Origin of Oils in“Subtle pools”in the Dongying Depression,Bohai Bay Basin, China

Subtle traps or oil pools have become an important exploration play in the Dongying Depression, Bohai Bay Basin, east China. Despite recent successes in exploration, the formation mechanisms of subtle traps are still not well understood. The majority of subtle oil pools in the Dongying Depression are developed in the middle interval of the Es3 Member of the Paleogene Shahejie Formation with the subtle traps being primarily of lenticular basin-floor turbidite sands encompassed in mudstones. Oil in the subtle traps was previously thought to have migrated directly from the surrounding source rocks of the same formation （Es3）. Detailed geochemical investigation of 41 oils and 41 rock samples from the depression now indicates that the oils from the subtle traps cannot be correlated well with the surrounding Es3 source rocks, which are characterized by high Pr/ Ph （〉1）, low Gammacerane/C30hopane, representing a freshwater lacustrine setting. In contrast the oils features low Pr/Ph （〈1） and relatively high Gammacerane content, showing a genetic affinity with the underlying Es4 source rocks, which also have the same qualities, indicating a brackish lacustrine setting. Oils in the Es3 subtle traps are probably derived from mixed sources with the contribution from the upper Es4 source rocks predominating. Therefore unconventional oil migration and accumulation mechanisms need to be invoked to explain the pooling of oils from the ES4 source rocks, which probably came through a thick low interval of the Es3 source rocks with no apparent structural or stratigraphic pathways. We suggest that the subtle oil migration pathway probably plays an important role here. This finding may have significant implications for future exploration and the remaining resource evaluation in the Dongying Depression.

Quantitative prediction of mixed-source crude oils and its significance for understanding oil accumulation in subtle pools in the Dongying Depression,Bohai Bay Basin

Conventional geochemical approaches were utilized in the quantitative prediction of the proportions of mixed-source crude oils derived from the Es3 and ES4 members of the Paleogene Shahejie Formation. The mixed-source oils are accumulated in the middle interval of the Es3 member （Es3 M） in the Niuzhuang Sag, which is one of the sags where subtle traps are primarily of lenticular basin-floor turbidite sands within mudstones mostly developed in the Dongying Depression, Bohai Bay Basin. The result showed that about 18-92% of the mixed-source oils were derived from the Es4 source rocks with an average of 55-60%）. Reservoirs associated with deep faults appear to have much more Es4 genetic affinity oils. A high proportion of the Es4-derived oils discovered in the Es3 M subtle lithological traps in the Niuzhuang Sag have long migration distances. This suggests that surrounding source rocks might not necessarily control the hydrocarbon supply for subtle traps. Subtle migration pathway may play an important role in the vertical oil migration. The traditional concept of hydrocarbons accumulation in these tenticular turbidite sandstone traps within a short migration distance from the surrounding source rocks is not supported by this study. The present result is also consistent with our previous findings that immature oils in the Bamianhe Oilfield in the south slope of the Niuzhuang Sag were actually mixed-source oils mostly sourced from the Es4 in the depocenter of the Niuzhuang Sag, and the petroleum potential of the ES4 member in the Dongying Depression should therefore be re-evaluated.

Discussion of the Mode and Mechanism of Oil and Gas Accumulation in the Nanbaxian Pool in the North of the Qaidam Basin

Because of the difference ofoil and gas accumulation condition between the hanging wall and the footwall of a fault, there is a peculiar accumulation mechanism that oil and gas mainly exists in the hanging wall of the basement fault, but in the footwall of the shallow detachment fault in the Nanbaxian pool. The oil and gas of the Nanbaxian pool came from the mature Jurassic hydrocarbon source rock of the Yibei depression located at the south of the Nanbaxian pool. Firstly, the oil and gas accumulated in the traps of the hanging wall of the basement fault by way of the unconformity and the basement faults, and turned into some primary deep pools; and then, the shallow detachment fault that formed in the later tectonic movement broke into the deep primary pools, which caused the oil and gas migration upwards along the basement faults and the shallow detachment faults and the evolvement into some secondary oil and gas pools later. The history of the Nanbaxian oil and gas accumulation can be summarized successively as the syndepositional upheaval controlled by faults; single hydrocarbon source rock; unconformities and faults as migration channels; buoyancy, overpressure and tectonic stress as dynamic forces; multistage migration and accumulation of oil and gas; and finally an overlapped double-floor pattern of oil and gas accumulation. The most important explorative targets in the north of the Qaidam Basin are traps connected with the primary pools in the footwall by shallow detachment faults.

