The first offshore natural gas hydrate production test in South China Sea

Natural gas hydrates (NGH)is one of key future clean energy resources.Its industrialized development will help remit the huge demand of global natural gas,relieve the increasing pressure of the environment, and play a vital role in the green sustainable growth of human societies.Based on nearly two decades' studying on the reservoir characteristics in the South China Sea (SCS)and the knowledge of reservoir system,the China Geological Survey (CGS)conducted the first production test on an optimal target selected in Shenhu area SCS in 2017.Guided by the "three-phase control"exploitation theory which focused on formation stabilization,technologies such as formation fluid extraction,well drilling and completing, reservoir stimulating,sand controlling,environmental monitoring,monitoring and preventing of secondary formation of hydrates were applied.The test lasted for 60 days from May 10^th when starting to pump, drop pressure and ignite to well killing on July 9^th,with gas production of 3.09×10^5 m^3 in total,which is a world record with the longest continuous duration of gas production and maximal gas yield.This successful test brings a significant breakthrough on safety control of NGH production.

Preliminary results of environmental monitoring of the natural gas hydrate production test in the South China Sea

Natural gas hydrate (NGH)is considered as one of the new clean energy sources of the 21st century with the highest potential.The environmental issues of NGH production have attracted the close attention of scientists in various countries.From May 10 to July 9,2017,the first offshore NGH production test in the South China Sea (SCS)was conducted by the China Geological Survey.In addition,environmental security has also been effectively guaranteed via a comprehensive environmental monitoring system built during the NGH production test.The monitoring system considered sea-surface atmosphere methane and carbon dioxide concentrations,dissolved methane in the sea water column,and the seafloor physical oceanography and marine chemistry environment.The whole process was monitored via multiple means, in multiple layers,in all domains,and in real time.After the production test,an environmental investigation was promptly conducted to evaluate the environmental impact of the NGH production test. The monitoring results showed that the dissolved methane concentration in seawater and the near-seabed environment characteristics after the test were consistent with the background values,indicating that the NGH production test did not cause environmental problems such as methane leakage.

A 3D basin modeling study of the factors controlling gas hydrate accumulation in the Shenhu Area of the South China Sea

Great advancement has been made on natural gas hydrates exploration and test production in the northern South China Sea.However,there remains a lot of key questions yet to be resolved,particularly about the mechanisms and the controls of gas hydrates enrichment.Numerical simulaution would play signficant role in addressing these questions.This study focused on the gas hydrate exploration in the Shenhu Area,Northern South China Sea.Based on the newly obtained borehole and multichannel reflection seismic data,the authors conducted an integrated 3D basin modeling study on gas hydrate.The results indicate that the Shenhu Area has favorable conditions for gas hydrate accumulation,such as temperature,pressure,hydrocarbon source,and tectonic setting.Gas hydrates are most concentrated in the Late Miocene strata,particularly in the structual highs between the Baiyun Sag and the Liwan Sag,and area to the south of it.It also proved the existence of overpressure in the main sag of source rocks,which was subject to compaction disequilibrium and hydrocarbon generation.It also shown that the regional fault activity is not conducive to gas hydrate accumulation due to excess gas seepage.The authors conjecture that fault activity may slightly weaken overpressure for the positive effect of hydrocarbon expulsion and areas lacking regional fault activity have better potential.