2004 Vol. 29, No. 4
Display Method:
2004, 29(4): 379-383.
PDF 223KB
Abstract:
Diffusive transport and volume flow of hydrocarbon may coexist and transform each other in the heterogeneous formation. Diffusive transport is helpful to hydrocarbon expulsion from source rock and directly contributes to oil and gas accumulation by transform of flow pattern. The calculated rates of the diffusive and volume flow in the tight mudstone, with the flow velocity of 4-18 m/Ma and 3-15 m/Ma respectively, show little difference, which indicates that Darcy's law is suitable for describing the flow behavior in the dense mudstone. Hydrocarbon migrates in the buoyancy-driven flow or the seepage flow through the subsurface porous media, but it moves upward in discontinuous phase in the course of buoyant ascent. Hence, the buoyant ascent does not relate with critical migration saturation and relative permeability, and can't obey the Darcy's law. Two concepts on hydrocarbon migration have been discussed, i.e. dominant migration pathway and effective migration space, the former implies main direction of hydrocarbon migration and the latter refers to the space in which the hydrocarbon migration really occurred. About 70% oil and gas reservoirs are situated in the dominant migration pathway, while the effective migration space occupies only about 5%-10% of total porous space in a carrier bed. There are three types of traps according to the different combinations of seal strength and trap closure, which are the key controlling factors on the distribution of oil and gas. On the basis of research and statistics, the half-life of petroleum reserve is inferred to be about 29 Ma, and the average age of a giant oil field is about 35 Ma. According to the calculated results of hydrocarbon microseepage fluxes, the average natural age of a median-giant oil and gas field is thought to be about 50-100 Ma.
Diffusive transport and volume flow of hydrocarbon may coexist and transform each other in the heterogeneous formation. Diffusive transport is helpful to hydrocarbon expulsion from source rock and directly contributes to oil and gas accumulation by transform of flow pattern. The calculated rates of the diffusive and volume flow in the tight mudstone, with the flow velocity of 4-18 m/Ma and 3-15 m/Ma respectively, show little difference, which indicates that Darcy's law is suitable for describing the flow behavior in the dense mudstone. Hydrocarbon migrates in the buoyancy-driven flow or the seepage flow through the subsurface porous media, but it moves upward in discontinuous phase in the course of buoyant ascent. Hence, the buoyant ascent does not relate with critical migration saturation and relative permeability, and can't obey the Darcy's law. Two concepts on hydrocarbon migration have been discussed, i.e. dominant migration pathway and effective migration space, the former implies main direction of hydrocarbon migration and the latter refers to the space in which the hydrocarbon migration really occurred. About 70% oil and gas reservoirs are situated in the dominant migration pathway, while the effective migration space occupies only about 5%-10% of total porous space in a carrier bed. There are three types of traps according to the different combinations of seal strength and trap closure, which are the key controlling factors on the distribution of oil and gas. On the basis of research and statistics, the half-life of petroleum reserve is inferred to be about 29 Ma, and the average age of a giant oil field is about 35 Ma. According to the calculated results of hydrocarbon microseepage fluxes, the average natural age of a median-giant oil and gas field is thought to be about 50-100 Ma.
2004, 29(4): 384-390.
Abstract:
The concept of "Hydrocarbon expulsion threshold" is taken as an important theoretical base in the identification of effective source rock, and therefore, plays a significant role in petroleum exploration and resource assessment. Occurrence of hydrocarbon expulsion threshold is discussed by means of geochemical approaches. The results show that the parameters of (S1+S2)/TOC, HI showing source rock potential and the abundance of resident hydrocarbons-"A" decrease obviously with increasing depth once source rocks reach the expulsion threshold, and obvious variation of chemical composition as well as (abundance) and relative distribution of biomarkers can also be observed. Similar chemical compositions between crude oils and soluble organic matters are observed after the source rocks entered the expulsion threshold, however, the discrepancies are present within the source rocks below the expulsion threshold. Taking as an example of the Dongying depression of the Bohaiwan basin, the expulsion thresholds of Es4 mudstone and shale in Bamianhe area are about 2 200 and 2 000 m respectively, with expulsion intensity of 0-1 100 and 0-150 kg/m2 and expulsed accumulative hydrocarbons of 7.365×108 and 1.435×108 t.
