我省海西州木里冻土区发现“可燃冰”

日前,中国地质调查局、中国地质科学院和青海煤炭地质局一0五队,共同承担的青藏高原冻土带天然气水合物勘查项目,在我省木里煤田聚乎更矿区常年冻土区以T200多米的钻孔中发现并成功提取俗称“可燃冰”的天然气水合物,这是我国首次在大陆发现并提取天然气水合物,     

琼东南盆地中央峡谷天然气水合物成藏模式

琼东南盆地是天然气水合物勘查开发先导示范区.选取琼东南盆地中央峡谷为研究对象,基于地球化学分析、地震资料解释和天然气水合物成藏条件等资料,分析天然气水合物成藏模式.结果表明:琼东南盆地天然气水合物的气源具有"热成因气为主、混合成因气为辅"的特征,主力气源岩具备充足的供烃能力.研究区发育的"通源连储"断裂、气烟囱—泥底辟—麻坑、海底滑塌体构成主要运移输导体系和储集体,在水合物形成聚集过程中具有重要控制作用,其中气烟囱为高效运移输导体,是有利勘查目标.琼东南盆地中央峡谷气田天然气水合物成藏模式为热成因气型渗漏型、渗漏—砂体复合型和生物成因气型扩散型3种.该结果为琼东南盆地天然气水合物资源评价和勘查提供参考.     

青海乌丽冻土区冷泉水溶烃对形成天然气水合物的指示意义

针对深处青藏高原腹地中低纬度高海拔(4 600~5 300m)永冻土地带的青海乌丽地区,开展了该地区天然气水合物形成的气源条件研究。冻土区地表沿断层发育若干冷泉,野外采集冷泉新鲜水500mL密封送实验室进行气相色谱分析。首先对水中溶解的烃在真空和60℃恒温条件下脱出气体,将脱出气体经ρ(NaOH)=300g/L的碱液吸收CO₂,余下气体经碱液驱赶至量气管上端,计量脱出气体的体积,并转移至另处;然后根据溶解烃含量注入适当体积的脱出气体进行色谱标定、单点外标定量。结果在冷泉中检测出CH₄体积分数一般在223.60~1 097.30 μL/L之间,最高达1 113.21 μL/L。野外工作查明烃源岩主要为上二叠统那益雄组含煤碎屑岩建造,次为上三叠统巴贡组碎屑岩。前者中赋存的煤层及炭质泥岩为天然气水合物气源供给的重要母质。此研究成果揭示该地区具备形成天然气水合物藏的良好气源条件及成藏潜力。      

海底泥底辟(泥火山)对天然气水合物成藏的影响

海底泥底辟(泥火山)与周缘发育的天然气水合物存在着密切的关联,表现在静态要素和动态成藏2个方面。作为一种重要而有效的运移通道类型,泥底辟(泥火山)携带的气体将是天然气水合物的重要气体来源。同时,含气流体沿着泥底辟(泥火山)的上侵,可能会导致上覆地层中温压场和地球化学组分的改变,进而引起天然气水合物稳定带厚度的变化。因此,泥底辟(泥火山)将控制天然气水合物的成藏,如位于构造中心部位的矿物低温热液成藏模式和位于构造边缘的矿物交代成藏模式。另一方面,泥底辟(泥火山)的不同演化阶段将对天然气水合物的形成和富集产生不同的影响。早期阶段,泥底辟(泥火山)形成的运移通道可能并未延伸到天然气水合物稳定带,导致气源供给不够充分;中期阶段,天然气水合物成藏条件匹配良好,利于天然气水合物的生成;晚期阶段,泥火山喷发带来的高热量含气流体引起天然气水合物稳定带的热异常,可能导致天然气水合物的分解,直至泥火山活动平静期,天然气水合物再次成藏。      

