Are you interested in understanding borehole seismic techniques? Do you want to know how this technology has developed in recent years, and what advancements can be expected in the future? In this article, we will discuss the latest advancements in borehole seismic techniques. These advancements help provide more efficient, accurate, and reduced-risk imaging of subsurface rock formations.

We will explore the differences between conventional methods and emerging fiber-optic technologies and how they are used in hydrocarbon exploration and subsurface formation characterization. By the end of this article, you will understand the current state of borehole seismic techniques. You will also be up-to-date with the latest trends, technologies, and approach-based solutions to improve borehole imaging.

Conventional Borehole Seismic Techniques

Conventional methods for borehole seismic imaging include seismic sources and receivers placed in a well, sonic logging, single-well imaging, and multiple-well techniques. These methods are frequently used to investigate lithology, fluid content, and pressure anomalies through elastic properties.

Well-to-surface surveys such as check shot surveys and VSP are also utilized, along with offset VSP (OVSP), walkaway VSP, three-component VSP, reverse VSP, and time-lapse VSP. These surveys require significant technical and engineering skills and a lot of time and costs. They require rig-up and rig-down processes, are prone to completion factors such as confined zones, and are notorious for low data assurance.

Some of the limitations and problems that users experience with these conventional seismic techniques include seismic wave scattering due to rocks’ complexity, significant environmental impact, the lack of spatially and temporally dense data, low signal-to-noise ratio (S/N) due to proximity to interfaces, poor information on subsurface fluid, and structural studies, and failure to calibrate their data.

However, borehole seismic techniques remain the preferred approach, particularly in carbon capture and storage (CCS) projects, due to their ability to generate storage volume characterization, reflection, seismic velocity models, and synthetic seismograms. 3D and 4D seismic surveys have been used extensively in reservoir characterization, especially for production and injectivity performance.

Emerging Fiber-Optic Technologies

Over the years, several fiber-optic technologies have emerged, which have revolutionized borehole seismic imaging significantly. Schlumberger’s Optiq seismic fiber-optic borehole measurement solution has made significant strides in providing an efficient and accurate solution for real-time measurements captured along the entire length of the strand. This capability has provided asset-light operations and accurate data acquisition immune to electrical noise and EMI/RFI.

In addition, Silixa’s Carina seismic services and iDAS utilize distributed acoustic sensing (DAS) technology and engineered constellation fibers. The technology has progressed from the laboratory phase to the field, and it is gradually replacing the traditional geophone-based VSP acquisition suite. It provides high-resolution seismic data throughout the well’s life eliminating the need for well intervention and production stoppages.

In summary, fiber optic wires positioned in either coiled tubing or completion systems capture continuous measurements along the borehole wall. This detects seismic waves up to 10 kHz. Eliminating well intervention, which can cause production stoppages or rig-time loss.

In particular, fiber optic technology is highly demanded by exploration drillers holding unconventional reservoirs, such as gas shale, tight gas, and tight oil. This is due to the high-quality images that engineers can interpret quickly and because the installation of permanent fiber optic cables allows for better surveillance over time.

Applications and Advancements

Advanced borehole seismic applications include high-resolution imaging, anisotropy determination, fracture analysis, alternative acquisition schemes, and reservoir monitoring. These applications are made possible by fiber optics such as distributed fiber optic sensing systems (DFOS), single-line fundamental and walkaway VSP, and borehole horizontal seismic imaging.

Borehole seismic techniques are evolving with tomographic techniques. This is a method that uses first-arrival travel times and full waveform inversion (FWI) to provide high-resolution 3D and 4D imaging. These techniques enable users to determine the actual physical properties of the earth, providing accurate estimates of subsurface seismic velocities and lithologic parameters.

Another emerging technique is seismic-while-drilling, which involves drilling a well and simultaneously imaging the formation to help the drillbit navigate through the formation accurately. This technique has given rise to zero-offset VSP, which is used to calculate borehole seismic sensors and calibrate their measurements.

Finally, permanent clamp and tubing-conveyed fiber-optic sensing is becoming more widely adopted, which captures continuous measurements of fluid and pressure monitoring, providing long-term surveillance for production tubing and completions. By installing permanently installed fiber optic cables, seismic imaging becomes more efficient with reduced seismic shot requirements. This results in enhanced efficiency gains and reduced risks to personnel.

Borehole seismic techniques are essential for hydrocarbon exploration and subsurface formation characterization. Technology has seen continual advancements in efficiency, accuracy, and risks, making borehole seismic techniques more accessible to the industry.

With emerging technology like fiber-optic cable, borehole seismic imaging is set to become more widespread and effective, and more techniques will emerge to provide better accuracy and efficiency. By keeping up-to-date with the latest trends and advancements in borehole seismic techniques, professionals can better understand how to use this technology and optimize its applications.