The concept of "Hydrocarbon expulsion threshold" is taken as an important theoretical base in the identification of effective source rock, and therefore, plays a significant role in petroleum exploration and resource assessment. Occurrence of hydrocarbon expulsion threshold is discussed by means of geochemical approaches. The results show that the parameters of (S1+S2)/TOC, HI showing source rock potential and the abundance of resident hydrocarbons-"A" decrease obviously with increasing depth once source rocks reach the expulsion threshold, and obvious variation of chemical composition as well as (abundance) and relative distribution of biomarkers can also be observed. Similar chemical compositions between crude oils and soluble organic matters are observed after the source rocks entered the expulsion threshold, however, the discrepancies are present within the source rocks below the expulsion threshold. Taking as an example of the Dongying depression of the Bohaiwan basin, the expulsion thresholds of Es4 mudstone and shale in Bamianhe area are about 2 200 and 2 000 m respectively, with expulsion intensity of 0-1 100 and 0-150 kg/m2 and expulsed accumulative hydrocarbons of 7.365×108 and 1.435×108 t.
2004, 29(4): 391-396.
Abstract:
The histories of stratigraphic burial, geotherm, diagenesis, hydrocarbon generation, expulsion and migration-accumulation are simulated quantitatively by means of the basin modeling software of BASIMS in order to provide the quantitative data for oil and gas exploration in Kuqa depression. Of them, hydrocarbon primary migration is simulated by the easy and practical methods, i.e. sedimentary compaction-filtration method is used to calculate the amount of expelled oil and the mass balance method to calculate the amount of expelled gas. The pseudo 3-D migration-accumulation model based on buoyancy and Darcy's Law is used to simulate on secondary hydrocarbon migration. The sensible parameters (parameter sensitivity and risk analyses, distribution ratio of hydrocarbons expelled, permeabilities in fault and unconformity zones, and determination of reservoir cell) in these numerical methods are discussed, and hydrocarbon expulsion and migration-accumulation histories have been simulated in detail. The modeling results are in agreement with the real pools not only on quantities but also on locations, and especially some predicted prospects have been proved by explorations later.
The histories of stratigraphic burial, geotherm, diagenesis, hydrocarbon generation, expulsion and migration-accumulation are simulated quantitatively by means of the basin modeling software of BASIMS in order to provide the quantitative data for oil and gas exploration in Kuqa depression. Of them, hydrocarbon primary migration is simulated by the easy and practical methods, i.e. sedimentary compaction-filtration method is used to calculate the amount of expelled oil and the mass balance method to calculate the amount of expelled gas. The pseudo 3-D migration-accumulation model based on buoyancy and Darcy's Law is used to simulate on secondary hydrocarbon migration. The sensible parameters (parameter sensitivity and risk analyses, distribution ratio of hydrocarbons expelled, permeabilities in fault and unconformity zones, and determination of reservoir cell) in these numerical methods are discussed, and hydrocarbon expulsion and migration-accumulation histories have been simulated in detail. The modeling results are in agreement with the real pools not only on quantities but also on locations, and especially some predicted prospects have been proved by explorations later.
2004, 29(4): 397-403.
Abstract:
Based on the organic geochemical analysis of oils and source rock in Wuerxun depression, Hailaer basin, hydrocarbons are thought to be derived from the Nantun Formation in south Wuerxun depression and to enter the oil pools through lateral migration. Apparent migration pathways along the Surennuoer fault belt can be traced by means of absolute abundance of pyrrolic nitrogen compounds and biomarkers from the oil samples. The results indicate that the large fault is the dominant pathway in which the oil can migrates for a long distance, and fill easily into the traps near the fault. According to the migration effects of pyrrolic nitrogen compounds in the oils, the maximum migratation distance is estimated to be about 20 km. The analysis of K-Ar illite age, fluid inclusion and history of source rock expulsion indicates that there are three oil filling and entrapment events, the major oil entrapment epoch occurrs in the Late Yimin period about 100 Ma before the present. It can be also observed that the farther the pools away from the source kitchen are, the earlier the ages of oil filling are.
Based on the organic geochemical analysis of oils and source rock in Wuerxun depression, Hailaer basin, hydrocarbons are thought to be derived from the Nantun Formation in south Wuerxun depression and to enter the oil pools through lateral migration. Apparent migration pathways along the Surennuoer fault belt can be traced by means of absolute abundance of pyrrolic nitrogen compounds and biomarkers from the oil samples. The results indicate that the large fault is the dominant pathway in which the oil can migrates for a long distance, and fill easily into the traps near the fault. According to the migration effects of pyrrolic nitrogen compounds in the oils, the maximum migratation distance is estimated to be about 20 km. The analysis of K-Ar illite age, fluid inclusion and history of source rock expulsion indicates that there are three oil filling and entrapment events, the major oil entrapment epoch occurrs in the Late Yimin period about 100 Ma before the present. It can be also observed that the farther the pools away from the source kitchen are, the earlier the ages of oil filling are.
