Rock-physics model of hydrate reservoirs considering fluid inhomogeneous mixing, the temperature dependence of hydrate elastic modulus, and simplified pore structure parameters

Abstract

Rock-physics modeling of hydrate reservoirs is an efficacious solution for assessing the macroscopic elastic responses of rocks induced by microphysical parameters, pore structure, and fluid properties. Although many applicable rock-physics models have been proposed successively for different research objectives, several issues still need attention. Firstly, the previous studies have mainly focused on the effects of hydrate distribution morphology and pore structure, ignoring the mixing characteristics of different components in the pore fluid. Secondly, since the elastic modulus of hydrates differs greatly from that of conventional fluids, the reasonable setting of its elastic parameters will significantly affect the estimation results of the model. Additionally, too many parameters describing the pore structure will bring great uncertainty to the calculation results, while how to further consider the unconsolidated characteristics of the hydrate sediments in the modeling needs to be further investigated. To address the above problems, CT images of cores were used to elucidate the mixing relationship of hydrate, water, and gas, and the calculation of the equivalent fluid elastic modulus was proposed. The temperature dependence of the hydrate elastic modulus is obtained from experimental data and the elastic parameters are assigned by temperature in the modeling process. On this basis, the descriptive parameters of the pore structure are simplified by using the equivalent shape factor, and the unconsolidated characteristic of the sediments is described by introducing the consolidation parameter. In this study, we proposed a new modeling process for hydrate reservoirs and elaborated the rationality and necessity of the modeling idea in the numerical analysis, which finally achieved satisfactory results in the field data collected at the South China Sea.