Seismic Facies in a Deepwater Area of a Marine Faulted Basin:Deepwater Area of the Paleogene Lingshui Formation in the Qiongdongnan Basin

In recent years, deep water areas have become popular exploration fields because of their abundant hydrocarbon resource potential. There are only relatively poor planar seismic profiles and no wells for deepwater areas of the Lingshui Formation in the Qiongdongnan Basin. A lot of faults developed and strata are fragmented due to high temperatures and high pressure, and this has resulted in dim sequence boundaries. Based on seismic data of the deepwater area and well data of bordering shallow water areas, Lingshui Formation was divided into four third class sequences; namely SI, SII, SIII and SIV, and the three-dimensional isochronous stratigraphic framework of the Lingshui Formation in the studied area was shaped. Based mainly on seismic attributes such as amplitude, continuity, internal structure and external shape, six typical seismic facies were identified, including mat-shaped, filling, wedge-shaped, foreset, moundy-shaped and lenticular-shaped, and a seismic facies distribution map was subsequently drawn. With studies on wells of bordering shallow water areas, regional sedimentary characteristics, and isopach map as references, sedimentary planar distribution features were analyzed. The deepwater area of the Lingshui Formation has mainly developed littoral and shallow sea. Sandstone bodies of fan delta, braided river delta, slope fan, basin floor fan, and turbidite fan are at an interdigitate junction to marine hydrocarbon source rocks and thus are favorable prospecting targets.

Kinetics and model of gas generation of source rocks in the deepwater area, Qiongdongnan Basin

In order to investigate the hydrocarbon generation process and gas potentials of source rocks in deepwater area of the Qiongdongnan Basin, kinetic parameters of gas generation （activation energy distribution and frequency factor） of the Yacheng Formation source rocks （coal and neritic mudstones） was determined by thermal simulation experiments in the closed system and the specific KINETICS Software. The results show that the activation energy （Ea） distribution of C1–C5 generation ranges from 50 to 74 kcal/mol with a frequency factor of 2.4×1015 s–1 for the neritic mudstone and the Ea distribution of C1–C5 generation ranges from 49 to 73 kcal/mol with a frequency factor of 8.92×1013 s–1 for the coal. On the basis of these kinetic parameters and combined with the data of sedimentary burial and paleothermal histories, the gas generation model of the Yacheng Formation source rocks closer to geological condition was worked out, indicating its main gas generation stage at Ro （vitrinite reflectance） of 1.25%–2.8%. Meanwhile, the gas generation process of the source rocks of different structural locations （central part, southern slope and south low uplift） in the Lingshui Sag was simulated. Among them, the gas generation of the Yacheng Formation source rocks in the central part and the southern slope of the sag entered the main gas window at 10 and 5 Ma respectively and the peak gas generation in the southern slope occurred at 3 Ma. The very late peak gas generation and the relatively large gas potential indices （GPI：20×10^8–60×10^8 m^3/km^2） would provide favorable conditions for the accumulation of large natural gas reserves in the deepwater area.

Analysis of the world deepwater oil and gas exploration situation

The global trends in deepwater oil and gas exploration,characteristics of deepwater oil and gas discovery,and layout of deepwater oil and gas exploration business by seven major international oil companies are systematically analyzed using commercial databases(e.g.S&P Global and Rystad)and public information of oil companies.The deepwater area is currently the most important domain for global oil and gas exploration and discovery,with the most discoveries and reserves in passive continental margin basins.The deepwater discoveries have the greatest contribution to the total newly discovered oil and gas reserves in the sea areas,with an increasing number of lithological reservoirs discovered,and oil and gas discoveries mainly distributed in the Mesozoic–Cenozoic.The seven major international oil companies are widely active in various aspects of deepwater oil and gas exploration and development,and play a leading role.Based on years of theoretical understanding of global oil and gas geology and resource evaluation,it is proposed that favorable deepwater exploration areas in the future will mainly focus on three major areas:the Atlantic coast,the Indian Ocean periphery,and the Arctic Ocean periphery.Six suggestions are put forward for expanding overseas deepwater oil and gas exploration business:first,expand the sources for obtaining multi-user seismic data and improve the scientific selection of deepwater exploration areas;second,increase efforts to obtain deepwater exploration projects in key areas;third,adopt various methods to access into/exit from resource licenses flexibly;fourth,acquire licenses with large equity and operate in“dual-exploration”model;fifth,strengthen cooperation with leading international oil companies in deepwater technology;and sixth,improve business operation capabilities and gradually transform from“non-operators”to“operators”.

