Volume 26,Issue 6,2019 Table of Contents
2019, 26(6):1-10.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.001
Abstract:
Hydrocarbon-bearing reservoirs found in buried hills are important targets with abundant reserves in Eastern China，but the reservoir space in buried hills is very complicated because of lithology changing，fault activity and fluid erosion. After observing cores from Chengdao buried hills composed of Ordovician carbonates，it is found that fractured carbonates（fracture density<10 fractures/m），cataclasites（fracture density>10 fractures/m）and breccias（2-8 cm gravels）are formed because of fault activity，among which breccias and cataclasites are clearly dissolved and rich in oil，but the fractured carbonates and ordinary carbonates are poor in oil. According to well logging and seismic interpretation，five assembles（fault frature zones）of fractured carbonates，cataclasites，and breccias are proposed，and the distribution of a new-type of reservoir body that mainly composed of breccias and cataclasites in buried hills is predicted. According to rock-mineral and geochemistry analysis，the dissolution of minerals with ground waters and thermal fluids flowing through the faults in the breccias and cataclasites is clarified，and it is believed that ground water plays a dominant role in the formation of reservoirs in fault frature zones during hydrocarbon accumulation. The prediction and evaluation of this new type of reservoir body is helpful to predict reservoir spaces and oil distributions in complicated buried hills，as well as to efficiently produce oil from the buried hills.
Hydrocarbon-bearing reservoirs found in buried hills are important targets with abundant reserves in Eastern China，but the reservoir space in buried hills is very complicated because of lithology changing，fault activity and fluid erosion. After observing cores from Chengdao buried hills composed of Ordovician carbonates，it is found that fractured carbonates（fracture density<10 fractures/m），cataclasites（fracture density>10 fractures/m）and breccias（2-8 cm gravels）are formed because of fault activity，among which breccias and cataclasites are clearly dissolved and rich in oil，but the fractured carbonates and ordinary carbonates are poor in oil. According to well logging and seismic interpretation，five assembles（fault frature zones）of fractured carbonates，cataclasites，and breccias are proposed，and the distribution of a new-type of reservoir body that mainly composed of breccias and cataclasites in buried hills is predicted. According to rock-mineral and geochemistry analysis，the dissolution of minerals with ground waters and thermal fluids flowing through the faults in the breccias and cataclasites is clarified，and it is believed that ground water plays a dominant role in the formation of reservoirs in fault frature zones during hydrocarbon accumulation. The prediction and evaluation of this new type of reservoir body is helpful to predict reservoir spaces and oil distributions in complicated buried hills，as well as to efficiently produce oil from the buried hills.
2019, 26(6):11-18.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.002
Abstract:
Many oil reservoirs that relate to Carboniferous volcanic weathering crust have been discovered in Junggar Basin.Taking Carboniferous volcanic rocks in Chepaizi area in the western margin of the basin as an example，the development of weathering crust is analyzed by geological，geochemical and well logging techniques，and the hydrocarbon accumulation in Carboniferous formations is clarified. Studies show that the volcanic weathering crust at the top of Carboniferous volcanic rocks in Chepaizi area consists three layers，including clay layer，hydrolyzed layer，and leaching layer. The weathering time determines the thickness of the weathering crust，the palaeography controls the integrity of structural layers，and the lithology and fault affect the local variation of the weathering crust. The petroleum geologic significance of weathering crust on hydrocarbon accumulation mainly includes：①Various volcanic rocks in the leaching layer can form favorable reservoirs；②Clay layer and hydrolyzed layer are effective caps for weathering crust stratigraphic traps；③Leaching layer and overlying carpet sand are important transverse transport layers for hydrocarbon migration. Controlled by the weathering crust structure，there are 3 kinds of transport modes in the Carboniferous volcanic weathering crust，including fault and carpet sand transport mode，fault and leaching layer transport mode，and carpet sand and hydrolyzed layer transport mode. The oil of Carboniferous volcanic weathering crust in the study area distributes in three zones，including fault-bonding zone between carpet sand and leaching layer，near fault zone，and overlap zone between carpet sand-sand leaching layer.
