Migration and accumulation characteristics of natural gas hydrates in the uplifts and their slope zones in the Qiongdongnan Basin,China

Various factors controlling the accumulation of natural gas hydrates(NGHs)form various enrichment and accumulation modes through organic combination.This study mainly analyzes the geological and geophysical characteristics of the NGHs occurrence in the uplifts and their slope zones within the deep-water area in the Qiongdongnan(QDN)Basin(also referred to as the study area).Furthermore,it investigates the dominant governing factors and models of NGHs migration and accumulation in the study area.The results are as follows.(1)The uplifts and their slope zones in the study area lie in the dominant pressure-relief direction of fluids in central hydrocarbon-rich sags in the area,which provide sufficient gas sources for the NGHs accumulation and enrichment through pathways such as gas chimneys and faults.(2)The top and flanks of gas chimneys below the bottom simulating reflectors(BSRs)show high-amplitude seismic reflections and pronounced transverse charging of free gas,indicating the occurrence of a large amount of gas accumulation at the heights of the uplifts.(3)Chimneys,faults,and high-porosity and high-permeability strata,which connect the gas hydrate temperature-pressure stability zones(GHSZs)with thermogenic gas and biogenic gas,form the main hydrate migration system.(4)The reservoir system in the study area comprises sedimentary interlayers consisting of mass transport deposits(MTDs)and turbidites.In addition,the reservoir system has developed fissure-and pore-filling types of hydrates in the pathways.The above well-matched controlling factors of hydrate accumulation enable the uplifts and their slope zones in the study area to become the favorable targets of NGHs exploration.

Strategic Thinking on Shallow-water Oil and Gas Exploration in Offshore China

The oil and gas exploration in offshore China has made great achievements,and as the important areas of offshore exploration,the shallow waters contribute most of the oil and gas reserves and production.However,the available area for exploration is diminishing and the cost of exploration is rising.The field changes and ever increasing difficulties of exploration bring new challenges technically and economically.Therefore,for effective exploration of shallow-water oil and gas in offshore China,it is necessary to center on the general requirements of becoming a powerful marine country and the ideas of value exploration,initiate key research projects in the fields of China's offshore stratigraphic-lithologic reserves,Paleogene reserves,buried-hill reserves,high temperature and pressure reserves and hydrocarbon-rich sags,and form geological theories and explorative technologies of large and medium size oil and gas field in offshore China.The measures regarding the challenges include:(1) Innovating theoretical understanding and optimizing new exploration fields,(2) developing technical capabilities and improving the success rate of exploration,and(3) enhancing management level and deepening value exploration.

Formation and mechanism of the abnormal pressure zone and its relation to oil and gas accumulations in the Eastern Jiuquan Basin, northwest China

Three abnormal overpressure zoes with a planar top at different depths occur in the Ying’er Depression in the Eastern Jiuquan Basin. The distance and the temperature difference between them are about 1 000 m and 30℃, respectively. The studies of sedimentary history, nature of formation water, variation of geothermal gradient and examination of thin sections, and the relationship between lithologic section and formation pressure show that there are conditions for formation of abnormal overpressure zones in the Ying’er Depression. Aquathermal pressuring and the overlying sediment load are main factors forming the abnormal overpressure zones. The study indicates that most of oil and gas in the Ying’er Depression accumulated in reservoirs above or under the seals or in the top of the compartments.

海外上游油气新项目开拓思考与分析

我国海外油气"走出去"战略实施已有25年,这一期间经历了油价高低起伏,也经历了国家地缘政治动荡,有收获亦有教训。主要的成果是形成了五大油气战略合作区,建立了具有战略意义的从北、西、南三个方向的重要油气管道。本文探讨了五大油气战略合作区功能的侧重点,认为不同资源类型资源应根据不同市场环境协调发展,最后提出海外上游油气新项目开拓想法和思考。

Formation and accumulation of oil and gas in marine carbonate sequences in Chinese sedimentary basins