Geochemical characteristics of Oligocene-Miocene sediments from the deepwater area of the northern South China Sea and their provenance implications

Geochemical and detrital zircon U-Pb dating data for drilled sediments from the Baiyun deepwater area of the northern South China Sea demonstrate a change of sedimentary sources from the Oligocene to the Miocene.Zircon ages of the pre-rift Eocene sequences are dominated by Yanshanian ages with various peak values（110–115 Ma for U1435 and L21; 150 Ma for H1）, indicating local sediment supply from the pre-existing Mesozoic magmatic belt. For the Oligocene sediments in the northern part of the basin, the rare earth elements show different distribution characteristics, indicating sediment supply from the paleo-Zhujiang River（Pearl River）, as also confirmed by the multimodal zircon age spectra of the Lower Oligocene strata in Well X28. By contrast, a positive Eu anomaly characterizes sediments from the western and southern parts of the basin, indicating potential provenances from intermediate to basic volcanic rock materials. The Baiyun Movement at the end of the Oligocene contributed to a large-scale subsidence in the deepwater area and also a northward retreat of continental shelf break, leading to deepening depositional environment in the basin. As a result, all the detrital zircon ages of the Upper Oligocene strata from Wells X28, L13, and L21 share a similar distribution, implying the possible control of a common source like the Zhujiang River. During the Miocene, whereas sediments in the northern area were mainly sourced from the Zhujiang River Delta, and those in the southern deepwater area continued to be affected by basic volcanic activities, the Dongsha Uplift could have contributed as the main source to the eastern area.

Geochemistry of borehole cutting shale and natural gas accumulation in the deepwater area of the Zhujiang River Mouth-Qiongdongnan Basin in the northern South China Sea

The Qiongdongnan Basin and Zhujiang River（Pearl River） Mouth Basin, important petroliferous basins in the northern South China Sea, contain abundant oil and gas resource. In this study, on basis of discussing impact of oil-base mud on TOC content and Rock-Eval parameters of cutting shale samples, the authors did comprehensive analysis of source rock quality, thermal evolution and control effect of source rock in gas accumulation of the Qiongdongnan and the Zhujiang River Mouth Basins. The contrast analysis of TOC contents and Rock-Eval parameters before and after extraction for cutting shale samples indicates that except for a weaker impact on Rock-Eval parameter S2, oil-base mud has certain impact on Rock-Eval S1, Tmax and TOC contents. When concerning oil-base mud influence on source rock geochemistry parameters, the shales in the Yacheng/Enping,Lingshui/Zhuhai and Sanya/Zhuhai Formations have mainly Type Ⅱ and Ⅲ organic matter with better gas potential and oil potential. The thermal evolution analysis suggests that the depth interval of the oil window is between 3 000 m and 5 000 m. Source rocks in the deepwater area have generated abundant gas mainly due to the late stage of the oil window and the high-supper mature stage. Gas reservoir formation condition analysis made clear that the source rock is the primary factor and fault is a necessary condition for gas accumulation. Spatial coupling of source, fault and reservoir is essential for gas accumulation and the inside of hydrocarbon-generating sag is future potential gas exploration area.

Tectono-thermal evolution of the Liwan Sag, deepwater area in the Zhujiang River Mouth Basin, northern South China Sea

The Liwan Sag, with an area of 4 000 km-2, is one of the deepwater sags in the Zhujiang River（Pearl River） Mouth Basin, northern South China Sea. Inspired by the exploration success in oil and gas resources in the deepwater sags worldwide, we conducted the thermal modeling to investigate the tectono-thermal history of the Liwan Sag,which has been widely thought to be important to understand tectonic activities as well as hydrocarbon potential of a basin. Using the multi-stage finite stretching model, the tectonic subsidence history and the thermal history have been obtained for 12 artificial wells, which were constructed on basis of one seismic profile newly acquired in the study area. Two stages of rifting during the time periods of 49–33.9 Ma and 33.9–23 Ma can be recognized from the tectonic subsidence pattern, and there are two phases of heating processes corresponding to the rifting.The reconstructed average basal paleo-heat flow values at the end of the rifting events are -70.5 and -94.2 mW/m^2 respectively. Following the heating periods, the study area has undergone a persistent thermal attenuation phase since 23 Ma and the basal heat flow cooled down to -71.8–82.5 mW/m^2 at present.

