MIGRATION AND ACCUMULATION OF OIL AND GAS ACCORDING TO THE SOURCE-ROCK THEORY

Practically all oil and gas accumulations throughout the world are associated with some extensive productive series which consist of highly permeable rocks containing oil and gas pools, interbedded with shales and marls containing dispersed organic matter. All of the important recent discoveries between the Volga and the Urals were based on the observed association of oil and gas pools with certain lithologic-stratigraphic complexes of the Devonian, Carboniferous, and part of the Permian; although accumulation is related to many diverse Structural zones. Here, the productive series is the source rock as well, for the pelites contain dispersed organic matter including bitumen whose composition is related to the oils.

Where accumulations occur in sediments deposited under oxidizing conditions, factors are sought which favor migration from possible source rocks along faults, unconformities, or surfaces of facies change. For example, in Azerbaidjan and Turkmenistan large oil and gas accumulations in Pliocene continental beds occur along structural zones that allowed migration from underlying, principally Paleogene and Miocene, deposits.

As shales compact, their organic constituents gradually change; the coaly part from a ligniferous to a carboniferous stage and, ultimately, to graphite. The mobile bituminous substances formed by dissociation of organic matter and disproportioning of hydrogen, change from asphaltines and resins to oils and then to methane in the subcapillary pores of pelites, where they are in a dispersed, loosely bound state. Compaction causes slow removal of the loosely bound water and molecular migration with differentiation of the bituminous substances. After differentiation, the more mobile hydrocarbons are carried by the water into reservoir rocks. The bituminous substances move from small to large pores also by capillary forces. Migration in subcapillary pores apparently ceases when rocks become lithified and are no longer plastic.

In the super-capillary pores and fissures of reservoir rock, free migration takes place as both molecular migration and movement in larger masses. Water circulates in reservoir beds from elevated areas of the outcrop toward lower discharge areas. When the hydrocarbon-bearing water moves into different environments of temperature and pressure, the hydrocarbons may come out of solution, rise to the top of the carrier-beds, and unite into oil and gas pools if traps are available. The location of oil and gas reflects the present equilibrium of fluids with the structural pattern and hydrogeological environment. --D. C. Van Siclen.     

Structure and petroleum potential of the Laptev Sea region

Analysis of specific features of the structure and petroleum potential of the Aptian Laptev Sea region is presented. Age and lithological composition of the sedimentary cover of the shelf are predicted. Oil- and-gas source sequences, catagenetic zonation of organic matter, and potential petroliferous objects in large structural zones are characterized. It is supposed that oil likely played a significant role in the phase composition of naphtides. Its formation in the land and coastal shelf zone was stipulated by the presence of high-quality oil source rocks in the Riphean–Phanerozoic cover of the Siberian Craton. In the remaining part of the shelf, where the Aptian–Cenozoic rift system is widespread, oil can also be present in pools, because the rocks likely accommodate not only gas source rocks, but also deltaic and prodeltaic oil-and-gas source rocks that are located in the main oil formation zone. The above properties are specific features of the study region, and its hydrocarbon potential will be increasing steadily with the shelf development.     

Composition and depositional environments of the Upper Jurassic-Lower Cretaceous Mar’yanovo formation (Southeastern West Siberian Sea Basin)

The study of the composition and depositional environments of sediments from the Mar’yanovo Formation (Upper Jurassic-Lower Cretaceous Bazhenov and Georgiev horizons) recovered by boreholes Vostok-1 and Vostok-3 in the southeastern part of the West Siberian Sea Basin revealed the following fact: in the latter hole located closer to the basin boundaries as compared with the former one, they are characterized by lower organic carbon and pyrite contents, indicating reduced salinity of the basin and higher oxidation degree of sediments. The same trend is derived from comparison of rocks from the Mar’yanovo Formation in both holes with the over- and underlying strata. In Borehole Vostok-4, the closet one to the former shoreline of the basin, the Mar’yanovo Formation is indistinguishable. Intense chemical weathering of rocks in provenances during their deposition noted by Kontorovich et al. (1971) is considered a most important factor responsible for its composition and formation conditions. Elevated influx of dissolved weathering products into the sea basin intensified its biogenic activity and stimulated the accumulation of high organic matter concentrations. This inference is valid for all Upper Jurassic-Lower Cretaceous organic carbon-rich sediments that are synchronous to the Mar’yanovo Formation and developed over a spacious area of the West Siberian basin.     

