Rock physics model of gas hydrate reservoir with mixed occurrence states

Abstract

Summary The relationship between gas hydrate saturation and elastic parameters can be influenced by gas hydrate occurrence state. Pore-filling type, load-bearing type and cementing type are three common occurrence states found in rock physics investigations, but many gas hydrate-bearing formations are observed to have mixed occurrence states. In this paper, we present a generalized rock physics model containing gas hydrate of all three occurrence states. The relative proportions of different types of gas hydrate to rock matrix and pore filler can be adjusted, and their influence on the apparent porosity of formation are also considered to simulate the effective elastic property of gas-hydrate bearing formation with mixed occurrence states. Besides, the effect of pore filler containing water and gas hydrate in shear modulus is considered in the modelling. The influence of gas hydrate saturation and mixed occurrence states on the velocities under the three cases is analyzed by using numerical examples. The modelled results are demonstrated by the calibration with the well log data and experimental data. The results show that it can well model gas hydrate-bearing formation or core samples with mixed occurrence states.