Evaluation of abundant hydrocarbon-generation depressions in the deepwater area of Qiongdongnan Basin,South China Sea

It has been confirmed that the key source rocks of Qiongdongnan Basin are associated with the Yacheng Formation, which was deposited in a transitional marine-continental environment. Because the distribution and evolution patterns of the source rocks in the major depressions are different, it is important to determine the most abundant hydrocarbon-generation depressions in terms of exploration effectiveness. Based on an analysis of organic matter characteristics of the source rocks, in combination with drilling data and seismic data, this paper establishes a model to evaluate the hydrocarbon-generation depressions in the deepwater area of Qiongdongnan Basin. First of all, by using the method of seismic-facies model analysis, the distribution of sedimentary facies was determined. Then, the sedimentary facies were correlated with the organic facies, and the distribution of organic facies was predicted. Meanwhile, the thickness of source rocks for all the depressions was calculated on the basis of a quantitative analysis of seismic velocity and lithology. The relationship between mudstone porosity and vitrinite reflectance（Ro） was used to predict the maturity of source rocks. Second, using the parameters such as thickness and maturity of source rocks, the quantity and intensity of gas generation for Yacheng and Lingshui Formations were calculated. Finally, in combination with the identified hydrocarbon resources, the quantity and intensity of gas generation were used as a guide to establish an evaluation standard for hydrocarbon-generation depressions, which was optimized for the main depressions in the Central Depression Belt. It is proposed that Lingshui, Ledong, Baodao and Changchang Depressions are the most abundant hydrocarbon depressions, whilst Songnan and Beijiao Depressions are rich hydrocarbon depressions. Such an evaluation procedure is beneficial to the next stage of exploration in the deep-water area of Qiongdongnan Basin.

Hydrocarbon Accumulation Condition and Exploration Direction in the Deepwater Area of Qiongdongnan Basin,Northern South China Sea

The deepwater area of southern Qiongdongnan Basin is a hydrocarbon exploration frontier and mainly located on the continental slope in the northwestern South China Sea.Its tectonic and depositional evolution is similar to the typical marginal deepwater areas abroad where oils have been discovered.Favorable hydrocarbon conditions in this area are as follows:(1) three sets of source rocks (including lacustrine mudstone of Eocene,coastal plain coal-bearing strata and semi-closed shallow sea mudstone of Oligocene,and marine mudstone

Velocity model and time-depth conversion for the northwestern South China Sea deepwater areas

There are rich natural gas resources in the northwestern South China Sea deepwater areas, with poor degree of exploration. Because of the unique tectonic, sedimentary background of the region, velocity model building and time-depth conversion have been an important and difficult problem for a long time. Recent researches in this direction have revealed three major problems for deepwater areas, i.e., the way to determine error correction for drilling velocity, the optimization of velocity modeling, and the understanding and analysis of velocity variations in the slope areas. The present contribution proposes technical solutions to the problems：（1） velocity correction version can be established by analyzing the geology, reservoir, water depths and velocity spectrum characteristics;（2） a unified method can be adopted to analyze the velocity variation patterns in drilled pale structural positions;and （3） across-layer velocity is analyzed to establish the velocity model individually for each of the layers. Such a solution is applicable, as shown in an example from the northwestern South China Sea deepwater areas, in which an improved prediction precision is obtained.