Prediction of the phase state of hydrocarbon accumulations in the Mesozoic deposits of northwestern Siberia

The phase state of hydrocarbon accumulations was predicted using recent drilling data for three oil and gas complexes of the northern regions of the West Siberian petroliferous basin: Lower and Middle Jurassic, Upper Jurassic, and Berriasian-lower Valanginian (Achimov member); these results were compiled in simplified maps presented in the paper. In order to develop a plausible model and distinguish the zones of hydrocarbon accumulation of various phase states, we analyzed and systematized the existing concepts on the distribution of oil, oil-gas condensate, and gas condensate pools in the Mesozoic sequences of this region, types of organic matter in rocks, and stages of catagenetic alterations. Based on the data of the Tyumen SG-6 superdeep well, the oil-generating capacity of source deposits was assessed. Three zones differing in the phase state of hydrocarbons, oil, gas condensate-oil (transitional), and gas condensate, were distinguished in the map of the distribution of hydrocarbon accumulations in the Early-Middle Jurassic petroliferous complex of northwestern Siberia. Only two zones of hydrocarbon accumulations, oil and transitional, were detected in the Late Jurassic complex of the Nadym-Taz and Ust’-Yenisei regions. The same zones but within different boundaries were distinguished in the Achimov sequence. In contrast to the Jurassic beds, the zone of occurrence of oil accumulations in the Achimov member occupies a larger area and extends further north. In terms of density, the oils of the Achimov deposits were subdivided into three types: ultralight, light, and medium. The zones of their occurrence are shown in the map. Original Russian Text ? S.A. Punanova, T.L. Vinogradova, 2006, published in Geokhimiya, 2006, No. 9, pp. 983–995.     

Petroleum Habitat of East Siberia,Russia

East Siberia comprises three petroleum provinces—Lena-Tunguska, Lena-Vilyuy, and Yenisey-Anabar—that occupy the area of the Siberian craton. Petroleum has been generated and has accumulated in Precambrian rifts beneath the sedimentary basins and, more importantly, within the section of the basin itself. The platformal deposits of the basins extend beneath overthrusts on the east and south and are covered by sedimentary rocks of the West Siberian overthrusts on the east and south and are covered by sedimentary rocks of the West Siberian province on the west. Permafrost and gas hydrate deposits are present throughout most of East Siberia.

In the Lena-Tunguska province, rifts that developed during Riphean time are filled by thick sedimentary rocks, in which petroleum deposits have formed. In Early Cambrian time a barrier reef extended across the East Siberian craton from southeast to northwest. A lagoon to the west of this reef was the site of thick rhythmic salt deposits, which are the main seal for petroleum in the province. The sedimentary section of the platform cover ranges in age from Late Proterozoic to Permian. More than 25 oil and gas fields have been discovered in the province, all in Riphean through Lower Cambrian rocks.

The Lena-Vilyuy province includes the Vilyuy basin and the Cis-Verkhoyansk foredeep. During Middle Devonian time, a rift formed along the axis of what was to become the Vilyuy basin. This rift is filled by Upper Devonian and Lower Carboniferous basalt, elastics, carbonates, and evaporites. During this rift stage the region that was to become the Cis-Verkhoyansk foredeep was an open geosynclinal sea. The sedimentary cover consists of Permian, coal-bearing sedimentary rocks as well as elastics from the Lower Triassic, Lower Jurassic, Lower Cretaceous, and Upper Cretaceous, the latter only in the Vilyuy basin. In the Lena-Vilyuy petroleum province as many as nine gas and gas-condensate fields have been discovered.

