Sensitivity and Uncertainty Analysis for Natural Gas Hydrate Production Tests in Alaska

Abstract

The Japan Research and Development Consortium for Pore Filling Hydrate in Sand (MH21-S), the U.S. Department of Energy National Energy Technology Laboratory (DOE NETL), and the U.S. Geological Survey (USGS) are planning a long-term production test from gas hydrate (methane hydrate) bearing reservoirs in the Prudhoe Bay Unit in northern Alaska. Prediction of gas and water production using 2D reservoir simulation models can be very useful for decision-making for long-term production testing. However, the input parameters applied to the simulation model, which are essentially based on the most likely values obtained from the well-log interpretation and core sample measurements of the Hydrate-01 stratigraphic test well (STW), have some degrees of uncertainty. In this study, to evaluate the impact of uncertainties in the input model on the prediction results of gas and water production as well as to analyze how each input parameter contributes to the uncertainties of prediction results, we conducted uncertainty analysis and parameter sensitivity analysis based on two different methods (the regression-based method and the Sobol’ method). The sensitivity analyses reveal that the parameters regarding relative permeability (exponential of the gas relative permeability (N g) and residual gas saturation (S gcr)) and the intrinsic/effective permeability of the lower B1 sand significantly contribute to the uncertainties of the gas and water production predictions. In addition, the uncertainty analyses reveal that the P50 value of cumulative gas production can result in less than the reference case with the most likely values for the input parameters due to the uncertainty of N g. These results indicate that reducing the uncertainties of gas relative permeability and residual gas saturation is essential for more reliable numerical simulations both for prediction of test well performance and subsequent history matching of field test results.

Geological Reservoir Characterization of a Gas Hydrate Prospect Associated with the Hydrate-01 Stratigraphic Test Well, Alaska North Slope

“…The following results are reported here: structural/stratigraphic evaluation and reservoir conditions of the target reservoir sands, using well data acquired from the Hydrate-01 well and the previously drilled Kuparuk State 7-11-12 well (see Figure , presented later in this work); petrophysical analysis using the Hydrate-01 well log and side-wall core data; and structural analysis using the 3-D VSP data. Finally, based on the integrated analysis of well and 3-D VSP data, together with the surface seismic data, as provided by the PBU Working Interest Owners, the reservoir heterogeneity related to geological structure and petrophysical properties are discussed. The results in this study have provided the geological models for the reservoir simulation studies conducted under this project, , and they can further refine the geological information for the final positioning of the producing and monitoring wells for the planned long-term production testing.…”

“…The well log and core-derived petrophysical data acquired from the Hydrate-01 well were analyzed to construct the geological and reservoir model for the subpermafrost section at the 7-11-12 test site (Figure ). These geological and reservoir models were utilized to conduct the reservoir simulation studies in order to predict the gas hydrate production performance. ,, …”

Numerical Simulations in Support of a Long-Term Test of Gas Production from Hydrate Accumulations on the Alaska North Slope: Reservoir Response to Interruptions of Production (Shut-Ins)

“…To address this issue, a long-term field test of hydrate production from a permafrost-associated reservoir on the Alaskan North Slope has been pursued, with the recent drilling of the Hydrate-01 Stratigraphic Test Well confirming the occurrence of a suitable test site within the Prudhoe Bay Unit . In preparation for this test, extensive geologic, − engineering, and numerical simulation studies , are being undertaken in an effort to assess the system response under a wide range of circumstances, explore the technical challenges of long-term production from hydrate reservoirs, and prepare an appropriate engineering design. This study is part a larger numerical simulation investigation seeking to provide answers and inputs to the design of the proposed production test in northern Alaska.…”

Energy Transition and Climate Mitigation Require Increased Effort on Methane Hydrate Research

“…International methane hydrate production programs (offshore in Japan, , China, , India, , and South Korea , and onshore in U.S. Alaska North Slope ,− ) have revealed high methane hydrate concentrations in sediments with significant permeabilities required for gas production. , …”