2004, 29(4): 404-412.
Abstract:
As a part of Junggar basin, the southern margin region has received the sediments from Permian to Quaternary period. The tectonic activities, occurring intensively in the area during recent million years, cause strange tectonic stress in SN direction and result in a series of anticlines accompanied with different scales of faults. Very high overpressures, the largest one with the pressure coefficient of 2.4, are observed in the area. Pressures measured with DST/RFT methods and those estimated from acoustic logging data are used in this paper to characterize overpressure distribution in the basin. Pressuring effect of different geological factors in permeable sandy and sealing shaly formations are discussed. It indicated that the occurrence and distribution of overpressures in the southern margin have been seriously influenced by many geological factors, such as deposition facies, the tectonic stress action, deformation of sediments, as well as fractures occurrences and so on. Synthetically, the extremely high pressures encountered in the research area result from the effect of compaction caused by both the gravity and the tectonic stress, in combination with faulting that makes hydraulic connection among permeable formations, and with folding that makes the permeable formations incline.
As a part of Junggar basin, the southern margin region has received the sediments from Permian to Quaternary period. The tectonic activities, occurring intensively in the area during recent million years, cause strange tectonic stress in SN direction and result in a series of anticlines accompanied with different scales of faults. Very high overpressures, the largest one with the pressure coefficient of 2.4, are observed in the area. Pressures measured with DST/RFT methods and those estimated from acoustic logging data are used in this paper to characterize overpressure distribution in the basin. Pressuring effect of different geological factors in permeable sandy and sealing shaly formations are discussed. It indicated that the occurrence and distribution of overpressures in the southern margin have been seriously influenced by many geological factors, such as deposition facies, the tectonic stress action, deformation of sediments, as well as fractures occurrences and so on. Synthetically, the extremely high pressures encountered in the research area result from the effect of compaction caused by both the gravity and the tectonic stress, in combination with faulting that makes hydraulic connection among permeable formations, and with folding that makes the permeable formations incline.
2004, 29(4): 413-419.
Abstract:
The gas source in Ordos basin mainly comes from the alternate marine-continental coal-bearing measures of Shanxi and Taiyuan formations. The Upper Shihezi Formation with a vast thick mudstone layer can be taken as a very good seal, so it is difficult for natural gas to pass through. Recently, some secondary gas pools have been found in Shiqianfeng Formation lying above the Upper Shihezi Formation in eastern Ordos basin. In this paper, according to the properties of secondary gas pools and the inclusion data, the secondary gas pools are thought to be formed due to the leakage of the original gas pools penetrating through the regional caprock when the overpressures within lower overpressured strata release. The forming process of gas reservoirs includes three stages, that is, the formation of the primary gas pools with high temperature and high pressure, the leakage of the primary gas pools and the formation of the secondary gas pools, and late adjustment and maintenance of the secondary pools.
The gas source in Ordos basin mainly comes from the alternate marine-continental coal-bearing measures of Shanxi and Taiyuan formations. The Upper Shihezi Formation with a vast thick mudstone layer can be taken as a very good seal, so it is difficult for natural gas to pass through. Recently, some secondary gas pools have been found in Shiqianfeng Formation lying above the Upper Shihezi Formation in eastern Ordos basin. In this paper, according to the properties of secondary gas pools and the inclusion data, the secondary gas pools are thought to be formed due to the leakage of the original gas pools penetrating through the regional caprock when the overpressures within lower overpressured strata release. The forming process of gas reservoirs includes three stages, that is, the formation of the primary gas pools with high temperature and high pressure, the leakage of the primary gas pools and the formation of the secondary gas pools, and late adjustment and maintenance of the secondary pools.
2004, 29(4): 420-426.
Abstract:
Uplift is one of the major patterns of tectonic movement in sedimentary basin. Its contribution to reservoir is neglected before, but the damage function is emphasized. Based on the rebounding simulation of sandstone by using different grain level sandstones under conditions of different temperatures and pressures, the quantitatively rebounding chart of sandstone in different geological conditions during uplift is established. Taking the Daqing placanticline as a typical example, the quantitative relationship between sandstone rebounding and reservoir formation was established based on integrated analysis of buried history, hydrocarbon generation and expulsion history. The contribution ratio due to rebounding of sandstone during uplift is 13.43%-40.46% in the Daqing placanticline. The new method provided in this paper can offer more scientific basis for forecasting hydrocarbon distribution.