Many oil reservoirs that relate to Carboniferous volcanic weathering crust have been discovered in Junggar Basin.Taking Carboniferous volcanic rocks in Chepaizi area in the western margin of the basin as an example，the development of weathering crust is analyzed by geological，geochemical and well logging techniques，and the hydrocarbon accumulation in Carboniferous formations is clarified. Studies show that the volcanic weathering crust at the top of Carboniferous volcanic rocks in Chepaizi area consists three layers，including clay layer，hydrolyzed layer，and leaching layer. The weathering time determines the thickness of the weathering crust，the palaeography controls the integrity of structural layers，and the lithology and fault affect the local variation of the weathering crust. The petroleum geologic significance of weathering crust on hydrocarbon accumulation mainly includes：①Various volcanic rocks in the leaching layer can form favorable reservoirs；②Clay layer and hydrolyzed layer are effective caps for weathering crust stratigraphic traps；③Leaching layer and overlying carpet sand are important transverse transport layers for hydrocarbon migration. Controlled by the weathering crust structure，there are 3 kinds of transport modes in the Carboniferous volcanic weathering crust，including fault and carpet sand transport mode，fault and leaching layer transport mode，and carpet sand and hydrolyzed layer transport mode. The oil of Carboniferous volcanic weathering crust in the study area distributes in three zones，including fault-bonding zone between carpet sand and leaching layer，near fault zone，and overlap zone between carpet sand-sand leaching layer.
2019, 26(6):19-27.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.003
Abstract:
Extra-high water-cut stage is an important period of continental reservoir development. Study on remaining oil is the basis of enhanced oil recovery in the oil reservoirs at extra-high water-cut stage. Based on data of three sealed coring wells and 17 newly drilled wells at extra-high water-cut stage in Zhongyi area of Gudao Oilfield，the distribution characteristics and enrichment regularities of the remaining oil are analyzed from plane，interlamination and interlayer. The results show that remaining movable oil distributes broadly and enriches locally at extra-high water-cut stage，which is also verified by the dynamic production behaviors of the oilfield. Based on interlayer distribution pattern and rhythm of the reservoir，three local enrichment modes of the remaining oil are established，including whole-barrier type，half-barrier type and rhythm type. The half-barrier type may be further classified into oil well barrier type，water well barrier type and cross-well barrier type. The rhythm type can be further classified into positive rhythm type and uniform type. The new results change the traditional understandings of high dispersion and local enrichment of the remaining oil at extra-high water-cut stage，which has important significance on tapping the potential of remaining oil in fluvial facies of old oilfields.
Extra-high water-cut stage is an important period of continental reservoir development. Study on remaining oil is the basis of enhanced oil recovery in the oil reservoirs at extra-high water-cut stage. Based on data of three sealed coring wells and 17 newly drilled wells at extra-high water-cut stage in Zhongyi area of Gudao Oilfield，the distribution characteristics and enrichment regularities of the remaining oil are analyzed from plane，interlamination and interlayer. The results show that remaining movable oil distributes broadly and enriches locally at extra-high water-cut stage，which is also verified by the dynamic production behaviors of the oilfield. Based on interlayer distribution pattern and rhythm of the reservoir，three local enrichment modes of the remaining oil are established，including whole-barrier type，half-barrier type and rhythm type. The half-barrier type may be further classified into oil well barrier type，water well barrier type and cross-well barrier type. The rhythm type can be further classified into positive rhythm type and uniform type. The new results change the traditional understandings of high dispersion and local enrichment of the remaining oil at extra-high water-cut stage，which has important significance on tapping the potential of remaining oil in fluvial facies of old oilfields.
2019, 26(6):28-35.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.004
Abstract:
The clay mineral content is high in tight sandstone of Taiyuan Formation in Block Linxing of Ordos Basin，and it is one of the important factors influencing reservoir properties. However，its characteristics and formation mechanism have not been systematically studied，affecting the description of high-quality reservoirs. According to core observation，thin section identification，X-ray diffraction and physical property analysis，the content and morphological characteristics of the clay minerals is clarified. Moreover，its formation mechanism and the relationships between the clay minerals and the reservoir physical properties are discussed. The results indicate that the relative contents of clay minerals in tight sandstone of Taiyuan Formation in Block Linxing from high to low are：illite，kaolinite，chlorite，and illite-montmorillonite mixed-layer.Most of them fill in the intergranular dissolution pores or intercrystalline micropores. Hot water erosion is the reason for the clay mineral formation. Zijinshan pluton affects the relative content and plane distribution of clay minerals. The relative contents of illite，kaolinite，chlorite，and illite-montmorillonite mixed-layer are high near Zijinshan pluton，while the relative content of kaolinite is low. There exists a negative correlation between reservoir physical properties and the three types of clay minerals，including illite，chlorite，and illite-montmorillonite mixed-layer，while there is a positive correlation between kaolinite and reservoir physical properties. Influenced by clay minerals，the high-quality reservoirs distribute in the northeast and southwest of the study area，and they are the favorable targets for the later exploration and development.
