Over 90% of the global hydrate resources are stored in very-low-permeability clayey silt reservoirs. The low permeability significantly restricts the efficiency of gas and water flow into the production well. To enhance gas production efficiency in low-permeability hydrate reservoirs, the high-pressure rotating water jets (HPRWJ) technology is proposed to construct near wellbore artificial fractures (NWAFs) in hydrate reservoirs. The HPRWJ avoid the risks of hydraulic fracturing as well as large-scale reservoir damage, which makes it more suitable for constructing fractures in hydrate-bearing sediments (HBS). In this article, the site SH7 in the South China Sea is studied to evaluate the feasibility of this technology for enhancing gas production of low-permeability hydrate reservoirs by numerical simulation. The results show that the gas productivity is increased by approximately three times by using the HPRWJ technology to construct NWAFs with a depth of 3 m. It is suggested that the proposed technology is a promising method for improving gas production from the low-permeability hydrate reservoirs. Furthermore, the gas production performance is closely related to NWAF depth, NWAF permeability, and NWAF spacing. For the site SH7 in the South China Sea, the NWAF depth, permeability, and spacing are recommended as 3 m, 3D, and 3 m, respectively.

The amount of natural gas contained in the world’s gas hydrate accumulations is enormous, but these estimates remain highly speculative. So far, it is still challenging to locate spatial distribution of marine gas hydrate and quantitatively characterize the evaluation parameters and systematic improvement of evaluation systems. Considering the systematic review of the key accumulation factors, such as heat flow, deposition rate and total organic carbon in the typical passive continental margin, the evaluation results of global marine gas hydrate resources were analyzed based on the characteristics of gas hydrate geology, geophysics and geochemistry anomalies in the South China Sea. We analyze the problems on the evaluation of marine gas hydrate resources, probing into the geological characteristics and distribution laws of marine gas hydrate resources in the South China Sea, and estimate the parameters for in-place resource evaluation, in which the volume method based on Monte Carlo probability was used to evaluate the gas hydrate potential resources in the South China Sea. The probability distribution ranges from 37.6 billion (with 90% probability) to 117.7 billion (with 10% probability) tons of oil equivalent, with an expected value of 74.4 billion tons of oil equivalent. The study results show that the gas hydrate resource density in the South China Sea is similar to that in the typical sea areas, and the estimated global resources are basically consistent with the assessment results at this stag; this shows that the South China Sea has great potential for gas hydrate resources. The research results can provide guidance for the evaluation of global climate change and the exploration and development of hydrate resources.

Natural gas hydrates (NGHs) are a new type of clean energy with great development potential. However, it is urgent to achieve safe and economical NGHs development and utilization. This study established a physical model of the study area using the FLAC3D software based on the key parameters of the NGHs production test area in the South China Sea, including the depressurization method, and mechanical parameters of strata, NGHs occurrence characteristics, and the technological characteristics of horizontal wells. Moreover, this study explored the law of influences of the NGHs dissociation range on the stability of the overburden strata and the casing structure of a horizontal well. The results are as follows. With the dissociation of NGHs, the overburden strata of the NGHs dissociation zone subsided and formed funnel-shaped zones and then gradually stabilized. However, the upper interface of the NGHs dissociation zone showed significant redistribution and discontinuity of stress. Specifically, distinct stress concentration and corresponding large deformation occurred in the build-up section of the horizontal well, which was thus prone to suffering shear failure. Moreover, apparent end effects occurred at the end of the horizontal well section and might cause the deformation and failure of the casing structure. Therefore, it is necessary to take measures in the build-up section and at the end of the horizontal section of the horizontal well to prevent damage and ensure the wellbore safety in the long-term NGHs exploitation.