Uplift is one of the major patterns of tectonic movement in sedimentary basin. Its contribution to reservoir is neglected before, but the damage function is emphasized. Based on the rebounding simulation of sandstone by using different grain level sandstones under conditions of different temperatures and pressures, the quantitatively rebounding chart of sandstone in different geological conditions during uplift is established. Taking the Daqing placanticline as a typical example, the quantitative relationship between sandstone rebounding and reservoir formation was established based on integrated analysis of buried history, hydrocarbon generation and expulsion history. The contribution ratio due to rebounding of sandstone during uplift is 13.43%-40.46% in the Daqing placanticline. The new method provided in this paper can offer more scientific basis for forecasting hydrocarbon distribution.
2004, 29(4): 427-432.
Abstract:
This paper discusses that heat can act as the driven force of oil migration in the point of view of thermodynamics. The energy formula for oil migration, that heat acts as the driven force of fluid movement, was established in the thermodynamic system based on the experimental results. The variation of enthalpy in the fluid flow indicates that heat and its enthalpy control the migration velocity and distance of oil flow. The enthalpy decreases with the increase of migration distance. The paper also discusses the dynamics of oil movement in semi-quantitative to quantitatively.At the same time, thermodynamic relation of fluid flow within the thermodynamic system is applied to the practical carriers, the results indicate that heat regime taking as the driven force shows more complicated patterns in practical basins. The distance of oil migration depends on the amount of heat and physical characteristics of carriers.
This paper discusses that heat can act as the driven force of oil migration in the point of view of thermodynamics. The energy formula for oil migration, that heat acts as the driven force of fluid movement, was established in the thermodynamic system based on the experimental results. The variation of enthalpy in the fluid flow indicates that heat and its enthalpy control the migration velocity and distance of oil flow. The enthalpy decreases with the increase of migration distance. The paper also discusses the dynamics of oil movement in semi-quantitative to quantitatively.At the same time, thermodynamic relation of fluid flow within the thermodynamic system is applied to the practical carriers, the results indicate that heat regime taking as the driven force shows more complicated patterns in practical basins. The distance of oil migration depends on the amount of heat and physical characteristics of carriers.
2004, 29(4): 433-439.
Abstract:
It is of importance to research characteristics and its nature of gas migration and accumulation within abnormal high pressure. Overpressures are observed in Xujiahe Formation, western Sichuan basin, in which a complete assemble of source, reservoir and caprock in interbedded pattern includes. Distribution of overpressure is plotted in vertical and in plane based on a number of data of measured pressure in sandstone reservoir. The evolution history of abnormal pressure is restored mainly by means of the numerical model on abnormal pressure, which are restrained by present measured pressures and ancient pressures calculated from compaction and fluid inclusion in sandstones. Vertical pattern of formation pressure includes a type of" two segments"in southern part and a type of" three segments" in northern part, and amplitude of overpressure in the latter is higher than in the former. The zone of strong overpressure is located in the Zitong sag.Overpressure increase in Xujiahe Fm from Early Jurassic to Paleocene is due to depositional factor, and comes from the effects of tectonic movement since Neocene. Three kinds of models of gas accumulation typically are put forward taking account of distribution and evolution of fluid pressure as well as other major elements of accumulation.
It is of importance to research characteristics and its nature of gas migration and accumulation within abnormal high pressure. Overpressures are observed in Xujiahe Formation, western Sichuan basin, in which a complete assemble of source, reservoir and caprock in interbedded pattern includes. Distribution of overpressure is plotted in vertical and in plane based on a number of data of measured pressure in sandstone reservoir. The evolution history of abnormal pressure is restored mainly by means of the numerical model on abnormal pressure, which are restrained by present measured pressures and ancient pressures calculated from compaction and fluid inclusion in sandstones. Vertical pattern of formation pressure includes a type of" two segments"in southern part and a type of" three segments" in northern part, and amplitude of overpressure in the latter is higher than in the former. The zone of strong overpressure is located in the Zitong sag.Overpressure increase in Xujiahe Fm from Early Jurassic to Paleocene is due to depositional factor, and comes from the effects of tectonic movement since Neocene. Three kinds of models of gas accumulation typically are put forward taking account of distribution and evolution of fluid pressure as well as other major elements of accumulation.
2004, 29(4): 440-444.
Abstract:
Petroleum accumulation system in the Kuqa fold-thrust belts consists of Jurassic coal source rocks, fault migration system and lateral ramp-related anticline traps. The lateral ramp fault is taken as an effective pathway of hydrocarbon migration in the strike-slip fault. The results indicate that hydrocarbon generated from the Jurassic coal migrates through lateral ramp fault upwards into the Cretaceous Bashenjiqike sandstone traps in the lateral ramp-related anticlines. Hydrocarbon migration may be associated with episodic expulsion of overpressure. The discovery of the Kela-2, Dina-2, Dina-1 and Tuzi-1 gas fields supports above hypoth- esis. Hence, the lateral ramp-related anticline may be a new potential realm for hydrocarbon exploration in the Kuqa fold-thrust belts, Tarim basin.
