As a part of a research program aiming to mobilize marine gas hydrate deposits as an energy resource, the worlds' first gas production attempt was performed in early 2013 in the Daini Atsumi Knoll, Eastern Nankai Trough, off Honshu Island, Japan.

The world-first offshore production test of gas hydrate was just performed in the deep water Nankai Trough along the Pacific coast of Japan in March, 2013. A week-long flow test successfully produced methane gas by depressurizing method from the subsea methane hydrate reservoir.While methane gas was successfully extracted from natural hydrate, there is a strong urge for understanding the dissociation behavior and characterizing production process of hydrate through the depressurization method. This is a crucial knowledge for the future commercial production of gas hydrate.The dissociation of methane hydrate is an endothermic reaction, and the drop of formation temperature is expected to occur as the dissociation progresses. By capturing the phenomenon of temperature decrease in-situ, the data attributed to the dissociation of methane hydrate can be obtained during production.Two monitoring wells, uniquely designed for minimizing thermal disturbance and better thermal coupling were drilled in the vicinity of the production well, and the two types of temperature sensors using DTS (Distributed Temperature Sensing) and array-type RTD (Resistance Temperature Detector) were deployed in the monitoring wells and recorded the data not only during the flow test period but also before and after the test. DTS covered the entire wellbore interval while the array-type RTD sensors were strategically placed across the gas hydrate reservoir with higher temperature resolution and accuracy.In both monitoring wells, the temperature decreases were observed distinctively with both sensors as the flow test progressed over a week. The data quality check confirmed both measurements were conformable to the design specification and demonstrated the strong advantages of having both sensors in this monitoring system for further interpretation to investigate the dissociation behaviors.The framework for temperature data analysis was defined to perform thermal characterization of gas hydrate reservoir during the production test stage. The preliminary analysis on the temperature transients was performed, and the results that could explain the dissociation behaviors were obtained.

The world's first offshore gas hydrate production was successfully carried out in the deepwater Japan at Nankai Troughin 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 was to capture the hydrate dissociation front dynamically changing during the production test and to monitor 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 the hydrate zone of interest and the entire wellbore. Due to operational constraints, the monitoring system was designed to be autonomous self-operated system by the 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 this shallow unconsolidated hydrate reservoir was an unprecedented and challenging operation. In this paper, we will show the details of the key system components of the sandface monitoring system and the deployment process.

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 coiled tubing (CT) e-line system is ideal to perform real time production logging (PL) in long horizontal wells, however, the wireline cable inside the CT can restrict the pump rate while the large volumes of acid normally pumped could potentially damage the CT pipe's integrity. Furthermore, using two different CT strings, one for pumping acid and another for performing the PL in real time is neither practical nor economical. A common approach is to use a memory PL tool (PLT), with the associated drawback of recording poor quality data or eventual misruns.To overcome these challenges, a new CT multipurpose system has been developed, allowing real time PL and conventional applications. Leveraging on the telemetry offered by the fiber optic enabled CT (FOECT), already used for downhole measurements while treating in the M field; the new downhole assembly enables the use of standard PLTs in real time mode. At the surface, the converted optical signal is transmitted wirelessly to the PL engineer's portable computer; eliminating the need for conventional acquisition equipment and personnel.In a world first application, the system was used in a land water injection well, after the stimulation job; obtaining the injection profile log with the same quality measurements as a conventional wireline conveyed log. Moreover, the data demonstrated a uniform injection profile. Additional field applications are also briefly discussed in this paper.The new multipurpose FOECT reduces the mobilization and logistics otherwise required, as well as the time and cost compared to existing alternatives. This new capability can be extended to other scenarios like offshore or remote environments, where operational costs have a larger impact. Ultimately, the system opens the door for performing diagnosis, treatment and evaluation in a single well intervention mobilization; making CT operations more efficient and providing more data for production engineers.