The Yenisey-Anabar province is largely an extension of the West Siberian petroleum province. Permian sedimentary rocks are present only in the east, where they consist of elastics and some salt. The Triassic, Jurassic, and Cretaceous each are represented by thick clastic deposits. Total thickness of the sedimentary cover is up to 15 km on the west and 8 km on the east. Twelve gas and gas-condensate fields have been discovered in the western part of the province.     

EMPLOYMENT OF GAS LOGGING IN PROSPECTING OPERATIONS

Gas logging may be used for the geochemical study of exploratory and other wells in prospecting for oil and gas pools in deep deposits. The analysis of gas logging data in known oil and gas deposits makes it possible to observe definite regularities in hydrocarbon-gas distribution that are associated with the process of the migration of these gases. The most important elements in the hydrocarbon characteristics of gas logging are: the depth of the first appearance of hydrocarbons in the well, the magnitude of the concentration gradient, and the shape of the hydrocarbon curve. Quantitative changes can be noted between the gas logging data of areas with the more permeable rocks of Tertiary and Cretaceous age and areas composed of more dense and less permeable strata of Paleozoic age. In the Stavropol province, Stalingrad region, and in western and eastern Siberia, studies of gas-logging data show the following: In structures containing significant accumulation of oil and gas, the hydrocarbon gases produce maxima in the crests of uplifts and minima on the flanks. These maxima have been traced in different stratigraphic horizons, and their intensity diminishes towards the earth's surface. In structures with insignificant accumulations of oil and gas, the hydrocarbon maxima are either poorly developed or absent entirely.

Also observed is a zonal distribution of nitrogen and carbon dioxide depending on the structural elements of the uplift. It is necessary to improve the apparatus used in core sampling and gas analysis. Apparatus used in gas analysis should be capable of fractional determinations of heavy hydrocarbons to within hundredths and thousandths of a percent. It is also necessary to be able to determine methane and nitrogen over a wider range of concentrations. — Auth. English Summ.     

TECTONIC STRUCTURE AND OIL AND GAS POTENTIAL OF THE KOLKHIDA PLAIN AND ADJACENT REGIONS

Western Georgia is in the eastern part of the Riono-Black Sea intermontane oil and gas reservoir. Coastal Abkhaziya and the Colchis Plain is favorable for oil and gas prospecting as Mesozoic sediments are here overlain by a series of Tertiary and Quaternary rocks. From the Recent tectonic pattern, evolution, age, and composition of the present complexes the authors could outline three tectonic regions: Guri, Colchis and Abkhazsko-Megrel.

The geological pattern of the Colchis region has recently become better known. Borehole data indicate the presence of a heavy Cretaceous carbonate series (over 1, 000 m thick) overlain with sharp angular unconformity by Pliocene and Quaternary argillo-arenaceous sediments.

From data obtained by seismic prospecting, drill-hole exploration and geological survey the conclusion that all brachyanticlines in the Colchis region might be grouped into three anticlinal zones, namely northern-Colchis, central Colchis and southern Colchis. Within the northern Colchis zone three brachyanticlines (Ingur, Ochemchiri and Kodor) are distinguished. The same confinement of separate uplifts to the anticlinal zones may be observed in the Abkhazsko-Megrel and Guri regions, where an overall complex of Tertiary sediments is developed. In the area under discussion two structural layers are isolated: the lower Domeotic and the upper, consisting of Pliocene- Quaternary rocks. The lower layer is characterized by intermittent folding, the upper one -- by nearly horizontal bedding. The oil content of the Cretaceous sediments in Western Georgia is known from drilling data and abundant oil and gas occurrences. In this connection certain Colchis brachyanticlines are of great interest for oil and gas prospecting within the Cretaceous carbonate complex.     