海底甲烷渗漏可能会影响海洋环境,乃至影响全球气候和碳循环,但目前人们对渗漏甲烷在海水中的运动行为了解有限.本文基于水体甲烷释放室内实验,研究了不同甲烷渗漏条件下的甲烷气泡行为及其运动特征.结果显示,甲烷气泡在上浮过程中发生合并、分离和破碎,运动轨迹呈"S"形;气泡尺寸及上浮速度随释放气体流量增大而增大;气泡运动还受水中障碍物影响,具体作用与释放气体流量、障碍物表面粗糙度及形态有关.采用 日本水合物试采数据开展甲烷喷发式释放模拟实验发现,短期释放大量甲烷会引起水流速度和动压力显著增大.此外,水体甲烷吸附实验表明,经白炭黑疏水处理后,活性炭吸附甲烷能力可提高5％.

天然气水合物分布广、埋藏浅、清洁无污染、储量巨大,是极具发展潜力的清洁能源.为实现天然气水合物商业化开采,急需探索基于多分支井的高效开采技术.在使用TOUGH+HYDRATE模拟器开展数值模拟中,复杂结构井建模是研究工作的难点.为此提出了基于mVIEW的复杂结构井快速建模方法,以多分支井为例简要介绍了建模流程;此外,结合TOUGH+HYDRATE模拟器,以中国地质调查局2017年在南海北部陆坡深水区白云凹陷神狐海域SHSC-4试采井测井曲线数据为基础,建立理想水合物藏分层地质模型,开展单一水平井和多分支井在水合物Ⅱ层中部的降压开采数值模拟.模拟结果表明:该建模方法提高了模拟器在复杂建模方面的能力,对天然气水合物高效开采数值模拟具有较好效果和参考意义;相较于单一水平井降压开采,多分支井开采技术能最大限度地增加天然气水合物藏的裸露面积和深度,有效提高水合物藏储量动用程度,是值得探索的高效开采技术方法.

深海溶解甲烷浓度数据连续获取的方法技术,对于海洋环境和天然气水合物开发过程中甲烷扩散作用及通量的动态监测,具有重要的科学意义和实际应用价值.本文较详细地介绍了依据“海水脱气、气体样品定量输入、电化学高精度检测”技术思路,采用“增压排液整机系统控制的海水循环、减压稳流、气液分离、烃类组分高精度检测技术改进”方法,研发“深海甲烷电化学原位长期监测技术”的关键环节和技术方法.结合原位传感器在胶州湾港口为期94天底水长期监测实验获取的数据成果,对原位传感器的技术性能、数据质量、地质效果进行了研究评价.结果 表明:①原位传感器量程甲烷指标达到0.01～ 10000 nmol/L,灵敏度达到0.01 nmol/L,对烃类组分检测具有较好的稳定性和选择性;②监测水域溶解甲烷数值范围19.01～106.87 nmol/L,正常甲烷背景32.41 nmol/L,局部异常甲烷背景80.60 nmol/L,资料显示异常与污水排放过程对海水环境污染有关;③实测甲烷数据成果地球化学特征与胶州湾海域海水环境以往调查研究成果符合,证明了实测数据的客观性和科学性;④海试监测试验成果证明,原位传感器测试性能可靠、结构设计合理、设计思路科学,基本具备了海洋科学调查中对海水甲烷浓度数据获取的能力,在未来海洋天然气水合物开发过程中对甲烷扩散作用的动态监测及深海甲烷浓度通量的长期监测中,具有实际应用价值和科学意义.

