中国叠合盆地超深层油气资源丰富,是重要的战略接替领域。勘探研究与实践揭示,超深层油气成藏条件具有两分性:有利成藏条件只存在于特定的盆地环境,具有地域性;不利成藏条件是超深层固有属性,具有普遍性。烃源灶有效且有规模、储集层至今保持有效储集性能且有规模、生-储-盖要素存在空间组合且至今保持有效性是超深层是否具有勘探价值的决定性要素。有利于超深层具备勘探潜力的盆地具有以下特征:①存在克拉通差异沉降演化,且在漫长地质历史时期未被深埋,烃源灶发育且至今仍在有效生烃窗口;②发育碳酸盐岩为主的沉积层系,存在颗粒型台缘和台内滩并经过建设性成岩作用改造,或者在地质历史时期曾经历地下 水溶蚀淋滤,使超深层孔隙(含裂缝、溶洞)发育的储层至今依然有效;③碎屑岩、基岩或火山岩储层发育需要满足长期浅埋+ 后期深埋且深埋时间不长、存在构造桥的托举作用、较少压实作用影响、构造作用产生裂缝或长期风化作用建设性改造结晶岩类等单一要素或多种要素组合作用;④盆地总体呈中—低地温场,或烃源岩发育阶段环境中无过量放射性物质存在,规模生烃过程不被速化。不利于超深层成藏的原因有:①机械压实和高温高压导致超深层成岩作用强、岩石颗粒塑性增加,不利于储层孔隙空间的保存;②超深层因埋藏深、埋藏历史长,多数烃源岩已经失去生烃能力,烃源灶有效性受限;③形成生-储-盖-圈有效组合的机会偏少,且有经济性的资源成矿几率降低。中国超深层油气资源丰富,勘探潜力大,但规模勘探面临着成藏理论有待完善、工程技术有待提高等挑战,亟待开展攻关研究。

The ultra-deep oil and gas resources are abundant in China’s superimposed basins, which are an important strategic replacement field. The exploration and research work has revealed that there is a dichotomy of accumulation conditions for ultra-deep oil and gas reservoirs; favorable accumulation conditions only exist in specific basin environments, characterized with regionality, while the unfavorable accumulation conditions are inherent attributes of ultra-deep layers, characterized with universality. The decisive factors determining whether ultra-deep layers have exploration value are the effectiveness and scale of source kitchens, the effective reservoir and its scale, as well as the spatial combination and effectiveness of source, reservoir, and cap. The basins with exploration potential in ultra-deep layers have the following characteristics: (1) there is differential subsidence evolution in cratons, which have not been deeply buried during a long geological history, and where source kitchens are developed and still in an effective hydrocarbon-generation window to this day; (2) sedimentary strata mainly composed of carbonate rocks are developed, with granular platform marginal-platform shoals and intraplatform shoals, and have undergone constructive diagenesis and modification, or have experienced groundwater dissolution and leaching during geological history, as result of which reservoirs with pores in ultra-deep layers (including fractures and caves) are developed and have been effective till today; (3) the development of clastic rock, basement, or volcanic reservoirs requires a combination of single or multiple factors, such as long-term shallow burial and later deep burial with a short burial time, the presence of structural bridges for supporting effect, less compaction, the generation of fractures by tectonism, or long-term weathering for constructive reformation of crystalline rocks; (4) the basin generally presents a medium to low geothermal field, or there is no excessive radioactive material in the environment during the development of source rock, and the large-scale hydrocarbon generation is not accelerated. The reasons for the occurrence of unfavorable accumulation conditions in ultra-deep layers include: (1) mechanical compaction and high temperature and pressure result in strong diagenesis and increased plasticity of rock particles in ultra-deep layers, which is not favorable to the preservation of reservoir pore space; (2) most source rocks in ultra-deep layers have lost their hydrocarbon-generation potential, and the effectiveness of source kitchens is limited due to deep burial and long burial history; (3) there is a low probability for forming an effective combination of source-reservoir-seal-trap, and the probability of economic resource mineralization is reduced. China has abundant oil and gas resources and great exploration potential in ultra-deep layers, but large-scale exploration faces challenges in terms of the hydrocarbon accumulation theory to be perfected and engineering technology, and it is urgent to carry out researches to achieve relevant breakthroughs.

中国海相碳酸盐岩具有年代老、埋藏深、后期成岩改造强的特点,随着油气勘探逐渐走向“更老”、“更深”、“更复杂”的深层和超深层,碳酸盐岩储集层成因和分布规律成为影响油气勘探开发效益的关键因素。近年来,在塔里木、四川和鄂尔多斯三大海相盆地多个领域取得了一系列的勘探新突破,古老超深层碳酸盐岩储集层地质理论和相关技术取得显著进展。地质理论进展包括: (1)近地表环境成因孔隙构成超深层碳酸盐岩储集层的基础; (2)浅埋藏阶段的孔隙保持是决定超深层储集层质量的关键; (3)构造活动驱动深部流体运动对储集层质量具有重要改造作用。技术进展包括微量稀土元素面扫、激光U-Pb定年、团簇同位素和非传统稳定同位素等储集层地球化学实验分析技术和高温高压溶蚀模拟技术。勘探的深入和分析技术手段的进步,显著提升了对三大盆地重点领域规模优质储集层发育及分布规律的认识,为下步油田勘探取得重大突破奠定了基础。

