Formation conditions and exploration direction of large natural gas reservoirs in the oil-prone Bohai Bay Basin, East China

The Bohai Bay Basin is a typical oil-prone basin, in which natural gas geological reserves have a small proportion. In this basin, the gas source rock is largely medium-deep lake mudstone with oil-prone type Ⅱ2-Ⅱ1 kerogens, and natural gas preservation conditions are poor due to active late tectonic movements. The formation conditions of large natural gas fields in the Bohai Bay Basin have been elusive. Based on the exploration results of Bohai Bay Basin and comparison with large gas fields in China and abroad, the formation conditions of conventional large-scale natural gas reservoirs in the Bohai Bay Basin were examined from accumulation dynamics, structure and sedimentation. The results show that the formation conditions of conventional large natural gas reservoirs in Bohai Bay Basin mainly include one core element and two key elements. The core factor is the strong sealing of Paleogene "quilt-like" overpressure mudstone. The two key factors include the rapid maturation and high-intensity gas generation of source rock in the late stage and large scale reservoir. On this basis, large-scale nature gas accumulation models in the Bohai Bay Basin have been worked out, including regional overpressure mudstone enriching model, local overpressure mudstone depleting model, sand-rich sedimentary subsag depleting model and late strongly-developed fault depleting model. It is found that Bozhong sag, northern Liaozhong sag and Banqiao sag have favorable conditions for the formation of large-scale natural gas reservoirs, and are worth exploring. The study results have important guidance for exploration of large scale natural gas reservoirs in the Bohai Bay Basin.

Technological progress and development directions of PetroChina overseas oil and gas field production

This study reviews the development history of PetroChina’s overseas oil and gas field development technologies, summarizes the characteristic technologies developed, and puts forward the development goals and technological development directions of overseas business to overcome the challenges met in overseas oil and gas production. In the course of PetroChina’s overseas oil and gas field production practice of more than 20 years, a series of characteristic technologies suitable for overseas oil and gas fields have been created by combining the domestic mature oil and gas field production technologies with the features of overseas oil and gas reservoirs, represented by the technology for high-speed development and stabilizing oil production and controlling water rise for overseas sandstone oilfields, high efficiency development technology for large carbonate oil and gas reservoirs and foamy oil depletion development technology in use of horizontal wells for extra-heavy oil reservoirs. Based on in-depth analysis of the challenges faced by overseas oil and gas development and technological requirements, combined with the development trends of oil and gas development technologies in China and abroad, overseas oil and gas development technologies in the future are put forward, including artificial intelligence reservoir prediction and 3 D geological modeling, secondary development and enhanced oil recovery(EOR) of overseas sandstone oilfields after high speed development, water and gas injection to improve oil recovery in overseas carbonate oil and gas reservoirs, economic and effective development of overseas unconventional oil and gas reservoirs, efficient development of marine deep-water oil and gas reservoirs. The following goals are expected to be achieved: keep the enhanced oil recovery(EOR) technology for high water-cut sandstone oilfield at international advanced level, and make the development technology for carbonate oil and gas reservoirs reach the international advanced level, and the development technologies for unconventional and marine deep-water oil and gas reservoirs catch up the level of international leading oil companies quickly.

Key technologies, engineering management and important suggestions of shale oil/gas development: Case study of a Duvernay shale project in Western Canada Sedimentary Basin

The Duvernay project in Canada was taken as an example to summarize the advanced technology and engineering management model of shale oil and gas development in North America.Preliminary suggestions were put forward to accelerate the commercial development of domestic continental shale oil and gas.The advanced technologies,valuable knowledge and rich experience were introduced,including the evaluation of geological target area of the project,rapid long horizontal drilling and completion,high-intensity fracturing,and well spacing optimization.In particular,the concept and connotation of the full-life cycle management of North American unconventional resource projects were analyzed.Its emphasis on early evaluation and risk management,and a highly competitive market environment have played an important role in promoting technological innovation and management innovation.In addition,the low-cost sharing system of industry-wide knowledge and experience and the management mode were applied.These management approaches are of great significance for reference in accelerating the exploration and development of unconventional resources in China.China possesses abundant shale oil and gas resources,which are an important replacement to guarantee the national oil and gas energy supply.However,due to the late start and special geological characteristics and engineering difficulties in China,there is a large gap in technology level and management mode compared with North America.According to the advanced experience and enlightenment of the shale oil and gas development in North America,a preliminary proposal to accelerate the development of shale oil and gas in China was made.