Advances in studies of formation and accumulation mechanisms of oil and gas in marine carbonate sequences have led to continuing breakthroughs of petroleum exploration in marine carbonate sequences in Chinese sedimentary basins in recent years. The recently discovered giant Tahe Oil Field and Puguang Gas Field have provided geological entities for further studies of the formation and accumulation of oil and gas in marine carbonate sequences. Marine carbonate sequences in China are characterized by old age, multiple structural deformation, differential thermal evolution of source rocks, various reservoir types (i.e. reef-bank complex and paleo-weathered crust karst reservoir), uneven development of caprocks, especially gypsum seal, and multi-episodes of hydrocarbon accumulation and readjustment. As a result, the formation of hydrocarbon accumulations in the Chinese marine carbonate sequences has the following features: (i) the high-quality marine source rocks of shale and calcareous mudstone are often associated with siliceous rocks or calcareous rocks and were deposited in slope environments. They are rich in organic matter, have a higher hydrocarbon generation potential, but experienced variable thermal evolutions in different basins or different areas of the same basin. (ii) High quality reservoirs are controlled by both primary depositional environments and later modifications including diagenetic modifications, structural deformations, and fluid effects. (iii) Development of high-quality caprocks, especially gypsum seals, is the key to the formation of large-and medium-sized oil and gas fields in marine carbonate sequences. Gypsum often constitutes the caprock for most of large sized gas fields. Given that Chinese marine carbonate sequences are of old age and subject to multiple episodes of structural deformation and superposition, oil and gas tend to accumulate in the slopes and structural hinge zones, since the slopes favor the development of effective assemblage of source-reservoir-caprock, high quality source rocks, good reservoirs such as reef-bank complex, and various caprocks. As the structural hinge zones lay in the focus area of petroleum migration and experienced little structural deformation, they are also favorable places for hydrocarbon accumulation and preservation.

Research achievements of the Qinghai-Tibet Plateau based on 60 years of aeromagnetic surveys

The Qinghai-Tibet Plateau(also referred to as the Plateau)has long received much attention from the community of geoscience due to its unique geographical location and rich mineral resources.This paper reviews the aeromagnetic surveys in the Plateau in the past 60 years and summarizes relevant research achievements,which mainly include the followings.(1)The boundaries between the Plateau and its surrounding regions have been clarified.In detail,its western boundary is restricted by West Kunlun-Altyn Tagh arc-shaped magnetic anomaly zone forming due to the arc-shaped connection of the Altyn Tagh and Kangxiwa faults and its eastern boundary consists of the boundaries among different magnetic fields along the Longnan(Wudu)-Kangding Fault.Meanwhile,the fault on the northern margin of the Northern Qilian Mountains serves as its northern boundary.(2)The Plateau is mainly composed of four orogens that were stitched together,namely East Kunlun-Qilian,Hoh-Xil-Songpan,Chamdo-Southwestern Sanjiang(Nujiang,Lancang,and Jinsha rivers in southeastern China),and Gangdese-Himalaya orogens.(3)The basement of the Plateau is dominated by weakly magnetic Proterozoic metamorphic rocks and lacks strongly magnetic Archean crystalline basement of stable continents such as the Tarim and Sichuan blocks.Therefore,it exhibits the characteristics of unstable orogenic basement.(4)The Yarlung-Zangbo suture zone forming due to continent-continent collisions since the Cenozoic shows double aeromagnetic anomaly zones.Therefore,it can be inferred that the Yarlung-Zangbo suture zone formed from the Indian Plate subducting towards and colliding with the Eurasian Plate twice.(5)A huge negative aeromagnetic anomaly in nearly SN trending has been discovered in the middle part of the Plateau,indicating a giant deep thermal-tectonic zone.(6)A dual-layer magnetic structure has been revealed in the Plateau.It consists of shallow magnetic anomaly zones in nearly EW and NW trending and deep magnetic anomaly zones in nearly SN trending.They overlap vertically and cross horizontally,showing the flyover-type geological structure of the Plateau.(7)A group of NW-trending faults occur in eastern Tibet,which is intersected rather than connected by the nearly EW trending that develop in middle-west Tibet.(8)As for the central uplift zone that occurs through the Qiangtang Basin,its metamorphic basement tends to gradually descend from west to east,showing the form of steps.The Qiangtang Basin is divided into the northern and southern part by the central uplift zone in it.The basement in the Qiangtang Basin is deep in the north and west and shallow in the south and west.The basement in the northern Qiangtang Basin is deep and relatively stable and thus is more favorable for the generation and preservation of oil and gas.Up to now,19 favorable tectonic regions of oil and gas have been determined in the Qiangtang Basin.(9)A total of 21 prospecting areas of mineral resources have been delineated and thousands of ore-bearing(or mineralization)anomalies have been discovered.Additionally,the formation and uplift mechanism of the Plateau are briefly discussed in this paper.