Formation and destruction processes of upper Sinian oil-gas pools in the Dingshan-Lintanchang structural belt, southeast Sichuan Basin, China

The lower Cambrian Niutitang Formation hydrocarbon source rocks at the Dingshan- Lintanchang structure in the southeast Sichuan Basin were of medium-good quality with two excellent hydrocarbon-generating centers developed in the periphery areas, with a possibility of forming a medium to large-sized oil-gas field. Good reservoir rocks were the upper Sinian （Dengying Formation） dolomites. The mudstone in the lower Cambrian Niutitang Formation with a good sealing capacity was the cap rock. The widely occurring bitumen in the Dengying Formation indicates that a paleo oil pool was once formed in the study area. The first stage of paleo oil pool formation was maturation of the lower Cambrian source rocks during the late Ordovician. Hydrocarbon generation from the lower Cambrian source rocks stopped due to the Devonian-Carboniferous uplifting. The lower Cambrian source rocks then restarted generation of large quantities of hydrocarbons after deposition of the middle Permian sediments. This was the second stage of the paleo oil pool formation. The oil in the paleo oil pool began to crack during the late Triassic and a paleo gas pool was formed. This paleo gas pool was destroyed during the Yanshan-Himalayan folding, uplifting and denudation. Bitumen can be widely seen in the Dengying Formation in wells and outcrops in the Sichuan Basin and its periphery areas. This provides strong evidence that the Dengying Formation in the Sichuan Basin and its periphery areas was once an ultra-large structural-lithologic oil-gas field, which was damaged during the Yanshan-Himalayan period.

Exploration Potential of Atectonic Oil-gas Pools in the Northern Shelf Basin of the South China Sea

Large-scale oil exploration has been done and large quantities of oil-gas fields have been found in the northern shelf basin of the South China Sea for more than 20 years. The tectonic oil-gas pools are the main type. With the exploration to be deepened, looking for atectonic oil-gas pools is listed in China's exploration strategy. There are advantages for the forming of atectonic oil-gas pools in the northern shelf basin of the South China Sea. Because the level of water has been frequently changing within all historical periods, lithozones are changed alternately in both vertical and lateral directions and formed lithologic deposition especially at low water level stages, such as the low-lying fans of basin-floor fans and slope fans. Due to frequent tectonic movement within all historical periods, many structural surfaces and structural unconformities were formed. At the same time, they also formed many kinds of structural unconformity oil-gas pools. According to our exploration and research, the promising areas of atectonic reservoirs within marine basins include: (1) the basin-floor fan of the deep water district, such as the central depression of the Southeast Qiong basin and Baiyun sag in the Zhujiangkou basin; (2) the frontal area of the large ancient delta, such as the Lingao structural belt in the Yingge Sea basin and Huizhou sag in the Zhujiangkou basin; (3) the unconformity pinchout belt or denudation belt in the slope area and the uplift area, for instance, the Yingdong slope belt in the Yingge Sea basin and Yacheng 13-1 structural belt in the southeast Qiong basin. All this proves that the prospects for atectonic oil-gas pools in the northern shelf basin of the South China Sea are very broad.

GEOTHERMAL EVOLUTION AND TECTONOSEDIMENTATION OF THE NORTH CHINA CRUSTOBLOCK AND THEIR EFFECTS ON THE FORMATION OF OIL/GAS POOLS

The geothermal history of North China can be divided into at least four stages, i. c. Archaean (much hisher geothermal) stage, Paleoprotcrozoic (hish geothermal)stage, which resulted in four geotectonic stages (pregeosynehoe, geosyncline, platform and diwa stage) in the region. The geothermal field consists of three subgeothermal fields, theupper subgeothermal field with its depth of less than 2000 m, the middle subgeothermal field ranging from 2000 m to 5000 m in depth and the lower subgeothcrmal field locating at more than 5000 m in depth in North China. Sis thermostructural layers are recognised in North China, i. e. the mantle, the lower erust with its heat generation ratc of 0. 6 HGU. Oeothermal field is Corresponding to tectonosedimentary divisions in North China, controlling the tectonosedimentation, the evolution of souree rocks and the formation oF the oil/gas pools.