Marine carbonate rocks in China are featured by old age,deep burial,and strongly diagenetic modification during the burial stage. As oil and gas exploration gradually extents towards “older”,“deeper”,and “more complex”deep and ultra-deep layers,the genesis and distribution patterns of carbonate reservoirs have become key factors affecting the efficiency of oil and gas exploration and development. In recent years,a series of exploration breakthroughs have been made in multiple exploration fields in the Tarim,Sichuan,and Ordos basins. Meanwhile,substantial progress has been made both in the geological theory and in the related technologies of ancient deep carbonate reservoirs. Advancements in geological theory include the following aspects: (1)porosity formecl under subaerial environment constitutes the basis of the deeply-buried carbonate reservoir size;(2)the preservation of porosity during shallow burial period is the key to the size and the quality of the deeply-buried dolomite reservoir;and(3)tectonic activity-driven deep fluid movements play an important role in modifying the quality of deeply-buried carbonate reservoir. Technological advancements include: (1)geochemically experimental analysis techniques such as surface scanning of trace rare earth elements,laser-ablation U-Pb dating,clumped isotopes and non-traditional stable isotopes;and(2)high-temperature and high-pressure dissolution simulation techniques. The deepening of exploration realm and the progress of analytical techniques have significantly improved the understanding of the development and distribution of large-scale high-quality reservoirs in deeply buried fields of the three major basins,and built the foundation for major breakthroughs in oil field exploration in the future.

近年来四川盆地蓬深10、合深9、潼深17和正阳1等井钻探证实深层上二叠统长兴组发育一套孔隙型礁滩复合体灰岩储层，突破了深层碳酸盐岩大油气田主要分布于孔隙型白云岩储层和岩溶缝洞型灰岩储层的传统认识。基于岩心和薄片观察、储层地球化学特征分析、井震联合的储层识别和追踪，开展深层礁滩灰岩孔隙形成机理研究，取得4个方面认识：①深层长兴组孔隙型礁滩复合体灰岩储集空间以粒间孔、格架孔、生物体腔孔、铸模孔和溶孔为主，形成于沉积和早表生环境；②断续分布的多孔礁滩复合体被相对致密的泥晶灰岩包裹，在复合体持续增温条件下导致局部异常高压的形成；③长兴组储层的底板为上二叠统吴家坪组互层的致密泥岩和灰岩，顶板为下三叠统飞仙关组一段致密泥晶灰岩夹泥岩，在致密顶底板的夹持下，导致长兴组区域异常高压的形成；异常高压（超压封存箱）是沉积和早表生环境形成的孔隙在深层得以保持的关键；④在顶底板和礁滩复合体识别基础上，通过井震联合预测有利礁滩灰岩储层分布面积达10.3×10⁴ km²。上述认识奠定了深层孔隙型灰岩储层发育的理论基础，拓展了四川盆地深层灰岩储层勘探新领域。

Cavern and vug porosities in the Ordovician carbonates in the Halahatang oil field are currently hot targets for hydrocarbon exploration in the Tarim Basin of northwestern China. However, crucially, the formation of cavern and vuggy porosities have not been fully understood due to multiphase tectonic-driven (e.g., faults, unconformities) diagenetic alterations. Here, we integrated petrology observations and geochemical analyses (C, O, Sr isotopes, trace and rare earth elements [REE], clumped isotopes, and laser-based U-Pb dating), aiming at determining the timing for tectonic-driven calcite precipitation, which is closely tied to karstic reservoir development. Vug-filling calcites were emplaced in the late Caledonian (460.8 ± 3.4 and 448.6 ± 5.3 Ma) and early Hercynian (335 ± 19 Ma), and the U-Pb ages for fracture-filling (ca. 364 ± 53 and 282.9 ± 5.4 Ma) and megacrystalline (from 324 ± 23 to 300.9 ± 4.8 Ma and 244.13 ± 13 to 240.5 ± 4.1 Ma) calcites predominantly fell within the Hercynian. In addition, the latest fracture-filling calcites show a slightly younger U-Pb age of ca. 158 ± 17 Ma. The combination of other geochemical analysis, including clumped isotopes, δ13C, δ18O, and 87Sr/86Sr isotopes, REE, and fluid δ18O calculation, suggest that these calcites were precipitated from formation fluids substantially influenced by meteoric water along with alternative hydrothermal fluid. Hence, this study emphasizes that fracture-related cavern reservoirs of the Halahatang oil field were well correlated with the early Hercynian, late Hercynian, and Yanshanian tectonic events and their associated fluids mixing activity. The methodologies and outcomes from the present study may be able to guide future hydrocarbon exploration in the Halahatang oil field and be applied to other oil fields with similar tectonic backgrounds.

Enhanced hydrogeologic circulations promoted by tectonics are commonly linked to karstic cavity formation in carbonate rocks, providing superb reservoirs for hosting energy resources (i.e., hydrocarbon and geothermal) in sedimentary basins. Predicting such cavern reservoirs in the deep subsurface is difficult mainly due to uncertainties in timing the tectonics and characterizing their associated fluids, which hamper the related hydrocarbon exploration. By combining carbonate U-Pb chronology, geochemistry, and seismic data analyses of fracture and cave-filling carbonates in cavern reservoirs from the Ordovician units of the Tarim Basin, northwestern China, the current study sought new evidence for fluid activities related to tectonics. Crucially, carbonate U-Pb ages confirm that these karstification events were closely related to syn- and/or postmineralization faulting by local tectonics. Geochemistry signatures in the authigenic minerals of fractures further suggest that the episodically developed meteoric water mixed with deep basinal brine. The carbonate dissolution rate might have been markedly enhanced by active hydrologic circulation and fluids mixing or even the formation of sulfuric acid, thus promoting the formation of karstic cavities that was closely related to the deep-rooted fractures and faults. This study highlights the indispensable role of hypogenic karstification in the formation of cavern carbonate reservoirs in the Ordovician units of the Tarim Basin and the outcome from this new contribution may provide useful guidelines for hydrocarbon exploration in the basin and other global analogues.

