Sonardyne’s 6G Wideband 2 acoustic technology has, and continues to be, the primary tool used for the subsea metrology measurement phase. Now, the company has expanded its offering to include acoustic-inertial capability and a complete software solution for all stages of the metrology process. Reporting for Sonardyne, Edd Moller, Global Business Manager – Construction and Survey, and Malik Chibah, Subsea INS Manager, take a look into Sonardyne’s metrology toolbox.
Subsea Metrology requires accurate, precise and robust measurements which are critical for successful fabrication and installation of spools and jumpers. Since its introduction, Sonardyne’s Wideband 2 signal technology has increased the speed, robustness and simplicity of acoustic measurements. Now, with the development of a dedicated software tool called Connect, complementary 6G inertial techniques and instruments, the scenarios in which Sonardyne can assist clients with their metrology campaigns have greatly expanded.
Connect is Sonardyne’s new metrology software, designed to assist the user with all phases of a metrology campaign. The software eases operator burden and complexity by introducing ‘expert’ settings, automated data collection scripts and robust reduction of measurement from planning to report delivery. Tailored customer reports are generated containing the final results with supporting data and QC, improving the speed and integrity of data processing for acoustic, inertial and implied metrology techniques.
Guiding the user through the key stages of metrology including planning, data collection, quality control, processing and reporting, both traditional and horizontal metrologies are supported. Measurements can be directly collected from the metrology instruments, including Sonardyne’s own 6G transceiver and transponders, depth sensors and gyrocompasses whilst the software can also provide results for points on the structures that are not directly measured by using implied methods.
All collected data is displayed for checking before proceeding to processing and reporting; this includes any intermediate processing stages and users are able to easily select which data they wish to include or exclude. The final metrology report contains summaries of calculations to support the results including hub-to-hub horizontal distances, slant range, depth differences, attitudes and more.
SPRINT inertial metrology
ROVs equipped with our SPRINT (Subsea Precision Reference Inertial Technology) technology can now perform hub-to-hub metrology using the acoustic inertial SLAM (simultaneous location and mapping) technique. Uniquely, ROV operators can seamlessly switch from construction and survey operations to metrology without recovering to mobilise specialist metrology equipment. This solution combines Sonardyne’s trusted 6G acoustic technology, the field-proven SPRINT INS platform and Janus post-processing software.
Metrology-ready ROVs combined with streamlined data collection and processing offer significant time savings compared to existing techniques, without compromising integrity and quality of data or increasing risk. The 6G hardware platform provides a uniquely reliable set of measurements rich in QC, speeding up traditional acoustic metrology and lending itself to inertial integration, resulting in SPRINT acoustic-inertial metrology.
How does it work?
The SPRINT-equipped ROV is used to place 6G transponders in each metrology hub and then manoeuvres around the hubs to collect acoustic ranges between each one. If there is direct line of sight between the transponders, an acoustic baseline will be collected and used as an independent QC measurement – in this scenario, no additional seabed transponders are required. The attitude of each hub can be measured using a GyroCompatt or a Compatt 6 transponder with an inclinometer endcap.
All data is logged in real time by the SPRINT surface software with ROV backup available. The unique architecture of Sonardyne INS provides real time performance monitoring, detecting systematic errors in the data. Once collected, Janus post-processing software is used to determine the position of one transponder relative to the other using the afore-mentioned SLAM technique. In combination with the hub orientation measurements, the transponder positions determined from the SLAM can then be used to provide hub-to-hub horizontal and depth difference along with the relative bearing between the hubs.
Real world results
An example of performance is given by a recent metrology campaign where SPRINT metrology has been compared to traditional techniques as a reference:
- SLAM computed horizontal transponder difference compared to acoustic baseline: 0.02m
- SLAM computed vertical difference compared to conventional depth loop: 0.01m
- Significant time savings were realised during mobilisation and data collection referenced to alternative techniques
- Quality checks and post processing of results were completed onboard using Janus software
The GyroCompatt 6 integrates Sonardyne’s Wideband acoustic positioning and Lodestar Attitude and Heading Reference technology in one small, highly versatile and robust instrument. This provides high update rate wireless attitude, heading, heave, surge, sway, pressure, sound velocity and acoustic positioning of any subsea object.
Compatible with USBL and LBL positioning systems, the GyroCompatt 6 product family provides real time motion data for structure deployment via the integrated high speed acoustic modem. It is small and light enough to be ROV installed and a mechanical stab enables precision alignment to any structure. Position and orientation can be accurately determined during lowering, set-down and as-built surveys. Using the GyroCompatt 6 for metrology delivers the measurements required for pipe-end coupling while autonomous logging negates the need for a vessel and ROV to be on standby for taking measurements.
15 hours saved
Using GyroCompatts, a leading offshore survey company recently completed an acoustic metrology project 15 hours quicker than anticipated. Taking place in the Gulf of Mexico, acoustic metrology was performed on four proposed jumpers, measuring from the manifold pressure caps to the wellhead casings.
Typically, the time taken for one measurement is approximately 12 hours, resulting in a total operational time for this project anticipated at 48 hours. However, using Sonardyne’s 6G® GyroCompatt technology, all metrologies were completed in just 33 hours with accurate results.