巴西桑托斯盆地盐下大发现及其勘探意义

2007—2008年间,巴西石油公司在巴西桑托斯深水盆地盐下层序接连发现了3个超大型油气田,使得该区盐下领域成为新的勘探热点。分析了桑托斯盆地的构造演化与沉积充填特征、基本石油地质条件,以及盐下油气成藏特征,指出巴西坎波斯盆地、大西洋彼岸的西非宽扎盆地、下刚果盆地的盐下层系,与桑托斯盆地盐下层系在沉积时期属同一盆地,并经历了相似的盐后被动大陆边缘盆地的构造演化。通过类比研究,认为这些盆地与桑托斯盆地盐下层系具有相似的石油地质条件与成藏特征,其盐下层系勘探前景十分广阔,应是未来重要的油气战略区。

Differences and controlling factors of composite hydrocarbon accumulations in the Tazhong uplift, Tarim Basin, NW China

Based on three-dimensional seismic interpretation, structural and sedimentary feature analysis, and examination of fluid properties and production dynamics, the regularity and main controlling factors of hydrocarbon accumulation in the Tazhong uplift, Tarim Basin are investigated. The results show that the oil and gas in the Tazhong uplift has the characteristics of complex accumulation mainly controlled by faults, and more than 80% of the oil and gas reserves are enriched along fault zones. There are large thrust and strike-slip faults in the Tazhong uplift, and the coupling relationship between the formation and evolution of the faults and accumulation determine the difference in complex oil and gas accumulations. The active scale and stage of faults determine the fullness of the traps and the balance of the phase, that is, the blocking of the transport system, the insufficient filling of oil and gas, and the unsteady state of fluid accumulation are dependent on the faults. The multi-period tectonic sedimentary evolution controls the differences of trap conditions in the fault zones, and the multi-phase hydrocarbon migration and accumulation causes the differences of fluid distribution in the fault zones. The theory of differential oil and gas accumulation controlled by fault is the key to the overall evaluation, three-dimensional development and discovery of new reserves in the Tazhong uplift.

牛东1风险探井重大发现及其意义

中国石油天然气股份有限公司重点风险探井牛东1井获高产工业油气流,这是继1976年任丘潜山发现后,渤海湾盆地冀中坳陷潜山勘探的重大突破。牛东1井深潜山油气藏勘探历时33年,经历了6个勘探阶段,华北几代勘探家持之以恒,持续进行先进物探技术和方法攻关,不断建立和完善潜山地质结构,最终在二次三维地震资料采集及叠前深度偏移处理后完全落实潜山形态,标定牛东1井。落实潜山圈闭的同时,深化研究、创新认识,综合评价潜山成藏条件,降低深潜山勘探的风险。牛东1井的成功,发现了渤海湾盆地乃至中国东部目前最深的高产油气藏,打开了冀中坳陷深潜山勘探的新局面,对于推动渤海湾盆地深层勘探具有里程碑意义。