通过对塔里木和四川盆地礁滩、岩溶和白云岩储集层的实例解剖，深入分析碳酸盐岩储集层发育的物质基础，碳酸盐岩储集层孔隙发育、调整和保存的机理及环境，厘清不同类型碳酸盐岩储集层发育的主控因素。碳酸盐岩储集层发育受控于3个因素：①礁滩相沉积，其不仅是礁滩储集层发育的物质基础，同样是白云岩储集层和岩溶储集层发育非常重要的物质基础；②表生环境，碳酸盐岩储集层孔隙主要形成于表生环境，可以是沉积原生孔隙，也可以是早表生及晚表生期淡水溶蚀形成的次生溶孔（洞）；③埋藏环境，埋藏环境是碳酸盐岩储集层孔隙保存和调整的场所。没有单一成因的古老海相碳酸盐岩储集层，其成因为上述3个控制因素的叠加，储集层发育的主控因素分别为礁滩相沉积、表生岩溶作用、蒸发相带、埋藏-热液溶蚀作用时，分别形成礁滩储集层、岩溶储集层、沉积型白云岩储集层和埋藏-热液改造型白云岩储集层。图6表5参22

Through case study of reef-shoal, karst and dolostone reservoirs in the Tarim and Sichuan Basins, the material base and the mechanisms of porosity creation, modification and preservation of carbonate reservoirs were examined carefully in order to figure out the major factors controlling the development of various types of carbonate reservoirs. Three factors control the development of carbonate reservoirs: (1) carbonate sediments of reef-shoal facies are the material base for not only reef-shoal reservoirs, but also dolostone and karst reservoirs; (2) epigenetic environment is crucial for porosity creation, i.e. reservoir space in ancient carbonates includes primary depositional porosity and/or secondary dissolution pores caused by epigenetic, freshwater dissolution; and (3) burial environment is the setting for porosity modification and preservation. There is no carbonate reservoirs of solely one origin, carbonate reservoirs are all the products of the combined effect of the above three factors. The four main controlling factors, reef-shoal sediments, epigenetic karstification, evaporation facies belt and burial-thermal fluid dissolution give rise to the reef-shoal, karst, sedimentary dolostone and burial-hydrothermal alteration dolostone reservoirs respectively.

The Middle Ordovician strata are well deposited in the south margin of northern Tarim Basin. Drill data reveale that no long-term exposed unconformity surface exists on the Middle Ordovician strata and the karst reservoirs develop in the strata. Bordered by the pinchout line of upper Ordovician Shangtamu Fm., a burial hill area in the north and an inner area in the south can be divided. Cavernous and fractured+vuggy reservoirs are predominant in the burial hill area. Fractured+porous+vuggy reservoirs are dominant while porous+vuggy and cavernous reservoirs are also common in the inner area. Generally, the development of karst reservoirs exhibits bed-liked in lateral and focuses vertically within the interval of 100 meters below the top surface of Yijianfang Fm., whereas the reservoirs get weak in deveploping extent from north to south and distribute locally along faults. By means of the analysis of cores, thinsections, FMI, hydrologic data and geologic setting, it is shown that the Middle Ordovician karst reservoirs originate considerably from karstification taking place along rock layers. The fact that the overlying upper Ordovician mud-rich strata in the inner area prevented phreatic underground water from flowing back to the surface brings in an unstable phreatic water table under which the slow flow zone provides high potential energy for underground water to flow. It is suggested that the geological setting incluidng paleouplift and slope is the prerequisite of developing karstifiaction, and permeable grainstone and fracture system may form available pathways for diagenetic fluids. The karstification along layers advancesa variety of reservoir spaces.

在深层碳酸盐岩层系中,已陆续发现了塔河、普光、元坝、安岳等一系列大型油气田,并形成了碳酸盐岩“三元控储”等成储理论认识。近年来,四川和塔里木盆地相继在超过7 000 m甚至8 000 m的超深层中发现了优质碳酸盐岩储层。深层储层类型更加多样,控储因素中,相带、流体、压力和断裂,以及它们之间相互作用的内涵更为丰富。结合近期大量新的超深钻探资料,持续开展了深层-超深层碳酸盐岩成储机理的研究。通过塔里木盆地塔河-顺北地区奥陶系和四川盆地二叠系栖霞组、茅口组的深化研究,进一步揭示了构造破裂和多类型流体耦合改造储集体的成储机制;通过上震旦统四川盆地灯影组和塔里木盆地奇格布拉克组的系统分析,揭示了新元古代“白云石海”沉积环境、早期溶蚀和早期油气充注在成储与孔隙保持中的关键作用;通过开展含膏岩层系白云岩成储的物理模拟实验,揭示了膏盐岩封盖及超压、较为封闭的环境下,白云石重结晶作用显著改善了储集物性。深层-超深层储层发育机理新认识丰富了“三元控储”理论,有效引领了超深层,乃至特深层的油气勘探。断控和断-溶双控储集体、古老微生物丘滩相白云岩储层,尤其是寒武系厚层膏盐岩之下的微生物丘滩相白云岩储层,在中西部叠合盆地海相碳酸盐岩层系中广泛分布,有望成为万米特深层钻探的主要对象。