Geological characteristics of large gas provinces and large gas fields in China

Based on the examination of the global researches on oil and gas provinces and large gas fields and the analysis of the features,attributes and distribution of large gas provinces and gas fields,this paper puts forward three indicators of determining large oil and gas provinces:spatial indicator,reservoir-forming indicator and resource indicator.It classifies the gas accumulated areas and large gas provinces in China and analyzes the controlling factors on the distribution of large gas provinces and large gas fields:the lateral distribution is mainly controlled by high-energy sedimentary facies and constructive diagenetic facies,palaeo-highs and their periclinal zones,deep faults,etc,and the vertical distribution is mainly controlled by unconformities,series of evaporates and deep low-velocity highly-conductive beds,etc.It also reveals the main geological characteristics of large gas provinces and large gas fields in China.Large gas fields in four-type basins have their own characteristics and onland large gas fields are dominantly developed in foreland basins and craton basins;there are three types of gas sources,of which,coal is the main source with high gas generating intensity and varying origins;reservoir rocks of the large gas fields(provinces)are of various types and dominated generally by low-middle permeability and porosity pore-type reservoirs;structural traps and litho-stratigraphic traps coexist in Chinese large gas fields and form dense high abundance and large-area low and middle-abundance large gas fields;most of the large gas fields have late hydrocarbon-generation peaks and reservoir formation,and experienced the process of multiple-stage charging and late finalization; large gas provinces(fields)have good sealing and preservation conditions,and evaporates seals are largely developed in large and extra-large gas fields.This paper intends to shed light on the exploration and development of large gas fields(provinces)through analyzing their geological characteristics.

Characteristics and accumulation mode of large-scale Sinian-Cambrian gas reservoirs in the Gaoshiti-Moxi region, Sichuan Basin

The Sinian-Cambrian formations of the Sichuan Basin have favorable hydrocarbon accumulation conditions,but the exploration for large-scale gas fields is quite challenging due to old strata and multiple tectonic movements.Since the Weiyuan Sinian large gas field was found in 1964,the largest monoblock gas field(Anyue Gasfield)was discovered in the Cambrian Longwangmiao Formation of the Moxi region in 2013 with proven gas reserves of 440.1×109 m3.Total proven,probable and possible reserves exceed one trillion cubic meters in the Sinian Dengying Formation and the Cambrian Longwangmiao Formation of the Gaoshiti-Moxi region.The natural gas components,light hydrocarbons,reservoir bitumen abundance and other evidences prove that the dry natural gas was mainly derived from oil-cracking,with methane(a content of 82.65%-97.35%),ethane(a content of 0.01%-0.29%),nitrogen(a content of 0.44%-6.13%),helium(a content of 0.01%-0.06%),and hydrogen sulphide(0.62-61.11 g/m^(3)).Gas reservoir pressure increases gradually from the Sinian normal pressure(a pressure coefficient of 1.07-1.13)to high pressure(a pressure coefficient of 1.53-1.70)in the Cambrian Longwangmiao Formation.The temperature of the gas reservoir is 137.5-163 ℃.Gas reservoir traps are divided into three categories:tectonic type,tectonic-formation type and tectonic-lithologic type.The large-scale enrichment of the Sinian-Cambrian natural gas results from effective configuration of the large stable inherited palaeo-uplift during the Tongwan tectonic movement,wide distribution of ancient source rocks,high-quality reservoirs with vast pore-cavity,crude oil cracking of large palaeo-reservoirs and favorable preservation conditions.According to the palaeo-structure pattern prior to crude oil cracking of the palaeo-reservoirs,and bitumen abundance as well as the distribution characteristics of current gas reservoirs,the accumulation patterns of the cracking gas reservoir can be classified into three types:accumulation type,semi-accumulation and semi-dispersion type,and dispersion type.This understanding will play an important role in guiding the exploration of the Sinian-Cambrian natural gas exploration in the Sichuan Basin.

