Research advances on the mechanisms of reservoir formation and hydrocarbon accumulation and the oil and gas development methods of deep and ultra-deep marine carbonates

Based on the new data of drilling, seismic, logging, test and experiments, the key scientific problems in reservoir formation, hydrocarbon accumulation and efficient oil and gas development methods of deep and ultra-deep marine carbonate strata in the central and western superimposed basin in China have been continuously studied.(1) The fault-controlled carbonate reservoir and the ancient dolomite reservoir are two important types of reservoirs in the deep and ultra-deep marine carbonates. According to the formation origin, the large-scale fault-controlled reservoir can be further divided into three types:fracture-cavity reservoir formed by tectonic rupture, fault and fluid-controlled reservoir, and shoal and mound reservoir modified by fault and fluid. The Sinian microbial dolomites are developed in the aragonite-dolomite sea. The predominant mound-shoal facies, early dolomitization and dissolution, acidic fluid environment, anhydrite capping and overpressure are the key factors for the formation and preservation of high-quality dolomite reservoirs.(2) The organic-rich shale of the marine carbonate strata in the superimposed basins of central and western China are mainly developed in the sedimentary environments of deep-water shelf of passive continental margin and carbonate ramp. The tectonic-thermal system is the important factor controlling the hydrocarbon phase in deep and ultra-deep reservoirs, and the reformed dynamic field controls oil and gas accumulation and distribution in deep and ultra-deep marine carbonates.(3) During the development of high-sulfur gas fields such as Puguang, sulfur precipitation blocks the wellbore. The application of sulfur solvent combined with coiled tubing has a significant effect on removing sulfur blockage. The integrated technology of dual-medium modeling and numerical simulation based on sedimentary simulation can accurately characterize the spatial distribution and changes of the water invasion front.Afterward, water control strategies for the entire life cycle of gas wells are proposed, including flow rate management, water drainage and plugging.(4) In the development of ultra-deep fault-controlled fractured-cavity reservoirs, well production declines rapidly due to the permeability reduction, which is a consequence of reservoir stress-sensitivity. The rapid phase change in condensate gas reservoir and pressure decline significantly affect the recovery of condensate oil. Innovative development methods such as gravity drive through water and natural gas injection, and natural gas drive through top injection and bottom production for ultra-deep fault-controlled condensate gas reservoirs are proposed. By adopting the hierarchical geological modeling and the fluid-solid-thermal coupled numerical simulation, the accuracy of producing performance prediction in oil and gas reservoirs has been effectively improved.

Hydrocarbon Charging and Accumulation Process of the Large Bozhong19-6 Condensate Gas Reservoirs in the Southwestern Bozhong Sub-Basin,Bohai Bay Basin,China

The Bozhong19-6(BZ19-6)condensate gas reservoirs,located in the southwestern Bozhong sub-basin,Bohai Bay Basin,China,were paleo-oil reservoirs in the geological past and have undergone at least three successive hydrocarbon charging events.The hydrocarbon migration and accumulation process of“early oil and late gas”has occurred in the current reservoirs.At the end of the sedimentation of the Guantao Formation(N_(1)g,∼12 Ma),the reservoirs began to fill with first stage low-moderate mature crude oil.At the late stage of the Lower Minghuazhen Formation(N_(1)ml)(∼6.7 Ma),the reservoirs were largely charged with second stage high mature crude oil.Since the deposition of the upper Minghuazhen Formation(N_(2)m^(u),∼5.1 Ma),the paleo-oil reservoirs were transformed into shallow Neogene reservoirs due to the reactivation of basement faults.From the late stage of the N_(2)m^(u)to the present day(∼2.8–0 Ma),the reservoirs were rapidly filled by natural gas within a short period.In addition,analysis of the formation of the reservoir bitumen and the conspicuous loss of the lower molecular weight n-alkanes in the crude oil reveal that the injection of a large amount of gas in the late stage caused gas flushing of the early charged oil.

