Effects of far-field boundary conditions on the simulation of hydrate production

Abstract

The world’s first offshore methane hydrate extraction was conducted in 2013 at the Daini-Atsumi Knoll located in the eastern Nankai Trough. The results indicated that the gas production rate of a single vertical well cannot meet the requirement for commercialisation of methane hydrate production. Therefore, a trial multi-well system has been considered for future hydrate production. Understanding the ‘influence distance’ of extraction wells within methane hydrate turbidite reservoir formations, such as that of the Nankai Trough, is significant to the design of the proposed multi-well system. In this study, the boundary effects are examined for cases involving different values of permeability and initial hydrate saturation for the modelled turbidite formations. A relationship is proposed to predict the longest simulation time for a given set of lengths and parameters. The two concepts of critical production time (CPT) and turbidity/homogeneity coefficient ratio (THCR) are introduced to analyse the interaction between the effects of model size and heterogeneities. It is found that the CPT can be normalised by the radius of the model; the THCR is affected by the relative thickness of the sand and clay layers.