Sichuan super gas basin in southwest China

A sedimentary basin is classified as a super basin when its cumulative production exceeds 5 billion barrels of oil equivalent(6.82×10^(8) t of oil or 7931.66×10^(8) m^(3) of gas)and its remaining recoverable resources are at least 5 billion barrels of oil equivalent.By the end of 2019,the total output of oil and gas in Sichuan Basin had been 6569×10^(8) m^(3),the ratio of gas to oil was 80:1,and the total remaining recoverable resources reached 136404×10^(8) m^(3),which makes it as a second-tier super basin.Because the output is mainly gas,it is a super gas basin.The reason why the Sichuan Basin is a super gas basin is that it has four advantages:(1)The advantage of gas source rocks:it has the most gas source rocks(9 sets)among all the basins in China.(2)The advantage of resource quantity:it has the most total remaining recoverable resources among all the basins in China(136404×10^(8) m^(3)).(3)The advantage of large gas fields:it has the most large gas fields(27)among all the basins in China.(4)The advantage of total production:by the end of 2019,the total gas production had been 6487.8×10^(8) m^(3),which ranked the first among all the basins in China.There are four major breakthroughs in natural gas exploration in Sichuan Basin:(1)Breakthrough in shale gas:shale gas was firstly found in the Ordovician Wufeng-Silurian Longmaxi formations in China.(2)Breakthrough in tight sandstone gas:the Triassic Xu2 Member gas reservoir in Zhongba gas field is the first high recovery tight sandstone gas reservoir in China.(3)Breakthrough in giant carbonate gas fields.(4)Breakthrough in ultra-deep gas reservoir.These breakthroughs have led to important progress in different basins across the country.Super basins are classified according to three criteria:accumulative oil and gas production,remaining recoverable resources,tectonic attributes of the basin and the proportion of oil and gas in accumulative oil and gas production.

Hydrocarbon source systems and formation of gas fields in Sichuan Basin

The formation of large and middle gas fields in Sichuan Basin is investigated based on source controlling theory and hydrocarbon source systems. It is indicated that (?)1, S1, P1, P2 and T3 are the main source beds and (?)1/Z2d, C2h/S1, P1/P2, P2ch/P2, T1,2/P, T3x/T3x are important hydrocarbon source systems in the basin. All these source systems are the prospective formations and exploration spaces of large and middle gas fields. It is also emphasized that hydrocarbon generation intensity is the most important geochemical factor to estimate large and middle gas fields.

油页岩大规模原位开采数值模拟研究及开采参数讨论

为了研究原位裂解过程中不同规模井组温度场和生烃量的差异,分别对六边形井组数量为7个、19个、37个和61个四种情况油页岩原位开采生产模型进行了建模,以吉林省扶余县油页岩开采试验区为试点区,在使用ANSYS软件的Mesh模块对模型进行加密网格化的基础上,使用Fluent进行了流体场和温度场模拟;通过求解化学反应动力学方程组进行了油页岩生烃过程模拟,并进行了不同井间距、注气速率和双裂缝间距情况下的模拟。模拟结果表明,大规模油页岩原位开采过程中油页岩生烃主要分为三个阶段,即快速生烃阶段(注热前500d)、缓慢生烃阶段(注热500~1 500d)和平稳阶段(注热1 500~3 000d)。增加井组数量可以提高热烟气对中心加热区域的热利用效率。但增加井组数量对单井组生烃量和能源回报率的增幅逐步减小,当井组数量从37个增加到61个时,加热为3 000d时的单井组生烃量增率小于3.1%,能源回报率增率小于8.7%,因此进行油页岩原位开采时选取37个或37以上的井组数量为获得高能源回报率的最佳方案。在61个井组条件下,不同开采参数模型达到最大能源回报率的开采参数为井间距30m、注气速率12m/s和裂缝间距1m,在该开采参数条件下获得最大能源回报率需要进行600~750d的持续注热。

埕岛油田勘探实践与认识

埕岛油田位于山东省东营市以北的浅海海域 ,是具有 7套含油层系、十余种油藏类型、4种流体性质的大型复式油气聚集区。针对 3套目的层系石油地质特征和海上勘探高投入、高风险的特点 ,采用不同三维地震储集层描述技术 :采用测井约束反演技术描述馆陶组河道砂储集层 ;采用地层基准面原理和基准面旋回对比技术预测东营组和沙一段的水下扇体储集层分布 ;采用合成声波测井等技术完成全区太古界、下古生界的储集层横向描述和预测。 1984年至 1999年 ,按选带、控层、逐层深入的思路进行勘探 ,探井部署中采用多参数、神经网络等储集层描述和油气检测技术 ,缩短了勘探开发进程 ,取得了较好的经济效益 ,每口井平均探明储量 560× 10 4 t。图 3参 2 (王孝陵摘 )