Petroleum accumulation system in the Kuqa fold-thrust belts consists of Jurassic coal source rocks, fault migration system and lateral ramp-related anticline traps. The lateral ramp fault is taken as an effective pathway of hydrocarbon migration in the strike-slip fault. The results indicate that hydrocarbon generated from the Jurassic coal migrates through lateral ramp fault upwards into the Cretaceous Bashenjiqike sandstone traps in the lateral ramp-related anticlines. Hydrocarbon migration may be associated with episodic expulsion of overpressure. The discovery of the Kela-2, Dina-2, Dina-1 and Tuzi-1 gas fields supports above hypoth- esis. Hence, the lateral ramp-related anticline may be a new potential realm for hydrocarbon exploration in the Kuqa fold-thrust belts, Tarim basin.
2004, 29(4): 445-450.
Abstract:
The source-contacting oil and gas are discovered under high extent of geological exploration. Conventional balance equation used for the accumulation process of oil and gas cannot be suitable for the source-contacting oil and gas because of their special mechanism and occurence patterns. According to the geological characteristics and evolution process, the analysis method on the ascending forces of continuous hydrocarbon columns within complex formation water environments has been put forward. In this paper, the balance equations of source-contacting oil and gas are established respectively in typical, complex, and special situations on the basis of equilibrium related to pressure difference of fluids.
The source-contacting oil and gas are discovered under high extent of geological exploration. Conventional balance equation used for the accumulation process of oil and gas cannot be suitable for the source-contacting oil and gas because of their special mechanism and occurence patterns. According to the geological characteristics and evolution process, the analysis method on the ascending forces of continuous hydrocarbon columns within complex formation water environments has been put forward. In this paper, the balance equations of source-contacting oil and gas are established respectively in typical, complex, and special situations on the basis of equilibrium related to pressure difference of fluids.
2004, 29(4): 451-456.
Abstract:
A large amount of heavy oils are discovered in the north steep slope (NSS) of the Dongying depression, the Bohai Bay basin, Eastern China, but the mechanism of oil accumulation for this oil pools is still not well understood. Based on detail investigation of the composition for the oils and their source rocks, pyrrolic nitrocompounds and fluid inclusions have been analyzed to trace the process of oil migration and accumulation in the Wangzhuang-Ninghai region. The results show that apparent migration effects of nitrogen compounds within the oils from south to north, indicate the oils in the north steep slope originated mainly from the Lijing sag in the Dongying depression. Obviously, migration effects from east to west observed in the Wangzhuang-Ninghai area indicate two main charging points respectively in the eastern and western areas. Composition of alkanes and non-alkanes and their distribution as well as pyrrolic nitrogen compounds show the origin of mixing of the oils. Alkanes with slight and/or no biodegradation and 25-norhopanes with strong biodegradation are observed in same oils, which indicates possibly multiple oil charging periods and/or redistribution of the oils due to tectonic movement. Two periods of oil formation and accumulation have been identified as evidenced from fluid inclusions. Oil pools in the Wangzhuang-Ninghai region were formed within 5 (?) Ma before present. The oils generated in nearly 36 (?) Ma ago as evidenced from inclusions in reservoir near the Lijing sag. A number of faults, several unconformities and a series of well developed fans with coarse sands and conglomerate in the NSS are taken as favored migration pathways for hydrocarbon in the study (area).
A large amount of heavy oils are discovered in the north steep slope (NSS) of the Dongying depression, the Bohai Bay basin, Eastern China, but the mechanism of oil accumulation for this oil pools is still not well understood. Based on detail investigation of the composition for the oils and their source rocks, pyrrolic nitrocompounds and fluid inclusions have been analyzed to trace the process of oil migration and accumulation in the Wangzhuang-Ninghai region. The results show that apparent migration effects of nitrogen compounds within the oils from south to north, indicate the oils in the north steep slope originated mainly from the Lijing sag in the Dongying depression. Obviously, migration effects from east to west observed in the Wangzhuang-Ninghai area indicate two main charging points respectively in the eastern and western areas. Composition of alkanes and non-alkanes and their distribution as well as pyrrolic nitrogen compounds show the origin of mixing of the oils. Alkanes with slight and/or no biodegradation and 25-norhopanes with strong biodegradation are observed in same oils, which indicates possibly multiple oil charging periods and/or redistribution of the oils due to tectonic movement. Two periods of oil formation and accumulation have been identified as evidenced from fluid inclusions. Oil pools in the Wangzhuang-Ninghai region were formed within 5 (?) Ma before present. The oils generated in nearly 36 (?) Ma ago as evidenced from inclusions in reservoir near the Lijing sag. A number of faults, several unconformities and a series of well developed fans with coarse sands and conglomerate in the NSS are taken as favored migration pathways for hydrocarbon in the study (area).
