Marine gas hydrates (MGHs), which have great potential for exploitation and utilization, account for around 99% of all global natural gas hydrate resources under current prospecting technique. However, there are several potential hazards associated with their production and development. These are classified into four categories by this paper: marine geohazards, greenhouse gas emissions, marine ecological hazards, and marine engineering hazards. In order to prevent these risks from occurring, the concept of “lifecycle management of hazards prevention” during the development and production from MGHs is proposed and divided into three stages: preparation, production control, and post-production protection. Of these stages, economic evaluation of the resource is the foundation; gas production methods are the key; with monitoring, assessment, and early warning as the guarantee. A production test in the Shenhu area of the South China Sea shows that MGH exploration and development can be planned using the “three-steps” methodology: commercializing and developing research ideas in the short term, maintaining economic levels of production in the medium term, and forming a global forum to discuss effective MGH development in the long term. When increasing MGH development is combined with the lifecycle management of hazards prevention system, and technological innovations are combined with global cooperation to solve the risks associated with MGH development, then safe access to a new source of clean energy may be obtained.

A thin coal seam mined as a protective coal seam above a gas outburst coal seam plays a central role in decreasing the degree of stress placed on a protected seam, thus increasing gas permeability levels and desorption capacities to dramatically eliminate gas outburst risk for the protected seam. However, when multiple layers of coal seams are present, stress-relieved gas from adjacent coal seams can cause a gas explosion. Thus, the post-drainage of gas from fractured and de-stressed strata should be applied. Comprehensive studies of gas permeability evolution mechanisms and gas seepage rules of protected seams close to protective seams that occur during protective seam mining must be carried out. Based on the case of the LongWall (LW) 23209 working face in the Hancheng coal mine, Shaanxi Province, this paper presents a seepage model developed through the FLAC3D software program (version 5.0, Itasca Consulting Group, Inc., Minneapolis, MI, USA) from which gas flow characteristics can be reflected by changes in rock mass permeability. A method involving theoretical analysis and numerical simulation was used to analyze stress relief and gas permeability evolution mechanisms present during broken rock mass compaction in a goaf. This process occurs over a reasonable amount of extraction time and in appropriate locations for comprehensive gas extraction technologies. In using this comprehensive gas drainage technological tool, the safe and efficient co-extraction of thin coal seams and gas resources can be realized, thus creating a favorable environment for the safe mining of coal and gas outburst seams.

In coal mines, underground reservoir systems can increase the availability of water and are an effective technical approach for the protection and utilization of water resources. The stability of coal pillar dams is the key factor in the safety and stability of these underground water storage systems. However, coal pillar dams must operate in complex environments that combine dynamic-static superimposed stress fields and water immersion; moreover, coal pillar dams subjected to both stress and seepage are more susceptible to damage and even collapse. In this study, a seepage-stress coupling model of a coal pillar dam was constructed using the Universal Distinct Element Code (UDEC) simulation software. This model provides a platform for analyzing the characteristics of fracture development in surrounding rock in active mines and the coupled development of crack fields and seepage fields in coal pillar dams. Methods were developed for (1) calculating the water content for the coal pillar dam numerical simulation model and (2) reducing water immersion weakening. The maximum seepage width of a coal pillar dam subjected to water immersion was obtained, and a damage and failure evolution mechanism for coal pillar dams experiencing flooding was developed. The results provide a scientific basis for enhancing the stability control of coal pillar dams and are of great significance for realizing water conservation in coal mines.