Buoyance-driven hydrocarbon accumulation depth and its implication for unconventional resource prediction

The discovery of unconventional hydrocarbon resources since the late 20th century changed geologists’understanding of hydrocarbon migration and accumulations and provides a solution to energy shortage.In 2016,unconventional oil production in the USA accounted for 41%of the total oil production;and unconventional natural gas production in China accounted for 35%of total gas production,showing strong growth momentum of unconventional hydrocarbons explorations.Unconventional hydrocarbons generally coexist with conventional petroleum resources;they sometimes distribute in a separate system,not coexisting with a conventional system.Identification and prediction of unconventional resources and their potentials are prominent challenges for geologists.This study analyzed the results of 12,237 drilling wells in six representative petroliferous basins in China and studied the correlations and differences between conventional and unconventional hydrocarbons by comparing their geological features.Migration and accumulation of conventional hydrocarbon are caused dominantly by buoyance.Wepropose a concept of buoyance-driven hydrocarbon accumulation depth to describe the deepest hydrocarbon accumulation depth driven dominantly by buoyance;beyond this depth the buoyance becomes unimportant for hydrocarbon accumulation.We found that the buoyance-driven hydrocarbon accumulation depth in petroliferous basins controls the different oil/gas reservoirs distribution and resource potentials.Hydrocarbon migration and accumulations above this depth is dominated by buoyancy,forming conventional reservoirs in traps with high porosity and permeability,while hydrocarbon migration and accumulation below this depth is dominated by non-buoyancy forces(mainly refers to capillary force,hydrocarbon volumeexpansion force,etc.),forming unconventional reservoirs in tight layers.The buoyance-driven hydrocarbon accumulation depths in six basins in China range from 1200mto 4200 m,which become shallowerwith increasing geothermal gradient,decreasing particle size of sandstone reservoir layers,or an uplift in the whole petroliferous basin.The predicted unconventional resource potential belowthe buoyance-driven hydrocarbon accumulation depth in six basins in China is more than 15.71×10^(9) t oil equivalent,among them 4.71×10^(9) t reserves have been proved.Worldwide,94%of 52,926 oil and gas reservoirs in 1186 basins are conventional reservoirs and only 6%of them are unconventional reservoirs.These 94%conventional reservoirs show promising exploration prospects in the deep area below buoyance-driven hydrocarbon accumulation depth.

Main progress and problems in research on Ordovician hydrocarbon accumulation in the Tarim Basin

The Tarim Basin is the largest petroliferous basin in the northwest of China, and is composed of a Paleozoic marine craton basin and a Meso-Cenozoic continental foreland basin. It is of great significance in exploration of Ordovician. In over 50 years of exploration, oil and gas totaling over 1.6 billion tonnes oil-equivalent has been discovered in the Ordovician carbonate formation. The accumulation mechanisms and distribution rules are quite complicated because of the burial depth more than 3,500 m, multi-source, and multi-stage accumulation, adjustment, reconstruction and re-enrichment in Ordovician. In this paper, we summarized four major advances in the hydrocarbon accumulation mechanisms of Ordovician carbonate reservoirs. First, oil came from Cambrian and Ordovician source rocks separately and as a mixture, while natural gas was mainly cracked gas generated from the Cambrian-Lower Ordovician crude oil. Second, most hydrocarbon migrated along unconformities and faults, with different directions in different regions. Third, hydrocarbon migration and accumulation had four periods： Caledonian, early Hercynian, late Hercynian and Himalayan, and the latter two were the most important for oil and gas exploration. Fourth, hydrocarbon accumulation and evolution can be generally divided into four stages： Caledonian （the period of hydrocarbon accumulation）, early Hercynian （the period of destruction）, late Hercynian （the period of hydrocarbon reconstruction and re-accumulation）, and Himalayan （the period of hydrocarbon adjustment and re-accumulation）. Source rocks （S）, combinations of reservoir-seal （C）, paleo-uplifts （M）, structure balance belt （B） matched in the same time （T） control the hydrocarbon accumulation and distribution in the Ordovician formations. Reservoir adjustment and reconstruction can be classified into two modes of physical adjustment and variation of chemical compositions and five mechanisms. These mechanisms are occurrence displacement, biodegradation, multi-source mixing, high-temperature cracking and late gas invasion. Late hydrocarbon accumulation effects controlled the distribution of current hydrocarbon. The T-BCMS model is a basic geological model to help understanding the control of reservoirs. At present, the main problems of hydrocarbon accumulation focus on two aspects, dynamic mechanisms of hydrocarbon accumulation and the quantitative models of oil-bearing in traps, which need further systemic research.