地球化学勘查技术在松辽十屋南地区的应用

经过研究发现，油气化探在松辽盆地东南隆起区具有较好的应用效果，烃类和蚀变碳酸盐法是该地区比较有效的方法。地球化学测量结果表明，十屋南地区烃类比较活跃和富集，这对在该地区利用地球化学技术寻找油气藏是个有利的前提条件。通过研究，在测区内发现了一些油气化探综合异常，这些综合异常的存在，客观地反映了研究区内具有成油气藏条件。     

Research and Application of New Methods to Oil-Gas Geochemical Exploration

Based on the results of researches and applications for many years, it has been discovered that new methods and techniques for geochemical exploration of oil and gas such as AC, altered carbonate, Hg in absorption phase, Ks, Fe2+ ,δ13C, fluorescence in two and three dimensions, and N2 and O2 in heat release can give full play in the following five fields: (1) optimization of the favourable target or hollow zones and structural zones in a region; (2) evaluation of oil traps and delineation of prospective oil and gas areas; (3) prediction of deep-seated oil-bearing horizons; (4) evaluation of the genesis of oil and gas geochemical anomalies and determination of the types of oil and gas accumulations; (5) forecast of the burial depths of oil and gas pools.     

Neoproterozoic and Lower Cambrian rock complexes in central areas of the Siberian Craton: Their structure and petroleum prospects

The paper summarizes data on the geology, lithology, and geochemistry of petroliferous Riphean, Vendian, and Lower Cambrian rocks in the central parts of the Siberian Craton. The petrological-geological properties of these sediments have been assessed based on results of paleogeographic analysis of these rocks, discrimination of oil reservoirs and oil-source successions, determination of secondary alterations of the rocks, and sources of oil generation and regional migration of hydrocarbons into various traps in zones of possible oiland-gas accumulation.     

四川叠合盆地西部中北段深层-超深层海相大型气田形成条件分析

绵阳-长宁拉张槽的发现,大大地提升了四川叠合盆地西部深层-超深层海相层系的油气勘探前景。本文利用钻井、地震和野外露头资料和前人研究成果系统分析川西深层-超深层油气地质条件和目前发现的雷口坡组气藏的成藏过程。结果表明,四川叠合盆地西部深层-超深层海相层系有以下寒武统为主的多源供烃系统,多时代(震旦系灯影组白云岩,二叠系白云岩和礁滩体,三叠系雷口坡组微生物岩和颗粒白云岩等)储集层叠合,致密碳酸盐岩、巨厚陆相泥质岩和中下三叠统膏盐岩多级封盖,以断裂(及不整合面)和优质储层构成的立体输导网络等,使得深层-超深层海相层系具备形成大气田的基本条件,是原生气藏和次生气藏共存的天然气富集区。近年来,川西发现的中三叠统雷口坡组四段气藏,其可能成藏过程为生烃中心(下寒武统烃源岩等)→生气中心(灯影组和二叠系古油藏等)→储气中心(灯影组和二叠系古气藏等)→保气中心(雷口坡组次生气藏)。这揭示其深层-超深层既可能还存在着符合四中心耦合成藏的原生气藏,也可能发育着次生气藏,极有可能发现新的大气田。     

Tectonics and petroleum potential of the East Arctic province

Tectonics and petroleum potential of the underexplored East Arctic area have been investigated as part of an IPY (International Polar Year) project. The present-day scenery of the area began forming with opening of the Amerasia Ocean (Canada and Podvodnikov—Makarov Basins) in the Late Jurassic—Early Cretaceous and with Cretaceous—Cenozoic rifting related to spreading in the Eurasia Basin. The opening of oceans produced pull-apart and rift basins along continental slopes and shelves of the present-day Arctic fringing seas, which lie on a basement consisting of fragments of the Hyperborean craton and Early Paleozoic to Middle Cretaceous orogens. By analogy with basins of the Arctic and Atlantic passive margins, the Cretaceous—Cenozoic shelf and continental slope basins may be expected to have high petroleum potential, with oil and gas accumulations in their sediments and basement.     