2004, 29(4): 457-460.
Abstract:
Based on data of more than 890 drilling wells, the controls of buried history on oil accumulation processes in the Daqing placanticline of northern Songliao basin have been elaborated by means of basin simulation and dating technique of oil reservoir. Northern Songliao basin had been undergone 3 subsidences and 2 uplifts. Duration of 3 subsidences are, respectively, Qingshankou-Nenjiang, Sifangtai-Mingshui and Tertiary-Quaternary periods, of them, during the periods, the biggest depositional rates with respectively 160 m/Ma and 180 m/Ma occur at Late Nenjiang and Mingshui periods. 2 uplifts respectively betided on the end of Nenjiang and Mingshui periods, which results in the formation of the Daqing placanticline. The oil generation and expulsion of the major source rocks of Qingshankou Formation maintain for a very long period, which started from about 77.4 Ma, and matched well with tectonic activity and formation of trap. The results indicate that two oil accumulation peaks occur respectively about 73 Ma and 65-40 Ma, which are in agreement with the processes of basin uplifts and structure formation.
Based on data of more than 890 drilling wells, the controls of buried history on oil accumulation processes in the Daqing placanticline of northern Songliao basin have been elaborated by means of basin simulation and dating technique of oil reservoir. Northern Songliao basin had been undergone 3 subsidences and 2 uplifts. Duration of 3 subsidences are, respectively, Qingshankou-Nenjiang, Sifangtai-Mingshui and Tertiary-Quaternary periods, of them, during the periods, the biggest depositional rates with respectively 160 m/Ma and 180 m/Ma occur at Late Nenjiang and Mingshui periods. 2 uplifts respectively betided on the end of Nenjiang and Mingshui periods, which results in the formation of the Daqing placanticline. The oil generation and expulsion of the major source rocks of Qingshankou Formation maintain for a very long period, which started from about 77.4 Ma, and matched well with tectonic activity and formation of trap. The results indicate that two oil accumulation peaks occur respectively about 73 Ma and 65-40 Ma, which are in agreement with the processes of basin uplifts and structure formation.
2004, 29(4): 461-466.
Abstract:
The fractionation of pyrrolic nitrogen compounds has been applied widely on studying secondary hydrocarbon migration. As for a biodegraded crude oil, the effect of biodegradation on pyrrolic nitrogen compounds should be studied. The normal crude oil occurs in the reservoirs of Wei 2, Wei 9 and Wei 11 in Weizhuang area of Gaoyou sag, but the oil with little biodegradation occurs in reservoirs of Wei 5, Wei 6 and Wei 8. By comparison among concentration of nitrogen compounds, relative contents of pyrrolic N-H shielded carbazoles and parameters of C21-/C22+, Pr/nC17, the results show that slight biodegradation has little effects on the relative contents and distribution of pyrrolic nitrogen compounds, but has certain effect on its concentration. Hence, variation of relative contents of pyrrolic nitrogen compounds would imply the secondary migration direction of hydrocarbon. The results indicate that hydrocarbon originated from the deep depression zone and Cheluo saddle and injected westward and southwestward in Weizhuang area.
The fractionation of pyrrolic nitrogen compounds has been applied widely on studying secondary hydrocarbon migration. As for a biodegraded crude oil, the effect of biodegradation on pyrrolic nitrogen compounds should be studied. The normal crude oil occurs in the reservoirs of Wei 2, Wei 9 and Wei 11 in Weizhuang area of Gaoyou sag, but the oil with little biodegradation occurs in reservoirs of Wei 5, Wei 6 and Wei 8. By comparison among concentration of nitrogen compounds, relative contents of pyrrolic N-H shielded carbazoles and parameters of C21-/C22+, Pr/nC17, the results show that slight biodegradation has little effects on the relative contents and distribution of pyrrolic nitrogen compounds, but has certain effect on its concentration. Hence, variation of relative contents of pyrrolic nitrogen compounds would imply the secondary migration direction of hydrocarbon. The results indicate that hydrocarbon originated from the deep depression zone and Cheluo saddle and injected westward and southwestward in Weizhuang area.
2004, 29(4): 467-472.