The clay mineral content is high in tight sandstone of Taiyuan Formation in Block Linxing of Ordos Basin，and it is one of the important factors influencing reservoir properties. However，its characteristics and formation mechanism have not been systematically studied，affecting the description of high-quality reservoirs. According to core observation，thin section identification，X-ray diffraction and physical property analysis，the content and morphological characteristics of the clay minerals is clarified. Moreover，its formation mechanism and the relationships between the clay minerals and the reservoir physical properties are discussed. The results indicate that the relative contents of clay minerals in tight sandstone of Taiyuan Formation in Block Linxing from high to low are：illite，kaolinite，chlorite，and illite-montmorillonite mixed-layer.Most of them fill in the intergranular dissolution pores or intercrystalline micropores. Hot water erosion is the reason for the clay mineral formation. Zijinshan pluton affects the relative content and plane distribution of clay minerals. The relative contents of illite，kaolinite，chlorite，and illite-montmorillonite mixed-layer are high near Zijinshan pluton，while the relative content of kaolinite is low. There exists a negative correlation between reservoir physical properties and the three types of clay minerals，including illite，chlorite，and illite-montmorillonite mixed-layer，while there is a positive correlation between kaolinite and reservoir physical properties. Influenced by clay minerals，the high-quality reservoirs distribute in the northeast and southwest of the study area，and they are the favorable targets for the later exploration and development.
5 Gas-water percolation law of tight sandstone reservoirs
with different pore types in western Sulige
2019, 26(6):36-45.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.005
Abstract:
In order to investigate the percolation law of tight sandstone reservoirs in the western Sulige，combined qualitative and quantitative methods are applied to analyze pore structure through thin section and conventional mercury injection data. Based on gas-water relative permeability test and visualized real sandstone models，gas-water displacement and pressure relief experiments are further carried out to simulate the percolation law and fluid distribution of different pore types during the process of gas reservoir formation and development. According to the proportion of different pores，the pore assemblage types can be divided into four categories：dissolution pore-intergranular pore，intercrystalline pore-dissolution pore，dissolution pore-intercrystalline pore and intercrystalline pore. The pore-throat characteristics and percolation law of representative samples of four types of pores are analyzed. The results show that the percolation law of different pore types varies obviously，and the irreducible water saturation decreases gradually with the physical properties of reservoirs with various pore types becoming better and better. The relative permeability of gas phase at irreducible water saturation increases gradually，the width of the two-phase percolation area increases continuously and the percolation ability is enhanced. The interaction between gas and water is reduced gradually. The visual gas-water displacement type gradually changes from finger displacement to homogeneous displacement with larger displacement degree with the improvement of pore type，which is beneficial to the formation of effective reservoirs filled with natural gas under the same hydrocarbon generation conditions. The pressure relief experiment shows that the time required for pressure relief of samples with pore type is short，the degree of pressure drop increases，and the recovery is higher. The residual water in samples with poor pore type increases，which decreases the relative permeability of gas phase and recovery. According to mercury injection and relative permeability test，the production pressure difference of the nodal point from the irreducible water to removable water in the formation is 7 MPa，which provides a theoretical basis for reducing the risk of producing water and enhancing gas recovery in the western Sulige.
In order to investigate the percolation law of tight sandstone reservoirs in the western Sulige，combined qualitative and quantitative methods are applied to analyze pore structure through thin section and conventional mercury injection data. Based on gas-water relative permeability test and visualized real sandstone models，gas-water displacement and pressure relief experiments are further carried out to simulate the percolation law and fluid distribution of different pore types during the process of gas reservoir formation and development. According to the proportion of different pores，the pore assemblage types can be divided into four categories：dissolution pore-intergranular pore，intercrystalline pore-dissolution pore，dissolution pore-intercrystalline pore and intercrystalline pore. The pore-throat characteristics and percolation law of representative samples of four types of pores are analyzed. The results show that the percolation law of different pore types varies obviously，and the irreducible water saturation decreases gradually with the physical properties of reservoirs with various pore types becoming better and better. The relative permeability of gas phase at irreducible water saturation increases gradually，the width of the two-phase percolation area increases continuously and the percolation ability is enhanced. The interaction between gas and water is reduced gradually. The visual gas-water displacement type gradually changes from finger displacement to homogeneous displacement with larger displacement degree with the improvement of pore type，which is beneficial to the formation of effective reservoirs filled with natural gas under the same hydrocarbon generation conditions. The pressure relief experiment shows that the time required for pressure relief of samples with pore type is short，the degree of pressure drop increases，and the recovery is higher. The residual water in samples with poor pore type increases，which decreases the relative permeability of gas phase and recovery. According to mercury injection and relative permeability test，the production pressure difference of the nodal point from the irreducible water to removable water in the formation is 7 MPa，which provides a theoretical basis for reducing the risk of producing water and enhancing gas recovery in the western Sulige.