Dongting Lake Basin has the conditions for forming biogenic gas reservoirs of certain scales.For the exploration of biogenic gas resources,the authors carried out a comprehensive exploration work mainly based on geochemical methods during the period of 2013 ～ 2016,and conducted fairly systematic surface sediments survey.Geochemical exploration covered an area of 2060 km2,and collected 1498 samples.All the samples were tested by in situ headspace gas (free hydrocarbon),indoor acidolysis hydrocarbon and a small quantity of methane isotope indexes.The results are as follows:1.The geochemical anomaly of methane in the Dongting Lake basin is composed of free hydrocarbon (headspace gas) and adsorbed hydrocarbon (acid hydrolysis hydrocarbon).The free hydrocarbon is a dynamic reflection of the existing underground biogenic gas,and the hydrocarbon accumulation of the acidolysis hydrocarbon is related to the distribution of the paleo-channel.2.The Dongting Lake basin is the area of a high background and high anomaly of methane,and the distribution of the abnormal area is basically consistent with the distribution of the Quaternary fault basin,especially in Yuanjiang sag.3.Acidolysis hydrocarbon anomaly of the Heba Town,bead-like anomaly in NE direction and southeastern secondary local anomalies form a ring anomaly zone surrounding the Yuanjiang sag,which means that the sag may be the potential supply area of biogenic gas in Dongting Lake basin.4.The area of Qingshuzuie-Heba Town north of Yuanjiang sag is the abnormal high value area of the hydrocarbon methane in Dongting Lake Basin,and this is the direct reflection of natural gas seepage in shallow surface.The high value of acidolysis hydrocarbon methane surrounds the anomaly area of free hydrocarbon methane in Qingshuzui,which constitutes the best combinational hydrocarbon reservoir model.The area of Qingshui-Haba Town is the'chimney'of the biogenic gas underlying the Dongting Lake Basin and hence the most hopeful breakthrough area for biogas survey in the Dongting Lake Basin.

洞庭盆地地处湘西古生界边缘,经历了中生代晚白垩世盆地基本成型和新生代断块运动为主的两期构造旋回,为终成于燕山(中生代)延续于喜马拉雅(新生代)的断陷盆地.盆内局部凹陷白垩系之上存在着持续砂泥岩沉积及第四纪河流湖泊相现代沉积,具备了形成一定规模生物气藏的地质条件.2013-2015年笔者通过洞庭盆地浅层沉积物系统地球化学勘探,基本搞清了盆地内渗漏甲烷气体异常的分布状况.根据各指标地球化学异常特征,发现洞庭盆地北部沅江凹陷北部斜坡、青树嘴—河坝镇一带是洞庭盆地内生物气资源最有可能突破的远景区.为了追索渗漏甲烷气体来源,深化地球化学异常解释评价以及浅层生物气系统研究,2015-2016年在发现的生物气远景区,部署完成5条广域电磁测深和两条汞气测量剖面.本研究旨在通过实测地球物理和地球化学综合剖面的对比研究,揭示本区第四系构造分布和地球化学异常机制,为洞庭盆地生物气资源远景和气藏靶区的预测划分提供科学依据,也为勘探第四系生物气资源方法技术的选择提供了建议.勘探成果表明:(1)本区第四系能够满足生物气系统“生储盖”条件,具有生物气资源潜力;(2)沉积物游离烃甲烷地球化学异常是下伏第四系内气体聚集沿断裂带或沉积层向表层渗漏运移所致.酸解烃指标是识别有利于生物气体生储环境的敏感因子之一;(3)洞庭盆地工区西北部,P2剖面南段和P2线北部与P3、P4剖面交汇区域,具有良好的“自生自储”型生物气藏资源远景,是本区勘探生物资源天然气最有希望的靶区;(4)洞庭湖北部工区东部,P6测线南部接近沅江凹陷中心的四季红一带,是本区寻找“自生自储”和“下生上储”型气藏的有利地带和资源远景区;(5)浅层沉积物地球化学勘探,有利于发现与生物气有关的气体渗漏、评价下伏沉积体系特性、缩小地球物理勘探靶区.地球化学与广域电磁剖面测量的结合是勘探生物成因天然气经济快速的方法技术.

