Depressurization and heat injection are viewed as the main methods to be used in natural gas hydrate(NGH)exploitation.However,these methods have limitations,such as low energy-utilization efficiency or a limited extra...Depressurization and heat injection are viewed as the main methods to be used in natural gas hydrate(NGH)exploitation.However,these methods have limitations,such as low energy-utilization efficiency or a limited extraction range,and are still far from commercial exploitation.In this work,we propose a potential commercial method to exploit NGHs by effectively using geothermal energy inside deep reservoirs.Specifically,a loop well structure is designed to economically extract geothermal energy.Based on an analysis of our developed model,when the looping well is coupled with depressurization,the profits of high NGH production can surpass the drilling costs of extracting geothermal energy.Moreover,as the temperature of fluids from the geothermal layer exceeds 62℃,the fluid heat is mainly consumed by the rock matrix of the hydrate formation,instead of promoting NGH dissociation.Based on this threshold temperature,a loop well drilled to a depth of about 4000 m for hydrate sediment in the Shenhu area of the South China Sea would be able to efficiently extract geothermal energy,leading to an approximate73%increase in gas production in comparison with conventional depressurization.An economic analysis suggests that our proposed method can reduce the exploitation cost of methane to 0.46 USD·m^(-3).Furthermore,as the hydrate saturation increases to 0.5,the exploitation cost can be further reduced to 0.14 USD·m^(-3).Overall,a looping well coupled with geothermal energy and depressurization is expected to pave the way for commercial NGH exploitation.展开更多
Sand production is one of the main obstacles restricting gas extraction efficiency and safety from marine natural gas hydrate(NGH)reservoirs.Particle migration within the NGH reservoir dominates sand production behavi...Sand production is one of the main obstacles restricting gas extraction efficiency and safety from marine natural gas hydrate(NGH)reservoirs.Particle migration within the NGH reservoir dominates sand production behaviors,while their relationships were rarely reported,severely constrains quantitative evaluation of sand production risks.This paper reports the optical observations of solid particle migration and production from micrometer to mesoscopic scales conditioned to gravel packing during depressurization-induced NGH dissociation for the first time.Theoretical evolutionary modes of sand migration are established based on experimental observations,and its implications on field NGH are comprehensively discussed.Five particle migration regimes of local borehole failure,continuous collapse,wormhole expansion,extensive slow deformation,and pore-wall fluidization are proved to occur during depressurization.The types of particle migration regimes and their transmission modes during depressurization are predominantly determined by initial hydrate saturation.In contrast,the depressurization mainly dominates the transmission rate of the particle migration regimes.Furthermore,both the cumulative mass and the medium grain size of the produced sand decrease linearly with increasing initial methane hydrate(MH)saturation.Discontinuous gas bubble emission,expansion,and explosion during MH dissociation delay sand migration into the wellbore.At the same time,continuous water flow is a requirement for sand production during hydrate dissociation by depressurization.The experiments enlighten us that a constitutive model that can illustrate visible particle migration regimes and their transmission modes is urgently needed to bridge numerical simulation and field applications.Optimizing wellbore layout positions or special reservoir treatment shall be important for mitigating sand production tendency during NGH exploitation.展开更多
Gas hydrates now are expected to be one of the most important future unconventional energy resources. In this paper, researches on gas hydrate exploitation in laboratory and field were reviewed and discussed from the ...Gas hydrates now are expected to be one of the most important future unconventional energy resources. In this paper, researches on gas hydrate exploitation in laboratory and field were reviewed and discussed from the aspects of energy efficiency. Different exploiting methods and different types of hydrate reservoir were selected to study their effects on energy efficiencies. Both laboratory studies and field tests have shown that the improved technologies can help to increase efficiency for gas hydrate exploitation. And it also showed the trend that gas hydrate exploitation started to change from permafrost to marine. Energy efficiency ratio （EER） and energy return on energy invested （EROI） were introduced as an indicator of efficiency for natural gas hydrate exploitation. An energy-efficient hydrate production process, called ＂Hydrate Chain Energy System （HCES）＂, including treatment of flue gas, replacement of CH4 with CO2, separation of CO2 from CH4, and storage and transportation of CH4 in hydrate form, was proposed for future natural gas hydrate exploitation. In the meanwhile, some problems, such as mechanism of C02 replacement, mechanism of CO2 separation, CH4 storage and transportation are also needed to be solved for increasing the energy efficiency of gas hydrate exploitation.展开更多
As a new clean energy resource in the 21st century,natural gas hydrate is considered as one of the most promising strategic resources in the future.This paper,based on the research progress in exploitation of natural ...As a new clean energy resource in the 21st century,natural gas hydrate is considered as one of the most promising strategic resources in the future.This paper,based on the research progress in exploitation of natural gas hydrate(NGH)in China and the world,systematically reviewed and discussed the key issues in development of natural gas hydrate.From an exploitation point of view,it is recommended that the concepts of diagenetic hydrate and non-diagenetic hydrate be introduced.The main factors to be considered are whether diagenesis,stability of rock skeleton structure,particle size and cementation mode,thus NGHs are divided into 6 levels and used unused exploitation methods according to different types.The study of the description and quantitative characterization of abundance in hydrate enrichment zone,and looking for gas hydrate dessert areas with commercial exploitation value should be enhanced.The concept of dynamic permeability and characterization of the permeability of NGH by time-varying equations should be established.The‘Three-gas co-production’(natural gas hydrate,shallow gas,and conventional gas)may be an effective way to achieve early commercial exploitation.Although great progress has been made in the exploitation of natural gas hydrate,there still exist enormous challenges in basic theory research,production methods,and equipment and operation modes.Only through hard and persistent exploration and innovation can natural gas hydrate be truly commercially developed on a large scale and contribute to sustainable energy supply.展开更多
基金supported by the National Natural Science Foundation of China(52288101,51991360,and U21B2069)。
文摘Depressurization and heat injection are viewed as the main methods to be used in natural gas hydrate(NGH)exploitation.However,these methods have limitations,such as low energy-utilization efficiency or a limited extraction range,and are still far from commercial exploitation.In this work,we propose a potential commercial method to exploit NGHs by effectively using geothermal energy inside deep reservoirs.Specifically,a loop well structure is designed to economically extract geothermal energy.Based on an analysis of our developed model,when the looping well is coupled with depressurization,the profits of high NGH production can surpass the drilling costs of extracting geothermal energy.Moreover,as the temperature of fluids from the geothermal layer exceeds 62℃,the fluid heat is mainly consumed by the rock matrix of the hydrate formation,instead of promoting NGH dissociation.Based on this threshold temperature,a loop well drilled to a depth of about 4000 m for hydrate sediment in the Shenhu area of the South China Sea would be able to efficiently extract geothermal energy,leading to an approximate73%increase in gas production in comparison with conventional depressurization.An economic analysis suggests that our proposed method can reduce the exploitation cost of methane to 0.46 USD·m^(-3).Furthermore,as the hydrate saturation increases to 0.5,the exploitation cost can be further reduced to 0.14 USD·m^(-3).Overall,a looping well coupled with geothermal energy and depressurization is expected to pave the way for commercial NGH exploitation.
