Understanding hydrocarbon migration and accumulation mechanisms is one of the key scientif ic problems that should be solved for effective hydrocarbon exploration in the superimposed basins developed in northwest Chin...Understanding hydrocarbon migration and accumulation mechanisms is one of the key scientif ic problems that should be solved for effective hydrocarbon exploration in the superimposed basins developed in northwest China. The northwest striking No.1 slope break zone, which is a representative of superimposed basins in the Tarim Basin, can be divided into five parts due to the intersection of the northeast strike-slip faults. Controlled by the tectonic framework, the types and properties of reservoirs and the hydrocarbon compositions can also be divided into five parts from east to west. Anomalies of all the parameters were found on the fault intersection zone and weakened up-dip along the structural ridge away from it. Thus, it can be inferred that the intersection zone is the hydrocarbon charging position. This new conclusion differs greatly from the traditional viewpoint, which believes that the hydrocarbon migrates and accumulates along the whole plane of the No.1 slope break zone. The viewpoint is further supported by the evidence from the theory of main pathway systems, obvious improvement of the reservoir quality (2-3 orders of magnitude at the intersection zone) and the formation mechanisms of the fault intersection zone. Differential hydrocarbon migration and entrapment exists in and around the strike- slip faults. This is controlled by the internal structure of faults. It is concluded that the more complicated the fault structure is, the more significant the effects will be. If there is a deformation band, it will hinder the cross fault migration due to the common feature of two to four orders of magnitude reduction in permeability. Otherwise, hydrocarbons tend to accumulate in the up-dip structure under the control of buoyancy. Further research on the internal fault structure should be emphasized.展开更多
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...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.展开更多
Located in the middle of the Tarim Basin, Tazhong is a typical area of compound reservoirs rich in oil and gas found in the Carboniferous, Silurian and Ordovician strata. The proved, probable and possible reserves (3...Located in the middle of the Tarim Basin, Tazhong is a typical area of compound reservoirs rich in oil and gas found in the Carboniferous, Silurian and Ordovician strata. The proved, probable and possible reserves (3P reserves) in the area amount to 5×108 tons, so it is of great significance to study the advances and problems in hydrocarbon exploration in the Tazhong area. On the basis of exploration history and analysis of scientific problems, we outline eight achievements: distribution characteristics of reservoirs, stages of reservoir formation, different sources of oil and gas and their respective contributions, the effective regional caprock and reservoir-caprock combinations dominating the vertical distribution of hydrocarbon reservoirs, the control of the Tazhong Palaeo-uplift on reservoir formation and establishing geologic models, structure balance belts influencing the reconstruction and residual potential of reservoirs after accumulation, the rules and mechanisms of fractures controlling oil and gas, and the types of favorable reservoirs and their characteristics of controlling oil and gas distribution. We further point out the main problems about the oil and gas exploration in the Tazhong area and put forward some relevant proposals.展开更多
The Tarim Basin is the largest petroliferous basin in the northwest of China, and is composed of a Paleozoic marine craton basin and a Meso-Cenozoic continental foreland basin. It is of great significance in explorati...The Tarim Basin is the largest petroliferous basin in the northwest of China, and is composed of a Paleozoic marine craton basin and a Meso-Cenozoic continental foreland basin. It is of great significance in exploration of Ordovician. In over 50 years of exploration, oil and gas totaling over 1.6 billion tonnes oil-equivalent has been discovered in the Ordovician carbonate formation. The accumulation mechanisms and distribution rules are quite complicated because of the burial depth more than 3,500 m, multi-source, and multi-stage accumulation, adjustment, reconstruction and re-enrichment in Ordovician. In this paper, we summarized four major advances in the hydrocarbon accumulation mechanisms of Ordovician carbonate reservoirs. First, oil came from Cambrian and Ordovician source rocks separately and as a mixture, while natural gas was mainly cracked gas generated from the Cambrian-Lower Ordovician crude oil. Second, most hydrocarbon migrated along unconformities and faults, with different directions in different