“Complementarity” Feature of Hydrocarbon Distribution in Oil-rich Sag

Based on the research and exploration of lithostratigraphic reservoir in the Jizhong depression of the Bohai Bay basin and Erlian basin, the hydrocarbon distribution in a continental oil-rich sag has "complementarity" feature, viz. the hydrocarbon resources configuration and plane distribution of the structural reservoir and lithostratigraphic reservoir have the "complementarity". This distribution feature is controlled by many factors such as the macroscopical geological setting, reservoir-forming condition, and the reservoir-forming mechanism of structural reservoir and lithostratigraphic reservoir. More research shows that the "complementarity" of hydrocarbon distribution is prevalent in every kind of continental basin. This "rule" helps to establish a new exploration theory, a scientific exploration program, and make proper exploration deployments in hydrocarbon exploration. Therefore, it is significant for the exploration work in continental petroliferous basins of China.

Formation and evolution of petroliferous basins in African continent and their hydrocarbon distribution

There are eighty sedimentary basins in five different types in African continent,i.e.craton sag basin,foreland basin,intermountain basin,passive margin basin and rift basin,which underwent the stress environment of stable depression-compression-extension.The first three types of basins had been intensely influenced by Hercynian and Alpine tectonic movement,while the later two types of basins always exist in a stable extension environment.Different basin evolution caused the obviously hydrocarbon distribution difference.In North Africa,marginal craton sag and rift basins show great expedition potential of hydrocarbon,marginal craton sag basins had good formation and preservation of Lower Silurian hot shale,tectonic-strata traps and migration pathway formed by Hercynian unconformity,and rift basins had excellent Upper Cretaceous marine source rocks and good hydrocarbon preservation with little tectonic activity.Meanwhile,in the salt-containing passive margin basins and delta basins of West Africa,thick strata containing high quality source rocks and plastic strata were well developed.Source rocks of high maturity,good hydrocarbon preservation,growth faults and deformational structure traps were formed by abundant overlying sediments and sources supplied from Tertiary large water system.

Correlation between hydrocarbon distribution and water-hydrocarbon ratio in Fischer-Tropsch synthesis

In order to shorten the evaluation cycle of cobalt catalyst before the optimized catalyst is fixed on, a mathematical method is proposed to calculate weight percentage of C5＋ hydrocarbons. Based on the carbide polymerization mechanism and the main hydrocarbons being linear alkanes and α-olefins, the correlation between hydrocarbon distribution and the molecular mass ratio of water to hydrocarbons is discussed. The result shows the ratio was within the range of 1.125-1.286 and the lower the ratio, the more gaseous hydrocarbons were obtained. Moreover, a linear equation between the weight percentage of C5＋ hydrocarbons and the weight ratio of C5＋ hydrocarbons to the total water is established. These results are validated by corresponding experiments. The weight percentage of C5＋ hydrocarbons could be immediately calculated by this linear equation without detailed gas chromatography （GC） analysis of them.

Hydrocarbon accumulation and orderly distribution of whole petroleum system in marine carbonate rocks of Sichuan Basin,SW China

Based on the situation and progress of marine oil/gas exploration in the Sichuan Basin,SW China,the whole petroleum system is divided for marine carbonate rocks of the basin according to the combinations of hydrocarbon accumulation elements,especially the source rock.The hydrocarbon accumulation characteristics of each whole petroleum system are analyzed,the patterns of integrated conventional and unconventional hydrocarbon accumulation are summarized,and the favorable exploration targets are proposed.Under the control of multiple extensional-convergent tectonic cycles,the marine carbonate rocks of the Sichuan Basin contain three sets of regional source rocks and three sets of regional cap rocks,and can be divided into the Cambrian,Silurian and Permian whole petroleum systems.These whole petroleum systems present mainly independent hydrocarbon accumulation,containing natural gas of affinity individually.Locally,large fault zones run through multiple whole petroleum systems,forming a fault-controlled complex whole petroleum system.The hydrocarbon accumulation sequence of continental shelf facies shale gas accumulation,marginal platform facies-controlled gas reservoirs,and intra-platform fault-and facies-controlled gas reservoirs is common in the whole petroleum system,with a stereoscopic accumulation and orderly distribution pattern.High-quality source rock is fundamental to the formation of large gas fields,and natural gas in a whole petroleum system is generally enriched near and within the source rocks.The development and maintenance of large-scale reservoirs are essential for natural gas enrichment,multiple sources,oil and gas transformation,and dynamic adjustment are the characteristics of marine petroleum accumulation,and good preservation conditions are critical to natural gas accumulation.Large-scale marginal-platform reef-bank facies zones,deep shale gas,and large-scale lithological complexes related to source-connected faults are future marine hydrocarbon exploration targets in the Sichuan Basin.

