging in complex subsurface structures using our continuously recording nodes.   

“We've also seen clients laying out multiple receiver lines (single shot lines) to achieve some great infill data quality, that not only gives denser coverage at a cheaper cost, but gives some degree of azimuth information as well. 

Where clients are using pseudo-3D methods for prospect evaluations and for understanding risks below the surface, we've seen them use the ability to lay out the nodes in large active patches in a conventional 3D geometry; then restrict the higher impact sources to an area where there is more accessible terrain. We've seen the generation of pseudo-3Ds that are giving viable results and generating beneficial insights, not only for the oil and gas industry but also for geothermal and CCUS too. 

Below is an example of the data acquired from a pseudo-3D survey.  Significant landowner access challenges and a desire to keep the environmental impact of source acquisition to a minimum resulted in an innovative design of a dense active patch of 3D receivers recording every shot along “random” roads or paths.  The resulting 3D is impressive and has led to some exploration success for the operator.  Map

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An example of how survey design can be optimized to overcome access restrictions with Pseudo 3D

 

Tactics for improving investment decisions in land seismic 

 

Once the exploration stage has been overcome, the next stage in the project lifecycle is the investment decision stage. Techniques that can be used to reduce the number of compromises that need to be made in the development or appraisal section of 2D/3D seismic surveys are:  

  1. Dense inline RP/ wide cross line 3D – for stratigraphy, reservoir characterisation, fault and lithology risk identification  
  1. Source acquisition optimisation – increasing  receiver density and reducing source acquisition to overcome terrain and environmental challenges  
  1. Dense deployment in inline only - enabling cost optimisation, nodes reduce logistics, and the ability to overcome land access limitations and minimise line preparation requirements 
  2. High-density receiver design - to enable rapid decision making denser seismic means better fast-track products, efficient deployment of equipment and less source acquisition  

Brendon commented, “With the equipment and technology that we have at our disposal now, the number of compromises we would usually have to make can be drastically reduced. 

“The surface challenges that might be associated with the development or appraisal part of a project due to environmental or structural considerations can be reduced. For example, in New Zealand, we managed to minimise source effort by 1/5 using a high-density receiver design (by implementing a carpet of receivers, in the order of 80,000 live nodes covering a 10x10 patch). This gave us that flexibility to acquire seismic through a dense, highly populous urban area and active surface infrastructure (wells, pipelines, and facilities) in a developed oil and gas field environment.  

Below is a comparison of conventional data vs data acquired through increased inline density, showcasing how this method will improve lateral resolution of seismic data. The example shows a 10x increase in inline density resulting in not only better imaging, but greater lateral continuity and definition, all achieved at no extra cost: 

An example of lateral resolution results from increasing the inline density

 

Tactics for elevating performance management land seismic 

 

The tactics for elevating performance management in the latter, more mature section of a project where well monitoring, increased recovery/storage, quantifying injection, and extraction impacts take place, was also discussed during the session. Some of these tactics include:  

  1. Dense inline and cross line 3D – for reservoir heterogeneity, improved imaging of subtle lithology and faults, quantitative geophysics, untapped resources, and fluid movement  
  1. Monitoring – instantaneous vs long-term, fracturing impact, fluid injection/extraction, fluid moment monitoring  
  1. Utilisation of low-cost receivers - resulting in cost optimisation – nodes reduce logistics, volume of equipment (when compared to cable seismic receiver crews), and flexibility in receiver vs source density 
  1. ISS/DSS combination - for source acquisition optimisation, combination of ISS/DSSS techniques will further increase trace density

John Naranjo, Seismic Acquisition Specialist from bp states, “The setback distances that we are conventionally used to are that sources maintain a far enough spacing away as not to damage any well heads or to any surface infrastructure.  

“What we are learning about the ability for the single component systems and lightweight nodes, is that they can go to a lot of places that would previously not be accessible in the source domain. This means that you can still maintain high-trace density by being able to activate sources in and around the oil fields even though there is heavy infrastructure – because you can repeat the seismic experiment more times by having more receivers in locations where you couldn’t previously get sources to. 

Below is a visual example of the options of acquiring data in large exclusion zones (magenta circles).  Traditionally we would have limited “acquisition” to sparse receivers and no source activity, compensated by dense source and receiver points outside the exclusions. The alternative is to maintain a dense blanket of receivers over the entire area and restrict source to accessible areas around infrastructure.  

A visual example of the options of acquiring data in large exclusion zones (magenta circles)

 

In summary...

  • Single sensors nodes are a proven enabler to allow onshore seismic to replicate the technological advances achieved in marine seismic  
  • Nodes give greater flexibility in survey design, balancing source and receiver effort to allow high channel counts in active spreads 
  • Lightweight nodes are overcoming environmental/infrastructure limitations and reducing survey logistics and costs  
  • Super high density, long offset, and wide azimuth land seismic is viable but some old practices (i.e., real-time QC) need to be moderated to avoid becoming project bottlenecks 
  • AI and easily accessible large-volume computing centres benefit the management of high-density land seismic, but processing algorithm R&D needs to respond to the demands  

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