regions. Third, hydrocarbon migration and accumulation had four periods: Caledonian, early Hercynian, late Hercynian and Himalayan, and the latter two were the most important for oil and gas exploration. Fourth, hydrocarbon accumulation and evolution can be generally divided into four stages: Caledonian (the period of hydrocarbon accumulation), early Hercynian (the period of destruction), late Hercynian (the period of hydrocarbon reconstruction and re-accumulation), and Himalayan (the period of hydrocarbon adjustment and re-accumulation). Source rocks (S), combinations of reservoir-seal (C), paleo-uplifts (M), structure balance belt (B) matched in the same time (T) control the hydrocarbon accumulation and distribution in the Ordovician formations. Reservoir adjustment and reconstruction can be classified into two modes of physical adjustment and variation of chemical compositions and five mechanisms. These mechanisms are occurrence displacement, biodegradation, multi-source mixing, high-temperature cracking and late gas invasion. Late hydrocarbon accumulation effects controlled the distribution of current hydrocarbon. The T-BCMS model is a basic geological model to help understanding the control of reservoirs. At present, the main problems of hydrocarbon accumulation focus on two aspects, dynamic mechanisms of hydrocarbon accumulation and the quantitative models of oil-bearing in traps, which need further systemic research.展开更多
Systematic analyses of the formation water and natural gas geochemistry in the Central Uplift of the Tarim Basin (CUTB) show that gas invasion at the late stage is accompanied by an increase of the contents of HeS a...Systematic analyses of the formation water and natural gas geochemistry in the Central Uplift of the Tarim Basin (CUTB) show that gas invasion at the late stage is accompanied by an increase of the contents of HeS and CO2 in natural gas, by the forming of the high total dissolved solids formation water, by an increase of the content of HCO3^-, relative to Cl^-, by an increase of the 2nd family ions (Ca^2+, Mg^2+, Sr^2+ and Ba^2+) and by a decrease of the content of SO4^2-, relative to Cl^-. The above phenomena can be explained only by way of thermochemicai sulfate reduction (TSR). TSR often occurs in the transition zone of oil and water and is often described in the following reaction formula: ∑CH+CaSO4+H-2O→H2S+CO2+CaCO3. (1) Dissolved SO4^2- in the formation water is consumed in the above reaction, when HeS and CO2 are generated, resulting in a decrease of SO4^2- in the formation water and an increase of both HeS and CO2 in the natural gas. If formation water exists, the generated CO2 will go on reacting with the carbonate to form bicarbonate, which can be dissolved in the formation water, thus resulting in the enrichment of Ca^2+ and HCO3^-. The above reaction can be described by the following equation: CO2+HeO+CaCO3→Ca^2++2HCO3^-. The stratigraphic temperatures of the Cambrian and lower Ordovician in CUTB exceeded 120℃, which is the minimum for TSR to occur. At the same time, dolomitization, which might be a direct result of TSR, has been found in both the Cambrian and the lower Ordovician. The above evidence indicates that TSR is in an active reaction, providing a novel way to reevaluate the exploration potentials of natural gas in this district.展开更多
The reservoirs in the TZ1-TZ4 well block of the Tarim Basin are complex, and the hydrocarbon enrichment shows differences. The three Carboniferous oil layers are characterized by "oil in the upper and lower layers an...The reservoirs in the TZ1-TZ4 well block of the Tarim Basin are complex, and the hydrocarbon enrichment shows differences. The three Carboniferous oil layers are characterized by "oil in the upper and lower layers and gas in the middle" in profile and "oil in the west and gas in the east" in plane view. In order to discuss the complex reservoir accumulation mechanisms, based on the petroleum geology and reservoir distribution, we studied the generation history of source rocks, the fault evolution and sealing, the accumulation periods and gas washing, and reconstructed the accumulation process of the TZ1-TZ4 well block. It is concluded that the hydrocarbon enrichment differences of oil layers CIII, CII and CI were caused by multiple sources and multi-period hydrocarbon charging and adjustment. The CII was closely related to CIII, but CI was formed by reservoir adjustment during the Yanshan period and was not affected by gas washing after it was formed. During the Himalayan period, different degrees of gas washing in the east and west led to hydrocarbon enrichment differences on the plane. The Carboniferous accumulation process of two-stage charging and one-stage adjustment is summarized: oil charging during the late Hercynian period is the first accumulation period of CIII and CII; oil reservoirs were adjusted into CI in the Yanshan period; finally gas washing in the Himalayan period is the second accumulation period of CIII and CII, but CI was not affected by gas washing. This complex accumulation process leads to the hydrocarbon enrichment differences in the TZ1-TZ4 well block.展开更多