硫化氢、相态烃和自然电位法综合测量勘查油气田方法

经近几年试验,我们提出用土壤吸附硫化氢气体作指标,勘查油气田新方法.并将它和相态烃法、自然电位法相配合,在已知油气田开展了试验,取得令人十分满意的效果.油气藏中含有大量硫化氢气体及含硫有机化合物.油气垂直微渗漏到近地表时,硫化物气体也随伴而至.运移过程中,硫化氢气体及含硫化合物在细菌及氧气作用下会发生一系列复杂的化学变化,如生成硫酸盐等,但经已知油气田试验结果表明,在油气藏上方近地表土壤中仍保留有明显的硫化氢气体异常,而且异常形态有一定的模式,有环状、半环状、片部和带状等不同形态.异常均和下伏油气藏或断裂构造相吻合,表明硫化氢气体测量法是勘查油气田的有效方法.更引人注目的是,它和相态烃、自然电位异常吻合的很好,异常均出现在油藏上方,表明综合使用这三种方法将会取得更好的找油气效果.     

Geological structure of the oil-and-gas plays and oil-and-gas potential of the southern Siberian Platform

The paper discusses modern views of the structure of the main producing plays in the southern Siberian Platform: Riphean, Vendian, and Lower Cambrian. The major zones of oil and gas accumulation have been distinguished. Forecast resources have undergone differentiated expert evaluation, and methods for their development have been recommended.     

PROSPECTS OF OIL-GAS DEPOSITS IN CRETACEOUS SEDIMENTS IN THE COLCHIS LOWLAND AND ADJACENT FIELDS

The Riono-Chernomorsk structural basin, which extends under the Black sea and part of western Georgia, is becoming increasingly important in oil and gas exploration. Tectonically, its western Georgia portion is divided into three regions: Guri, Abkhazsk-Megrel, and the Colchis lowland. A structure-contour map drawn on the surface of Upper Cretaceous sediments in the Colchis area revealed, generally, brachyanticlinal structures. These sediments, largely composed of carbonates as thick as 2,000 meters, occur throughout the Colchis area within drilling depth (1,000 to 3,000 meters). It is postulated that bitumen formation could have occurred in the sediments; however, processes of oil migration into the area are discussed. The character of Tertiary sediments in relation to regional-structural-stratigraphic control indicates that they are possible oil and gas reservoirs. --D.D. Fisher.     

南海东北部潮汕坳陷中生代构造特征及其油气勘探潜力

钻探资料证实南海东北部发育海相中生界。潮汕坳陷是南海东北部最大残留坳陷，面积达3. 7×10 4 km2，经历了晚三叠世张裂初期、侏罗纪坳陷期、晚侏罗世末期第一次构造反转期、早白垩世再沉降期、晚白垩世晚期第二次构造反转期及新近纪区域热沉降期等6个构造演化阶段，充填了滨浅海、半深海等海相沉积及河湖相等陆相沉积。潮汕坳陷侏罗系半封闭海湾型烃源岩有机质丰度相对较高，泥岩地层厚，生烃能力强，油气地质条件好，具有较好的油气勘探前景。     

Silicification of Riphean Carbonate Sediments (Yurubcha-Tokhomo Zone,Siberian Craton)

Types and lateral and vertical distribution of silicification in Riphean (largely dolomitic) rocks of the Yurubcha-Tokhomo zone of the Siberian Craton are discussed. It is shown that quartz and pyroclastic material in sediments were subjected to intense dissolution in a highly alkaline Riphean basin with the release of silica. Rapid and abrupt decrease in alkalinity during hiatus and desiccation periods resulted in the precipitation of dissolved silica and silicification of near-surface sediments. Lateral distribution of silicification was controlled by the redistribution of silica during the pre-Vendian hiatus, when surface waters were filtered through a carbonate massif with the simultaneous karst formation and silica dissolution. In the water discharge area, secondary silica was precipitated owing to changes in pH values and other physicochemical conditions.     