A Business Ecosystem＇s Model for Harnessing Nigeria＇s Ocean Economy

The reassessment of ocean economy contribution of nations has become a new strategy for frontier states adjacent to the coastal region for the improvement of their position in the efficiency frontier curve. The continuity of a coastal state to remain a leader in the production and efficiency frontier curve of modem day development will thus depend on their ability to sustainably develop their most strategic economic resource base such as the ocean economy. The major economic bases include sustainable fishing, offshore oil field developments, offshore biodiversity development and marine biotechnology, offshore mining of manganese nodules, offshore wind farm potentials, international shipping （marine transport） and adjoining corridor development, ship dry docking potentials, marine renewable energy as well as other potentials outlined in the definition of African Union strategy for the development of her blue economy. Adopting the regression analysis and analysis of variance analytical tools, the study found that about 90% association exist between the GDP （gross domestic product） of the West African state （Nigeria） and her GDP. It equally found that offshore oil and gas energy sector more significantly impact on the GDP of Nigeria than other ocean economy business clusters. Given the various contributing marine environment business cluster used in the work, the model depicting the influence of the ocean economy of Nigeria is： Y = 2295334779895 - 294733（1 ＋ 3436995749 - 59276863（2 ＋ e.

Reservoir forming conditions and key exploration technologies of Lingshui 17-2 giant gas field in deepwater area of Qiongdongnan Basin

On September 15,2014,China National Offshore Oil Co.,Ltd announced that a high production of oil and gas flow of 1.6
106 m3/d was obtained in Well LS17-2-1 in deepwater area in northern South China Sea,which is the first great oil and gas discovery for self-run deepwater exploration in China sea areas,and a strategic breakthrough was made in natural gas exploration in deepwater area of Lingshui sag in Qiongdongnan Basin.Under the combined action of climax of international deepwater exploration,high oil prices,national demands of China,practical needs of exploration,breakthroughs in seismic exploration and testing technologies,innovations in geological cognition and breakthroughs in deepwater operation equipment,Lingshui 17-2 gas field is discovered.Among these factors,the innovation in reservoir forming geological cognition directly promotes the discovery.The quality of seismic data in the early time is poor,so key reservoir forming conditions such as effective source rocks,high quality reservoirs and oil-gas migration pathways are unable to be ascertained;with support of new seismic acquisition and processing technology,some researches show that Lingshui sag is a successive large and deep sag with an area of 5000 km2 and the maximum thickness of Cenozoic stratum of 13 km.In the Early Oligocene,the Lingshui sag was a semi-closed delta-estuarine environment,where the coalmeasure and marine mudstones in Lower Oligocene Yacheng Formation were developed.The Lingshui sag is a sag with high temperature,and the bottom temperature of source rocks in Yacheng Formation can exceed 250C,but the simulation experiment of hydrocarbon generation at high temperature indicates that the main part of this set of source rock is still in the gas-generation window,with resources of nearly 1 trillion cubic meters,so the Lingshui sag is a hydrocarbon-rich generation sag.In the Neogene,the axial canyon channel from the Thu Bon River in Vietnam passed through the Lingshui sag,and five stages of secondary channels were developed in the axial canyon channel,where four types of reservoirs with excellent physical properties including the axial sand,lateral accretion sand,natural levee sand as well as erosion residual sand were developed,and lithologic traps or structural-lithologic traps were formed.The diapiric zone in the southern Lingshui sag connects deep source rocks in Yacheng Formation and shallow sandstones in the channels,and the migration pattern of natural gas is a T-type migration pattern,in other words,the natural gas generated from Yacheng Formation migrates vertically to the interior of the channel sandbody,and then migrates laterally in the channel reservoirs and forms the reservoirs.Innovations of geophysical exploration technologies for complicated geological conditions of deepwater areas are made,such as the detuning comprehensive quantitative amplitude hydrocarbon detection technology,which greatly improves the success rate of deepwater exploration;key technologies of deepwater safety exploratory well testing represented by the platform-dragged riser displacement technology are developed,which greatly reduces the drilling test cost.The above key exploration technologies provide a strong guarantee for the efficient exploration and development of Lingshui gas field.

