4D seismic is a method that uses 3D seismic exploration to conduct reservoir dynamic monitoring in the oil and gas industry. The term “4D seismic” refers to a series of 3D seismic explorations on the same study that includes a fourth dimension—time—instead of the traditional three dimensions.
4D seismic is one of the essential monitoring methods since it can locate areas where oil hasn’t been swept up or bypassed. It keeps an eye on the gas and water flow in the reservoir, enhancing a successful exploration project with high-quality seismic reflection.
The acquisition, processing, and inversion parameters for a 4D VSP study are determined through presurvey evaluation and plan studies. Adequate 4D studies strive to maximize output while keeping costs down. A seismic study must be thoroughly optimized for any exploration or development project to be successful.
Seismic survey design services include:
- Survey evaluation
- Seismic design services
- Seismic feasibility studies
- Seismic illumination studies
- Survey planning
- Seismic modeling
- Seismic (re)-processing studies
4D Seismic Survey Acquisition
Any exploration or development project starts with preparing a thorough study model that balances price and quality. Surface obstructions present a significant challenge for all target seismic operations. The fundamental objective of 4D feasibility studies is to synthesize seismic amplitude responses to changes in reservoir conditions.
Numerous feasibility studies are used to select the ideal processing settings, acquisition setup, and inversion parameters. The ability to repeat numerous seismic observations in the field is the most crucial factor to consider when collecting 4D seismic data.
4D seismic data production and interpretation help improve reservoir characterization. As a result, appropriate parameters and geometry design must be adopted to ensure the repeatability of the environment, instrument, and parameter variables.
Illumination studies are widely used to examine the impacts of different review layouts on seismic quality and to determine how the study geometry may affect the final seismic quality.
Benefits of Survey evaluation and design (SED)
- The objectives for geology and geophysics are made clear.
- Clarification of seismic imaging’s geophysical dangers.
- Identifying seismic noise and signal.
- Independent evaluation and suggestions.
- The ideal 3D processing and design approach.
- Compromise 3D designs and processing flow based on equipment, survey logistics, and budget constraints in the real world.
- Budget management may analyze the cost efficiency of various 3D acquisition and processing scenarios using the quality, cost, and value of information as helpful tools.
Detectability and repeatability in 4D acquisition
A baseline seismic study of an underground (sea, borehole) area is required for 4D seismic data acquisition. A subsequent “monitor” study of the same area is also required, and it must closely resemble the characteristics and conditions of the initial acquisition study. This method allows for the comparison and analysis of seismic data over different timescales of months or years. This allows us to detect changes brought on by either fluid injection or hydrocarbon extraction.
How closely the baseline survey geometry can be duplicated in subsequent surveys strongly influences the design of a 4D monitor study. Baseline study data may occasionally be reprocessed to represent the current methods better, even though baseline and repeat studies should ideally employ the same processing techniques.
Operational Limitations and Repeatability Errors
When conducting the baseline study, it is critical to be aware of the location of any potential infrastructure. This is because the direction of the seismic lines must be the same for baseline and monitor studies. The acquisition system automatically integrates errors brought on by receiver sensitivity/calibration, source calibration, and positional accuracy.
Isometric seismic technology aims to reconstruct the wave field to more effectively illustrate the minor differences in seismic responses associated with changes in reservoir fluids and pressure.
The seismic signal’s frequency must be high enough to capture a geological layer’s tiniest significant depth interval. It is still feasible to make pertinent observations of the subsurface even if the resolution of the significant layer cannot be resolved. And seismic data comparisons can be used to establish this. Seismic data analysis for noise is crucial to understand how noise affects the ability to image geological events.