南堡凹陷天然气成藏模式及其主控因素

为研究南堡凹陷天然气成藏分布规律,在天然气藏类型及分布特征研究的基础上,分析天然气分布与成藏条件之间空间匹配关系,研究南堡凹陷天然气成藏模式及其主控因素.结果表明:南堡凹陷天然气存在4种成藏模式:源内断裂输导中—浅层断层圈闭天然气成藏模式,天然气聚集层位受输导断裂与馆陶组三段火山岩盖层配置和储层发育共同控制;源内断裂输导中—深层断层圈闭天然气成藏模式,天然气聚集层位受输导断裂与东营组二段泥岩盖层配置控制;源内断裂输导深—浅层断层圈闭天然气成藏模式,天然气聚集层位受储层发育和源岩供给程度共同控制;源外边部断裂输导深层断层圈闭天然气成藏模式,天然气聚集层位受储层发育和源岩供给程度共同控制.该结论对指导南堡凹陷天然气勘探具有指导意义.     

柴达木盆地昆北油田成藏主控因素分析

通过对柴达木盆地昆北油田成藏地质条件及成藏过程的系统深入研究,结合近几年该区石油勘探实践经验,总结出其油气形成主要受到6种因素的控制:①紧邻主力生烃凹陷;②持续隆起的古构造背景;③断裂-不整合良好的输导体系;④广泛发育各类优质储层;⑤储盖组合配置良好;⑥发育多种类型圈闭.这六种主控因素在时间、空间上的有利匹配,共同决定了昆北油田油气藏的形成与分布.     

天然气水合物开采储层出砂研究进展与思考

天然气水合物开采井眼出砂问题是当前水合物产业化急需突破的瓶颈之一,解决水合物开采时防砂与产能平衡问题是实现水合物安全高效、长期可控开采的关键.我国海域典型水合物储层属于弱固结的低渗泥质粉砂储层,其面临的防砂控泥与增产矛盾较为突出.厘清不同水合物储层和开采条件下的井眼出砂规律并揭示其机理,进而制定科学合理的防砂控泥措施以实现产能最大化是解决上述矛盾的途径所在.从理论分析、数值模拟、室内实验和现场试采4个角度介绍了世界范围内已开展的水合物出砂防砂情况,分析总结了水合物储层出砂影响因素及出砂机理,最后探讨了目前出砂研究存在的问题和挑战,并给出了相应的建议,旨在为后续水合物开采井眼出砂预测和防控研究提供思路和参考.     

英台断陷火山岩气藏特征及有利区预测

基于英台断陷深部火山岩气藏的烃源岩及储层特征,分析火山岩气藏源/储品质、耦合关系、输导体系和气藏特征等,研究成藏主控因素和成藏规律,预测研究区天然气勘探有利区.结果表明,英台断陷火山岩气藏存在下生上储和侧生侧储两种类型,其中下生上储型主要发育于大屯地区,主要以断裂为输导通道沟通沙河子组源岩,沟通源储的断裂控制气藏的分布;侧生侧储型主要发育于五棵树地区,成藏的关键在于火山岩储层能否在侧向上与营城组二段有效烃源岩直接相连,对接面处易于气藏的形成,且气藏规模大、丰度高,随着天然气运移距离的增加,气藏规模和丰度逐渐降低.该成果有助于认识英台断陷火山岩气藏及剩余资源的分布,确定勘探有利区.     

天然气水合物储层地震波振幅属性研究

以实际水合物存在的美国布莱克海台地震数据为例,利用地震剖面中4个层位(海底层、水合物顶层、水合物层和游离气层)地震数据进行了地震属性的提取及属性分析,研究了各层位的属性特征。结果表明:均方根振幅、平均绝对振幅、平均能量变化、振幅峰态、绝对振幅积分、总能量、功率谱最大值、有限带宽能量等8种属性值在各层位的分布情况基本相同,即海底最高,其余依次是水合物层、游离气层和水合物顶层,可区分出水合物层和游离气层。由此,通过对比各层位的振幅属性值,可以指示天然气水合物的存在,为水合物识别及其开采提供参考依据。     

