Knowing Where To Start: Assessment of Methane Resources with Petroleum Systems Modeling

摘要

Gas hydrates are typically pressure- and temperature-controlled accumulations of mostly methane that occur in sediments at relatively shallow depths. They contain significant amounts of gas, perhaps more than any other conventional or unconventional source, and could ensure energy supplies for many years. Their production has not yet proved to be commercial, but recent progress in developing appropriate production methods is encouraging. There is, therefore, an increasing need to understand and predict gas hydrate distributions and resources; this can be done using a new module developed for industry-recognized petroleum systems modeling software. Petroleum systems modeling software was designed to simulate the generation, expulsion, migration, accumulation, and loss of hydrocarbons in conventional petroleum systems. Recent technological advances in this software have produced a new hydrate module that can be applied to assess unconventional hydrocarbon resources. Pressure and temperature modeling is the core task of petroleum systems models, so they are also obviously suited to gas hydrate modeling. The numerical simulation of accumulations in marine and permafrost environments is done with algorithms describing (1) the physical, thermodynamic, and kinetic properties of gas hydrates; (2) a kinetic model for the microbially mediated, low- temperature degradation of particulate organic carbon in sediments; and (3) the transport of dissolved and free-phase constituents in the pore fluid. In contrast to the resolution of conventional resource assessments, the temporal and spatial resolutions have been increased to enable simulation timesteps of 100 years and a minimum cell thickness of one decimeter. The gas hydrate module was tested on the petroleum systems model of the Alaska North Slope region, where the hydrates have been drilled in fine-grained sand layers in marine and permafrost environments. Hydrate saturations and the methane source rock are well known in the drilled well. Simulations were run to predict the thickness of the Gas Hydrate Stability zone, the generation and migration of biogenic and thermogenic methane gas, the formation and dissociation of gas hydrates under marine and permafrost conditions, and the evolution of these properties over the geological past. The module is now being used by E&P companies and gas hydrate research centers in Japan, Korea, China, Germany, Norway, and the USA.