Accessing Data from a Deepwater Sandface Monitoring System Using an Autonomous, Unmanned Surface Vehicle - Japan Case Study

Abstract

Gas hydrate production commenced from two production wells drilled in 1,000 m of water in the Nankai Trough, Japan, in May 2016. Two adjacent monitoring wells were drilled to monitor the in-situ event change of the hydrate reservoir over a two-year monitoring period. To achieve this monitoring purpose, an innovative design of wellbore gauges was installed downhole to provide valuable temperature and pressure data to show the dynamic nature of the gas hydrate dissociation front. Using two seabed located autonomous subsea monitoring systems, data were continually logged from the monitoring gauges since they were installed in May 2016. To gain access to the recorded wellbore data, early project thoughts revolved around either recovering the large subsea monitoring systems or deploying remotely operated vehicles (ROVs) to tieback umbilical cables from the two subsea monitoring systems to the drillship, once it arrived at the field site. These techniques proved to be expensive and of increased risk to both personnel and equipment. With a view to future safe and more cost-effective data harvesting techniques, a project was instigated to investigate using autonomous, unmanned surface vehicle (USV) along with vessel-based "dunker" methods to upload data from each of the monitoring wells using integrated high telemetry acoustic modem technology. The main objectives of the study were to verify data could be harvested and delivered to the client using a USV along with safe and repeatable piloting of the USV from a remote location. Two USV missions have since been conducted, one in June 2016 and the other in March 2017. Lessons learnt from the initial USV mission, such as higher than expected sea surface currents and thrust limitations of the USV, were incorporated into the second deployment. This resulted in roughly 200 days' worth of data being uploaded and delivered from each of the two monitoring wells. In this paper, we will outline how the project objectives were met and how some of the challenges, both technical and environmental, were overcome.

The second offshore production of methane hydrate in the Nankai Trough and gas production behavior from a heterogeneous methane hydrate reservoir

“…Moreover, some technical developments were made for long-term monitoring of the thermal and hydraulic conditions, such as (i) downhole pressure sensing in the monitoring holes, (ii) subsea data storage, (iii) rechargeable batteries, and (iii) an acoustic system for communication between subsea and a surface vessel. 32 In the producer holes, a length of approximately 60 m in each hole was selected as the production zone in which "lower-completion" (a portion of the well contacting the production formation) with sand-control and zonal isolation devices were set. The device comprises a combination of a porous shape memory polymer (fully activated GeoFORM † on the installation in the AT1-P3 well, and in situ activation through an activation uid in AT1-P2), metal bead insert, and a premium screen.…”

“…Moreover, some technical developments were made for long-term monitoring of the thermal and hydraulic conditions, such as (i) downhole pressure sensing in the monitoring holes, (ii) subsea data storage, (iii) rechargeable batteries, and (iii) an acoustic system for communication between subsea and a surface vessel. 32 …”