Abstract:
The structures in deep and shallow strata are different in Junggar basin. The NE-trending structures developed in Middle-Late Permian and Triassic in Junggar basin have been analyzed by means of seismic and geologic data. The results indicate that the sedimentation of Middle-Upper Permian and Triassic is controlled by NE- and NW-trending normal faults. Depo-centers controlled by NE-trending faults show an echelon pattern. The NE-trending structures formed in the basin formation result from the sinistral strike-slip movement of marginal faults. NE-trending reverse faults mainly formed on the end of Triassic because of the basin inversion. The belts of NE-trending structures during extension and inversion stages are (available) for hydrocarbon accumulation. The draping sediments of post-Triassic period superposed on the middle-late Permian and Triassic basin are very important for the preservation of oil and gas.
The structures in deep and shallow strata are different in Junggar basin. The NE-trending structures developed in Middle-Late Permian and Triassic in Junggar basin have been analyzed by means of seismic and geologic data. The results indicate that the sedimentation of Middle-Upper Permian and Triassic is controlled by NE- and NW-trending normal faults. Depo-centers controlled by NE-trending faults show an echelon pattern. The NE-trending structures formed in the basin formation result from the sinistral strike-slip movement of marginal faults. NE-trending reverse faults mainly formed on the end of Triassic because of the basin inversion. The belts of NE-trending structures during extension and inversion stages are (available) for hydrocarbon accumulation. The draping sediments of post-Triassic period superposed on the middle-late Permian and Triassic basin are very important for the preservation of oil and gas.
2004, 29(4): 473-482.
Abstract:
In order to establish the formation models of the Silurian paleo-pools and predict the distribution of the original hydrocarbon pools, hydrocarbon migration directions during the first Silurian pools filling stage in Tazhong and Tabei areas of the Tarim basin have been studied based on analysis of carbazole compounds. The results indicate that hydrocarbons in the Silurian paleo-pools of the Tazhong uplift mainly originated from the Lower and Middle Cambrian source rocks in the Manjiaer sag. These hydrocarbons flowed firstly southwest-southward into the Silurian reservoir beds in the Tazhong area. Then, they further migrated southeastward and southwestward, respectively, to the Silurian pinchouting zone in the Tazhong through unconformable surfaces or the reservoir beds. Hydrocarbons in Silurian pools in the Tabei uplift were also from the Lower and Middle Cambrian source rocks in the Manjiaer sag. They migrated northwestward firstly into the Silurian reservoir beds in the Tabei uplift, and then continued to flow into the traps in high positions in the same direction through the Silurian reservoirs or unconformable surfaces.
In order to establish the formation models of the Silurian paleo-pools and predict the distribution of the original hydrocarbon pools, hydrocarbon migration directions during the first Silurian pools filling stage in Tazhong and Tabei areas of the Tarim basin have been studied based on analysis of carbazole compounds. The results indicate that hydrocarbons in the Silurian paleo-pools of the Tazhong uplift mainly originated from the Lower and Middle Cambrian source rocks in the Manjiaer sag. These hydrocarbons flowed firstly southwest-southward into the Silurian reservoir beds in the Tazhong area. Then, they further migrated southeastward and southwestward, respectively, to the Silurian pinchouting zone in the Tazhong through unconformable surfaces or the reservoir beds. Hydrocarbons in Silurian pools in the Tabei uplift were also from the Lower and Middle Cambrian source rocks in the Manjiaer sag. They migrated northwestward firstly into the Silurian reservoir beds in the Tabei uplift, and then continued to flow into the traps in high positions in the same direction through the Silurian reservoirs or unconformable surfaces.
2004, 29(4): 483-488.
Abstract:
Lenticular sandbody reservoir is an important subtle reservoir type for increase of reserve, but its accumulation and filling mechanism is not well understood. Driven force and resistance during lenticular sandbody reservoir-filling have been analyzed based on integrated research on the process of compaction and diagenesis in interbedded sand/mud strata. The results indicate that the driven forces resulting in the filling of reservoir include pressure due to the generation of hydrocarbon, diffusion by hydrocarbon concentration difference, capillary pressure between sand and mud. Rock absorption and adhibition are taken as resistance of reservoir-filling. Hydrocarbon and water spill into the reservoirs in the mixing pattern through pore, fracture and joint fissure. Hydrocarbon is filled in early phase of late-diagenetic stage and preserved in late phase of late-diagenetic stage.