Conditions for the Formation of Oil and Gas Pools in Tertiary Volcanics in the Western Part of the Huimin Sag, Shandong and Their Distribution

Conditions for the Formation of oil and gas pools in Tertiary volcanics in the western part of the Huimin sag, Shandong and then (?)stribution have been studied based on the geological, seismic and well-logging information. In this paper, the types and lithofacies of the volcanic rocks in the western part of the Huimin sag are described; the relationship between rocks and electrical properties, the seismic reflection structures, the development and distribution of the volcanic rocks are expounded; and the fourfold role of the volcanic activities in the formation of the oil and gas pools is also dealt with. It is considered by the authors that the volcanic activities were not destructive to the formation of oil and gas pools but a factor favourable to the accumulation of organic matters and their conversion to hydrocarbon. The volcanic rocks might have served as reservoir rocks and cap rocks, or as a synsedimentary anticline. The prerequisites and important factors for the formation of oil and gas pools and their distribution are pointed out in the paper.

Oil Pool in Volcanic Reservoir Discovered in Dagang

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THE RELATIONS BETWEEN DEEP DYNAMIC PROCESS AND THE FORMATION OF OIL-GAS POOLS IN THE SONGLIAO BASIN,CHINA

THE RELATIONS BETWEEN DEEPDYNAMIC PROCESS AND THEFORMATION OF OIL-GAS POOLS INTHE SONGLIAO BASIN, CHINALi Zhi’an(Changsha Institute of Geotectonics, Academia Sinica, Changsha, 410013, Hunan, China)Songliao basin, crust structure, deep dynamics, the formation of oil-gas poolsThis essay deals in detail with the inhomogeneity of the crust structure and the variation of the Moho, the process of deep dynamics and also relations of deep dynamic process to the formation of oil-gas pools in Songliao Basin.

高高原受限空间内小尺度油池火燃烧特性试验研究

为研究我国高高原地区的受限空间内液体燃料小尺度油池火燃烧特性,在高高原康定机场自主搭建受限空间内油池火的试验平台。共选取3类典型液体燃料(航空煤油、航空汽油、正庚烷)进行燃烧试验,测量火焰高度、火焰温度和烟气成分等变化规律,研究了高高原受限空间内小尺度油池火行为。研究发现:在高高原地区,正庚烷稳定燃烧阶段的平均火焰高度可以通过模型L/D=k+0.254Q^(2/5)/D表示,其中,火焰高度与压力之间的关系式为L/D~p^(-2/9)。3种燃料的火焰最高温度均超过600℃,而羽流轴线温升与火焰高度呈现-5/3的指数关系。产烟速率则表现出对环境压力的依赖性,其关系可表示为:v~p^(-1/3)。

沉井法在变电站事故集油池工程中的应用研究

在变电站改扩建工程中,事故集油池等地下水池结构的施工场地条件受限,基坑开挖极易对周边的已有建、构筑物造成影响。因此,提出了一种事故集油池沉井施工工艺,可用于各电压等级的新建或改、扩建变电站工程中。该施工工艺将事故集油池设计为井筒状结构,通过沉井法施工池壁开挖土体,由井壁的自重作用克服土壤摩阻力下沉,最后在池壁设计标高位置封底,并施工事故集油池顶板及其他附属设施。事故集油池沉井法具备施工安全风险较低、施工操作面较小、无需额外基坑支护、对邻近建构筑物影响小等优点。在新疆某变电站扩建工程中成功应用事故集油池沉井施工工艺,缩短了施工工期并产生了较高的经济效益。

卷积神经网络在油浸式变压器故障诊断的应用

变压器作为变电站的主要电气设备,其智能化程度直接决定了智能变电站的发展程度,是电力系统中关系国民生产生活的重要环节。采集变压器油中溶解气体的含量及类型,通过建立卷积神经网络模型确定变压器的故障类型。在卷积神经网络算法原理的基础上,利用Java编程构建模型,将一维卷积神经网络应用到变压器故障诊断中,以变压器油中溶解的5种气体含量值作为输入向量,变压器的6种状态对应的编码值作为输出向量,并对网络中的池化层进行改进。在模型建立过程中讨论了卷积核的大小、数量、样本长度对模型精度的影响,并通过优选函数的方法确定激活函数。实验表明,将该方法生成的网络应用于变压器故障诊断,可为合理诊断变压器故障提供有价值的参考。