中国各类陆相盆地斜坡区大中型岩性型油气田形成特征

我国陆相含油气盆地斜坡区大中型岩性型油气田主要发育于4类盆地之中:a)陕甘宁中生界稳定克拉通盆地具有中等油气资源丰度,盆地东北部的大型河流-三角洲砂体成为大型汇烃系统,将西南部生烃中心的油气源源不断地导向盆地东北部,在燕山Ⅳ幕东部强烈隆升改造作用下,呈南北向展布的盆地东北部三角洲砂体向东尖灭,形成大中型岩性油气田;b)松辽盆地为晚白垩世大型热衰减坳陷盆地,具有高—特高油气资源丰度,东部斜坡区发生反转掀斜改造,使纵向叠置、呈径向展布的大中型三角洲砂体与区域性断层及深部隆起复合形成大中型岩性-断层型油气田;c)准噶尔、川西、塔里木等中新生代大型前陆盆地,主力凹陷常发育大中型汇烃单元,且具有中等油气资源丰度,其斜坡区发育呈径向展布的一系列中小型裙边状扇体,配合斜坡区的大型古隆起背景、地层超覆尖灭和断层,形成大中型岩性型油气田;d)我国东部中新生界张性断陷盆地构造分割性极强,以发育小型汇烃单元为主,在具有高—特高油气资源丰度的凹陷,其斜坡区坡折带纵向叠置的大型扇三角洲及水下冲积扇体,与断层、火山岩体、泥底辟等叠合形成大中型岩性型油气藏。

中国中、低丰度大油气田基本特征及形成条件

近年中国陆上发现的一批中、低丰度大型油气田具有低孔渗、小油(气)柱、低储量丰度和规模大等特点。中、低丰度油气藏大面积成藏的有利条件是:大型敞流湖盆腹地发育大型牵引流成因砂体,与烃源岩呈"三明治"结构大面积间互,为成藏奠定了基础;小油气柱、常压—低压系统降低成藏对盖层质量的要求;储集体内部非均质性强烈,气藏整体连通性差,降低了气体逸散能量,保证油气在包括地质条件相对劣质区的大范围成藏;抬升卸载环境导致气源岩解吸面状排烃,有利于晚期大面积成藏。研究表明,中国陆上大型坳陷盆地向斜区具有发现大型岩性油气藏的良好前景,这一认识已在鄂尔多斯、松辽和四川盆地向斜区油气勘探中发挥了指导作用,推动油气储量大幅度增长,未来仍有良好发展潜力。

东海西湖凹陷大中型油气田形成条件及勘探方向

为了解决东海西湖凹陷保俶斜坡带勘探成效差以及中央背斜带勘探效果南北差异大的问题,通过盆地分析理论体系对西湖凹陷石油地质条件进行了系统研究和重新认识,认为保俶斜坡带和中央背斜带由于构造格局及构造演化的差异形成了不同的油气成藏体系,有利成藏要素的叠合区为大中型油气田的发育区。保俶斜坡带以断陷构造层为主,晚期挤压弱,构造定型早,具有"紧邻富生烃洼陷、发育多期叠置的规模储集体、形成多类型构造-岩性复合圈闭、具有良好的垂向封盖条件以及发育网毯式高效输导体系"的有利成藏条件。近生烃洼陷的断层坡折带及地貌坡折带处形成的大型潮控三角洲砂体上倾尖灭带为大中型油气田发育区。中央背斜带经历了拗陷期强烈挤压,形成了大型反转背斜,具有"先存古构造背景、发育大型构造-岩性复合圈闭、断砂配置条件好以及具备高效储盖组合"四元控藏的特征,成藏条件叠合较好的龙井、古珍珠、湖心亭等地区是大中型气田发育区。