西湖凹陷中央反转带中北部天然气高效成藏主控因素及富集规律

西湖凹陷中央反转带中北部大型气田成藏因素及动态匹配关系至今不明。通过针对烃源岩、储层、输导体系及成藏期等成藏关键因素进行系统分析,建立"源-储-圈-输"的动态成藏过程分析中央反转带中北部大气田的成藏主控因素。研究表明始新统宝石组与平湖组煤系烃源岩不仅生气强度大,而且中新世晚期以来的快速生、排气为中央反转带中北部的大中型天然气藏提供了充足油气源;花港组小于4 000 m地层的酸性地层水是形成有利储层的关键;中新世晚期发生的龙井运动强烈挤压作用使中央反转带发生了构造变形和断层开启活动,为圈闭和油气输导通道的形成创造了条件。综合"源-储-圈-输"分析认为成藏主控因素在生烃期的有机耦合造就了始新统煤系烃源岩高效生气及天然气的有效运移聚集成藏的全过程。本次研究为研究区大气田的勘探提供了借鉴。      

Heat calculation and numerical simulation in steam mining of permafrost gas hydrate

Steam mining method was injecting hot steam into the borehole to heat the hydrate strata at the same time of depressurization mining,which could promote further decomposition and expand mining areas of gas hydrate. Steam heat calculation would provide the basis for the design of heating device and the choice of the field test parameters. There were piping heat loss in the process of mining. The heat transfer of steam flowing in the pipe was steady,so the heat loss could be obtained easily by formula calculation. The power of stratum heating should be determined by numerical simulation for the process of heating was dynamic and the equations were usually nonlinear. The selected mining conditions were 500-millimeter mining radius,10 centigrade mining temperature and 180 centigrade steam temperature. Heat loss and best heating power,obtained by formula calculation and numerical simulation,were 21. 35 W/m and 20 kW.     

巴麦地区石炭系小海子组储层特征及控制因素分析

在岩心观察、铸体薄片、扫描电镜资料分析的基础上,结合孔隙度、渗透率等物性资料,分析巴麦地区石炭系小海子组储层特征及控制因素.结果表明:该组的储集层岩石类型中,白云岩储层物性较灰岩好,而颗粒灰(云)岩物性也较非颗粒灰(云)岩好;储集空间类型以粒间溶孔、粒内溶孔和晶间溶孔为主;沉积相带、成岩作用及构造作用等是影响研究区储层物性的重要条件,其中高能的台地滩相储集岩是有利储层的发育地带,大气淡水暴露溶蚀作用和白云岩化作用改善了储集空间,构造破裂作用所产生的裂缝使储层物性得到进一步改善.该研究对认识巴麦地区小海子组储层特征及主控因素有参考意义.     

Estimation of potential distribution of gas hydrate in the northern South China Sea

Gas hydrate research has significant importance for securing world energy resources, and has the potential to produce considerable economic benefits. Previous studies have shown that the South China Sea is an area that harbors gas hydrates. However, there is a lack of systematic investigations and understanding on the distribution of gas hydrate throughout the region. In this paper, we applied mineral resource quantitative assessment techniques to forecast and estimate the potential distribution of gas hydrate resources in the northern South China Sea. However, current hydrate samples from the South China Sea are too few to produce models of occurrences. Thus, according to similarity and contrast principles of mineral outputs, we can use a similar hydrate-mining environment with sufficient gas hydrate data as a testing ground for modeling northern South China Sea gas hydrate conditions. We selected the Gulf of Mexico, which has extensively studied gas hydrates, to develop predictive models of gas hydrate distributions, and to test errors in the model. Then, we compared the existing northern South China Sea hydrate-mining data with the Gulf of Mexico characteristics, and collated the relevant data into the model. Subsequently, we applied the model to the northern South China Sea to obtain the potential gas hydrate distribution of the area, and to identify significant exploration targets. Finally, we evaluated the reliability of the predicted results. The south seabed area of Taiwan Bank is recommended as a priority exploration target. The Zhujiang Mouth, Southeast Hainan, and Southwest Taiwan Basins, including the South Bijia Basin, also are recommended as exploration target areas. In addition, the method in this paper can provide a useful predictive approach for gas hydrate resource assessment, which gives a scientific basis for construction and implementation of long-term planning for gas hydrate exploration and general exploitation of the seabed of China.     