Lenticular sandbody reservoir is an important subtle reservoir type for increase of reserve, but its accumulation and filling mechanism is not well understood. Driven force and resistance during lenticular sandbody reservoir-filling have been analyzed based on integrated research on the process of compaction and diagenesis in interbedded sand/mud strata. The results indicate that the driven forces resulting in the filling of reservoir include pressure due to the generation of hydrocarbon, diffusion by hydrocarbon concentration difference, capillary pressure between sand and mud. Rock absorption and adhibition are taken as resistance of reservoir-filling. Hydrocarbon and water spill into the reservoirs in the mixing pattern through pore, fracture and joint fissure. Hydrocarbon is filled in early phase of late-diagenetic stage and preserved in late phase of late-diagenetic stage.
2004, 29(4): 489-494.
Abstract:
The concepts and methods of petroleum system are applied to analyze the Ordovician petroleum accumulation process in Tazhong low uplift of central Tarim basin. Hydrocarbon in the Ordovician petroleum accumulation system originated from the Cambrian and Lower Ordovician source rocks. Sand beds and unconformities in the Manjiaer depression are taken as the pathway of lateral petroleum migration and deep faults as the pathway of vertical petroleum migration. Main traps are composed of stratigraphic and structural typed traps developed in palaeo structural high. The results indicate that the area in the No.1 fault in Tazhong structure is inferred to be the most favorable zone of petroleum accumulation, and next, the northern slope of Tazhong structure, and the worst one, the middle fault-horst zone. Of them, the No.1 fault zone in Tazhong structure would be taken as the favorable prospect of next exploration.
The concepts and methods of petroleum system are applied to analyze the Ordovician petroleum accumulation process in Tazhong low uplift of central Tarim basin. Hydrocarbon in the Ordovician petroleum accumulation system originated from the Cambrian and Lower Ordovician source rocks. Sand beds and unconformities in the Manjiaer depression are taken as the pathway of lateral petroleum migration and deep faults as the pathway of vertical petroleum migration. Main traps are composed of stratigraphic and structural typed traps developed in palaeo structural high. The results indicate that the area in the No.1 fault in Tazhong structure is inferred to be the most favorable zone of petroleum accumulation, and next, the northern slope of Tazhong structure, and the worst one, the middle fault-horst zone. Of them, the No.1 fault zone in Tazhong structure would be taken as the favorable prospect of next exploration.
2004, 29(4): 495-499.
Abstract:
NMR (nuclear magnetic resonance) method is used to obtain the property of porous media without damage. But the measurement of wettability in the porous media is still in quasi-quantitative. The capillary and surface tension methods are used to measure the relationship between the concentration of the reagent and the wettability of the glass plate. And then the wettabilities of the porous media are demarcated by NMR and the scales of a series of porous media are obtained. The results of analysis indicate that the variation of wettability in porous media corresponds with the measured data under the condition of dichlorodimethylsilane concentration from water-wet to oil-wet (?) from 0% to 0.7%. If out of this range, resonance time still increases with the concentration of reagent but it does not relate with the scale of the wettability.
NMR (nuclear magnetic resonance) method is used to obtain the property of porous media without damage. But the measurement of wettability in the porous media is still in quasi-quantitative. The capillary and surface tension methods are used to measure the relationship between the concentration of the reagent and the wettability of the glass plate. And then the wettabilities of the porous media are demarcated by NMR and the scales of a series of porous media are obtained. The results of analysis indicate that the variation of wettability in porous media corresponds with the measured data under the condition of dichlorodimethylsilane concentration from water-wet to oil-wet (?) from 0% to 0.7%. If out of this range, resonance time still increases with the concentration of reagent but it does not relate with the scale of the wettability.
2004, 29(4): 500-504.
Abstract:
Two dimensional experimental model of hydrocarbon migration and accumulation has been built up according to the geological model of the Dina 2 structure including the database of structure, assemble of reservoir and caprock, and hydrocarbon sources. The results indicate that (1) faults are predominant pathways for oil and gas migration in the Dina 2 structure; (2) the pressure released zones are available for oil and gas migration; (3) capillary and buoyancy play an important role in sandstone with similar permeability; (4) hydrocarbon migrates always along the predominant pathways, such as faults and associated sandstone in both sides; (5) pathways of oil and gas migration have the nature of succession, such as oil driving water and following gas driving oil.
Two dimensional experimental model of hydrocarbon migration and accumulation has been built up according to the geological model of the Dina 2 structure including the database of structure, assemble of reservoir and caprock, and hydrocarbon sources. The results indicate that (1) faults are predominant pathways for oil and gas migration in the Dina 2 structure; (2) the pressure released zones are available for oil and gas migration; (3) capillary and buoyancy play an important role in sandstone with similar permeability; (4) hydrocarbon migrates always along the predominant pathways, such as faults and associated sandstone in both sides; (5) pathways of oil and gas migration have the nature of succession, such as oil driving water and following gas driving oil.