松辽盆地断陷层系大、中型油气田形成条件及勘探方向

松辽盆地断陷层系大、中型油气田主要分布于贯穿松辽盆地中央区域的北北东向孙吴-双辽岩石圈断裂两侧的深断陷之中。这些深断陷具有良好的成油气地质条件:1)断陷持续快速沉降,且周边断陷阻隔了盆缘大型物源,使之发育继承性大型深水、半深水湖泊,形成巨厚烃源岩系;2)在早-中燕山期的强烈走滑拉张时期,发生强烈走滑拉分作用,引发盆地火山活动及快速深陷,发育深水、半深水湖相泥岩夹火山岩、碎屑岩建造,由此形成火山岩、砂岩两类储集体;3)在断陷形成后,仍继承性快速沉降,披覆坳陷层系多套具有异常压力的巨厚湖相泥、页岩系,使断陷烃源岩持续热演化生烃,并使断陷具有良好的天然气封盖条件;4)后期稳定沉降,未发生强烈抬升,区域盖层保存良好,从而具有良好的气藏保存条件;5)基底深断裂在晚白垩世活动性明显减弱,对天然气藏的破坏明显减小。主要深断陷油气聚集规律研究表明,大、中型油气田分布在箕状深断陷生烃中心周缘发育的缓坡坡折带、坡垒带及陡坡坡折带上的一批近东西向继承性鼻状隆起构造与地层超覆尖灭、岩性复合圈闭之中,其中两个深断陷之间的隆起带是大油气田最有利的分布区域。

阿尔金斜坡东段新生代断裂系统及大型油气田形成

利用钻井和地震资料,对柴达木盆地阿尔金斜坡东段新生代断裂系统的几何学特征和演化过程进行了系统的梳理,根据平面展布,把研究区新生代断裂分为北西向、北东东向和北西西向三组;根据断裂演化特征,又将其分为古新世-始新世形成尖顶山地区北西西向北倾断裂,东坪—牛鼻子梁—鄂博梁鼻状构造带北西向断裂正反转,中新世北东向断裂形成和上新世北西西向南倾压扭断裂发育3个阶段;采用趋势法地层恢复技术与回剥法构造平衡手段,结合材料力学原理,恢复了新生代各主要地质时期古应力场的最大主压应力方向;根据最大主压应力方向与断裂活动之间的关系,对各主要断裂的封闭、开启作用进行了讨论,认为新生代断裂在山前斜坡带大气田形成过程中起着重要作用。

巴西坎普斯盆地盐下层系油气发现及其勘探潜力

2002—2012年间,在巴西坎普斯盆地盐下层系接连发现了15个油气田,可采储量7×108t油当量,其中大型油气田11个,凸显了坎普斯盆地的石油潜力,使得该盆地盐下层系成为继桑托斯盆地之后新的勘探热点。坎普斯盆地经历了裂谷期、过渡期和漂移期3个构造演化阶段,盐下层系是裂谷期(侏罗纪晚期—阿普特早期)沉积的典型陆相沉积体系,包括欧特里夫阶裂缝发育的玄武岩基岩和阿普特阶至巴雷姆阶的碳酸盐岩。盆地的主要烃源岩是下白垩统LagoaFeia群黑色钙质页岩,该烃源岩有极好的生烃潜力;盆地发育多套储层。坎普斯盆地盐下层系勘探程度低,目前油气探明率只有约50%,油气潜力巨大。坎普斯盆地盐下层系勘探前景十分广阔,应是未来储量增长最快的领域。勘探的重点地区是中央隆起带;主要油藏类型是LagoaFeia群自生自储型油气藏;主要圈闭类型是碳酸盐岩岩性—构造型圈闭。

管道周围土壤温度场变化的大型环道试验

借助大型试验环道,对热油管道预热和停输温降过程中土壤温度场的变化进行了试验研究。考察了流量变化、油温升降、停输等工况对土壤温度场的影响。频繁的停输再启动不利于温度场的建立和恢复;停输过程中,土壤降温幅度随管道距离的增大而减小;土壤的降温幅度与停输降温影响的范围以及测点获得热量和散失的热量有关。对于土壤温度场变化规律的认识和所获得的大量试验数据,可用于相关计算程序的检验和校核。