In deep carbonate strata of the Sichuan and Tarim Basins a series of large scale oil and gas fields have been discovered successively, including the Jingbian, Tahe, Puguang and Yuanba fields, and a “ternary reservoir control” theory for reef-shoal carbonate reservoirs has been developed. In recent years, high-quality carbonate reservoir rocks are discovered in ultra-deep layers at depths of greater than 7000 m or even 8000 m. The deep reservoirs show diverse rock types and complex interactions between the reservoir controlling factors such as facies belt, fluid, pressure, and fault. Using the newly obtained ultra-deep drilling data we carried out a systematic investigation into the formation mechanism of the ultra-deep carbonate reservoir rocks. In-depth studies of the Ordovician strata of Tahe-Shunbei-Shunnan area, Tarim Basin and the Permian Qixia and Maokou Formations in the Sichuan Basin provided further insights into reservoir formation by mechanisms of fault-related fracturing and coupled multi-type fluid alteration. Results for the Upper Sinian Dengying Formation in the Sichuan Basin and the Upper Sinian Qigebulake Formation in the Tarim Basin suggested that the Neoproterozoic “dolomite sea” depositional environment, early dissolution, and early hydrocarbon charging are the key factors for reservoir formation and preservation. Physical simulation experiment on dolomite reservoir formation in gypsum-bearing facies revealed that dolomite recrystallization can significantly improve reservoir properties under gypsum-salt capping and overpressure and relatively closed environment. The new insights enriched the “ternary reservoir control” theory and provided guidance for oil and gas exploration in ultra-deep and even extra-deep strata. In superimposed basins in central and western China, fault-controlled and fault/dissolution dual-controlled reservoirs, ancient microbial mound-shoal dolomite reservoirs, especially those with Cambrian thick gypsum-salt caprocks, are widely distributed in marine carbonate rocks and can be considered the main exploration targets at > 10000 m depths.

针对古生代中国中西部华北、华南和塔里木三大陆块在全球洋-陆格局中的古地理位置还存在的争议问题,本论文以国际最新的古地理位置重建研究方法和思路,在对中国三大陆块盆地(鄂尔多斯、四川和塔里木盆地)古生界钻井岩心的古地磁实测研究、全球古生代古地磁数据收集与有效性筛选处理、全球主要地质事件约束等多参数融合分析的基础上,采用最新的 GPlates 板块重建方法,对中国华北、华南和塔里木三大陆块在全球洋-陆格局中的古地理位置进行了重建和定位。研究结果表明:古生代三大陆块主要在全球 ±30° 之间的南北中低纬度之间迁移;三大陆块在古生代至少发生了 3 次不同的顺时针旋转和方位角转换;三大陆块运移速率至少经历了 3 次以上不同高、低速度间的转换与变化过程;响应于古生代全球洋-陆形成与演化,中国三大陆块古构造格局总体上经历了洋盆扩张下的“多岛洋”离散、俯冲碰撞下的离散-汇聚并存、俯冲消减下的差异汇聚隆升、新旧洋盆转换下的差异汇聚-离散、拼合与地幔柱控制下的差异汇聚-离散内部拉张的差异性演变过程。古生代中国三大陆块在全球洋-陆格局中的位置与差异性演变,奠定了中国三大陆块古生代不同性质盆地的形成与演化、不同层系油气烃源、储集原始物质差异性发育的基础。

The Paleozoic paleogeographic position of the three continental blocks of central and western China—namely the North China, South China and Tarim blocks—in the global ocean-continent pattern has been under debate. Applying the latest research methods and ideas of paleogeographic reconstruction, along with the paleomagnetic measurements of Paleozoic cores (from the Ordos, Sichuan and Tarim basins in the study area), global Paleozoic paleomagnetic data, and constrains from major global geological events, this paper reconstructs and locates the paleogeographic position of the North China, South China and Tarim blocks using the GPlates software. The results indicate that the three continental blocks migrate mainly between the mid and low latitudes of ±30° during the Paleozoic and undergo at least three different clockwise rotations and azimuth conversions. And the migration rates of the three blocks oscillate at least three times between different high and low velocities. In response to the breakup and assembly of Paleozoic global oceans/supercontinents, the three continental blocks experience a series of crustal movements, including “archipelagic ocean” dispersion under ocean basin expansion, divergence/convergence coexistence under ocean basin subduction and collision, differential convergence/uplift under ocean basin subduction, differential divergence/convergence under transformation between old and new ocean basins, and differential divergence/convergence under the control of mantle plume. Obviously, the Paleozoic position of the three continental blocks of China in the global ocean-supercontinents pattern, along with differential tectonic settings, provide basic conditions for the formation and evolution of different types of basins or petroleum reservoirs of different strata and for the differential development of primitive reservoir materials within the three continental blocks.

Structurally controlled hydrothermal dolomite (HTD) reservoir facies and associated productive leached limestones are major hydrocarbon producers in North America and are receiving increased exploration attention globally. They include multiple trends in the Ordovician (locally, Silurian and Devonian) of the Michigan, Appalachian, and other basins of eastern Canada and the United States, and in the Devonian and Mississippian of the Western Canada sedimentary basin. They also occur in Jurassic hosts along rifted Atlantic margins, in the Jurassic–Cretaceous of the Arabian Gulf region and elsewhere.