Hydrocarbon Distribution and Accumulation Model in the South of Lixian Slope,Raoyang Subbasin

The exploration level in the south of Lixian slope is relatively low that causes the hydrocarbon distribution pattern and hydrocarbon accumulation model of discovered reservoirs un- clear. It was assumed that the hydrocarbon accumulation model was mainly ＂stepped-like＂ type, but this model is contradicted with newly discovered reservoirs. Through comprehensive study of faults ac- tivity stages and depositional system, it can be concluded that the late period developed and late period attenuation faults act as the vertical migration path, while connected sandbodies provide lateral migra- tion path for oil and gas. Combining with the distribution of the known reservoirs and oil-source corre- lation, the hydrocarbon accumulation model in the south of Lixian slope is characterized by dual source rocks generating; connected sandbodies parallel transporting; shallow fault nose traps accumulating. This model reveals the direction and clue of the following exploration and development, which are based on shallow formation; finding subtle structure traps by fine seismic interpretation and accurate sedimentary microfacies characterization.

Orderliness of Hydrocarbon Accumulation Distribution in Rift Basins of Eastern China

The Cenozoic rift basins in eastern China show a clear temporal and spatial zonation and episodic tectonic evolution, which control their episodic hydrocarbon generation and zonal accumulation. In this paper, based on the study of depositional architecture, hydrocarbon migration system and dynamic evolution in the rift basins, combinations of hydrocarbon accumulation elements were analyzed using sequence stratigraphy. Hydrocarbon distribution in system tracts with different sequence orders was further studied. And we summarized stacking patterns and horizontal combination relationships for different types of reservoirs, such as lithological, tectonic-lithological, tectonic and stratigraphical reservoirs which can be observed from depression center to basin margin. The result reveals that various scales of pools exhibit significant distribution and evolution orderliness in different pool-forming units, i.e., depositional systems, plays and depressions. The regular distribution of various scales of pools is closely related to tectonic evolution and depositional filling in the rift basins. The result can be applied to the fine petroleum exploration in rift basins in eastern China. It will promote the scientific prediction and evaluation of reservoir types and their spatial distribution, lead to the active shifts of exploration targets in different zones, and thus support the stable progress of fine exploration in mature exploration areas.

Distribution Patterns of Remaining Hydrocarbons Controlled by Reservoir Architecture of Distributary Channel with Different Channel Style: S2 Formation of Songliao Basin, China

1 Introduction Reservoir architecture analysis of distributary channel of Daqing oilfield has drawn consistent interest among development geologists and petroleum engineers over the last decade(Lv et al.,1999;Zhou et al.,2008;Zhang et

Differential Hydrocarbon Enrichment and its Main Controlling Factors in Depressions of the Bohai Bay Basin Differential Hydrocarbon Enrichment and its Main Controlling Factors in Depressions of the Bohai Bay Basin

Significant differential hydrocarbon enrichment occurs in depressions in a petroliferous basin.There are multiple depressions in the Bohai Bay Basin, and each depression as a relatively independent unit of hydrocarbon generation, migration and accumulation, contains significantly different hydrocarbon generation conditions and enrichment degree. On the basis of previous documents and a large number of statistical data, this work comparatively analyzed the differential hydrocarbon enrichment and its major controlling factors in depressions of the Bohai Bay Basin. The results show that depressions in the Bohai Bay Basin have various hydrocarbon enrichment degrees, and can be categorized into four types, namely enormously oil-rich, oil-rich, oily and oil-poor depressions. In general, the enormously oil-rich and oil-rich depressions are distributed in the eastern part of the basin along the Tan-Lu and Lan-Liao faults, whereas depressions in the western part of the basin are poor in hydrocarbons. Moreover, the vertical distribution of hydrocarbons is also highly heterogeneous, with Pre-Paleogene strata rich in hydrocarbons in the northern and western depressions, Paleogene strata rich in hydrocarbons in the entire basin, and Neogene strata rich in hydrocarbons in the off-shore areas of the Bohai Bay Basin. From early depressions in onshore areas to the late depressions in offshore areas of the Bohai Bay Basin, the source rocks and source-reservoir-cap rock assemblages gradually become younger and shallower, and the hydrocarbon resource abundance gradually increases. Hydrocarbon supplying condition is the key factor constraining the hydrocarbon enrichment for different depressions,while the main source-reservoir-cap rock assemblage, sufficient hydrocarbons and the transportation capacity of faults control the vertical distribution of hydrocarbons. The main factors controlling hydrocarbon enrichment are different for different layers. The hydrocarbon supplying condition of source rocks is the key controlling factor, whereas the source-reservoir configuration, the main sourcereservoir-cap rock assemblages, and the fault transportation are the main factors of hydrocarbon enrichment in the Paleogene, Paleogene and Neogene, respectively.