Estimation of potential distribution of gas hydrate in the northern South China Sea

Gas hydrate research has significant importance for securing world energy resources, and has the potential to produce considerable economic benefits. Previous studies have shown that the South China Sea is an area that harbors gas hydrates. However, there is a lack of systematic investigations and understanding on the distribution of gas hydrate throughout the region. In this paper, we applied mineral resource quantitative assessment techniques to forecast and estimate the potential distribution of gas hydrate resources in the northern South China Sea. However, current hydrate samples from the South China Sea are too few to produce models of occurrences. Thus, according to similarity and contrast principles of mineral outputs, we can use a similar hydrate-mining environment with sufficient gas hydrate data as a testing ground for modeling northern South China Sea gas hydrate conditions. We selected the Gulf of Mexico, which has extensively studied gas hydrates, to develop predictive models of gas hydrate distributions, and to test errors in the model. Then, we compared the existing northern South China Sea hydrate-mining data with the Gulf of Mexico characteristics, and collated the relevant data into the model. Subsequently, we applied the model to the northern South China Sea to obtain the potential gas hydrate distribution of the area, and to identify significant exploration targets. Finally, we evaluated the reliability of the predicted results. The south seabed area of Taiwan Bank is recommended as a priority exploration target. The Zhujiang Mouth, Southeast Hainan, and Southwest Taiwan Basins, including the South Bijia Basin, also are recommended as exploration target areas. In addition, the method in this paper can provide a useful predictive approach for gas hydrate resource assessment, which gives a scientific basis for construction and implementation of long-term planning for gas hydrate exploration and general exploitation of the seabed of China.     

Numerical analysis of wellbore instability in gas hydrate formation during deep-water drilling

Gas hydrate formation may be encountered during deep-water drilling because of the large amount and wide distribution of gas hydrates under the shallow seabed of the South China Sea. Hydrates are extremely sensitive to temperature and pressure changes, and drilling through gas hydrate formation may cause dissociation of hydrates, accompanied by changes in wellbore temperatures, pore pressures, and stress states, thereby leading to wellbore plastic yield and wellbore instability. Considering the coupling effect of seepage of drilling fluid into gas hydrate formation, heat conduction between drilling fluid and formation, hydrate dissociation, and transformation of the formation framework, this study established a multi-field coupling mathematical model of the wellbore in the hydrate formation. Furthermore, the influences of drilling fluid temperatures, densities, and soaking time on the instability of hydrate formation were calculated and analyzed. Results show that the greater the temperature difference between the drilling fluid and hydrate formation is, the faster the hydrate dissociates, the wider the plastic dissociation range is, and the greater the failure width becomes. When the temperature difference is greater than 7℃, the maximum rate of plastic deformation around the wellbore is more than 10%, which is along the direction of the minimum horizontal in-situ stress and associated with instability and damage on the surrounding rock. The hydrate dissociation is insensitive to the variation of drilling fluid density, thereby implying that the change of the density of drilling fluids has a minimal effect on the hydrate dissociation. Drilling fluids that are absorbed into the hydrate formation result in fast dissociation at the initial stage. As time elapses, the hydrate dissociation slows down, but the risk of wellbore instability is aggravated due to the prolonged submersion in drilling fluids. For the sake of the stability of the wellbore in deep-water drilling through hydrate formation, the drilling fluid with low temperatures should be given priority. The drilling process should be kept under balanced pressures, and the drilling time should be shortened.     

Simulating the effect of hydrate dissociation on wellhead stability during oil and gas development in deepwater

It is well known that methane hydrate has been identified as an alternative resource due to its massive reserves and clean property. However, hydrate dissociation during oil and gas development (OGD) process in deep water can affect the stability of subsea equipment and formation. Currently, there is a serious lack of studies over quantitative assessment on the effects of hydrate dissociation on wellhead stability. In order to solve this problem, ABAQUS finite element software was used to develop a model and to evaluate the behavior of wellhead caused by hydrate dissociation. The factors that affect the wellhead stability include dissociation range, depth of hydrate formation and mechanical properties of dissociated hydrate region. Based on these, series of simulations were carried out to determine the wellhead displacement. The results revealed that, continuous dissociation of hydrate in homogeneous and isotropic formations can causes the non-linear increment in vertical displacement of wellhead. The displacement of wellhead showed good agreement with the settlement of overlying formations under the same conditions. In addition, the shallower and thicker hydrate formation can aggravate the influence of hydrate dissociation on the wellhead stability. Further, it was observed that with the declining elastic modulus and Poisson’s ratio, the wellhead displacement increases. Hence, these findings not only confirm the effect of hydrate dissociation on the wellhead stability, but also lend support to the actions, such as cooling the drilling fluid, which can reduce the hydrate dissociation range and further make deepwater operations safer and more efficient.     