Porosity in carbonate rocks results from many processes, both depositional and postdepositional. An understanding of these processes and of the textural history of porosity is necessary to a full appreciation of the history of the rock and is important in the location of potential hydrocarbon reservoir rocks. Several mechanisms appear particularly important in producing or changing porosity and pore-size distribution in carbonate rocks. Primary interparticle porosity is formed by deposition of a well-sorted calcareous sand or gravel under the influence of strong currents or waves or by local production of calcareous sand-size particles with sufficient rapidity to deposit particle on particle with little or no interstitial mud. Dissolution of interstitial mud in a calcareous sand can produce a microvuggy porosity resembling interparticle pore space. Simple cementation by calcite, anhydrite, dolomite, or quartz destroys porosity and pore size. Calcite cement appears to be especially common where the particles are monocrystalline, such as crinoid fragments. Primary constructional vugs are produced by formation of a rigid or semirigid framework. This framework may be organic or inorganic, and the inter-framework pockets may be filled with sediment or later with cement. Sucrose dolomite contains the most common North American carbonate pore type. Available petrographic evidence indicates that it is formed by growth of randomly oriented, uniformly sized dolomite euhedra, accompanied by or followed by dissolution of the nonreplaced calcite. The interpretation of time and mechanism of dissolution depends on whether a local or a distant source of carbonate is assumed. Available evidence suggests that local source of carbonate and thus the development of porosity through dolomitization may be quite common. The intercrystalline pore geometry is produced by dissolution of the nonreplaced calcite. Thus only those limestones that have been converted to nearly pure dolomite by replacement and loss of nonreplaced calcite appear to be potential dolomite reservoir rocks. This porosity may be destroyed by calcite or by optically continuous dolomite cement. Limestone deposited originally as lime muds with abundant floating sand-size particles appears to be commonly preferred by the replacing dolomite euhedra. The patchy growth of either scattered dolomite euhedra or masses of interlocking dolomite anhedra, followed or accompanied by dissolution of the non-replaced limestone relict patches, produces vugs. A similar textural history of replacement by one mineral and dissolution of the nonreplaced patches is found in limestone replaced by fine networks of chert. Dissolution of the nonreplaced limestone produces porosity. Dolomitization of a limestone with inter-particle or vuggy porosity without cementation of the earlier void space permits preservation of that void space. Replacement by a mineral more susceptible to solution alteration, such as anhydrite, followed by dissolution of the replacement anhydrite appears to be a common vug-making mechanism. Vugs are also produced by simple dissolution of the more soluble particles or parts of particles, by fracturing, and by dissolution along fractures.

Although the process of dolomitization is not well known at present, the requirement of conservation of mass of the chemical constituents of the rock and the interstitial solution places definite limits on the process. Most subsurface waters contain relatively small concentrations of bicarbonate compared to their Mg and Ca contents. For these waters, the process of dolomitization must proceed by a mole-for-mole exchange of Ca by Mg without macrotransport of carbonate. This can be expressed by the chemical equation Mg (super 2+) +2CaCO 3 -->MgCa(CO 3 ) 2 +Ca (super 2+). The porosity of the rock is not only affected by the 13% volume shrinkage on mole-for-mole dolomitization, but it also depends on the amount of compaction which takes place. If a lime mud is dolomitized, the mud will be compacted as the dolomite crystals grow, resulting in a decrease in porosity. Once the dolomite crystals form a space-supporting framework, the rate of compaction will decrease considerably. Replacement of the remaining mud will then lead to a marked increase in permeability and may also result in a porosity increase.

对南方地区震旦系灯影组未遭受溶蚀改造作用的泥粉晶白云岩、遭受溶蚀改造的富含溶蚀孔隙白云岩储层(包括粗晶砂糖状白云岩)以及孔洞中充填的粗晶白云石开展了碳、氧和锶同位素以及稀土元素分析,以判别白云岩储层发育经历的流体改造作用类型、过程和机制。未溶蚀白云岩的δ¹³C、δ¹⁸O和⁸⁷Sr/⁸⁶Sr比值平均分别为3.0‰、-3.5‰ 和0.708 779;稀土元素组成上无显著的Ce和Eu异常,属于正常的海水成因白云岩。溶蚀改造后的砂糖状白云岩的δ¹³C、δ¹⁸O和⁸⁷Sr/⁸⁶Sr比值平均分别为1.7‰、-7.7‰ 和0.709 579,与未溶蚀改造白云岩相比具有略偏轻的碳、氧同位素组成和较高的⁸⁷Sr/⁸⁶Sr比值;稀土元素组成上,具有较高的REE含量和显著的Ce负异常,δCe平均值为0.5,表明多孔的砂糖状白云岩储层是大气降水和含油气流体溶蚀改造的产物。孔洞中充填的粗晶白云石的δ¹³C、δ¹⁸O和⁸⁷Sr/⁸⁶Sr比值平均分别为0.3‰、-11.3‰ 和0.710 334,具有显著偏轻的碳、氧同位素组成和显著高的⁸⁷Sr/⁸⁶Sr比值;稀土元素组成上,具有显著的Eu正异常,δEu平均值为3.0,最大达到9.8,表明孔隙充填白云石是从热液流体中沉淀出来的,并受地层中有机成因流体的影响。根据所确定流体作用类型并结合构造地质演化背景,探讨了灯影组白云岩储层流体改造过程和机制。南方地区在震旦纪灯影组沉积时期发育海水台地相泥粉晶白云岩沉积,局部见藻纹层结构。震旦纪末期遭受大气降水溶蚀改造,下渗至地下深处,促使白云岩溶蚀和重结晶作用;在此后的埋藏过程中,进一步遭受含油气流体的溶蚀改造作用,最终形成富含溶蚀孔隙和沥青的中粗晶白云岩储层。埋藏过程中,受盆地深部热液的改造作用,在孔隙中形成白云石充填,使白云岩储层发生了一定程度的致密化作用。

