Comparison of the Vertical Gas-Hydrate Production Profile with the Simulation Results Obtained Using Geophysical Log-Based Reservoir Characteristics and Reasons for Their Discrepancies in the Nankai Trough

Abstract

In this study, we analyzed the temperature and pressure measurement data obtained from the production test of methane hydrates in the second offshore production wells of Nankai Trough (2017). Based on the analysis, we derived timeseries information on the vertical profile and the gas and water influxes in the wells via an optimization process. The time-series information revealed variations in the vertical production profiles and behavior between two production wells. Some discrepancies were observed in the petrophysical characteristics, particularly in the permeability between the wells, while comparing the measurement-based profile and simulation results based on geophysical log-based reservoir models. The discrepancies are attributed to the water-producing layers and some near-wellbore phenomena, which also inhibit stable and increasing gas production in the well. Current studies on gas hydrate by the Japanese national gas-hydrate resource development project focus on identifying the causes of these problems and possible countermeasures.

Numerical History-Matching of Modeling and Actual Gas Production Behavior and Causes of the Discrepancy of the Nankai Trough Gas-Hydrate Production Test Cases

“…The reason why the initial reservoir model that was constructed with geophysical logging data did not give good results is an issue of not only the geophysics but also well completion and other distortion of the reservoir condition during the drilling. When the details of the monitoring data are observed, some discrepancies between the modeling and the measurements are seen in the vertical gas and water influx profiles . Both large extent of three-dimensional heterogeneity and mesoscale wellbore conditions should be more carefully studied.…”

“…When the details of the monitoring data are observed, some discrepancies between the modeling and the measurements are seen in the vertical gas and water influx profiles. 27 Both large extent of three-dimensional heterogeneity and mesoscale wellbore conditions should be more carefully studied.…”

Sand Migration Simulation during Gas Production from Gas Hydrate Reservoir at Kuparuk 7–11–12 site in the Prodhoe Bay Unit, Alaska

“…However, recent analysis of production and monitoring data indicated that the development of "skin" across the near-wellbore zone possibly caused a low apparent permeability zone due to potential clogging of the sand control device and formation around the well. 4,5 International collaboration between U.S. and Japan plans gas production from the gas hydrate reservoir in the Prudhoe Bay Unit, Alaska North Slope. Therefore, it is important to model sand migration during the planned test, predict where sand might originate, and understand the effect of sand accumulation near the well on the mechanical behavior of sediments over a period of one year.…”

Virtual Special Issue of Recent Advances on Gas Hydrates Scientific Drilling in Alaska

“…Similarly, gas hydrate reservoirs were initially envisioned as fully solidified deposits, indicating the need for thermal-stimulation-based approaches; however, the initial field testing programs conducted at the Mallik site in arctic Canada revealed the presence of mobile water, and further testing at the site demonstrated the greater potential for pressure-reduction strategies, the success of which was subsequently extended to the marine environment . Later field data acquisition programs in the Nankai Trough and in the Indian Ocean have revealed the critical role of dynamic reservoir geomechanics and have revealed the surprising complexity of hydrate reservoir systems that are requiring ever more complex approaches to the well design and production simulation. , …”

“…11 Later field data acquisition programs in the Nankai Trough 12 and in the Indian Ocean 13 have revealed the critical role of dynamic reservoir geomechanics and have revealed the surprising complexity of hydrate reservoir systems 14 that are requiring ever more complex approaches to the well design and production simulation. 15,16 The progression toward environmentally sound and commercially viable production systems will require multiple scientific field experiments to further refine our understanding of the nature of hydrate systems, their dynamic evolution during induced dissociation, and the most optimal systems for managing the production process. Unfortunately, the complexity of arctic and deepwater field programs has limited the tests conducted to date to a relatively short duration.…”