Abstract: Abstract:This paper describes fluid migration patterns about mud diapir with different origins, then discusses the relationship between natural gas hydrate accumulation and the evolution of mud diapir migration system, and analyzes the effect of mud diapir migration system on gas hydrate accumulation in Shenhu area.The fluid migration systems for diapir consist of external associated fault and fracture, the internal overpressured fluid fracture and structural fracture in the margin of diapir. Depending on migration conduit and migration dynamics, two kinds of fluid migration patterns have been proposed: overpressureconducting fracturing fluid migration type and marginal fracture migration type. In addition, the mud diapir (mud volcano) has different effects on formation and stability of the hydrate in the different evolution stages. The migration channel may not extend to the hydrate stability zone in the early stages of mud diapiric formation, which results in insufficient supply of CH4. It is conducive to the formation of natural gas hydrates in the middle stage, because of good matching in hydrate metallogenic conditions; the abnormal heat in the hydrate stability zone, caused by high temperature gasbearing fluid from mud volcano eruption, may lead to the decomposition of hydrates in the late stage. Until the quiet period of mud volcano activity, hydrates can be reserved again. According to morphological characteristics of diapirs in Shenhu Area, mud diapirs could be classified into two types: corolliform and domeform diapirs. The fluid migration pattern of corolliform diapirs belongs to overpressureconducting fracturing fluid migration type; the fluid migration pattern of domeform diapirs belongs to marginal fracture migration type. Different diapiric migration patterns may be one of main factors of nonhomogeneous distribution of gas hydrate in Shenhu area.

Key words: mud diapir, fluid migration system, gas hydrate, reservoir mechanism, Shenhu area