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.

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 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.

A Study of Thin Sandstone Reservoirs by High-resolution Seismic Inversion

In this paper seismic inversion was used as a key technique and the seismic wavelet most suitable to the actual underground situation was extracted with the higher-order statistics algorithm. The wavelets extracted in this way and the wavelets extracted with the seismic statistics techniques were used separately for inverting the seismic data of the southern part of Tahe oilfield, Tarim basin. The results showed that the resolution of the wavelet inversion with the higher-order statistics method was greatly improved, and the wavelet-inverted section could better distinguish the thin sandstone reservoirs of the upper and lower Carboniferous and their lateral distribution, providing a reliable basis of analysis for the study of thin sandstone reservoirs.

Formation Models and Distribution of Oil and Gas Pools in Tarim Basin, China

This article reports the main formation models and distribution of the oil and gas pools in Tarim basin, China, including （1） occurrence of the found oil and gas pools, （2） main formation models of oil and gas pools, and （3） distribution law of oil/gas pools. Petroleum is distributed widely in the strata of Tarim basin from the Sinian at the bottom to the Neogene at the top. However, the found oil and gas fields are mainly distributed in Shaya （沙雅） uplift, Tazhong （塔中） uplift, and Kuche （库车） depression. This article presents 4 main formation models, namely, early formation and long-term preservation, early formation and late reformation, middle-late multiphase-multisource formation, late single-stage formation. Tarim basin is very rich in petroleum resources. Long-term inherited intrabasinal paleohighs and slope zones are the most favorable areas for accumulation of hydrocarbons, but the types of oil and gas pools are different from area to area. The control of unconformities and faults on hydrocarbon accumulating is prominent in Tarim basin. Preservation conditions are of utmost importance. Formation of some oil and gas pools is the result of reforming and re-accumulating of early accumulated hydrocarbons.

Characteristics of China’s oil and gas pool formation in latest geological history

The structural activities took place extensively in the Asia continent during the Cenozoic era owing to the strong continent-to-continent collision and continuous compression between the India Plate and the Eurasia Plate. Huang Jiqing called such structural activities Himalayan movement. China’s sedimentary basins developed and took shape mainly during the Himalayan movement period. It is also the main period for formation and development of the oil and gas reservoirs. Of 366 large and medium-sized oil and gas fields currently found in China, 212 reservoirs were formed in the Neo- gene-Quaternary period. The proportion is as high as 68.2%. The oil and gas migration and accumu- lation in the latest geological period, which were controlled by the times, properties, styles and strength of the Himalayan movement, took place mainly in eight regions, such as the low uplift area of Bohai Sea, the onshore faulted sag area of Bohai Bay, anticlinorium zone in Daqing, the foreland fold-and-thrust belt in West China, the tilted structural zone in West China, the cratonic palaeohigh in the Tarim Basin, the zone of fault and fold belt in the East Sichuan Basin, and the biological gas zone in the East Qaidam Basin. The oil and gas pool formations in those regions have their own charac- teristics. With the great potential and broad prospect, those regions are the main exploration areas in China in the future.

Petroleum Exploration of Craton Basins in China

Craton basins are a significant petroliferous provenance. Having undergone multiple open- dose tectonic cycles and strong reworking of the late Cenozoic tectonic movement, the craton basins in China are highly broken. This has resulted in multi-source and multiphase hydrocarbon generation and later hydrocarbon accumulation so that a complicated spatial assemblage of primary, paraprimary and secondary oil-gas pools has been formed. The primary factors controlling hydrocarbon accumulation include hydrocarbon-generating depressions, paleouplifts, paleoslopes, unconformity surfaces, paleo-karst, faults and fissure systems as well as the later conservation conditions. In consequence, the strategy of exploration for China＇s craton basins is to identify the effective source rocks, pay attention to the different effects of paleohighs and late reworking, enhance studies of the secondary storage space, attach importance to the exploration of lithologic oil-gas reservoirs and natural gas pools, and approach consciously from the secondary oil pools to the targets near the source rocks. At the same time, a complete system of technologies and techniques must be built up.

Geological constraints of giant and medium-sized gas fields in Kuqa Depression

There is a gas-rich and well-charged petroleumsystem in the Kuqa Depression where Triassic and Jurassicsource rocks play important roles. Distributed in an area ofmore than 10000 km and with a thickness of up to 1000 m,they are composed of dark mudstones, carbonaceous mud-stones and coal seams containing 6%, 40% and 90% of TOC,respectively, and are mainly the humic organic matter. Ashigh-quality regional cap rocks, the Neogene and Eogenegypsum rocks and gypseous mudstones matched well withthe underlying Neogene and Cretaceous-Eogene sandstones.They have formed the most favorable reservoir-seal assem-blages in the Kuqa Depression. Also the Jurassic sandstonesand mudstones formed another favorable reservoir-seal as-semblage. The traps are shaped late in the fold-thrust belt,mainly fixed in the Tertiary-Quaternary, where ten structurestyles have been distinguished. These traps spread as a zonein N-S, are scattered like a segmental line in W-E and showtier-styled vertically. The best traps are gypsum-salt coveredfault-bend anticlines related to the passive roof duplex. Thispetroleum system is characterized by late accumulation. Inthe early Himalayan Movement, mainly gas condensate andoil accumulated and were distributed in the outer circularregion of the kitchen; whereas in the middle and late Hima-layan the gas accumulations mainly formed and were dis-tributed in the inner circular region near the kitchen. Theoverpressure of gas pools is common and is formed by sealcapacity of thick gypsum layers, extensive tectonic compres-sion and large uplift. The well-preserved anticline traps un-derlying the high-quality regional cap rocks of the Tertiarygypsum rocks and gypseous mudstones are the main targetsfor the discovery of giant and medium-sized gas fields. Aboveconclusions are important for the petroleum geology theoryand the exploration of the fold-thrust belt in foreland basinsin central and western China.