Based on the analysis of in-situ detection technology of ocean floor seawater in China and abroad,this article introduces a self-developed product used in the ir-situ measurement of water-soluble methane,and elaborates on the research idea,key technical points and differences from technology used abroad.We have collected a large amount of data of water-soluble methane in the north of the South China Sea,including in the surface and bottom seawaters,and in-situ exploratory data by our own product.Aimed at providing a reference for the geochemical prospecting of marine gas hydrate,we have compared the geochemical characteristics of stratified seawater-mainly about methane concentration,analyzed different seawater detection technologies and evaluated their significance when used as important indicators in gas hydrate exploration.The results show that:(1) there is a medium level methane concentration of about 10-50 nmol · L-1 and a large area of methane geochemical anomaly (＞1000 km2) of surface seawater in the gas hydrate prospect areas;(2) the bottom seawater has a certain regional methane geochemical anomaly and the methane anomaly background value is above 100 nmol · L-1;and (3) the in-situ detection of bottom seawater has an extra-high level methane concentration of about 300-800 nmol · L-1 in the hydrate bearing area.The achievements of the exploration technologies in fluid geochemistry reveal that:(1) the methane anomaly obtained from surface seawater by the conventional techniques and CTD are helpful for finding the exploration prospect areas of gas hydrate;and (2) the methane anomaly of bottom seawater detected by in-situ online and core top seawater has a strong correlation with hydrocarbon seepage below the seafloor,and the isotopic characteristics indicate that we can seek out and identify methane seepage zone related to gas hydrate through biogenic methane.We believe the in-situ geochemical exploration technology has a promising prospect of application in finding marine gas hydrate.

We analyzed a number of samples from the typical drilling sites of ODP/IODP and by means of correlation of the collected data.We studied the geological process and geochemical characteristics in the formation of various free hydrocarbon and their relevant indicators,and studied the relationship between the acidolysis hydrocarbon,the composition of the surrounding rock,the authigenic carbonate during the sedimentation and the turbidite and the related geochemical features.Based on these,it provides us a new scientific method to find out the exact location of gas hydrate stable zone (GHSZ).The results show that,(1) The free methane anomaly in the underlying formation reflects that there is dynamic methane in the pores of the gas hydrate stable zone.In the deep gas hydrate stable zone there are two types of specific models of free hydrocarbon index anomaly appeared due to the differences in testing methods and the state of sediments;(2) Acidolysis hydrocarbon is closely related to the methane adsorption ability of the formation and the componental properties of the surrounding rock.Corresponding to the best hydrate occurrence conditions of the authigenic carbonates and turbidites the relation of acidolysis hydrocarbon is characteristic of significantly quantified anomaly;(3) In the process of hydrate formation,methane flux promotes the anaerobic methane oxidation (AMO) and the formation of authigenic carbonates.The acidolysis hydrocarbon is prominently corresponding to the near-surface authigenic carbonate which makes up the deficiency of multiple sources and multiple solutions of free hydrocarbon methane anomaly in shallow sediments;(4) The anomaly patterns of free hydrocarbon methane and the quantitative anomaly distribution of acidolysis hydrocarbon methane are the comprehensive response for the GHSZ and the favorite occurrence conditions of hydrates and can provide the basis for the determination of the gas hydrate stable zone and the hydrate accumulation in the zone.

近年来,海水中溶解甲烷的探测技术成为国内外学者的研究热点.与传统的实验室利用气相色谱法检测离散海水甲烷浓度的方法相比,基于膜脱气技术的METS甲烷传感器具有体积小、操作简便、原位实时连续观测等特点,并且可与其他化学、物理传感器集为一体进行甲烷探测.主要介绍了METS传感器的基本原理、特点,给出了技术指标和规格参数,分析了其性能制约因素与校正方法,并总结了METS传感器在性能测试、麻坑成因、潮汐作用机理等方面的应用成果.

In many kinds of geochemical exploration methods such as acidolysis hydrocarbon, dissolved hydrocarbon and thermally re?leased hydrocarbon, the geochemical pretreatment of the sample is very important. Nevertheless, China?s sample retreatment technique remains at the stage of manual operation, which does not match the widely used high?precision analytical instruments. On the basis of researches on the intelligent?control geochemical sample pretreatment system, this paper deals with in detail the working mechanism, control structures, implementation methods, performance indexes and quality inspection results of this system, and describes the appli?cation achievements in gas hydrate exploration with acidolysis hydrocarbon methods in ODP204 and dissolved hydrocarbon methods in Dongsha area, the South China Sea. Practices have proved that the intelligent?control system is capable of completing the geochemical sample pretreatment work under the automatic condition, and has properties of fastness, precision, safety and portableness. It has promising application prospect in China?s marine gas hydrates exploration and terrestrial petroleum geochemical exploration, and also has great significance for improving China?s geochemical sample pretreatment equipment techniques.