Basic characteristics of Ordovician carbonate reservoir beds in the Lungudong region of northeastern part of the Tarim Basin are described in detail and the reservoir-forming conditions of oil and gas are preliminaril...Basic characteristics of Ordovician carbonate reservoir beds in the Lungudong region of northeastern part of the Tarim Basin are described in detail and the reservoir-forming conditions of oil and gas are preliminarily discussed in this paper by collecting and sorting out a large amount of data. The carbonate reservoir beds are mainly developed in open-platform and platform marginal facies; the reservoir beds have large changes in and low average values of physical property; the main type is fractured reservoir beds with the fracture-porous type second. The reservoir bed development is chiefly controlled by the distribution of sedimentary facies, tectonic activity and karstification. Whereas the accumulation and distribution of hydrocarbons in the region are controlled by an advantageous structural location, a good reservoir-caprock combination and a favorable transporting system, with the distribution characterized by zones horizontally and belts vertically, the oil and gas are mainly concentrated in areas with structural uplift, densely developed fractures, and surface karst, a vertical vadose zone, and a horizontal undercurrent belt of palaeokarst.展开更多
The Songliao Basin is famous for the Daqing Oilfield, the biggest in China. However, no economic hydrocarbon reservoir has been found in the northeastern Binbei district. Its thermal history, which is of great importa...The Songliao Basin is famous for the Daqing Oilfield, the biggest in China. However, no economic hydrocarbon reservoir has been found in the northeastern Binbei district. Its thermal history, which is of great importance for hydrocarbon generation and migration, is studied with apatite fission track (AFT) thermochronology. Samples with depositional ages of the late Cretaceous (-108-73 Ma) are analyzed. The AFT ages of the samples from reservoir rock (depositional age 〉 76.1 Ma) fall between the late Cretaceous (724-5 Ma) and the early Eocene (414-3 Ma) period, indicating their total annealing after deposition. In contrast, two samples from the main seals of the Qingshankou (depositional age 〉 89.3 Ma) and the Nenjiang Formation (depositional age 〉 73.0 Ma) are not annealed or partially annealed (AFT ages of 974-9 Ma and 704-4 Ma, respectively). Because the maximum burial temperature (〈90 ℃) evidenced by low vitrinite reflectance (Ro〈0.7) is not high enough to account for the AFT total annealing (110-120 ℃), the transient thermal effect arising from the syntectonic fluid flow between the late Cretaceous and the early Eocene is proposed. Transient thermal effects from fluid flow explains the indicated temperature discrepancies between the AFT thermometer and the Ro thermometer because the transient thermal effect from the fluid flow with a temperature high enough (110-120 ℃) to anneal the AFT thermometer does not last long enough (104-105 yrs.) for an enhancement of the Ro (minimum 106- 107 yrs. under the same temperature). This indicates that dating thermal effect from fluid flow might be a new means to reconstruct the tectonic history. It also answers why the samples from the main seals are not annealed because the seals will prohibit fluid flow and supply good thermal insulation. The large-scale fluid flow in the Binbei district calls for a new idea to direct the hydrocarbon exploration.展开更多
A common way to trace fluid flow and hydrocarbon accumulation is by studying the geochemistry of formation water. This paper focuses on the spacial distribution of the geochemical features of the formation water in th...A common way to trace fluid flow and hydrocarbon accumulation is by studying the geochemistry of formation water. This paper focuses on the spacial distribution of the geochemical features of the formation water in the Shiwu Rifled Basin and its indication of the water-rock interaction processes. The hydrodynamic field controls the spacial distribution of formation water. Due to the penetration of meteoric water, the salinity is below 4,500mg/L at the basin margin and the severely faulted central ridge and increases basin ward to 7,000-10,000mg/L. The vertical change of formation water can be divided into 3 zones, which correspond respectively to the free replacement zone (〈1,250m), the obstructed replacement zone (1,250m-1,650m) and the lagged zone (〉 1,650m) in hydrodynamics. In the free replacement zone, the formation water is NaHCO3-type with its salinity increased to 