第四纪沉积物磁性勘查油气法的原理及应用

本文介绍了利用第四纪沉积物磁性调查油气的原理,地下油气藏会在近地表第四纪沉积物中产生磁性矿物并形成多种磁性参量异常。检验了形成磁性异常的磁性矿物的种类;发现了油田地区土壤中存在着趋磁细菌。在5个油田地区近450km²范围应用该方法调查油气分布的研究结果表明,各种磁性异常(κ、Mn、Mr、Ir、Iκ)呈综合异常的形式,它们的形成及分布特征受油气活动、通道及环境条件的控制。实际资料证实,磁性综合异常能反映油田地区油气活动的分布状态。该方法作为综合勘查方法之一,应进一步推广。     

Main Controlling Factors on Hydrocarbon Accumulation and Distribution in Marine Sedimentary Sequences in South China

Multiple source rock assemblages were deposited in the sedimentary provinces in South China in geologic history,and some of them were destructed by and some survived against multiple tectonic movements.Therefore,multiple sources,mixed sources,and uneven distribution of sources occurred in the marine sedimentary basins in South China during the late stage of hydrocarbon pooling.Epidiagenesis of the marine carbonate reservoirs and its modification to reservoir poroperm characteristics determined the formation and the scale of natural gas pools.The exploration practices show that the large to medium gas fields mainly occur in areas with high-quality reservoirs.Detailed study of the paleo-oil accumulations and typical oil and gas reservoirs reveals that the basins experienced multiphase superimposition and modification,leading to the distribution of the Paleozoic paleo-oil accumulations and bitumen in the peripheral areas.The phenomenon that oil and gas production concentrates in the Sichuan basin indicates that the overall sealing conditions of a basin determine the oil/gas potentials and the scale of oil and gas production.This is a critical factor controlling the accumulation and distribution of gas in the marine sequences in South China.The early oil and gas pools in the Yangtze platform left billions of bitumen in the peripheral areas due to the destruction of seals.Since the Himalayan,"late-generation and late-accumulation" gas pools represented by the gas pools in the Sichuan (四川) basin were formed in the marine sedimentary sequences in South China as a result of the change of the sealing conditions.Current gas discoveries appear to be "paleo-generation and paleo-accumulation" gas pools but actually are "late-generation and late-accumulation" gas pools.These patterns of hydrocarbon pooling clearly depict themselves in western Sichuan basin and Weiyuan (威远)gas field.It is revealed that the gas pools in the Sichuan basin were mainly formed as a result of hydrocarbon phase change (thermal cracking of oil to gas),miscible migration,and dynamic equilibration since the Himalayan.A large number of gas pools were formed in the Himalayan and the gas pools in the marine sequences are characterized by late pooling; this kind of gas fields/pools are controlled by:(1) effectiveness of modification and superimposition of the marine basins,(2) effectiveness of the source rocks,(3) effectiveness of the overall preservation conditions,and (4) effectiveness of plays.     

金衢盆地上白垩统金华组湖相页岩油气地质特征

以金衢盆地白垩系金华组为研究对象,在钻井资料分析的基础上,结合区域沉积背景,通过分析暗色泥页岩有机质丰度、厚度和分布范围,研究和探索了金衢盆地上白垩统金华组湖相页岩油气地质特征。金衢盆地金华组湖相暗色泥页岩样品的有机质丰度特征表明,TOC值一般小于0.5%,属于非烃源岩,个别样品达到1.57%,属于优质烃源岩; 富有机质层段以富砂夹泥型或富泥夹砂型为主,具多产层特征,盆地北部凹陷具备一定的页岩油气勘探潜力。金华组湖相暗色泥页岩主要发育在西北部衢州—龙游沉积中心区,区域较为局限,厚度不均,范围5~100 m,平均孔隙度3.867%,平均最大渗透率0.087 2×10^-3 μm²,属于典型的致密型储层。将富有机质层段砂泥地层作为一个整体进行页岩油气勘探,源储一体是今后陆相页岩油气的重要勘探思路。