SURFACE VSP / OBN
Enabling cost-effective sweep efficiency
Deepwater brownfield exploitation generally involves operating in remote, environmentally sensitive areas that have geologic basins with complex overburden, structure and stratigraphy.
In these geologically challenging areas, Ocean Bottom Node (OBN) seismic acquisition is the technology of choice for a number of reasons; the most important being its ability to capture a high quality seismic image, which is critical for characterizing time-lapse response of the reservoir. Due to the high acquisition cost, many mature reservoirs using an OBN approach for time-lapse imaging are surveyed several years apart, resulting in the missed opportunity to effectively manage and understand the reservoir.
To eliminate this risk, OptaSense provides a low-cost alternative that enables higher quality seismic surveys at more frequent intervals.
For Deepwater Imaging, Borehole Seismic Makes Economic Sense
Technology plays crucial role in providing the information to make sound exploration decisions. Given the complexity and high cost of deepwater development, there is great value in being able to identify the best spots to drill wells and manage production methods for field exploitation. Vertical Seismic Profiling (VSP) has long been considered a possible solution for deepwater seismic imaging. However, high cost and practicality have made it unfeasible for many operators. Since the introduction of Distributed Acoustic Sensing (DAS) VSP technology, these concerns have essentially been eliminated.
Borehole Seismic Delivers More Value
This low-cost, on-demand DAS-VSP solution offers several benefits, such as being able to survey reservoirs lying below thick salt formations which are notoriously challenging to image. Additional benefits include enabling repeat DAS acquisition using multimode fiber, acquiring DAS on active production and injection wells, and providing quick on-demand service for time-lapse monitoring of sweep efficiency.
To meet effectively attain these benefits, OptaSense recommends running their DAS-VSP borehole seismic acquisition service, capable of acquiring 2D, 3D and 4D VSP data, and the fourth generation ODH-4 DAS interrogator unit (IU) for its unmatched imaging and measurement performance. The ODH-4 provides a 6 dB improvement in signal-to-noise ratio over its predecessor—delivering the highest fidelity VSP measurements available.
In addition to higher quality seismic imaging, the ODH-4 offers increased sensitivity, finer spatial sampling (1.02m) and finer spatial resolution of (4.02m gauge length) to capture high-caliber image resolution.
Capabilities for Deepwater Seismic Imaging
Subsalt Imaging
Oil and gas is commonly trapped subsalt, or near salt flanks. Incidentally, imaging near and below the large salt structures is naturally problematic for any surface or OBN seismic program. One of the best known methods to properly image these areas is a VSP survey, which enables access to these obscure locations. However, these wellbores commonly have high deviation and high entry to access costs, making the use of conventional geophones unfeasible. The ODH-4 IU instead transforms existing fiber optic cable attached to production casing into an array aperture to acquire VSP data across the entire wellbore.
Multimode Fiber Acquisition
By retro-fitting our DAS technology to preexisting multimode fibers, OptaSense provides permanent, on-demand DAS-VSP access at no extra cost to the operator. Although DAS was originally developed for single-mode fibers, most legacy fiber optic installations are multimode. By continuously pioneering the evolution of DAS technology, OptaSense has proven quality DAS measurement can be acquired on either single-mode or multimode fiber—enabling on-demand acquisition of quality seismic surveys from wellbores with existing fiber.
VSP Acquisition On Active Production and Injection Wells
With OptaSense DAS-VSP borehole seismic acquisition service, operators can successfully acquire VSP data on actively producing and injecting wellbores during acquisition operations. Such a practice would be unthinkable with geophones. In some cases, a mature field may not have suitable placement for, or the existence of, an observation well. This can impact an operator’s ability to monitor production, as well as optimize future well placement. Our DAS-VSP eliminates the requirement of observation wellbores for VSP imaging, while providing on-demand, direct monitoring of production and injection zones. This ensures operators receive the subsurface insight required to control current operations and optimize future placement of injector and producer wells. OptaSense DAS-VSP also provides the ability to acquire data on active wellbores without shutting in operations—resulting in greater VSP imaging coverage at favorable economic costs.
Unmanned VSP Services
Manned operations for recording instruments can amount to significantly increased risk and cost depending on the duration and location of the program. Through the use of a suitable internet connection OptaSense can provide unmanned VSP services through remote monitoring of OptaSense equipment and data. This significantly reduces cost and HSE exposure for our clients by reducing lodging, substance and day rates for an onsite operator, in exchange for a daily remote monitoring fee.