Exploring the potential of oil and gas resources in Sichuan Basin with Super Basin Thinking

Based on the contemporary strategy of Petro China and the“Super Basin Thinking”initiative,we analyze the petroleum system,the remaining oil and gas resource distribution,and the Super Basin development scheme in the Sichuan Basin with the aim of unlocking its full resource potential.We conclude that,(1)The three-stage evolution of the Sichuan Basin has resulted in the stereoscopic distribution of hydrocarbon systems dominated by natural gas.The prospecting Nanhua-rift stage gas system is potentially to be found in the ultra-deep part of the basin.The marine-cratonic stage gas system is distributed in the Sinian to Mid-Triassic formations,mainly conventional gas and shale gas resources.The foreland-basin stage tight sand gas and shale oil resources are found in the Upper Triassic-Jurassic formations.Such resource base provides the foundation for the implementation of Super Basin paradigm in the Sichuan Basin.(2)To ensure larger scale hydrocarbon exploration and production,technologies regarding deep to ultra-deep carbonate reservoirs,tight-sand gas,and shale oil are necessarily to be advanced.(3)In order to achieve the full hydrocarbon potential of the Sichuan Basin,pertinent exploration strategies are expected to be proposed with regard to each hydrocarbon system respectively,government and policy supports ought to be strengthened,and new cooperative pattern should be established.Introducing the“Super Basin Thinking”provides references and guidelines for further deployment of hydrocarbon exploration and production in the Sichuan Basin and other developed basins.

Regional unconformities and their controls on hydrocarbon accumulation in Sichuan Basin, sW China

Based on outcrop,seismic and drilling data,the main regional unconformities in the Sichuan Basin and their controls on hydrocarbon accumulation were systematically studied.Three findings are obtained.First,six regional stratigraphic unconformities are mainly developed in the Sichuan Basin,from the bottom up which are between pre-Sinian and Sinian,between Sinian and Cambrian,between pre-Permian and Permian,between middle and upper Permian,between middle and upper Triassic,and between Triassic and Jurassic.Especially,16 of 21l conventional(and tight)gas fields discovered are believed to have formed in relation to regional unconformities.Second,regional unconformity mainly controls hydrocarbon accumulation from five aspects:(1)The porosity and permeability of reservoirs under the unconformity are improved through weathering crust karstification to form large-scale karst reservoirs;(2)Good source-reservoir-caprock assemblage can form near the unconformity,which provides a basis for forming large gas field;(3)Regional unconformity may lead to stratigraphic pinch-out and rugged ancient landform,giving rise to a large area of stratigraphic and lithologic trap groups;(4)Regional unconformity provides a dominant channel for lateral migration of oil and gas;and(5)Regional unconformity is conducive to large-scale accumulation of oil and gas.Third,the areas related to regional unconformities are the exploration focus of large gas fields in the Sichuan Basin.The pre-Sinian is found with source rocks,reservoir rocks and other favorable conditions for the formation of large gas fields,and presents a large exploration potential.Thus,it is expected to be an important strategic replacement.

冀中坳陷潜山油气藏特征

由于碳酸盐岩储集体非均质性极强,造成油气分布十分复杂,使得冀中坳陷潜山油气勘探难度加大。该文利用石油地质、地球物理、有机地球化学等理论和方法,结合勘探实践,对冀中坳陷潜山油气藏特征进行了系统的研究。结果表明:潜山油气主要来源于古近系和石炭系—二叠系烃源岩;储集层主要由中上元古界和下古生界碳酸盐岩组成,储集空间主要为孔、洞、缝系统;古近系泥质岩、石炭系—二叠系煤系地层和潜山内幕泥质岩隔层构成了潜山油气藏良好的盖(隔)层,并发育2类、8套储盖组合;潜山发育的断层和不整合是油气的主要运移通道。根据圈闭类型的差异,将潜山油气藏分为潜山顶油气藏、潜山坡油气藏和潜山内幕油气藏3种类型。潜山油气近油源分布,具东富西贫、南油北气的特征,并在断裂带附近的潜山及潜山内幕圈闭中富集,构成了复式油气聚集带。研究成果有助于深入揭示冀中坳陷潜山油气成藏规律,对今后潜山圈闭评价、区带优选等也具有很好的指导作用。

鄂尔多斯大型含煤盆地岩性气藏成藏规律与勘探技术

鄂尔多斯盆地为—大型含煤盆地,天然气资源丰富。已发现了榆林、苏里格、乌审旗和米脂4大 气田,资源探明率lO．6％,勘探潜力较大。上古生界广泛发育的煤系地层为主要的烃源岩层,在晚侏罗 世至早白垩世末期盆地含煤烃源岩大面积成熟,表现为“广覆型”生烃模式。在大面积的低渗背景下, 天然气以近距离运移为主,生气强度控制气田的形成和分布;相对高孔高渗的三角洲平原分流河道砂体 为主要的储集体,是天然气富集的主要场所;由多个岩性圈闭组成的大型岩性圈闭是天然气成藏的主要圈闭类 型。针对上古生界的天然气地质特征,在勘探中,形成了一套适合长庆低渗透岩性气藏的勘探技术方法。