2019, 26(6):46-52.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.006
Abstract:
Taking the glutenite formation in tight gas reservoir of Songbei area as an example，the brittleness characteristics of glutenite containing different gravel size are studied by performing tri-axial compression tests. Based on the theory of energy evolution，the influence of gravel size on the mechanical properties and brittleness of glutenite is analyzed according to the investigation of the characteristics of broken rock and deviator stress-strain curve. Additionally，the acoustic emission response during the rock being broken process is analyzed. The experimental results of tri-axial compression test show that gravel size has a significant influence on the characteristics of broken rock samples. Compared with small size（<1 mm）gravel-dominated rock samples，large size（2-6 mm）gravel-dominated glutenite samples are sheared and broken at lower confining pressures with a smaller dip angle of fracture plane. Because of the existence of a large number of weak cemented gravel interfaces，the rock samples with larger size gravel are usually of lower compressive strength，while the broken pattern is more complex. In addition，the unevenness of the fracture surface leads to a part of the energy dissipated by the friction of the fracture surface during the failure process of the rock sample. Consequently，the brittleness of the gravel with larger gravels is lower. Moreover，the interpretation results of acoustic emission show that the proportion of shear events is higher in small size gravel-dominated rock samples，indicating shear failure tended to be dominant.
Taking the glutenite formation in tight gas reservoir of Songbei area as an example，the brittleness characteristics of glutenite containing different gravel size are studied by performing tri-axial compression tests. Based on the theory of energy evolution，the influence of gravel size on the mechanical properties and brittleness of glutenite is analyzed according to the investigation of the characteristics of broken rock and deviator stress-strain curve. Additionally，the acoustic emission response during the rock being broken process is analyzed. The experimental results of tri-axial compression test show that gravel size has a significant influence on the characteristics of broken rock samples. Compared with small size（<1 mm）gravel-dominated rock samples，large size（2-6 mm）gravel-dominated glutenite samples are sheared and broken at lower confining pressures with a smaller dip angle of fracture plane. Because of the existence of a large number of weak cemented gravel interfaces，the rock samples with larger size gravel are usually of lower compressive strength，while the broken pattern is more complex. In addition，the unevenness of the fracture surface leads to a part of the energy dissipated by the friction of the fracture surface during the failure process of the rock sample. Consequently，the brittleness of the gravel with larger gravels is lower. Moreover，the interpretation results of acoustic emission show that the proportion of shear events is higher in small size gravel-dominated rock samples，indicating shear failure tended to be dominant.
2019, 26(6):53-61.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.007
Abstract:
The proven reserves of the Ordovician fracture-cave reservoir in Tahe Oilfield are nearly1.4 billion tons. At present，the oilfield has entered the middle-late stage of development. Problems such as high water cut，contradictory injectionproduction relationship，strong heterogeneity and low recovery factor appear. Therefore，the establishment of a fine reservoir geological model is urgent. According to the genesis，the karst reservoirs can be divided into three types，including weathering crust type，fault-controlled type，and underground river type. The development characteristics of karst reservoirs with three different genesis are analyzed in typical fracture-cave Units S74，S65，T7-615，respectively. Taking Unit S65 in which all three types are developed as an example，a discrete reservoir geological model is established for each type，and then a complete reservoir model is formed by combining pores，caves and fractures together. For the establishment of property parameter model，based on the numerous reservoir types identified from imaging well logging，and combining with the wave impedance of reservoir and porosity interpreted from well logging of single well，the relationship between the wave impedance and porosity of different types of fracture-cave reservoirs is quantitatively summarized，and the porosity data volume is obtained directly from the inversion of wave impedance data volume. The final reserves calculation result is consistent with the dynamic prediction results.
The proven reserves of the Ordovician fracture-cave reservoir in Tahe Oilfield are nearly1.4 billion tons. At present，the oilfield has entered the middle-late stage of development. Problems such as high water cut，contradictory injectionproduction relationship，strong heterogeneity and low recovery factor appear. Therefore，the establishment of a fine reservoir geological model is urgent. According to the genesis，the karst reservoirs can be divided into three types，including weathering crust type，fault-controlled type，and underground river type. The development characteristics of karst reservoirs with three different genesis are analyzed in typical fracture-cave Units S74，S65，T7-615，respectively. Taking Unit S65 in which all three types are developed as an example，a discrete reservoir geological model is established for each type，and then a complete reservoir model is formed by combining pores，caves and fractures together. For the establishment of property parameter model，based on the numerous reservoir types identified from imaging well logging，and combining with the wave impedance of reservoir and porosity interpreted from well logging of single well，the relationship between the wave impedance and porosity of different types of fracture-cave reservoirs is quantitatively summarized，and the porosity data volume is obtained directly from the inversion of wave impedance data volume. The final reserves calculation result is consistent with the dynamic prediction results.