Identification methods of coal-bearing source rocks for Yacheng Formation in the western deepwater area of South China Sea

Owing to the fact that the coal-beds are with the characteristics of multi-beds, thin single-bed, rapid lateral changes and deep burial, coal-bearing source rocks are difficult to be identified and predicted, especially in the lower exploration deepwater area. In this paper, a new integrative process utilizing geology and geophysics is proposed for better predicting the distribution of coal-bearing source rocks. Coal-beds were identified by the logging responses of“three higher, three lower, and one expand”and carbargilite were recognized by the characteristics of“four higher and one lower”. Based on the above logical decision, coal-beds and carbargilite can be distinguished automatically by cluster analysis of logging curves in verticality. Within the constraints of well-seismic calibration, the coal-beds group also can be detected in horizontality by the integrated representation of“negative phase, higher Q, lower impedance and lower frequency”within the seismic data. However, the distribution of coal-bearing source rocks utilizing geophysical methodology may do not conform to the geological rules of coal accumulation. And then the main geological controlling factors of coal accumulation are comprehensively analyzed as follows：（1） Paleotopography and tectonic subsidence determine the planar range of terrestrial-marine transitional facies markedly;（2） The relative sea level changes affect the accommodation space and shoreline migration, and limit the vertical range of coal-beds. More specifically, the relationship between the accommodation creation rate and the peat accumulation rate is a fundamental control on coal accumulation. The thickest and most widespread coals form where those two factors reached a state of balance;（3） The supply of autochthonous clasts and the distance between deposition places and paleovegetation accumulated area are the critical factor to form abundant coal, which means that if deposition area is close to paleouplift, there would be sufficient organic matters to form abundant source rocks. The results show that the integrated methods can significantly improve prediction accuracy of coal-bearing source rocks, which is suitable for early exploration of western deepwater area of South China Sea.

南海北部陆缘盆地深水区油气勘探新认识及攻关方向

南海北部陆缘盆地深水区已成为我国海洋油气勘探增储上产的重要领域,但由于构造演化史复杂,该区不同凹陷的沉积—构造特征、烃源岩生烃—储层成岩演化和成藏模式均存在明显差异。为准确认识该区油气勘探潜力和方向,基于前人研究成果和勘探实践,在综合分析烃源岩、储层、差异成藏等地质条件的基础上,剖析了南海北部陆缘盆地深水区成藏特征、油气勘探作业面临的挑战,并指出了下一步油气攻关研究方向。研究结果表明:①受地壳拆离作用及强烈薄化影响,该区地层沉积特征特殊,岩石地球物理性质多样;②软流圈差异抬升形成深水区独特的高热流背景,促使区域性湖相、煤型及叠合型等3类烃源灶快速、高强度生烃,生烃门限变浅;③深水盆地群的演化和成盆规模差异大,构造演化控制了盆地几何形态和储集体时空展布,深水区独特的板块构造位置、复杂的构造演化史、温压变化剧烈的地质特征等控制了油气成藏模式。结论认为:①该区油气勘探面临地震资料解析度低、规模有效储层预测困难、勘探成本高等技术与经济的双重挑战;②需要创新形成高地温背景下优质储层差异化分布规律的研究思路;③亟需提升勘探设备能力建设,攻关高效地震采集、“重磁电震”地球物理一体化采集处理、双井架钻探作业、多井段“一趟钻”等勘探关键技术,为我国海洋深水油气勘探开发的高质量发展做好理论和技术支撑。

深水油气高效开发技术装备发展与展望

近年来,深水油气成为国内外油气勘探开发的热点。“十一五”至“十四五”期间,我国深水油气勘探开发取得显著进步,实现从浅水开发到深水开发、合作开发到自营开发、跟跑到并跑甚至局部领跑的“三大跨越”,逐步形成了“区域开发一体评价、少井高产高效开发、智能少人降本增效、高端装备自主可控”的深水油气高效开发理念。中国海油通过立足深水油气勘探高效开发理念,聚焦深水油气高效经济和安全开发,构建了深水油气“勘探—开发—钻采—工程”一体化技术体系,形成了南海北部陆缘深水油气勘探地质理论、深水宽频地震勘探技术、深水油气田储层精细描述技术等10个标志性深水高效开发理论技术,以及地球物理勘探装备、深水半潜式钻井平台及装备等6类高效开发装备。未来将进一步加强深海勘探理论与技术、深水油气田高效开发、超深水钻完井、深水浮式液化天然气开发、全水下油气处理等方面的关键技术与装备攻关,推进我国南海深水油气田高效开发,为我国南海大开发奠定坚实基础。