10,000mg/L. The formation water in the obstructed replacement zone is Na2SO4-type with its salinity decreased to 5,000mg/L-7,000mg/L because of the dehydration of mud rocks. The formation water in the lagged zone is CaC12-type, but its salinity decreases sharply at a depth of 1,650m and then increases vertically downward to 10,000mg/L. This phenomenon can be best explained by the osmosis effect rather than the dehydration of mud rocks. The relationships between Cl^--HCO3^- and Na^++K^+-Ca^2+ show that the initial water-rock interaction is the dissolution of NaCl and calcium-beating carbonate, causing an increase of Na^+-K^+-Ca^2+-Cl^- and salinity. The succeeding water-rock interaction is albitization, which leads to a decrease of Na^+ and an increase of Ca2+ simultaneously, and generates CaCl2-type fluid. The above analysis shows that the geochemical evolution of formation water is governed by the water-rock interactions, while its spacial distribution is controlled by the hydrological conditions. The water-rock interaction processes are supported by other geological observations, suggesting that formation water geochemistry is a viable method to trace the fluid-rock interaction processes and has broad applications in practice.展开更多
The relation between oil and water in reservoirs with low and ultra-low permeability is very complicated. Gravitational separation of oil and water is not obvious. Normal reservoirs are located in depression and struc...The relation between oil and water in reservoirs with low and ultra-low permeability is very complicated. Gravitational separation of oil and water is not obvious. Normal reservoirs are located in depression and structural high spot, oil and water transitions are located in their middle. Stagnation is the key fact of oil-forming reservoir in the axis of a syncline based on the research of oil, gas and water migration manner, dynamics and non-Darcy flow in the Songliao basin. In low and ultra-low permeable reservoir, gas and water migrate easily through pore throats because their molecules are generally smaller than the pore throats; but the minimum diameter of oil droplets is larger than pore throats and they must be deformed to go through. Thus, gas and water migrate in advance of oil, and oil droplets remain behind. Pressure differential and the buoyancy force in a syncline reservoir are a main fluid driving force; and capillary force is the main resistance to flow. When the dynamics force is less than resistance, oil is immobile. When the buoyancy force is less than the capillary force, a gravitational separation of oil and water does not occur. The reservoir in the mature source rock of a syncline area with the low and ul- tra-low permeability belongs to an unconventional petroleum reservoir.展开更多
基金supported by the National 973 Basic Research Program (Grant No.2006CB202308)the Major National Science & Technology Program (2008ZX05008-004-012)
文摘Understanding hydrocarbon migration and accumulation mechanisms is one of the key scientif ic problems that should be solved for effective hydrocarbon exploration in the superimposed basins developed in northwest China. The northwest striking No.1 slope break zone, which is a representative of superimposed basins in the Tarim Basin, can be divided into five parts due to the intersection of the northeast strike-slip faults. Controlled by the tectonic framework, the types and properties of reservoirs and the hydrocarbon compositions can also be divided into five parts from east to west. Anomalies of all the parameters were found on the fault intersection zone and weakened up-dip along the structural ridge away from it. Thus, it can be inferred that the intersection zone is the hydrocarbon charging position. This new conclusion differs greatly from the traditional viewpoint, which believes that the hydrocarbon migrates and accumulates along the whole plane of the No.1 slope break zone. The viewpoint is further supported by the evidence from the theory of main pathway systems, obvious improvement of the reservoir quality (2-3 orders of magnitude at the intersection zone) and the formation mechanisms of the fault intersection zone. Differential hydrocarbon migration and entrapment exists in and around the strike- slip faults. This is controlled by the internal structure of faults. It is concluded that the more complicated the fault structure is, the more significant the effects will be. If there is a deformation band, it will hinder the cross fault migration due to the common feature of two to four orders of magnitude reduction in permeability. Otherwise, hydrocarbons tend to accumulate in the up-dip structure under the control of buoyancy. Further research on the internal fault structure should be emphasized.
基金supported by the National Basic Research Program of China (Grant No: 2011CB201100)
文摘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.