2019, 26(6):62-69.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.008
Abstract:
The southwest Huizhou area in Pearl River Mouth Basin is the preferred target for lithologic trap exploration in the northeastern continental shelf of South China Sea. Nearly100 million square meters of petroleum geological reserves have been found in lithologic reservoirs. The analysis of forming conditions for lithologic traps and its developing types is beneficial to clarify exploration direction and enhance exploration potential of lithologic trap in marine sedimentary of the continental shelf. Influenced by multi-stage origin，relative sea-level change and complex hydrodynamic environment，multi-genesis sand bodies formed at Neogene paleo-Pearl River Delta are characterized by zonal development and vertical overlapping of multi-layer reservoir-cap assemblages，which are the material basis for lithologic traps development. Dongsha Movement makes Dongsha Uplift rise upper at the late Neogene and faults relatively develop，which provides tectonic background for lithologic traps formation. The lithologic traps in the southwestern Huizhou area distribute in three belts which are delta plain，delta front，and belt sand development zone. The channel sand bodies mainly develop in delta plain.The lithologic updip pinchout traps mainly develop at delta front，which can be further subdivided into three categories：the end sand body of progradation，the inner sand body of progradation，and the sand body of retrogradation. The strip sandstone traps develop mainly in strip sandstone development belts formed under the limited paleogeomorphic background.Based on the analysis of the development location，pinchout characteristics and reservoir physical properties of different types of traps，it is concluded that the lithologic updip pinchout traps of the sand bodies of retrogradation have the best reservoir physical properties and trap boundary conditions.
The southwest Huizhou area in Pearl River Mouth Basin is the preferred target for lithologic trap exploration in the northeastern continental shelf of South China Sea. Nearly100 million square meters of petroleum geological reserves have been found in lithologic reservoirs. The analysis of forming conditions for lithologic traps and its developing types is beneficial to clarify exploration direction and enhance exploration potential of lithologic trap in marine sedimentary of the continental shelf. Influenced by multi-stage origin，relative sea-level change and complex hydrodynamic environment，multi-genesis sand bodies formed at Neogene paleo-Pearl River Delta are characterized by zonal development and vertical overlapping of multi-layer reservoir-cap assemblages，which are the material basis for lithologic traps development. Dongsha Movement makes Dongsha Uplift rise upper at the late Neogene and faults relatively develop，which provides tectonic background for lithologic traps formation. The lithologic traps in the southwestern Huizhou area distribute in three belts which are delta plain，delta front，and belt sand development zone. The channel sand bodies mainly develop in delta plain.The lithologic updip pinchout traps mainly develop at delta front，which can be further subdivided into three categories：the end sand body of progradation，the inner sand body of progradation，and the sand body of retrogradation. The strip sandstone traps develop mainly in strip sandstone development belts formed under the limited paleogeomorphic background.Based on the analysis of the development location，pinchout characteristics and reservoir physical properties of different types of traps，it is concluded that the lithologic updip pinchout traps of the sand bodies of retrogradation have the best reservoir physical properties and trap boundary conditions.
2019, 26(6):70-79.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.009
Abstract:
The turbidite reservoirs in Dongying Sag in limestone background mainly exist in forms of thin beds or thin interbeds. It is difficult to identify them on seismic section because there is little difference in wave impedance between limy mudstone and turbidite reservoir. Thus a method combining numerical simulation of post-stack elastic wave equation and prestack seismic inversion is proposed. In order to eliminate the interference of limy mudstone and take full usage of elastic information of prestack seismic inversion，on the basis of logging-constrained prestack inversion，a sensitivity factor R is introduced to quantitatively evaluate the lithological sensitivity，and considering multi-elastic lithological information fusion，a mathematical model is constructed to optimize elastic parameters that sensitive to limy mudstone and turbidite. Meanwhile，combined with the numerical simulation of poststack elastic wave equation，the identification methods of thick turbidite and thin interbedded turbidite reservoirs in limestone background are studied to achieve the purpose of reservoir optimization. For turbidite reservoirs in limestone background in Well Tuo71 Area，Dongying Sag，combining multi-elastic lithological information fusion with the numerical simulation of elastic wave equation，an effective identification method of turbidite and thin interbeds of turbidite in limestone background is proposed，which is important to guide the reservoir identification and optimization.
