A Deepwater Sandface Monitoring System for Offshore Gas Hydrate Production
The world’s first offshore gas hydrate production has been
successfully carried out in the deepwater Japan at Nankai Trough in Q1 2013. In
this project, one production well and two sandface monitoring wells were
drilled and installed with a combination of distributed temperature sensing
(DTS) and array-type RTD (Resistance Temperature Detector) sensors.
The objective of the sandface monitoring system is to capture the
hydrate dissociation front dynamically changing during the production test and
long-term reservoir stability with the selected temperature sensors. An ability
to continuously monitor the response of these temperature data during
production test would facilitate tracking of the dissociation front and yield
valuable information for engineering design and verification of numerical
reservoir simulators. The temperature sensors are cemented behind the casing
and also strategically installed to cover both the hydrate zone of interest and
entire wellbore. Due to operational constraints, the monitoring system was
designed to be autonomous self-operated system by subsea battery without cable
connection from the sea surface for a period of 18 months from the day of
installation of the monitoring system.
The deployment of this monitoring system in shallow unconsolidated
openhole hydrate reservoir was an unprecedented and challenging operation. In
this paper, we will show the details of key system components of the sandface
monitoring system and the deployment process.