A hydrocarbon enrichment model and prediction of favorable accumulation areas in complicated superimposed basins in China

The geologic conditions of superimposed basins in China are very complicated. This is mainly shown by multi-phase structural evolution, multiple sets of source-reservoir-cap rock combinations, multiple stages of hydrocarbon generation and expulsion from source rocks, multi-cycle hydrocarbon enrichment and accumulation, and multi-phase reservoir adjustment and reconstruction. The enrichment, accumulation and distribution of hydrocarbon is mainly controlled by the source rock kitchen, paleo- anticline, regional cap rock and intensity of tectonic movement. In this paper, the T-BCMS model has been developed to predict favorable areas of hydrocarbon accumulation in complicated superimposed basins according to time and spatial relationships among five key factors. The five factors include unconformity surface representing tectonic balancing （B）, regional cap rock representing hydrocarbon protection （C）, paleo-anticline representing hydrocarbon migration and accumulation （M）, source rock kitchen representing hydrocarbon generation and expulsion （S） and geological time （T）. There are three necessary conditions to form favorable areas of hydrocarbon accumulation. First, four key factors BCMS should be strictly in the order of BCMS from top to bottom. Second, superimposition of four key factors BCMS in the same area is the most favorable for hydrocarbon accumulation. Third, vertically ordered combination and superimposition in the same area of BCMS should occur at the same geological time. The model has been used to predict the most favorable exploration areas in Ordovician in the Tarim Basin in the main hydrocarbon accumulation periods. The result shows that 95% of the discovered Ordovician hydrocarbon reservoirs are located in the predicted areas, which indicates the feasibility and reliability of the key factor matching T-BCMS model for hydrocarbon accumulation and enrichment.

Dynamic Field Division of Hydrocarbon Migration,Accumulation and Hydrocarbon Enrichment Rules in Sedimentary Basins

Hydrocarbon distribution rules in the deep and shallow parts of sedimentary basins are considerably different, particularly in the following four aspects. First, the critical porosity for hydrocarbon migration is much lower in the deep parts of basins： at a depth of 7000 m, hydrocarbons can accumulate only in rocks with porosity less than 5%. However, in the shallow parts of basins （i.e., depths of around 1000 m）, hydrocarbon can accumulate in rocks only when porosity is over 20%. Second, hydrocarbon reservoirs tend to exhibit negative pressures after hydrocarbon accumulation at depth, with a pressure coefficient less than 0.7. However, hydrocarbon reservoirs at shallow depths tend to exhibit high pressure after hydrocarbon accumulation. Third, deep reservoirs tend to exhibit characteristics of oil （-gas）-water inversion, indicating that the oil （gas） accumulated under the water. However, the oil （gas） tends to accumulate over water in shallow reservoirs. Fourth, continuous unconventional tight hydrocarbon reservoirs are distributed widely in deep reservoirs, where the buoyancy force is not the primary dynamic force and the caprock is not involved during the process of hydrocarbon accumulation. Conversely, the majority of hydrocarbons in shallow regions accumulate in traps with complex structures. The results of this study indicate that two dynamic boundary conditions are primarily responsible for the above phenomena： a lower limit to the buoyancy force and the lower limit of hydrocarbon accumulation overall, corresponding to about 10%-12% porosity and irreducible water saturation of 100%, respectively. These two dynamic boundary conditions were used to divide sedimentary basins into three different dynamic fields of hydrocarbon accumulation： the free fluid dynamic field, limit fluid dynamic field, and restrain fluid dynamic field. The free fluid dynamic field is located between the surface and the lower limit of the buoyancy force, such that hydrocarbons in this field migrate and accumulate under the influence of, for example, the buoyancy force, pressure, hydrodynamic force, and capillary force. The hydrocarbon reservoirs formed are characterized as ＂four high,＂ indicating that they accumulate in high structures, are sealed in high locations, migrate into areas of high porosity, and are stored in reservoirs at high pressure. The basic features of distribution and accumulation in this case include hydrocarbon migration as a result of the buoyancy force and formation of a reservoir by a caprock. The limit fluid dynamic field is located between the lower limit of the buoyancy force and the lower limit of hydrocarbon accumulation overall; the hydrocarbon migrates and accumulates as a result of, for example, the molecular expansion force and the capillary force. The hydrocarbon reservoirs formed are characterized as ＂four low,＂ indicating that hydrocarbons accumulate in low structures, migrate into areas of low porosity, and accumulate in reservoirs with low pressure, and that oil（-gas）-water inversion occurs at low locations. Continuous hydrocarbon accumulation over a large area is a basic feature of this field. The restrain fluid dynamic field is located under the bottom of hydrocarbon accumulation, such that the entire pore space is filled with water. Hydrocarbons migrate as a result of the molecular diffusion force only. This field lacks many of the basic conditions required for formation of hydrocarbon reservoirs： there is no effective porosity, movable fluid, or hydrocarbon accumulation, and potential for hydrocarbon exploration is low. Many conventional hydrocarbon resources have been discovered and exploited in the free fluid dynamic field of shallow reservoirs, where exploration potential was previously considered to be low. Continuous unconventional tight hydrocarbon resources have been discovered in the limit fluid dynamic field of deep reservoirs; the exploration potential of this setting is thought to be tremendous, indicating that future exploration should be focused primarily in this direction.

