Case Study: Autonomous Vehicle Efficiently Harvests and Securely Transmits Subsea Data off West Africa

Challenge: Improve access to important well information from subsea tree-mounted acoustic data loggers (ADLs) used during a well testing program in 1,200-m water depth.

Solution: Deploy an autonomous marine vehicle equipped with an acoustic modem to harvest downhole pressure and temperature (DHPT) measurements collected by the ADLs for subsequent recording, transfer via satellite to a secure server, and analysis by Tullow Oil’s London-based reservoir team.

Result: Better informed decision making and decreased data retrieval costs through autonomous harvesting by an unmanned surface vehicle (USV) of raw data for automatic transmission by satellite to the reservoir team foranalysis.

Retrieving data from wellbore monitoring

To understand reservoir characteristics prior to wellhead tie-back, reservoir engineers rely upon conventional vessel-based “dunker” techniques performed by offshore engineering teams for data retrieval. However, there is significant lag time in the data availability, and gaining access to equipment, personnel, and vessel time has become increasingly expensive and difficult. Tullow Oil wanted a more efficient process for retrieving and transmitting this critical data.

Deploying a versatile autonomous USV for data harvesting and real-time transmission

To counter the challenges of retrieving data offshore, Schlumberger Robotics Services recommended deploying GATEWAY services to upload the DHPT data via acoustic modems. The acquired data would be stored at the sea surface and transmitted in real time by satellite to shore for converting to engineering units for use by Tullow Oil’s reservoir team. Having on-demand DHPT data would enhance the management of challenges during this critical early stage of field development. In addition, the real-time provision of more frequent and timely data would decrease Tullow Oil’s logistical burden and operational cost.

Using a USV removes the need for a conventional vessel because it is capable of operating at sea in most weather conditions, autonomously transiting between wellhead locations to collect data.

Efficiently and reliably accessing data on demand

By using Robotics Services technology, the Tullow Oil reservoir team gained broader and timelier access to critical DHPT data. On average, the USV uploaded data once per week from designated wellheads. When not performing an uploading mission, the vehicle remained in a secure holding zone performing a figure 8 pattern.

When a request was made for data to be uploaded from a particular wellhead, the USV, powered solely by wave energy and traveling at an average speed of 1 knot (approximately 0.5 m/s), moved from the secure holding area to the wellhead. Any vessel traffic in the area was avoided by monitoring their Automatic Identification System (AIS) transmissions and navigating the USV accordingly. Upon arriving at a preset series of waypoints, the USV would navigate in a circle on the sea surface at a radius of 250 m centered on the wellhead.

During these maneuvers, an integrated Sonardyne 5G acoustic modem transceiver communicated through 1,200 m of water to a Sonardyne 5G ADL situated on the subsea wellhead. After a series of handshake commands between the vehicle and the ADL, the previously recorded and stored DHPT information was transmitted through the water column to the USV on the surface. Once the raw data was received on the vehicle, it was immediately transmitted to a secure storage server using Iridium satellite communications. The final step was the shore-based operator downloading the raw data and converting it to engineering units using software supplied by Robotics Services for delivery to the Tullow Oil reservoir team.

This cost-efficient alternative to conventional methods used to harvest DHPT information typically accessed several wellheads sequentially to provide valuable data in real time.

Download: Autonomous Vehicle Efficiently Harvests and Securely Transmits Subsea Data off West Africa (0.23 MB PDF)

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“Data acquired using the Wave Glider provided valuable insight into reservoir communication pathways between development wells, and in turn enabled robust planning for the start-up phase of the TEN Project. This was all achieved at low cost when compared to standard industry practices and reduced exposure of manpower and support vessel resources in the field. As with all projects, people interfaces and communication lines are key to success—it was a pleasure working with all of the contributors to the highly successful Wave Glider project and we look forward to looking for additional opportunities to apply this technology again.”
Robin Rindfuss
TEN Project, Subsurface Manager
Tullow Oil

USV Harvest Data and Transmits Data in Real Time

Deployment of Wave Glider USV offshore West Africa for the data harvesting mission.Figure 8 route designated by red x’s around waypoints over a period of 24 hours.
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