松南长岭地区坳陷层油气富集规律

以构造、层序和沉积研究为基础,从'层序控砂'和'微相控储'的角度预测有利储层分布;结合油气成藏条件分析,探讨松南长岭地区坳陷层油气富集规律。研究结果表明:层序旋回控制油气富集部位,重点含油层位靠近成熟烃源岩;沉积相控制有利储层发育区带,主要含油区呈环带状分布于三角洲前缘与滨浅湖的交互区域,水下分流河道和河口坝微相中的油气显示较多,且含油气性较好,为有利储集相带;基底断裂带和有利油气聚集区紧密相联,含油气带主要受继承性发育的基底断裂控制与影响;油气富集与地层展布形态、圈闭类型密切相关,中部平缓区为低幅度构造圈闭发育带,东部构造反转区为反转上倾尖灭的岩性和构造-岩性复合型圈闭发育带,而西部斜坡区于西掉断层上升盘,可形成低幅度构造和构造-岩性油气藏。

塔里木盆地巴楚—麦盖提地区志留—泥盆系油气成藏规律

塔里木盆地巴楚—麦盖提地区以寒武—奥陶系海相碳酸盐岩为烃源岩,志留—泥盆系三角洲-滨岸砂岩为储层,潮坪环境形成的致密泥岩为盖层,形成了断裂型生储盖组合,具有较好的油气勘探前景。通过对研究区志留—泥盆系沉积相带展布、断层发育特征以及古隆起和古斜坡的综合研究,结合烃源岩排烃及已发现油气特征,认为巴楚—麦盖提地区志留—泥盆系油气成藏规律主要受沉积和构造的共同控制,在二叠纪末,寒武—奥陶系烃源岩排烃期已经形成的单斜构造或斜坡带,被长期活动断层沟通了寒武—奥陶系烃源岩的志留—泥盆系储层分布区易于形成油气藏。区内有利油气成藏区带主要为康2-方1井之间的断裂带与玉1-BK8-巴5井之间的斜坡带,可能发育的油气藏类型为岩性油气藏和构造-岩性复合油气藏。

长垣南—古龙地区黑帝庙油层油气分布规律

为了认清长垣南—古龙地区黑帝庙油层油气分布规律,通过地层格架建立与沉积相划分、油源对比等方法,结合构造发育及圈闭特征,采用油气成藏地质条件综合分析方法,研究了油气成藏主控因素及油气藏特征。研究表明:黑帝庙油层发育构造、岩性2种类型油气藏,构造油气藏主要沿长垣南部地区葡萄花、敖包塔及敖包塔南构造带发育,岩性油气藏主要沿古龙地区砂岩上倾尖灭带分布;长垣南地区的油气主要来自供给相对不足的青山口组远源烃源岩,形成远源次生构造油气藏,古龙地区的油气主要来自供给充足的嫩一、二段近源烃源岩,形成近源原生岩性油气藏。

古龙凹陷向斜区油气聚集规律与勘探方法

针对古龙凹陷向斜区葡萄花油层岩性油藏的勘探潜力、勘探中面临的岩性油藏发育部位预测、油气聚集规律和薄储层预测技术等问题，分析了古龙凹陷具有形成大面积岩性油藏的地质条件。在葡萄花油层3个成藏带认识指导下，开展了以高分辨率层序地层研究为基础的大比例尺沉积微相工业制图、油藏精细解剖研究和薄储层预测技术攻关，进一步深化了向斜区岩性油气分布特征及油气成藏规律认识。通过深化勘探开发一体化评价提交了整装亿吨级储量，从而实现了古龙凹陷岩性油藏勘探的重大突破。在实践中探索形成的岩性油藏区带精细勘探及一体化评价思路和方法，对今后的油气勘探一体化评价工作具有重要的指导意义。

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.

东濮凹陷成藏动力学系统划分及其意义

根据高精度层序地层高频沉积旋回、泥岩欠压实、有机地球化学特征.结合封闭条件和盐湖盆地地层发育盖异性特征,东濮凹陷古近系—第四系地层自上而下可划分为5个成藏动力学系统,即顶部它源常压开放成藏动力学系统、上部混源常压开放成藏动力学系统、中部混合源弱超压半封闭成藏动力学系统、下部自源超压半封闭成藏动力学系统、底部自源超压封闭成藏动力学系统,其中、下部成藏动力学系统是东濮凹陷最重要的油气系统。这种成藏动力学系统划分对深化东濮凹陷油气勘探、寻找隐蔽性油气藏具有重要意义。