准噶尔盆地西北缘油气藏保存及破坏定量研究

准噶尔盆地西北缘构造运动复杂 ,其油气藏破坏因素多 ,油气显示也呈多样化形式 (稠油、油砂、沥青 )。该地区油气藏虽然破坏量很大 ,但同时也是盆地油气的最富集区。对油气藏破坏因素的分析表明 ,西北缘的油气藏破坏类型以断裂活动、油藏抬升和褶皱变动为主。多种估 (计 )算方法 (盆地模拟法、区带地质分析法、地质锚链法 ) ,分别定量地估 (计 )算了西北缘油气原始聚集量、保存量、破坏量、残留量和散失量。结果表明 ,西北缘油气总散失量占原始总聚集量的 72 1%～ 78 1% ,其散失量在燕山期最大 ,印支期次之 ,喜山期最小 ,这与西北缘油源丰富、单斜地质构造、多期成藏。

油气耗散--油气地质研究和资源评价的弱点和难点

油气生成后运移的结果有3种:1)聚集成藏;2)散于岩层和流体中;3)与途经的流体-围岩相互作用所耗损或暴露地表而散失,后者称之为"耗散"。在油气运移过程中,耗散部分最为活跃,与聚集成藏的油气联系最为密切;为油气地质研究、勘探部署和资源评价等不可或缺的重要研究内容。根据油气耗散前、后数量和性质等方面的差异,将油气耗散划分为数量减少、相态转变、成份改变和性质转化4种类型,分别不同程度地体现了油气耗散的环境、条件和特点等方面的差异。其中性质转化类通常发生在埋藏不很深的表浅层或地表,油气与围岩、流体或大气等相互作用所形成的各种还原蚀变等后生产物及矿产,一般已不具烃类的表观特征。但其油气耗散量通常十分巨大,应给以足够的重视。将这类一般不具烃类特征的产物与直接显示油气耗散的结果(如油气苗、沥青、稠油等)相结合,对其追根溯源,可能为探讨和解决油气耗散及其规模这一国际难题的重要途径;也是示踪、发现和预测相关矿床的有效线索和重要标志。本文探讨了鄂尔多斯盆地东北部与上古生界天然气耗散有关的各种后生产物的类型、基本特征、地球化学性质、形成环境和分布特点等。

油气藏破坏机理分析

油气藏破坏是一种普遍的自然现象 ,地质历史时期任何类型的油气聚集都是短暂的动态变化实体 ,均随着时间的推移 ,在某些地质因素的影响下遭到破坏 .对国内外被破坏油气藏的地质因素进行了分析 ,研究了油气藏破坏机理 ,将油气藏破坏机理划分为物理破坏、化学破坏、生物化学破坏和物理化学破坏 4种类型 11种亚类型 ,其中物理破坏是油气藏破坏的最主要原因 ,而物理破坏中的构造变动是绝大多数油气藏破坏的直接因素 。

油气藏成因模式探讨

油气藏模式是对油气藏赋存特征的高度概括，也是对油气藏形成机制和破坏作用的科学解释。油气藏模式分为描述模式与成因模式。本文依据翔实的资料，探讨并初步建立了油气藏成因模式。

南山坪古油藏的形成及其破坏因素分析

南山坪古油藏以南山坪背斜(圈闭)为依托,油藏的形成、破坏与背斜(圈闭)的形成及演化息息相关。加里东晚期-海西早期的构造运动形成了南山坪背斜的雏形,与之对应的是最初的油藏形成;南山坪背斜在印支运动得到加强,形成构造圈闭,与之对应的是原油藏裂解生气及烃源岩进入生气阶段,形成气藏及部分沥青。之后的燕山运动幕使得南山坪背斜(圈闭)被褶皱和断层复杂化,形成由东南向北西的逆冲断裂,其上覆盖层抬升、剥蚀,原油藏彻底破坏,成为古油藏。分析认为,南山坪古油藏的破坏因素主要是印支期的热裂解和燕山运动幕的构造抬升、剥蚀,且后者更为主导因素。比较南山坪古油藏、余杭泰山古油藏及威远气藏,力图寻找其共性及差异性,从而为中国南方的油气勘探提供借鉴意义。

火电厂新型事故贮油池设计研究

基于连续性方程和伯努利方程,探讨了虹吸管内液体平均流速的影响因素。设计并制作了虹吸破坏试验装置,用于研究排水管的虹吸破坏机制。在此基础上,详细阐述了新型事故贮油池的设计方案及工作原理。研究表明:在进油水管的端部设置90°弯头,并在油水分离室内设置交错隔墙,能有效改善整流效果;将连通孔布置于集水坑内,既可实现水封,又能增加有效储油容积;设置于U形排水管驼峰段下方的L形进气管,能有效触发虹吸破坏,避免事故油排出池外,造成环境污染;此外,排水管外接的雨水井应就近布置,以减小沿程水头损失,从而实现快速排水。