基金supported by the National Basic Research Program of China (973 Program, Grant No. 2006CB202308)
文摘Located in the middle of the Tarim Basin, Tazhong is a typical area of compound reservoirs rich in oil and gas found in the Carboniferous, Silurian and Ordovician strata. The proved, probable and possible reserves (3P reserves) in the area amount to 5×108 tons, so it is of great significance to study the advances and problems in hydrocarbon exploration in the Tazhong area. On the basis of exploration history and analysis of scientific problems, we outline eight achievements: distribution characteristics of reservoirs, stages of reservoir formation, different sources of oil and gas and their respective contributions, the effective regional caprock and reservoir-caprock combinations dominating the vertical distribution of hydrocarbon reservoirs, the control of the Tazhong Palaeo-uplift on reservoir formation and establishing geologic models, structure balance belts influencing the reconstruction and residual potential of reservoirs after accumulation, the rules and mechanisms of fractures controlling oil and gas, and the types of favorable reservoirs and their characteristics of controlling oil and gas distribution. We further point out the main problems about the oil and gas exploration in the Tazhong area and put forward some relevant proposals.
基金supported by the National Basic Research Program of China (973 Program, Grant No.2006CB202308)
文摘The Tarim Basin is the largest petroliferous basin in the northwest of China, and is composed of a Paleozoic marine craton basin and a Meso-Cenozoic continental foreland basin. It is of great significance in exploration of Ordovician. In over 50 years of exploration, oil and gas totaling over 1.6 billion tonnes oil-equivalent has been discovered in the Ordovician carbonate formation. The accumulation mechanisms and distribution rules are quite complicated because of the burial depth more than 3,500 m, multi-source, and multi-stage accumulation, adjustment, reconstruction and re-enrichment in Ordovician. In this paper, we summarized four major advances in the hydrocarbon accumulation mechanisms of Ordovician carbonate reservoirs. First, oil came from Cambrian and Ordovician source rocks separately and as a mixture, while natural gas was mainly cracked gas generated from the Cambrian-Lower Ordovician crude oil. Second, most hydrocarbon migrated along unconformities and faults, with different directions in different regions. Third, hydrocarbon migration and accumulation had four periods: Caledonian, early Hercynian, late Hercynian and Himalayan, and the latter two were the most important for oil and gas exploration. Fourth, hydrocarbon accumulation and evolution can be generally divided into four stages: Caledonian (the period of hydrocarbon accumulation), early Hercynian (the period of destruction), late Hercynian (the period of hydrocarbon reconstruction and re-accumulation), and Himalayan (the period of hydrocarbon adjustment and re-accumulation). Source rocks (S), combinations of reservoir-seal (C), paleo-uplifts (M), structure balance belt (B) matched in the same time (T) control the hydrocarbon accumulation and distribution in the Ordovician formations. Reservoir adjustment and reconstruction can be classified into two modes of physical adjustment and variation of chemical compositions and five mechanisms. These mechanisms are occurrence displacement, biodegradation, multi-source mixing, high-temperature cracking and late gas invasion. Late hydrocarbon accumulation effects controlled the distribution of current hydrocarbon. The T-BCMS model is a basic geological model to help understanding the control of reservoirs. At present, the main problems of hydrocarbon accumulation focus on two aspects, dynamic mechanisms of hydrocarbon accumulation and the quantitative models of oil-bearing in traps, which need further systemic research.
基金supported by the State 973 Project(Grant No.2006CB202308)the National Natural Science Foundation of China(Grant No.40872097)
文摘Systematic analyses of the formation water and natural gas geochemistry in the Central Uplift of the Tarim Basin (CUTB) show that gas invasion at the late stage is accompanied by an increase of the contents of HeS and CO2 in natural gas, by the forming of the high total dissolved solids formation water, by an increase of the content of HCO3^-, relative to Cl^-, by an increase of the 2nd family ions (Ca^2+, Mg^2+, Sr^2+ and Ba^2+) and by a decrease of the content of SO4^2-, relative to Cl^-. The above phenomena can be explained only by way of thermochemicai sulfate reduction (TSR). TSR often occurs in the transition zone of oil and water and is often described in the following reaction formula: ∑CH+CaSO4+H-2O→H2S+CO2+CaCO3. (1) Dissolved SO4^2- in the formation water is consumed in the above reaction, when HeS and CO2 are generated, resulting in a decrease of SO4^2- in the formation water and an increase of both HeS and CO2 in the natural gas. If formation water exists, the generated CO2 will go on reacting with the carbonate to form bicarbonate, which can be dissolved in the formation water, thus resulting in the enrichment of Ca^2+ and HCO3^-. The above reaction can be described by the following equation: CO2+HeO+CaCO3→Ca^2++2HCO3^-. The stratigraphic temperatures of the Cambrian and lower Ordovician in CUTB exceeded 120℃, which is the minimum for TSR to occur. At the same time, dolomitization, which might be a direct result of TSR, has been found in both the Cambrian and the lower Ordovician. The above evidence indicates that TSR is in an active reaction, providing a novel way to reevaluate the exploration potentials of natural gas in this district.