Mechanism of Silurian Hydrocarbon Pool Formation in the Tarim Basin

There are three formation stages of Silurian hydrocarbon pools in the Tarim Basin. The widely distributed asphaltic sandstones in the Tazhong （central Tarim） and Tabei （northern Tarim） areas are the results of destruction of hydrocarbon pools formed in the first-stage, and the asphaltic sandstones around the Awati Sag were formed in the second-stage. The hydrocarbon migration characteristics reflected by the residual dry asphalts could represent the migration characteristics of hydrocarbons in the Silurian paleo-pools, while the present movable oil in the Silurian reservoirs is related to the iater-stage （the third-stage） hydrocarbon accumulation.

Development of Low Permeability Oilfields in Shengli Oil Province

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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.

The new finding of Neogene marine low-resistivity light oil field in the western part of Pearl River Mouth Basin

Based on the new finding of Wenchang L low-resistivity light oil field, the finding process, reservoir characteristics and pool-forming pattern were studied. The oil-rock correlation, neritic reservoir type, hydrocarbon conduct system and dominant migration and accumulation direction,and new techniques were discussed. The results showed that large amount of hydrocarbon generated by shallow lacustrine mudstone and shale of Eocene Wenchang formation could migrate from sag to Qionghai uplift distantly; neritic shoal-bar reservoir have developed in the 1st member of Zhujiang formation, dip-sag faults and regional good marine sandstone layers of the 1st and the 2nd member of Zhujiang formation have constituted hydrocarbon conduct system in Qionghai uplift; the late fault system which were controlled by Dongsha tectonic movement constructed the connection between lower hydrocarbon and upper neritic shoal-bar reservoir. Therefore, the pool-forming pattern with "vertical migration and accumulation, secondary structure-lithology-dominated" was proposed. Finally the enlightenment of explorating new findings was discussed.

柴达木盆地北缘马海东地区基岩油藏成藏条件分析

柴达木盆地阿尔金山前基岩风化壳气藏勘探取得了重大突破,位于柴北缘马北凸起东段的马海东地区基岩勘探也获得了新发现,展现出良好勘探前景。由于对该区基岩油藏的成藏背景和关键要素缺乏系统认识,制约了勘探步伐。利用露头、岩心、分析化验、测井、试油等资料对基岩储层的基本特征及成藏条件进行分析,研究表明:马海东地区基岩发育3类9种岩性,储集空间以构造缝、溶蚀缝为主,其次为溶蚀孔,为低孔低渗储层;紧邻富烃凹陷、良好的储盖组合、有效的网状输导体系构成基岩优越的“源-断-储”配置,是基岩成藏的关键;马海东地区成藏条件最为有利,具备发育基岩风化壳构造、低位潜山断块和内幕断块等多种类型油藏的有利条件,是下步勘探的有利方向和目标类型之一。研究以期对马海东地区基岩油藏的勘探提供地质理论依据。

松辽盆地古龙凹陷青山口组页岩油储层中有机质微孔特征

页岩油储层中的有机质一直是页岩油研究的重点。用电子背散射(HDBSD)详细地研究了松辽盆地古龙凹陷古龙页岩油储层中的有机质中的微孔,发现了古龙页岩油储层有机质中的微孔非常发育。有机质微孔可以分为4种类型:①结构镜质体微孔;②均质镜质体微孔;③沥青质体微孔;④有机黏土微孔。有机质微米孔的直径多在1μm到数微米,圆形、近圆形或不规则;研究还发现,古龙页岩油储层中的孔隙度与有机碳呈一定的正相关关系。对有机质中的微孔孔隙度进行了初步的定量分析,获得了平均值为22.39%;初步计算表明有机微孔对储层孔隙度总的贡献在0.44%左右(有机碳取2.0%)。有机质中的微米孔(包括其他微米孔)可以与更高一级的微缝和页理缝互相联结,构成了一个很好的空间连通网络系统,为松辽盆地古龙页岩油的有效开发奠定了物质基础。