Oil and Gas Distribution in Hailar Basin,Northeast China

Through petroleum exploration of 20 years, a new petroleum production area has been constructed in Hailar Basin. Their petroleum geological characteristics and hydrocarbon distribution has been known in detail. The Hailar Basin is a basin group consisted of many scattered sub-basins with similar structural developed history. Each sub-basin has unique hydrocarbon distributing rules, including (1) oil/gas reservoir distribution is controlled by the oil/gas sag, and the oil/gas bearing in big sag is rich; (2) underwater fan and turbidity fan are the most favorable reservoirs; structure zone controlled by main fault is favorable zone of forming composite oil/gas accumulation; (3) lower fault-block in higher rise and higher fault-block in lower rise are favorable to oil/gas accumulation; (4) deep fault and granite body are closely re-lated to oil/gas reservoir, its distributing area is favorable area of oil and mantle source non-hydrocarbon gas formation; (5) higher geothermal area is favorable oil/gas bearing area.

The concept and the accumulation characteristics of unconventional hydrocarbon resources

Unconventional hydrocarbon resources, which are only marginally economically explored and developed by traditional methods and techniques, are different from conventional hydrocarbon resources in their accumulation mechanisms, occurrence states, distribution models, and exploration and development manners. The types of unconventional hydrocarbon are controlled by the evolu- tion of the source rocks and the combinations of different types of unconventional reservoirs. The fundamental dis- tinction between unconventional hydrocarbon resources and conventional hydrocarbon resources is their non- buoyancy-driven migration. The development of the micro- to nano-scale pores results in rather high capillary resis- tance. The accumulation mechanisms of the unconven- tional and the conventional hydrocarbon resources are also greatly different. In conventional hydrocarbon resources, oil and gas entrapment is controlled by reservoir-forming factors and geological events, which is a dynamic balance process; while for unconventional hydrocarbon resources, the gas content is affected by the temperature and pressure fields, and their preservation is crucial. Unconventional and conventional hydrocarbons are distributed in an orderly manner in subsurface space, having three distribution models of intra-source rock, basin-centered, and source rock interlayer. These results will be of great significance to unconventional hydrocarbon exploration.

Bohai crude oil identification by gas chromatogram fingerprinting quantitative analysis coupled with cluster analysis

By gas chromatogram, six crude oils fingerprinting distributed in four oilfields and four oil platforms were analyzed and the corre- sponding normal paraffin hydrocarbon （ including pristane and phytane） concentration was obtained by the internal standard methed. The normal paraffin hydrocarbon distribution patterns of six crude oils were built and compared. The cluster analysis on the normal paraffin hydrocarbon concentration was conducted for classification and some ratios of oils were used for oils comparison. The results indicated： there was a clear difference within different crude oils in different oil fields and a small difference between the crude oils in the same oil platform. The normal paraffin hydrocarbon distribution pattern and ratios, as well as the cluster analysis on the nomad paraffin hydrocarbon concentration can have a better differentiation result for the crude oils with small difference than the original gas chromatogram.