<p>The analyses were carried out on carbon, oxygen and strontium isotopes and rare earth elements (REEs) of the unaltered muddy-micritic dolomites, pore-rich dolomite reservoirs altered by corrosion (including coarse crystalline sucrosic dolomite) and pore-filling coarse crystalline dolomites in Sinian Dengying Formation of the southern China, so as to identify the type, process and mechanism of fluid alternation in the development process of dolomite reservoirs. The average values of &delta;¹³C, &delta;¹⁸O and ⁸⁷Sr/⁸⁶Sr of unaltered dolomites are 3.0&permil;, -3.5&permil; and 0.708 779 respectively. There is no significant Ce and Eu anomaly in REE composition, indicating normal dolomites formed by the action of seawater. The average values of &delta;¹³C, &delta;¹⁸O and ⁸⁷Sr/⁸⁶Sr of altered sucrosic dolomites are 1.7&permil;, -7.7&permil; and 0.709579 respectively. The carbon and oxygen isotope compositions are slightly lighter and ⁸⁷Sr/⁸⁶Sr ratio is higher than unaltered dolomites. Moreover, altered dolomites have higher REE content and significant negative Ce anomaly (&delta;Ce average = 0.5). It is proven that pore-rich sucrosic dolomite reservoirs are the products of meteoric water and oil-bearing fluid alteration. The average values of &delta;¹³C, &delta;¹⁸O and ⁸⁷Sr/⁸⁶Sr of pore-filling coarse crystalline dolomites are 0.3&permil;, -11.3&permil; and 0.710 334 respectively. The carbon and oxygen isotope compositions are significantly lighter, while ⁸⁷Sr/⁸⁶Sr ratio is markedly higher. Meanwhile, there is significant positive Eu anomaly (&delta;Eu average = 3.0, maximum &delta;Eu = 9.8). It is demonstrated that pore-filling dolomites were precipitated from hydrothermal fluids and affected by organically generated stratigraphic fluids.Based on the identified fluid types and geological evolution background, the fluid alteration process and mechanism of dolomite reservoirs in Dengying Formation were discussed in this study. Muddy-micritic dolomite sediments with seawater platform facies were developed in Sinian Dengying Formation of the southern China, where laminar algal structure was shown in some zones. At the end of Sinian period, the dolomites in Dengying Formation were altered by meteoric water, and then infiltrated to deep subsurface, promoting dolomite dissolution and recrystallization. In the subsequent burial process, these dolomites further underwent the dissolution and alteration of oil-bearing fluids. As a result, coarse crystalline dolomite reservoirs were formed rich in dissolution pores and bitumen. Due to alteration of hydrothermal fluids in the burial process, pores were filled by dolomites, leading to densification of dolomite reservoirs to a certain extent.</p>

沉积盆地超深层(&gt;4500 m)不仅具有与浅层和中深层不同的温压条件,而且流体体制也存在显著差异。以塔里木盆地塔中地区北坡NE向走滑断裂带上的SN4井超深层的中下奥陶统碳酸盐岩硅化段为研究对象,在详细的成岩作用研究基础上,开展了成岩矿物流体包裹体、稳定O-C和Si-O同位素以及常量、微量和稀土元素等系统分析。结果表明,超深层中下奥陶统碳酸盐岩储层存在3种流体端元类型:1深成上升流热液;2外源同生卤水;3这2种热流体与储层同生海水的混合流体。其为经历2种流体-岩石相互作用体制演化的结果:1大气淡水-同生海水重力流演化体制;2火成岩活动驱动远端热液与同生卤水混合上升流演化体制。其中,上升流具有2个流体来源:1受火成岩活动驱动远端热液,具有中低温度、中高盐度、富Si质和富含CO₂和H₂S挥发份水解成强酸的特征,不仅成为缝洞型储层热液-岩石相互作用的溶剂,而且可能发生了第1期天然气充注;2来源于下伏寒武系烃源岩层的中低温、富Ca和CH₄的碱性热卤水,不仅形成了晚期裂缝刀刃状方解石脉,而且发生了第2期天然气充注成藏。依据成岩矿物组合和温度控制矿物学原理构筑其储层化学反应路径模型,结合储层物性测定结果,初步估算这种上升流热液蚀变作用对储层孔隙度的贡献达约8%。由此表明,多期火成岩活动和多期断裂活动不仅为深成上升流提供了动力和通道,而且作为一个独立因素对超深层缝洞型碳酸盐岩储层的形成和天然气的成藏起到了重要的控制作用。综上可推论,塔里木盆地中央火成岩带超深层将是这类热液蚀变缝洞型储层发育带和有利的天然气聚集带。

