Classification of mass-transport complexes and distribution of gashydrate-bearing sediments in the northeastern continental slope of the South China Sea

Abstract

The drilling areas in Shenhu and Dongsha, South China Sea, studied from 2007 to 2015, reveal great heterogeneity in the spatial distribution of the gas hydrate reservoir. Various types of mass-transport complexes (MTCs) were developed in the study areas, which served as ideal reservoirs. To conduct exploration in these areas, it is necessary to study the different types of MTCs and the corresponding gashydrate accumulations. By integrating seismic reflection and log coring data, we classified three types of MTCs according to their stress distribution: the tension, extrusion, and shear types, and their corresponding gashydrate accumulation patterns. The results show that the accumulation of the gas-hydrate varies with the type of MTC and stress distribution depending on the MTC’s position (e.g., in the headwall, translational, or toe areas). Owing to this variance of the MTC’s position, the corresponding kinemics situation in the MTCs also varies. Accordingly, we determined the corresponding location in which the gashydrate develops for various types of MTCs. Based on the bottom simulating reflectors (BSRs) and the hydrate core and image logging data, the gashydrate reservoir shows an obvious heterogeneity in various types of MTCs. The gashydrate in the tension-type MTCs are mostly borne in the toe and the headwall parts. In extrusion-type MTCs, the translational and toe parts constitute an ideal hydrate reservoir. In shear-type MTCs, the headwall and toe parts’ coarse-grained sediments show an obviously hydrate response. After comparing the gas-hydrate saturation and MTCs morphology statics data, we were able to quantitatively prove that the main factors determining gashydrate accumulation in the different types of MTCs are the fault displacement, sedimentary rate, and flow erosion rate.