基金supported by the 973 Program (2006CB202308)the Foundation of State Key Laboratory of Petroleum Resources and Prospecting (PRPDX2008-05) the National Natural Science Foundation of China (Grant No. 40972088)
文摘The reservoirs in the TZ1-TZ4 well block of the Tarim Basin are complex, and the hydrocarbon enrichment shows differences. The three Carboniferous oil layers are characterized by "oil in the upper and lower layers and gas in the middle" in profile and "oil in the west and gas in the east" in plane view. In order to discuss the complex reservoir accumulation mechanisms, based on the petroleum geology and reservoir distribution, we studied the generation history of source rocks, the fault evolution and sealing, the accumulation periods and gas washing, and reconstructed the accumulation process of the TZ1-TZ4 well block. It is concluded that the hydrocarbon enrichment differences of oil layers CIII, CII and CI were caused by multiple sources and multi-period hydrocarbon charging and adjustment. The CII was closely related to CIII, but CI was formed by reservoir adjustment during the Yanshan period and was not affected by gas washing after it was formed. During the Himalayan period, different degrees of gas washing in the east and west led to hydrocarbon enrichment differences on the plane. The Carboniferous accumulation process of two-stage charging and one-stage adjustment is summarized: oil charging during the late Hercynian period is the first accumulation period of CIII and CII; oil reservoirs were adjusted into CI in the Yanshan period; finally gas washing in the Himalayan period is the second accumulation period of CIII and CII, but CI was not affected by gas washing. This complex accumulation process leads to the hydrocarbon enrichment differences in the TZ1-TZ4 well block.
基金supported by the State Key Development Program for Basic Research of China(Grant No.2006CB202308)
文摘Basic characteristics of Ordovician carbonate reservoir beds in the Lungudong region of northeastern part of the Tarim Basin are described in detail and the reservoir-forming conditions of oil and gas are preliminarily discussed in this paper by collecting and sorting out a large amount of data. The carbonate reservoir beds are mainly developed in open-platform and platform marginal facies; the reservoir beds have large changes in and low average values of physical property; the main type is fractured reservoir beds with the fracture-porous type second. The reservoir bed development is chiefly controlled by the distribution of sedimentary facies, tectonic activity and karstification. Whereas the accumulation and distribution of hydrocarbons in the region are controlled by an advantageous structural location, a good reservoir-caprock combination and a favorable transporting system, with the distribution characterized by zones horizontally and belts vertically, the oil and gas are mainly concentrated in areas with structural uplift, densely developed fractures, and surface karst, a vertical vadose zone, and a horizontal undercurrent belt of palaeokarst.
