OptaSense Distributed Acoustic Sensing for Offshore and Onshore Well Monitoring
OptaSense is a leading specialist in Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS) technology, providing real-time observations of well operations in the oil and gas industry.
OptaSense DAS offers many advantages over traditional wellbore surveillance methods. The technology is revolutionising significant areas of oil field services management:
- It provides images for wells that were previously inaccessible to conventional geophone arrays
- It removes the need for well intervention
- It reduces HSE and operational risks
- It provides cost-effective surveillance
- Surveys can be conducted continuously at any time and in real-time along the entire wellbore
- Time-lapse fibre-optic surveys can provide critical reservoir surveillance data for the optimisation of production and recovery
Distributed acoustic sensing technology
OptaSense DAS essentially turns a standard optical fibre into an array of virtual microphones. Short pulses of highly coherent light are transmitted down the fibre by an interrogater unit, and backscatter returns are observed coming from the inherent physical imperfections present in any standard fibre optic. The backscatter observations detect minute cable strains induced by acoustic or seismic signals. The backscatter is then passed through to a processing unit which provides interpretations and visualisation of the signal.
The optical fibre is either deployed on a production string or temporarily on coiled tubing. Once the fibre is installed, there is no need for further well intervention, making it possible to perform Vertical Seismic Profiling (VSP) on multiple wells from a single pad location.
High-temperature wells, such as those used for steam injection, can now be imaged with DAS. The process uses fibres that can withstand temperatures in excess of 300°C. It is also possible to make repeatable borehole seismic measurements safely in producer wells, injector wells, wells with restricted access and wells which are highly deviated.
Vertical seismic profiling
The OptaSense DAS VSP service allows for seismic measurements without geophones. The service enables the interfacing and synchronised control of seismic sources for accurate timing, real-time correlation and the stacking of virbroseis data. This produces standard seismic data files in SEG-Y or SEG-D format in real-time, with fully populated headers. It also provides a secure live internet feed of the acquisition of seismic records for remote quality control and assessment.
DAS VSP provides the ability to take repeated time-lapse measurements on a dense array of hundreds of virtual sensors, with full coverage of the well from top to bottom, without well intervention. This provides a unique capability for enhanced imaging of reservoirs. It has been used and certified for the monitoring of carbon dioxide injection, for example.
OptaSense DAS also enables permanent borehole micro-seismic monitoring, especially of larger-magnitude events that originate at existing fault locations. The broad bandwidth and high dynamic range of OptaSense DAS technology enable the accurate measurement of large low-frequency seismic signals generated at existing fault locations. The technology’s long array sensing aperture enables geolocation of these events in deviated wells.
Hydraulic fracture monitoring
OptaSense DAS also makes it possible to monitor the entire hydraulic fracturing process at the treatment zone. This includes monitoring of packer deployment, perforation detonation, sleeve opening, fluid and proppant entry, and plug setting.
In-situ monitoring provides an unrivalled ability to visualise and hear exactly what is happening along the well, in particular at the treatment zone. This delivers the following entirely new benefits:
- Improved yields through process optimisation
- Measurement of the traditionally unmeasurable
- Control and optimisation of the hydraulic fracturing process as a whole
Hydraulic fracture profiling
The OptaSense DAS Hydraulic Fracture Profiling (HFP) service continually monitors and records acoustic signals measured by DAS, temperatures measured by a fibre-optic DTS system, and pump rates provided by the on-site pumping contractor. It also delivers:
- Real-time monitoring of hydraulic fracture treatment operations, including running and shot characterisation of perforation guns, deployment of diversion and sleeve balls, placement of plugs, and tooling operations on coiled tubing, enabling the completions engineer to rapidly identify and correct issues as they arise
- A unique ability to acoustically monitor hydraulic fractures directly at the treatment zone
- An estimation of the fluid and proponent uptake at each perforation cluster, which can be used for optimisation of the hydraulic fracture design on other wells within the field
Production flow logging
Permanent production flow logging is now possible using DAS, and OptaSense is working to provide the ability to measure flow rates along the well, zone and perforations. With no need for well intervention, and with minimal interference with the flow, DAS permanent production logging is developing rapidly as an exciting alternative to conventional Production Logging Tools (PLTs).
Flow / no flow assessment
The first of OptaSense’s production services is to offer the ability to assess flow / no flow behaviour across different perforations. With repeat measurements, this information can be used to monitor the effectiveness of each perforation entry point and through-life production profile. The tool can also be used to determine the flow / no flow across In-flow Control Valves (ICVs), Electrical Submersible Pumps (ESPs) and gas-lift valves in smart well completions.