The turbidite reservoirs in Dongying Sag in limestone background mainly exist in forms of thin beds or thin interbeds. It is difficult to identify them on seismic section because there is little difference in wave impedance between limy mudstone and turbidite reservoir. Thus a method combining numerical simulation of post-stack elastic wave equation and prestack seismic inversion is proposed. In order to eliminate the interference of limy mudstone and take full usage of elastic information of prestack seismic inversion，on the basis of logging-constrained prestack inversion，a sensitivity factor R is introduced to quantitatively evaluate the lithological sensitivity，and considering multi-elastic lithological information fusion，a mathematical model is constructed to optimize elastic parameters that sensitive to limy mudstone and turbidite. Meanwhile，combined with the numerical simulation of poststack elastic wave equation，the identification methods of thick turbidite and thin interbedded turbidite reservoirs in limestone background are studied to achieve the purpose of reservoir optimization. For turbidite reservoirs in limestone background in Well Tuo71 Area，Dongying Sag，combining multi-elastic lithological information fusion with the numerical simulation of elastic wave equation，an effective identification method of turbidite and thin interbeds of turbidite in limestone background is proposed，which is important to guide the reservoir identification and optimization.
2019, 26(6):80-86.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.010
Abstract:
Since the coal rocks are soft and brittle，and has low mechanical strength，the coalbed methane reservoirs have strong stress sensitivity. In the process of development and drainage，due to the decrease of pore fluid pressure an the increase of effective stress，the pores and fractures in reservoirs tend to close，the porosity and permeability decrease，the compaction degree enhances and the response degree of coal body to stress changes. Based on the theory of mechanical deformation，the varying trend of porosity and permeability of coals under axial stress is calculated through the deduction and establishment of porosity and permeability model coupling mechanical strain. The“average pore compressibility”function is used to replace the pore compressibility constant in the traditional match beam model to form an improved match beam model. Then，the influence of the change of pore compressibility on the pore permeability parameters is analyzed. The results show that the porosity，permeability and pore compressibility decrease with the increase of axial stress；There is a negative exponential relationship between the porosity/permeability and the axial stress；The dynamic variation of pore compressibility with axial stress causes the porosity and permeability to decrease with the decrease of axial stress. Therefore，there is a geological correlation between physical parameters and stress-strain of coalbed methane reservoirs，and the stress sensitivity of physical parameters should be considered when judging reservoir physical properties.
Since the coal rocks are soft and brittle，and has low mechanical strength，the coalbed methane reservoirs have strong stress sensitivity. In the process of development and drainage，due to the decrease of pore fluid pressure an the increase of effective stress，the pores and fractures in reservoirs tend to close，the porosity and permeability decrease，the compaction degree enhances and the response degree of coal body to stress changes. Based on the theory of mechanical deformation，the varying trend of porosity and permeability of coals under axial stress is calculated through the deduction and establishment of porosity and permeability model coupling mechanical strain. The“average pore compressibility”function is used to replace the pore compressibility constant in the traditional match beam model to form an improved match beam model. Then，the influence of the change of pore compressibility on the pore permeability parameters is analyzed. The results show that the porosity，permeability and pore compressibility decrease with the increase of axial stress；There is a negative exponential relationship between the porosity/permeability and the axial stress；The dynamic variation of pore compressibility with axial stress causes the porosity and permeability to decrease with the decrease of axial stress. Therefore，there is a geological correlation between physical parameters and stress-strain of coalbed methane reservoirs，and the stress sensitivity of physical parameters should be considered when judging reservoir physical properties.
2019, 26(6):87-91.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.011
Abstract:
Based on statistical analysis and theoretical research on the declining production data of oilfield oil wells，Arps proposed three classical decline models of exponential，hyperbolic and harmonic，which have been highly valued by the world and have been widely used in the evaluation of global oil and gas industry production and recoverable reserves. It should be noted that the Arps exponential decline is a decline model in which the decline rate is constant and the production is declining faster. Because the predicted indicators are relatively stable，it is widely adopted by evaluation companies.The hyperbolic and harmonic declines of Arps are two models with slower decrement，which are not widely used in practice.The linear decline model established by Chen Yuanqian et al.in 2015 is only applicable to the linear decline of production over time，and the decline rate increases with time. The power function decline model is established in this paper，and its decline rate decreases with time. According to the decline exponent n proposed by Arps：linear decline model n=-1，exponential decline model n=0，hyperbolic decline model 0
Based on statistical analysis and theoretical research on the declining production data of oilfield oil wells，Arps proposed three classical decline models of exponential，hyperbolic and harmonic，which have been highly valued by the world and have been widely used in the evaluation of global oil and gas industry production and recoverable reserves. It should be noted that the Arps exponential decline is a decline model in which the decline rate is constant and the production is declining faster. Because the predicted indicators are relatively stable，it is widely adopted by evaluation companies.The hyperbolic and harmonic declines of Arps are two models with slower decrement，which are not widely used in practice.The linear decline model established by Chen Yuanqian et al.in 2015 is only applicable to the linear decline of production over time，and the decline rate increases with time. The power function decline model is established in this paper，and its decline rate decreases with time. According to the decline exponent n proposed by Arps：linear decline model n=-1，exponential decline model n=0，hyperbolic decline model 0