基金supported by the Laoshan Laboratory(No.LSKJ LSKJ202203506)the Taishan Scholars Program,and the National Natural Science Foundation of China(Grant No.41976074).
文摘Sand production is one of the main obstacles restricting gas extraction efficiency and safety from marine natural gas hydrate(NGH)reservoirs.Particle migration within the NGH reservoir dominates sand production behaviors,while their relationships were rarely reported,severely constrains quantitative evaluation of sand production risks.This paper reports the optical observations of solid particle migration and production from micrometer to mesoscopic scales conditioned to gravel packing during depressurization-induced NGH dissociation for the first time.Theoretical evolutionary modes of sand migration are established based on experimental observations,and its implications on field NGH are comprehensively discussed.Five particle migration regimes of local borehole failure,continuous collapse,wormhole expansion,extensive slow deformation,and pore-wall fluidization are proved to occur during depressurization.The types of particle migration regimes and their transmission modes during depressurization are predominantly determined by initial hydrate saturation.In contrast,the depressurization mainly dominates the transmission rate of the particle migration regimes.Furthermore,both the cumulative mass and the medium grain size of the produced sand decrease linearly with increasing initial methane hydrate(MH)saturation.Discontinuous gas bubble emission,expansion,and explosion during MH dissociation delay sand migration into the wellbore.At the same time,continuous water flow is a requirement for sand production during hydrate dissociation by depressurization.The experiments enlighten us that a constitutive model that can illustrate visible particle migration regimes and their transmission modes is urgently needed to bridge numerical simulation and field applications.Optimizing wellbore layout positions or special reservoir treatment shall be important for mitigating sand production tendency during NGH exploitation.
基金supported by the National Natural Science Foundation of China (51176051 and 51106054)the Fundamental Research Funds for the Central University (2015ZM057, 2013ZZ0032 and 2014ZP0007)+1 种基金China Postdoctoral Science Foundation (2015M572321)the Petro China Innovation Foundation (2013D-5006-0107)
文摘Gas hydrates now are expected to be one of the most important future unconventional energy resources. In this paper, researches on gas hydrate exploitation in laboratory and field were reviewed and discussed from the aspects of energy efficiency. Different exploiting methods and different types of hydrate reservoir were selected to study their effects on energy efficiencies. Both laboratory studies and field tests have shown that the improved technologies can help to increase efficiency for gas hydrate exploitation. And it also showed the trend that gas hydrate exploitation started to change from permafrost to marine. Energy efficiency ratio （EER） and energy return on energy invested （EROI） were introduced as an indicator of efficiency for natural gas hydrate exploitation. An energy-efficient hydrate production process, called ＂Hydrate Chain Energy System （HCES）＂, including treatment of flue gas, replacement of CH4 with CO2, separation of CO2 from CH4, and storage and transportation of CH4 in hydrate form, was proposed for future natural gas hydrate exploitation. In the meanwhile, some problems, such as mechanism of C02 replacement, mechanism of CO2 separation, CH4 storage and transportation are also needed to be solved for increasing the energy efficiency of gas hydrate exploitation.
文摘As a new clean energy resource in the 21st century,natural gas hydrate is considered as one of the most promising strategic resources in the future.This paper,based on the research progress in exploitation of natural gas hydrate(NGH)in China and the world,systematically reviewed and discussed the key issues in development of natural gas hydrate.From an exploitation point of view,it is recommended that the concepts of diagenetic hydrate and non-diagenetic hydrate be introduced.The main factors to be considered are whether diagenesis,stability of rock skeleton structure,particle size and cementation mode,thus NGHs are divided into 6 levels and used unused exploitation methods according to different types.The study of the description and quantitative characterization of abundance in hydrate enrichment zone,and looking for gas hydrate dessert areas with commercial exploitation value should be enhanced.The concept of dynamic permeability and characterization of the permeability of NGH by time-varying equations should be established.The‘Three-gas co-production’(natural gas hydrate,shallow gas,and conventional gas)may be an effective way to achieve early commercial exploitation.Although great progress has been made in the exploitation of natural gas hydrate,there still exist enormous challenges in basic theory research,production methods,and equipment and operation modes.Only through hard and persistent exploration and innovation can natural gas hydrate be truly commercially developed on a large scale and contribute to sustainable energy supply.