Accumulation and exploration of gas hydrate in deep-sea sediments of northern South China Sea

The large deep-sea area from the southwestern Qiongdongnan Basin to the eastern Dongsha Islands,within the continental margin of northern South China Sea,is a frontier of natural gas hydrate exploration in China.Multiform of deep-sea sedimentations have been occurred since late Miocene,and sediment waves as a potential quality reservoir of natural gas hydrate is an most important style of them.Based on abundant available data of seismic,gravity sampling and drilling core,we analyzed the characteristics of seismic reflection and sedimentation of sediment waves and the occurrence of natural gas hydrate hosted in it,and discussed the control factors on natural gas hydrate accumulation.The former findings revealed the deep sea of the northern South China Sea have superior geological conditions on natural gas hydrate accumulation.Therefore,it will be of great significance in deep-sea natural gas hydrate exploration with the study on the relationship between deep-sea sedimentation and natural gas hydrate accumulation.     

Response of biomass spatial pattern of alpine vegetation to climate change in permafrost region of the Qinghai-Tibet Plateau,China

Alpine ecosystems in permafrost region are extremely sensitive to climate changes.To determine spatial pattern variations in alpine meadow and alpine steppe biomass dynamics in the permafrost region of the Qinghai-Tibet Plateau,China,calibrated with historical datasets of above-ground biomass production within the permafrost region's two main ecosystems,an ecosystem-biomass model was developed by employing empirical spatialdistribution models of the study region's precipitation,air temperature and soil temperature.This model was then successfully used to simulate the spatio-temporal variations in annual alpine ecosystem biomass production under climate change.For a 0.44°C decade-1 rise in air temperature,the model predicted that the biomasses of alpine meadow and alpine steppe remained roughly the same if annual precipitation increased by 8 mm per decade-1,but the biomasses were decreased by 2.7% and 2.4%,respectively if precipitation was constant.For a 2.2°C decade-1 rise in air temperature coupled with a 12 mm decade-1 rise in precipitation,the model predicted that the biomass of alpine meadow was unchanged or slightly increased,while that of alpine steppe was increased by 5.2%.However,in the absence of any rise in precipitation,the model predicted 6.8% and 4.6% declines in alpine meadow and alpine steppe biomasses,respectively.The response of alpine steppe biomass to the rising air temperatures and precipitation was significantly lesser and greater,respectively than that of alpine meadow biomass.A better understanding of the difference in alpine ecosystem biomass production under climate change is greatly significant with respect to the influence of climate change on the carbon and water cycles in the permafrost regions of the Qinghai-Tibet Plateau.     

四川盆地震旦系灯影组储层特征及成因

为明确四川盆地震旦系灯影组的储层特征及成因,以钻井岩心、薄片观察、扫描电镜和碳氧稳定同位素分析等资料为基础,分析研究区储层的储集空间类型及储层特征、成因。结果表明:灯影组储集岩类以凝块状云岩、砂屑云岩为主,储集空间以次生孔隙、溶蚀孔洞为特征;沉积相是储层的物质基础,藻丘和颗粒滩亚相控制储层在平面上的分布范围和规模;溶蚀是储层形成的关键,同生期溶蚀增加储层的比表面积,为后期岩溶提供有利的物性条件;表生期溶蚀控制优质储层在纵向上的分布,主要分布在距离不整合面100m以内;埋藏期溶蚀对储层总孔隙度改变不大,但使前期较分散的储层趋于富集。早期裂缝(第一~三期)为各期流体及烃类充注提供导引作用,晚期裂缝(第四~五期)改善灯影组储层的渗透能力。该结果对研究区气田的勘探和开发具有参考意义。