2019, 26(6):92-99.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.012
Abstract:
The crossflow of the displacement medium caused by the reservoir heterogeneity is one of the key issues that restrict the water flooding and polymer flooding in the conglomerate oil reservoirs. According to the heterogeneous distribution of Karamay conglomerate oil reservoir，three visualized sand packed models are designed for the connected，scattered and composite high-permeability areas respectively. Experiments of waterflooding and polymer flooding with high and low mass concentrations are carried out to analyze the crossflow characteristics of waterflooding and polymer flooding under different heterogeneous distributions. Two kinds of profile control and flooding agents，weak gel and particle gel，are used to plug the crossflow channel to explore effective treatment methods for the crossflow of various kinds of heterogeneity. The results show that the connected，scattered and composite distribution among the high-permeability zones in the reservoir are easy to cause crossflow during water flooding. It is difficult to effectively produce the crude oil from the medium and lowpermeability zones as well as the high-permeability zones distributed along non-main stream lines. The crossflow characteristics and treatment methods for the polymer flooding in various heterogeneous models are different. When the high-permeability zone is connected or compositely distributed，crossflow is still obvious for the low-concentration polymer flooding （1 000 mg/L），and the increase of polymer concentration（2 000 mg/L）can expand the swept volume in high-permeability zones distributed along non-main stream lines. The recovery has been increased significantly，but the crude oil in the medium and low-permeability areas has not been effectively produced. Particle gel flooding is the best method for the treatment of crossflow. If the high-permeability area is scattered，the recovery of the low-concentration polymer flooding（1 000 mg/L）is greatly increased. While recovery is difficult to be significantly increased by the high-concentration polymer flooding（2 000 mg/L）. Weak gel flooding is the best way to control crossflow.
The crossflow of the displacement medium caused by the reservoir heterogeneity is one of the key issues that restrict the water flooding and polymer flooding in the conglomerate oil reservoirs. According to the heterogeneous distribution of Karamay conglomerate oil reservoir，three visualized sand packed models are designed for the connected，scattered and composite high-permeability areas respectively. Experiments of waterflooding and polymer flooding with high and low mass concentrations are carried out to analyze the crossflow characteristics of waterflooding and polymer flooding under different heterogeneous distributions. Two kinds of profile control and flooding agents，weak gel and particle gel，are used to plug the crossflow channel to explore effective treatment methods for the crossflow of various kinds of heterogeneity. The results show that the connected，scattered and composite distribution among the high-permeability zones in the reservoir are easy to cause crossflow during water flooding. It is difficult to effectively produce the crude oil from the medium and lowpermeability zones as well as the high-permeability zones distributed along non-main stream lines. The crossflow characteristics and treatment methods for the polymer flooding in various heterogeneous models are different. When the high-permeability zone is connected or compositely distributed，crossflow is still obvious for the low-concentration polymer flooding （1 000 mg/L），and the increase of polymer concentration（2 000 mg/L）can expand the swept volume in high-permeability zones distributed along non-main stream lines. The recovery has been increased significantly，but the crude oil in the medium and low-permeability areas has not been effectively produced. Particle gel flooding is the best method for the treatment of crossflow. If the high-permeability area is scattered，the recovery of the low-concentration polymer flooding（1 000 mg/L）is greatly increased. While recovery is difficult to be significantly increased by the high-concentration polymer flooding（2 000 mg/L）. Weak gel flooding is the best way to control crossflow.
2019, 26(6):100-106.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.013
Abstract:
The pore throat structure is complex and the pore throat radius is small in low permeability reservoirs. The fluid flow in the low permeability reservoir shows obvious non-linear percolation characteristics，and there is a certain start-up pressure gradient. The thickness variation characteristics of boundary layer within the capillary is analyzed. Based on the boundary-layer theory of fluid and capillary model of the low permeability reservoir，a new non-linear percolation model in the low-permeability reservoir is established. The new model is verified by the flow experiments of the low-permeability cores，and the radial non-linear percolation model of a single well is summarized. Based on the differences of different percolation regions，the differential development strategies of the low permeability reservoirs are determined. The theoretical analysis shows that the non-linear percolation model of the low permeability reservoir based on boundary-layer theory can accurately describe the flow characteristics of fluid in the low permeability reservoir. The percolation area of the low permeability reservoir can be divided into fast flow area，slowly flow area and detention area. The difference between the boundary of fast flow zone and that of slowly flow zone is different，and the technical approach of enhancing oil recovery is different for different types of low permeability reservoirs. For the general low permeability reservoirs，the effective displacement pressure gradient can be established by well-pattern matching，which promotes the boundary docking of slowly flow zones between injection and production wells and improves sweep coefficient of reservoirs. The slowly flow area can be transformed into fast flow area through reservoir stimulation and other measures in the ultra-low permeability reservoirs. By optimizing well spacing，dead oil areas can be reduced and the producing degree of reservoir reserves can be increased in the tight reservoirs.