埕岛东部潜山油气成藏分析

针对埕岛东部潜山地质格局及油气成藏规律比较复杂、成藏特征认识不够深入等问题,通过对钻井、录井、构造解释及测试资料等的综合分析,研究其构造及地层特征,对其油气分布规律及成藏主控因素进行深入探讨。结果表明,受多期强烈构造运动的影响,研究区地层分布非常复杂,不同构造带或同一构造带不同构造部位的地层发育均存在差异。纵向上,埕岛东部潜山在太古界、下古生界、上古生界和中生界均有不同程度的油气富集,其中以下古生界最为富集,且主要分布于构造较高部位; 平面上,由构造主体向翼部,油气分布层位由老到新,油气藏类型由断块—残丘型油气藏向地层不整合油气藏过渡。通过对典型井的解剖,认为储盖组合和侧向封堵条件为研究区油气成藏的主控因素,由此建立埕岛东部潜山的油气成藏模式。

肇州油田扶杨油层油气富集规律

在肇州油田扶杨油层的构造特征,沉积特征研究基础之上,综合运用岩心、录井、测井及分析资料,通过对单井沉积相、已知探井的油气显示情况及试油结果进行分析,总结了扶杨油层的成藏影响因素和油气富集的规律,指出已发现的油气主要富集在垒堑带和复杂断裂带等有利构造区及厚度大、粒度大、分布稳定的分流河道中。研究结果为三肇凹陷扶杨油层油气富集区及有利勘探目标的预测提供了可靠的依据,满足了油田开发和生产的需求。

南皮斜坡孔二段成藏模式与富集规律

通过对沧东凹陷南皮斜坡构造特征及其砂体、成藏的控制作用研究,指出南皮继承性斜坡孔二段分布3种不同成因类型断裂(走滑断裂、同沉积断裂及继承性断裂),并且受燕山期构造翻转背景控制的古地貌呈沟谷相间的态势分布。认为古地貌凹槽区辫状河三角洲前缘富砂,其常规砂岩与湖盆区发育的泥质粉砂岩、白云岩、过渡岩类等致密储集层叠合连片,奠定连片成藏基础。详细阐述了南皮斜坡近源充注,源内砂体控藏新认识,构建斜坡区常规油藏聚集与远端细粒沉积区形成致密油叠加连片的油气富集模式。经有效指导勘探生产,部署实施预探井位10口,均见到良好油气显示并获得油流,形成整装规模增储区,成为大港油田增储上产的重点领域。

马东油田东南缘沙河街组一段下亚段油气成藏规律

马东油田东南缘深层油气资源(沙河街组一段下亚段)整体勘探程度低,对于油气成藏要素、油气藏类型及油气分布规律认识尚不明确。通过对该区油气藏分布特征的分析认为,马东油田东南缘主要发育构造油气藏、岩性油气藏以及构造-岩性复合油气藏共3种类型。针对不同的油气藏类型,进行成藏要素及成藏规律的深入研究表明,马东地区古近系以来的构造演化控制了该区的沉积体系、圈闭类型及油气富集规律,现今的油气分布与各成藏要素形成时间及匹配关系密切相关,MD8井区及MD5井区为马东油田东南缘的主要油气富集区。

Theory, Technology and Practice of Unconventional Petroleum Geology

0 INTRODUCTION The breakthroughs in unconventional petroleum have a great impact on world petroleum industry and innovation in petroleum geology(Dou et al,2022;Jia,2017;Zou et al.,2015b,2014a;Yerkin,2012;Pollastro,2007;Schmoker,1995).The exploration and development evolution from conventional petroleum to unconventional petroleum and more and more frequent industrial activities of exploring petroleum inside sources kitchen have deepened theoretical understanding of unconventional petroleum geology and promoted technical research and development(Jia et al.,2021,2017;Jin et al.,2021;Zhao W Z et al.,2020;Ma Y S et al.,2018,2012;Zou et al.,2018b,2016,2009;Dai et al.,2012).We have introduced and extended the theory of continuous hydrocarbon accumulation since 2008 and published several papers/books(in Chinese and English)with respect to unconventional petroleum geology since 2009,basically forming the theoretical framework for this discipline(Yang et al.,2022a,2021a,2019a,,2015a;Zou et al.,2019c,2017b,2014a,,2013a).In this paper,we present the background of unconventional petroleum geology,review the latest theoretical and technological progress in unconventional petroleum geology,introduce relevant thinking and practices in China,and explore the pathway of unconventional petroleum revolution and multi-energy coordinated development in super energy basins,hopefully to promote the unconventional petroleum geology and industry development.