The ultra-deep reservoirs(>4500 m) in the sedimentary basin have different temperature and pressure conditions from shallow and mid-deep reservoirs,and a significant difference also exists in fluid system.The research object is the silicified segment of ultra-deep Middle to Lower Ordovician carbonate reservoirs in Well SN4 along the NE strike-slip faulted belt on northeastern slope of Tazhong uplift,Tarim Basin.Based on deep diagenesis research,systematical analyses were carried out on the fluid inclusion of daigenetic minerals,stable O-C and Si-O isotopes,as well as constant,trace and rare earth elements.The results show that three types of fluid end-members exist in the ultra-deep Middle to Lower Ordovician carbonate reservoirs,i.e.,plutonic upwelling hydrotherm,exogenous syngenetic brine and the mixed fluid of the former two types of fluids and reservoir syngenetic seawater.These three types of fluid end-members evolved from the following two types of fluid-rock interaction system,i.e.,the evolution system of meteoric water-syngenetic seawater gravity flow and that of remote hydrotherm-syngenetic brine mixed upwelling flow driven by igneous activities.The upwelling flow has two fluid sources,i.e.,(1) remote hydrotherm driven by igneous activities,characterized by mid-low temperature,mid-high salinity,rich Si and strong acidity resulting from CO₂ and H₂S hydrolysis reactions,which is the solvent generated in interaction between fractured-vuggy reservoir hydrotherm and rock,and may induce the first phase of natural gas charging;(2) the hot alkaline brine with mid-low temperature,rich in Ca and CH₄,and sourced from the underlying Cambrian source rocks,leading to the formation of late fissure-type bladed calcite and the second phase of natural gas charging for accumulation.Based on diagenetic mineral assemblages and temperature control mineralogy principle,the path model of chemical reaction in reservoirs was created.In combination with the measurements of reservoir physical properties,it was preliminarily estimated that the alternation of such upwelling hydrotherm contributed 8% to reservoir porosity.Therefore,it is indicated that multi-phase igneous activities and fault movements could provide driving force and access for upwelling hydrotherm.Meanwhile,it is an independent factor that plays a very important role in controlling the formation of ultra-deep fractured-vuggy carbonate reservoirs and natural gas accumulation.It is concluded that the central igneous zone in Tarim Basin will become the development zones of hydrothermal fractured-vuggy reservoirs and favorable natural gas accumulation zones.

Siliceous minerals with the property of resistance to diagenetic alteration precipitate during the migration of hydrothermal fluids through strike-slip faults and the interaction of these fluids with host rocks during fault activity. Based on petrological analyses and U-Pb dating of siliceous minerals, the stages of strike-slip faulting of the ultra-deep-burial Ordovician in the Fuman oilfield were subdivided and their evolutionary process was discussed in combination with seismic interpretation. The results reveal the following: (1) the strike-slip faults contain hydrothermal siliceous minerals, including cryptocrystalline silica, crystalline silica, and radial silica. (2) Based on the twelve U-Pb ages of siliceous minerals (ranging from 458 ± 78 Ma to 174 ± 35 Ma) and five U-Pb ages of calcite, the activity of the strike-slip faults was divided into six stages: the Middle Caledonian, Late Caledonian, Early Hercynian, Middle Hercynian, Late Hercynian, and Yanshanian, corresponding to twelve siliceous U-Pb ages ranging from 458 ± 78 Ma to 174 ± 35 Ma, and five calcitic U-Pb ages. The Late Caledonian and Early Hercynian were the main periods of strike-slip fault activity, while the Late Hercynian period marked the final period of the fault system. (3) Later-stage faults inherited and developed from pre-existing faults. Steep linear strike-slip faults formed during the Middle and Late Caledonian movements. During the Late Hercynian and Yanshanian movements, mid-shallow faults, branch faults, and shallow echelon faults developed on the foundation of these linear faults. The methods and results of this study can guide future hydrocarbon exploration in the Fuman oilfield and can be applied to areas with similar tectonic backgrounds.

The effects of hydrothermal fluids on carbonate reservoirs are a critical issue in petroleum geology. Here we present a comprehensive study of the lower Permian Qixia Formation in the Sichuan Basin, southwestern China, based on petrology, geochemistry, and geochronology. We identified universal effects of hydrothermal fluids on sucrosic dolomites of the Qixia Formation. These dolomites are classified on the basis of petrologic characteristics as anhedral medium- to coarse-crystalline dolomites (Dol-1), euhedral medium- to coarse-crystalline dolomites (Dol-2), and saddle dolomites (SD). The Dol-2 is further subclassified as dark-red Dol-2a and bright-rimmed Dol-2b according to the cathodoluminescence. The Dol-1 and Dol-2a, which, respectively, originated from remnant-grain-bearing matrix limestones and those modified by eogenetic karstification, are the products of horizontal thermal convective dolomitization by marine-related fluids during the shallow burial just after deposition (from 274.5 ± 9.9 to 269.1 ± 12.0 Ma). They are both geochemically characterized by left-leaning rare earth elements (REE) patterns with positive Y anomalies and relatively low fluid-inclusion homogenization temperatures (70°C–150°C). The Dol-2a have flatter REE patterns and lower Y/Ho values than Dol-1. The Dol-2b are the products of Dol-2a superimposed by fault-controlled thermal convective dolomitization by marine-related fluids during the Emeishan Large Igneous province (from 263.2 ± 10.3 to 258.7 ± 8.1 Ma). The SD are the cements of the dolomitizing fluids. The Dol-2b and SD are both geochemically characterized by left-leaning REE patterns with positive Eu and Y anomalies and relatively high fluid-inclusion homogenization temperatures (120°C–220°C). The SD have more positive Eu anomalies than Dol-2b. Hydrothermal dolomitization in the Qixia Formation made a limited contribution to reservoirs, which were inherited and modified during the early stage of hydrothermal dolomitization and infilled and destroyed during the late stage. Our study highlights that hydrothermal effects on reservoirs cannot be generalized and that the origin and properties of hydrothermal fluids and modified lithologic associations should be comprehensively considered, as they produce diverse hydrothermal effects. Whether or not high-quality carbonate reservoirs develop in deep to ultradeep zones is highly dependent on the occurrence of original favorable sedimentary facies and early constructive diagenetic modification. Burial diagenesis during the late stage may improve reservoirs conditionally.

