Advanced Reservoir Modeling and Fluid Flow Studies of Natural Gas Production from the Hydrate Reservoirs of the Alaska North Slope.

摘要

The emerging possibility of the production of gas hydrates as an unconventional source of energy have spurred many objectives for research studies going on in this area. One of these is the U.S national hydrate research program with a primary goal of determining the tools and technologies for environmentally safe gas production from hydrate reservoirs. The work presented in this thesis is motivated by the need to provide reliable reservoir model-based predictions to support proposed long-term hydrate field production tests on the Alaska North Slope permafrost. While first order predictions have been made from reservoir models based on assumptions of homogeneity of properties, it has been shown that the degree of reservoir heterogeneity can significantly affect the quantitative and qualitative results.;This study is an advanced and robust evaluation of the gas production potential of hydrate reservoirs. The hydrate deposits within the region of Prudhoe Bay Unit (PBU) "L-Pad" and Mt. Elbert Well vicinity of the Milne Point Unit of the Alaska North Slope are primary subjects of investigation. It is an effort to build data-driven heterogeneous hydrate reservoir models by applying both conventional and novel methods of reservoir characterization to maximize the utilization of the available field data. Using well log data obtained from 78 L-Pad wells, geostatistical techniques were employed to obtain stochastic simulations of the 3D distribution of reservoir properties in the target hydrate units of the L-Pad region. Models for the Mt. Elbert deposit were developed by combining data obtained from well logs obtained during the 2007 Mt. Elbert stratigraphic test and a 3D seismic survey of the region. Additionally, wellbore flow assurance studies were coupled with reservoir models in order to predict potential production issues arising from the formation of secondary hydrates or ice within the wellbore fluids being produced under high pressure and low temperature conditions.;CMG STARS, a finite difference reservoir modeling software package, was used to solve the material and energy balance equations in which an equilibrium model of hydrate dissociation was used. The simulator also provides a means to couple artificial lift design of the wellbore with the reservoir model using established pressure drop-heat loss correlations. Gas and water production rates and the evolution of reservoir properties were extensively studied in varying production scenarios with depressurization as the primary recovery technique.;Predictions from 10 geostatistical realizations of the L-Pad model were within narrow ranges, which is an indication of the robustness and reliability of the model. Uncertainty assessment and sensitivity studies on the Mt. Elbert model showed that higher gas production rates were achieved in deeper (hence warmer) reservoirs and confirmed earlier studies that production from the Mt. Elbert prospect may too cold to be economically feasible. Furthermore, contrary to predictions from homogeneous models, the effect of secondary hydrate formation in the reservoir on gas flow was found to be very minimal. However, flow assurance and artificial lift design studies show that wellbore pressure and temperature conditions must be effectively managed to prevent formation of secondary hydrates or ice.