地震横波建模技术及其在深水天然气田储层预测中的应用

深水区缺少横波资料,在叠前反演的建模环节中,一般通过线性关系或者相控将纵波模型转换为横波模型,但实现过程受人为因素影响较大,反演结果无法完整、可靠地表征地层特点和储层分布。为此,结合生产需求,提出基于远道地震数据提取三维空间的泊松比信息,作为纵、横波数据之间的转换关系,进而获得泊松比约束的横波低频模型。具体步骤为:(1)优选对岩性敏感的地震波入射角;(2)反演泊松比弹性阻抗PEI;(3)建立横波低频模型。在白云深水区的勘探实践表明,由于初始模型更好地反映了地层岩性背景,减少了反演结果的异常值,2号砂体的平面分布与气/水边界吻合,与实钻结果一致,落实了储层分布,扩大了天然气探明储量,取得了较好的经济效益。

世界深水油气勘探形势分析与思考

利用标普全球、睿咨得等商业数据及各油公司的公开信息,对全球深水油气勘探趋势、深水油气发现特点、七大国际油公司深水油气勘探业务布局进行系统分析。结果表明:深水领域是当前全球油气勘探发现最重要的领域,被动大陆边缘盆地深水大发现油气田个数及储量均最多,深水油气大发现对海域新发现油气总储量的贡献最大。岩性油气藏发现越来越多,且油气发现主要分布于中—新生界;七大国际油公司广泛活跃在深水油气勘探和开发各个环节,并发挥着全球引领作用。结合多年对全球油气地质与资源评价形成的理论认识,提出未来有利的深水勘探领域主要集中在大西洋两岸、印度洋周缘、北冰洋周缘等3大领域。提出了开拓海外深水油气勘探业务的6点建议:拓宽多用户地震资料获取渠道,提高深水勘探科学选区水平;加大重点领域深水勘探项目获取力度;灵活进退勘探区块;以大权益获取区块,采用“双勘探模式”经营;加强与深水技术领先国际油公司的合作;提升商务运作能力,逐步实现“非作业者”向“作业者”转变。

Paleogene Tectonic Evolution Controls on Sequence Stratigraphic Patterns in the Central Part of Deepwater Area of Qiongdongnan Basin, Northern South China Sea

In active rift basins, tectonism is extremely important for sequence stratigraphic patterns, affecting both the sequence architecture and internal makeup. Sequence stratigraphic framework of a Paleogene rift succession in Qiongdongnan Basin, northern South China Sea, was built using seismic profiles, complemented by well logs and cores. One first-order and three second-order sequences were identified on the basis of basin-scale unconformities, and seven third-order sequences are defined by unconformities along the basin margins and correlative conformities within the central basin. Through unconformity analysis and backstripping procedure, the Paleogene synrift tectonic evolution of deep- water area of Qiongdongnan Basin was proved to be episodic, which can be divided into rifting stage-I, rifting stage-II and rifting stage-III. Episodic rifting resulted in the formation of various types of struc- tural slope break belts, which controlled different architectures and internal makeup of sequences. This study enhances the understanding of the control of tectonic evolution on sequence stratigraphic pat- terns and establishes relevant patterns in a typical rift basin, and further proposes the favorable sand- stone reservoirs developing in different sequence stratigraphic patterns, which will be pretty helpful for subtle pool exploration in deepwater area of petroliferous basins.

南海北部深水区白云凹陷中深层油气成藏过程初探

珠江口盆地深水区白云凹陷具有极为特殊的油气地质条件,近几年,在中深层渐新统珠海组及下伏始新统恩平组见到了规模且连续分布的气层,并具有超压特征,其研究对白云凹陷中深层油气富集规律的认识和勘探实践有重要意义。目前由于受样品等资料少的限制,对其油气成藏过程的研究非常薄弱。通过白云凹陷深层超压的研究,认为其成因为生烃增压传导所致,说明白云凹陷具有极强的生烃能力,同时由于超压封闭原因,大部分油气应被封存在超压箱内。在此基础上,对B-2低渗超压气藏进行解剖,运用天然气地球化学与成藏动态研究方法,在明确天然气成因、成熟度及来源的基础上,分析天然气充注期与储层孔隙、压力演化的关系,解析该低渗气藏成藏过程。研究认为,珠海组下段-恩平组大型三角洲沉积“甜点”储层分布区与具备“原油早期充注-储层低渗化-超压-天然气晚期充注”型成藏过程的叠合区,是有利勘探区带,为白云凹陷中深层勘探指明了一定方向。