Hydrocarbon accumulation conditions and key exploration and development technologies for PL 19-3 oilfield

The PL 19e3 Oilfield is the only super-large monolithic oilfield with oil and gas reserves up to 1×10^(9) t in the Bohai Bay Basin,and it has been successfully developed.Exploration and development practices have provided abundant data for analyzing formation conditions of this super-large oilfield.On the basis of the exploration and development history,fundamental reservoir features,and with available geological,geophysical and test data,the hydrocarbon accumulation conditions and key exploration&development technologies of the PL 19e3 Oilfield were discussed.The key conditions for forming the super-large Neogene oilfield include four aspects.Firstly,the oilfield is located at the high position of the uplift that contacts the brachy-axis of the multi-ridge slope in the biggest hydrocarbon-rich sag in the Bohai Bay Basin,thus it has sufficient hydrocarbon source and extremely superior hydrocarbon migration condition.Secondly,the large-scale torsional anticlines which formed in the Neogene under the control of the Tanlu strike-slipping movement provide sufficient storage spaces for oil and gas preservation.Thirdly,the“multiple sets of composite reservoir-caprock assemblages”developing in the special shallow-water delta further contributes greatly to the effective storage space for oil and gas preservation.Fourthly,due to the coupling of the uplift and strike slip in the neotectonic period,extensive faulting activities constantly released the pressure while the late period massive hydrocarbon expulsion of the Bozhong took place at the same time,which assures the constant and intense charging of oil and gas.The super-large PL 19e3 Oilfield was controlled by the coupling effects of all those special geologic factors.In view of this oilfield's features(e.g.violently reformation caused by strike slip,and the special sedimentary environment of shallow-water delta),some key practical technologies for exploration and development have been developed.Such technologies include:the special prestack depth migration processing for gas cloud zones,the prediction of thin interbed reservoirs based on high-precision inversion of geologic model,the reservoir description for the shallow-water braided river delta,the quantitative description for remaining oil in the commingled oil reservoirs with wide well spacing and long well interval,and the well pattern adjustment for formations during high water cut period in the complex fluvial-facies oilfields.

The study on exploitation potential of original low-oil-saturation reservoirs

It is preliminary estimated that the proved geological reserves of original low-oil-saturation reservoirs(OLOSRs)of 54 blocks in China are more than 820 million tons.As same as the high water-cut stage of a reservoir after water flooding,the initial water cut of OLOSRS is higher than 80%.The industrial application of EOR technology could efficiently enhance oil recovery rate from 8.4% to 20.1% of reservoirs after water flooding.The suitable measurements of EOR to the OLOSRs probably have a profound impact on achieving higher oilfield reserves and production.In this paper,the main characteristics and reserves potential of OLOSRs have been studied by investigations and laboratory experiments.The relationship between initial oil saturation and displacement efficiency is also analyzed.The feasibility of EOR technologies for different OLOSRs is discussed.The results show that the OLOSRs could be divided into two categories(primary and secondary)by origin of low oil saturation.The two categories contain abundant reserves in China’s major oilfields,but their occurrence states of crude oil are quite different.If the average oil saturation of the OLOSR is defined at 40%,there are 13.1%-54.2%crude oil that could be recovered by using the existing EOR technology,especially in the primary OLOSRs with low permeability and the secondary OLOSRs with high permeability.

中国海外油气战略选区——西伯利亚地台油气资源研究

西伯利亚地台油气总资源量约为1 000亿吨油当量,油气储量丰厚,勘探潜力与储量增长潜力巨大,俄联邦东部的所有油气勘探开发规划和计划,均以其丰厚的油气资源为基础。东西伯利亚—太平洋石油管道及中国支线、三大油气战略开采区、"西伯利亚力量"天然气管线及中国支线为西伯利亚地台油气开发规划中的重中之重。西伯利亚地台是未来中国最重要的海外油气战略选区,亦是俄联邦未来国家第四大油气基地,其能为中国提供油气战略资源保障。