塔里木盆地大中型油气田成控因素与展布规律

塔里木盆地油气分布十分复杂,油气藏形成及分布受多种因素控制。烃源岩分布及其热演化决定了油气田的平面分布,优质区域盖层和储盖组合控制油气富集的纵向分布,长期继承发育的大型稳定古隆起、古斜坡以及前陆逆冲构造带是大中型油气田形成的最有利地区,构造-岩性圈闭及低幅度构造圈闭控制上古生界—中生界油气成藏,多源多期动态成藏-早期成藏改造、晚期充注调整是塔里木盆地油气成藏的重要机理。碳酸盐岩领域重点突出大型表生岩溶型和礁滩相溶蚀孔隙型等复合圈闭的勘探,碎屑岩领域应突出志留系大型地层超覆型、构造-岩性圈闭。塔北地区的阿克库勒凸起及雅克拉断凸是近期增储上产的地区,应加强该区的多层系复合油气藏立体勘探。塔中古隆起、和田河古隆起、巴楚隆起、古城墟古隆起、玛南断褶带是进一步寻找大油气田的有利目标区。超深层及寒武系盐下白云岩领域值得进一步探索。

中国近海油气勘探进展

近年来,中国近海的油气勘探坚持以寻找大中型油气田为指导思想,以区域研究为基础,以科学合理部署为保证,针对中国近海独特的油气地质特征,通过创新认识和技术进步,坚持走高效勘探之路,取得了丰硕成果,新发现储量屡创历史新高,步入了历史上最好时期。然而,随着勘探程度的提高和勘探领域的拓展,中国近海油气勘探也面临越来越多的挑战。

塔里木盆地塔河油田奥陶系大型油气藏形成条件

塔河油田位于塔里木盆地北部沙雅隆起阿克库勒凸起的西南部,它是在长期发育的阿克库勒鼻状古隆起基础上形成的下奥陶统碳酸盐岩岩溶-缝洞型大型油气田。受区域构造-沉积背景控制,塔河地区下奥陶统属于碳酸盐岩开阔台地环境,一直处于继承性隆起状态,是油气运聚的长期指向区,并经历了多期次的构造运动、岩溶作用和成岩作用的叠加改造,形成了具强烈非均质性的岩溶-缝洞型储层,油气主要赋存于距风化壳不整合面200m范围内的岩溶缝洞系统中。勘探成果表明,长期发育的继承性古隆起、丰富的多油源供给、强烈非均质性的岩溶-缝洞型储层及优良的储盖配置、多层次和多类型圈闭的广泛发育、以及由岩溶缝洞-断裂-不整合面组成的疏导体系,是形成塔河大型油气田的重要条件。

全球5个深水盆地带油气地质特征

深水油气是当今世界勘探的三大热点之一。基于板块构造理论,全球海洋深水油气盆地沿“三竖两横”5个巨型带分布,“三竖”是近南北走向的大西洋陆缘深水盆地带、东非陆缘深水盆地带、西太平洋陆缘深水盆地带;“两横”是近东西走向的新特提斯构造域陆缘深水盆地带与环北冰洋陆缘深水盆地带。在以上5个盆地带均有巨型—大型油气区发现,共15个。研究发现,巨型—大型油气区形成受三大因素控制。首要因素是发育世界级烃源岩,包括大型湖相、海陆过渡相和海相3类烃源岩,其中湖相烃源岩主要发育于南大西洋陆缘盆地,海相烃源岩分布在北大西洋陆缘盆地、东非陆缘盆地等海湾环境,海陆过渡相烃源岩主要分布在西太平洋陆缘盆地和新特提斯构造域陆缘盆地大型煤系河流三角洲。第二个因素是发育世界级优质储层,包括碎屑岩和碳酸盐岩两类:碎屑岩储层主要是受大型河流—三角洲控制发育的浊积扇,碳酸盐岩主要与介壳灰岩等有关。第三个因素是世界级圈闭群发育,包括盐构造圈闭、重力滑脱构造圈闭、巨型逆冲退覆构造圈闭、大型浊积体岩性圈闭等。全球海洋深水盆地勘探具有不平衡、不充分特征,存在战略拓展、战略突破、战略发现和战略准备4个战略领域。战略拓展方向包括已证实巨型—大型油气区已证实的富油气成藏组合,是目前获取储量的主要领域,是投资风险小、见效快的投资方向。战略突破方向主要包括已证实巨型—大型油气区的新成藏组合,是烃源岩条件已证实的领域,实现商业性发现的风险小。战略发现方向是已有油气显示或潜在商业发现的潜在油气区,存在规模性发现的潜力。战略准备方向是目前还没有发现、但存在大发现可能的区域。总体看,全球深水油气勘探潜力巨大。