基金supported by the National Natural Science Foundation of China (Grant Nos.40872097 and 41272161)the Major National Science & Technology Program (Grant Nos.2011ZX05006-005 and 2011ZX05006-006)partly funded by the State Key Laboratory for Petroleum Resource and Prospecting (Grant No.KYJJ2012-01-12)
文摘The Songliao Basin is famous for the Daqing Oilfield, the biggest in China. However, no economic hydrocarbon reservoir has been found in the northeastern Binbei district. Its thermal history, which is of great importance for hydrocarbon generation and migration, is studied with apatite fission track (AFT) thermochronology. Samples with depositional ages of the late Cretaceous (-108-73 Ma) are analyzed. The AFT ages of the samples from reservoir rock (depositional age 〉 76.1 Ma) fall between the late Cretaceous (724-5 Ma) and the early Eocene (414-3 Ma) period, indicating their total annealing after deposition. In contrast, two samples from the main seals of the Qingshankou (depositional age 〉 89.3 Ma) and the Nenjiang Formation (depositional age 〉 73.0 Ma) are not annealed or partially annealed (AFT ages of 974-9 Ma and 704-4 Ma, respectively). Because the maximum burial temperature (〈90 ℃) evidenced by low vitrinite reflectance (Ro〈0.7) is not high enough to account for the AFT total annealing (110-120 ℃), the transient thermal effect arising from the syntectonic fluid flow between the late Cretaceous and the early Eocene is proposed. Transient thermal effects from fluid flow explains the indicated temperature discrepancies between the AFT thermometer and the Ro thermometer because the transient thermal effect from the fluid flow with a temperature high enough (110-120 ℃) to anneal the AFT thermometer does not last long enough (104-105 yrs.) for an enhancement of the Ro (minimum 106- 107 yrs. under the same temperature). This indicates that dating thermal effect from fluid flow might be a new means to reconstruct the tectonic history. It also answers why the samples from the main seals are not annealed because the seals will prohibit fluid flow and supply good thermal insulation. The large-scale fluid flow in the Binbei district calls for a new idea to direct the hydrocarbon exploration.
文摘A common way to trace fluid flow and hydrocarbon accumulation is by studying the geochemistry of formation water. This paper focuses on the spacial distribution of the geochemical features of the formation water in the Shiwu Rifled Basin and its indication of the water-rock interaction processes. The hydrodynamic field controls the spacial distribution of formation water. Due to the penetration of meteoric water, the salinity is below 4,500mg/L at the basin margin and the severely faulted central ridge and increases basin ward to 7,000-10,000mg/L. The vertical change of formation water can be divided into 3 zones, which correspond respectively to the free replacement zone (〈1,250m), the obstructed replacement zone (1,250m-1,650m) and the lagged zone (〉 1,650m) in hydrodynamics. In the free replacement zone, the formation water is NaHCO3-type with its salinity increased to 10,000mg/L. The formation water in the obstructed replacement zone is Na2SO4-type with its salinity decreased to 5,000mg/L-7,000mg/L because of the dehydration of mud rocks. The formation water in the lagged zone is CaC12-type, but its salinity decreases sharply at a depth of 1,650m and then increases vertically downward to 10,000mg/L. This phenomenon can be best explained by the osmosis effect rather than the dehydration of mud rocks. The relationships between Cl^--HCO3^- and Na^++K^+-Ca^2+ show that the initial water-rock interaction is the dissolution of NaCl and calcium-beating carbonate, causing an increase of Na^+-K^+-Ca^2+-Cl^- and salinity. The succeeding water-rock interaction is albitization, which leads to a decrease of Na^+ and an increase of Ca2+ simultaneously, and generates CaCl2-type fluid. The above analysis shows that the geochemical evolution of formation water is governed by the water-rock interactions, while its spacial distribution is controlled by the hydrological conditions. The water-rock interaction processes are supported by other geological observations, suggesting that formation water geochemistry is a viable method to trace the fluid-rock interaction processes and has broad applications in practice.
文摘The relation between oil and water in reservoirs with low and ultra-low permeability is very complicated. Gravitational separation of oil and water is not obvious. Normal reservoirs are located in depression and structural high spot, oil and water transitions are located in their middle. Stagnation is the key fact of oil-forming reservoir in the axis of a syncline based on the research of oil, gas and water migration manner, dynamics and non-Darcy flow in the Songliao basin. In low and ultra-low permeable reservoir, gas and water migrate easily through pore throats because their molecules are generally smaller than the pore throats; but the minimum diameter of oil droplets is larger than pore throats and they must be deformed to go through. Thus, gas and water migrate in advance of oil, and oil droplets remain behind. Pressure differential and the buoyancy force in a syncline reservoir are a main fluid driving force; and capillary force is the main resistance to flow. When the dynamics force is less than resistance, oil is immobile. When the buoyancy force is less than the capillary force, a gravitational separation of oil and water does not occur. The reservoir in the mature source rock of a syncline area with the low and ul- tra-low permeability belongs to an unconventional petroleum reservoir.