Effects of Irreducible Fluid Saturation and Gas Entry Pressure on Gas Production from Hydrate-Bearing Clayey Silt Sediments by Depressurization

Xiaolong Ma,Bing Li,Wei Guo,Youhong Sun,Rui Jia

doi:10.1155/2020/9382058

Abstract

Gas hydrates in the Shenhu area are mainly hosted in clayey silt sediments, which have the relatively high irreducible fluid saturation and gas entry pressure. And then, they will have an impact on gas production from hydrate-bearing clayey silt sediments, which was evaluated by the numerical simulations of SH2 site in Shenhu area in this paper. The results showed that, with the increase in irreducible water saturation and irreducible gas saturation, the amount of water production and gas production was obviously reduced. When the irreducible water saturation increased from 0.10 to 0.50, the cumulative CH4 production volume decreased from 1668799 m3 to 1536262 m3, and the cumulative water production volume dropped from 620304 m3 to 564797 m3, respectively. When the irreducible gas saturation increased from 0.01 to 0.05, the cumulative CH4 production volume dropped from 1812522 m3 to 1622121 m3, and the cumulative water production volume dropped from 672088 m3 to 600617 m3, respectively. In addition, the capillary pressure increased obviously with the increase in gas entry pressure, but the effect on gas production was small and the effect on water production could be negligible. In conclusion, irreducible water and gas saturation had an important effect on the gas production from gas hydrate, whereas the effects of gas entry pressure could be ignored.

Highlights

Natural gas hydrate (NGH) is an ice-like crystalline compound formed by water molecules and natural gas molecules, such as methane, ethane, and propane, under high pressure and low temperature [1]
(1) When the irreducible water saturation decreases from 0.10 to 0.50, the cumulative gas production decreases from 1668799 m3 to 1536262 m3, and the total water production drops from 620304 m3 to 564797 m3, respectively
When the irreducible gas saturation increases, a large number of gas will be trapped in the pores, and the increase in irreducible gas saturation will affect the relative permeability of the gas, so the gas production would decrease with the increase in irreducible gas saturation

Summary

Introduction

Natural gas hydrate (NGH) is an ice-like crystalline compound formed by water molecules and natural gas molecules, such as methane, ethane, and propane, under high pressure and low temperature [1]. NGH is considered one of the potentially clean energies in future, and it is widely distributed in marine sediments and the permafrost regions [2, 3]. It has attracted more and more attentions from researchers all over the world. According to the preliminary estimates, the total amount of energy hosted in the NGH reservoir is two times that of conventional oil and gas resources [4]. Different from the production of oil and natural gas resources, gas hydrate should be decomposed into gas and water at first, which is an endothermic phase transition Because of the characteristics of unconsolidated and permeable overburden layer, submarine hydrate decomposition may cause geological hazards and climate change [5,6,7].

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