Q偏移技术在陵水凹陷气云模糊区地震资料处理中的应用研究

深水石油勘探要求更高品质的地震成像数据作为基础,然而气云区、气烟囱及其他速度异常体等高吸收异常构造的存在,造成深层地震波振幅变弱,频率降低,严重影响目标构造成像精度。本文以陵水凹陷气云模糊区为目标靶区,系统分析工区地震资料品质特点,针对性地采用Q(Geological Quality Factor,地质品质因子)偏移技术补偿浅层气云造成的吸收衰减。首先采用谱比法建立初始的等效Q场;然后基于等效Q场进行Q层析反演建立准确的异常Q场模型;最后基于高精度Q场进行克希霍夫Q叠前深度偏移。实际资料表明,重处理后浅层气云低速异常造成的能量吸收、频率衰减现象得到解决,目的砂体横向连续性更好,有效频带拓宽30%,气云下方模糊区的成像质量得到明显改善,为工区砂体展布落实及后续圈闭目标研究提供了高品质基础资料。

南海北部陆坡白云深水区深水沉积结构要素

在回顾深水沉积结构要素研究的基础上,结合白云深水区的勘探实践,对白云深水区深水沉积的结构要素进行了研究。将白云深水区深水沉积划分为4种结构要素,分别为水道、天然堤-溢岸沉积、席状砂和块体搬运沉积。水道是白云深水区深水沉积的主要组成部分,也是重要的储层;水道按成因可分为侵蚀型、侵蚀/加积型和加积型;水道充填沉积物的岩性变化较大,有砾岩、砂岩、泥岩以及几种岩性的混合。天然堤-溢岸沉积主要以泥岩、粉砂岩为主,平面上,天然堤-溢岸沉积与水道走向平行,横向上远离水道扩散,侧向连续性好但垂向连续性差。席状砂位于水道末端,具有朵叶状外形,分为层状和合并状2种类型:层状席状砂具有相对低的砂岩体积分数,泥岩和砂岩互层;而合并状席状砂岩体积分数高,砂层和砂层接触,夹有少量的泥。块体搬运沉积包括滑塌、滑块、块体流、碎屑流、坡身失稳复合体、块体搬运复合体等;块体搬运沉积常直接位于层序界面上,对下伏地层侵蚀明显,分布广泛,可作为良好的油气封盖层。

南海北部大陆边缘盆地深水区储层类型及沉积演化

南海北部大陆边缘盆地深水区储层类型与构造、沉积演化有密切的关系。南海北部陆缘盆地深水区经历了裂陷期、裂坳过渡期、坳陷期3个沉积演化阶段,不同沉积演化阶段发育不同类型的储层。深水区的储层主要包括:始新统—下渐新统裂陷期的河流和扇三角洲相砂岩;上渐新统裂坳过渡期的(扇)三角洲—滨浅海相砂岩;裂后坳陷期中新统的滨海相砂岩、台地碳酸盐岩及深水浊积砂岩。其中,南海北部陆缘深水区广泛分布的斜坡扇、盆底扇、进积楔形体和峡谷水道等低位砂体具有巨大的勘探潜力。

世界深水油气勘探现状及面临的挑战

分析了世界深水油气勘探现状。指出,由于陆地和浅水石油勘探程度较高,油气产量已接近峰值。世界新增油气储量已由陆地、浅水转向广阔的深水水域。近年全球获得的重大勘探发现中,有近50%来自深水水域。深水海域探明储量约为1000×108t油当量。墨西哥湾、巴西海域、西非海域以及被称为第2个波斯湾的南中国海是最有希望的深水油气区。为了开发南海深水油气资源,中海油总公司已迈出了重要的一步。笔者重点介绍了能适应深水勘探的主要钻井设备的研发现状,世界主要的钻井承包商及其市场占有情况,深水设备的日费以及使用情况。最后分析了世界深水勘探中所面临的挑战和技术难题,以及解决的方法。