Neoproterozoic marine dolomite cements represent reliable, albeit complex, archives of their palaeoenvironment. Petrological and high-resolution geochemical data from well-preserved fibrous dolomite and pyrite in the upper Ediacaran (ca 551 center dot 1 to 548 center dot 0 Ma) Dengying Formation in south-west China are presented and discussed here. The aim of this research is to reconstruct the redox state of late Ediacaran shallow seawater and porewater in the Sichuan Basin using early marine diagenetic fabrics. Based on crystalline texture and axis, four basic types of fibrous dolomite cements formed penecontemporaneously in a microbialite reef setting at the platform margin: (i) bladed dolomites (replacement from a high-Mg calcite precursor); (ii) fascicular fast dolomites (replacement from an aragonitic precursor); (iii) fascicular slow dolomites; and (iv) radial slow dolomites. The latter two fabrics are considered direct marine porewater precipitates due to their length-slow character, cathodoluminescent zonation, and enriched copper and cobalt concentrations. Marine cements yield rare earth element and yttrium patterns comparable to modern seawater and represent a refined set of archive data relative to previously published bulk dolostones. Redox-sensitive elements and cathodoluminescence indicate that the fascicular fast dolomites formed in suboxic seawater, while fascicular slow and radial slow dolomites formed in euxinic marine porewaters. Microbial sulphate reduction during the formation of fascicular slow and radial slow dolomites is recognized by nanometre-scale spheroidal ankerite and sulphur-containing dolomite, and intergrown pyrite grains with U-shaped delta S-34 transects. Data shown here suggest predominantly suboxic shallow late Ediacaran seawater and euxinic marine porewaters, with microbial activity promoting the direct precipitation of dolomite.

膏盐岩层系作为理想的盖层被广泛关注，随着勘探和研究的不断深入，逐步发现膏盐岩层系在油气运移、储存、圈闭等过程中都发挥着重要作用。近年来，中国海相油气勘探在鄂尔多斯盆地东部、塔里木盆地中部、四川盆地西部等地区的含膏盐岩层系中不断取得突破，从而引发了高演化、低丰度膏盐岩层系成为油气来源这一问题的思考。在概要梳理膏盐岩层系在储-盖方面研究进展的同时，主要从烃源岩发育环境及成烃机理方面对膏盐岩层系烃源岩的发育和生烃潜力进行探究，认为膏盐岩层系包括中国高演化低有机碳含量的膏盐岩层系可以作为良好的烃源岩，这突破了低有机碳含量膏盐岩层系无法作为有效烃源的传统观点。高演化低有机碳含量膏盐岩层系中被低估的生烃物质、优质的生烃物质在地质历史中大量生烃转化和以有机酸盐形式存在的生烃物质是认识其生烃机理的关键。

Gypsum strata series have attracted wide attention as the ideal cap. Along with the continuous deepening of exploration and research, it is gradually found that gypsum strata series play an important role in the process of hydrocarbon migration, preservation and trap. In recent years, constant breakthroughs have been made in the gypsum-bearing strata of eastern Ordos Basin, central Tarim Basin and western Sichuan Basin during China's marine hydrocarbon exploration, thus leading to the consideration on the possibility of high-evolution and low-abundance gypsum strata series as hydrocarbon source. This paper briefly summarizes the research process of gypsum strata series in the aspect of reservoir and cap rock, and also explores the development and hydrocarbon generation potential of source rocks in gypsum strata series from the perspectives of the development environment and hydrocarbon generation mechanism of source rocks. It is believed that the gypsum strata series including China's high-evolution and low-TOC gypsum strata series are favorable source rocks, thus breaking through the traditional viewpoint that gypsum strata series were unable to be effective source rocks. In the high-evolution and low-TOC gypsum strata series, the underestimated hydrocarbon generation materials, the massive hydrocarbon generation and conversion of high-quality hydrocarbon generation materials in the geological history as well as the hydrocarbon generation materials in the form of organic acid salt are the keys to understanding the hydrocarbon-generation mechanism.

The uppermost Middle Triassic Leikoupo Formation in the western Sichuan Basin of China has recently been shown to host as much as 5.3 tcf (1.5 × 1012 m3) of natural gas resources. The reservoir rocks, composed mainly of microbially derived dolomudstone (e.g., thrombolites and stromatolites), are characterized by low porosity (&amp;lt;8%) and permeability (&amp;lt;0.001 to 10 md). The limestone is commonly tight and not of reservoir quality because of abundant meteoric calcite cementation, whereas the dolostone has various types of pores dominated by solution-enlarged pores and vugs, microbial framework pores, and micropores. Breccias are well developed in places, probably because of dissolution of underlying evaporites (e.g., anhydrite) by an influx of low-salinity fluids (e.g., freshwater and seawater) during an early burial stage. Early dolomitization created micropores in the dolomudstone, and subsequent diagenetic events were dominated by calcite, dolomite, quartz cementation, pyrite replacement, compaction, fracturing, and development of stylolites. Localized hydrothermal activity has been evidenced by high homogenization temperatures (∼160°C–200°C) obtained from fluid inclusions in fracture-filling cements. Bacterial sulfate reduction probably resulted in H2S generation, pyrite precipitation, and solution-enlarged pore and vug formation, whereas part of the current H2S in these reservoirs may have been sourced from thermochemical sulfate reduction or an underlying formation (e.g., the Feixiangguan Formation). Development of microfractures and associated micropores was probably the final diagenetic event, which improved pore interconnectivity. This study confirms the effect of diagenesis on the development of a microbial dolomudstone reservoir, which may be applicable to other similar microbial carbonate reservoirs elsewhere, for example, Middle Triassic sections of the Tethys region and offshore Brazil.