The pore throat structure is complex and the pore throat radius is small in low permeability reservoirs. The fluid flow in the low permeability reservoir shows obvious non-linear percolation characteristics，and there is a certain start-up pressure gradient. The thickness variation characteristics of boundary layer within the capillary is analyzed. Based on the boundary-layer theory of fluid and capillary model of the low permeability reservoir，a new non-linear percolation model in the low-permeability reservoir is established. The new model is verified by the flow experiments of the low-permeability cores，and the radial non-linear percolation model of a single well is summarized. Based on the differences of different percolation regions，the differential development strategies of the low permeability reservoirs are determined. The theoretical analysis shows that the non-linear percolation model of the low permeability reservoir based on boundary-layer theory can accurately describe the flow characteristics of fluid in the low permeability reservoir. The percolation area of the low permeability reservoir can be divided into fast flow area，slowly flow area and detention area. The difference between the boundary of fast flow zone and that of slowly flow zone is different，and the technical approach of enhancing oil recovery is different for different types of low permeability reservoirs. For the general low permeability reservoirs，the effective displacement pressure gradient can be established by well-pattern matching，which promotes the boundary docking of slowly flow zones between injection and production wells and improves sweep coefficient of reservoirs. The slowly flow area can be transformed into fast flow area through reservoir stimulation and other measures in the ultra-low permeability reservoirs. By optimizing well spacing，dead oil areas can be reduced and the producing degree of reservoir reserves can be increased in the tight reservoirs.
2019, 26(6):107-114.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.014
Abstract:
The types of reservoir spaces in the fracture-cave carbonate reservoir are various and its shapes are complex. Attic oil and bypassing oil are easily formed during the process of water flooding. Gas flooding can effectively supplement formation energy and improve the recovery of remaining oil. In order to observe the displacement performance of injected gas in the fracture-cave reservoir，a two-dimensional visual physical model of fracture-cave reservoir is designed and made according to the actual geological data and injection-production characteristics of Tahe Oilfield as well as similarity principle.At the same time，the experimental study on enhanced oil recovery by gas injection in the karst-reservoir model of fracturecave reservoir is carried out. The results show that the macroscopic characteristics of oil-water interface are basically similar after displacement at 20 and 5 mL/min of gas injection rate，and there are obvious gas-water coning phenomenon and gas-water synergistic effect during nitrogen flooding. The ultimate recovery is about 70.5% at 20 mL/min of gas injection rate，and it is 78.9% at 5 mL/min of gas injection rate. High gas injection rate easily causes gas breakthrough. Low gas injection rate can prolong the time of nitrogen injection，so that gas breakthrough is not easy to occur prematurely. However，nitrogen can only enter caves and fractures with relatively low resistance due to low injection rate and low driving energy.Therefore，it is found that reasonable gas injection rate can enhance the potential of gas flooding in improving oil recovery.
The types of reservoir spaces in the fracture-cave carbonate reservoir are various and its shapes are complex. Attic oil and bypassing oil are easily formed during the process of water flooding. Gas flooding can effectively supplement formation energy and improve the recovery of remaining oil. In order to observe the displacement performance of injected gas in the fracture-cave reservoir，a two-dimensional visual physical model of fracture-cave reservoir is designed and made according to the actual geological data and injection-production characteristics of Tahe Oilfield as well as similarity principle.At the same time，the experimental study on enhanced oil recovery by gas injection in the karst-reservoir model of fracturecave reservoir is carried out. The results show that the macroscopic characteristics of oil-water interface are basically similar after displacement at 20 and 5 mL/min of gas injection rate，and there are obvious gas-water coning phenomenon and gas-water synergistic effect during nitrogen flooding. The ultimate recovery is about 70.5% at 20 mL/min of gas injection rate，and it is 78.9% at 5 mL/min of gas injection rate. High gas injection rate easily causes gas breakthrough. Low gas injection rate can prolong the time of nitrogen injection，so that gas breakthrough is not easy to occur prematurely. However，nitrogen can only enter caves and fractures with relatively low resistance due to low injection rate and low driving energy.Therefore，it is found that reasonable gas injection rate can enhance the potential of gas flooding in improving oil recovery.
LI Zongyang
,
TAN Heqing
,
LI Linxiang
,
CAO Xulong
,
CUI Wenfu
,
CHEN Xiaozhi
,
WANG Yefei
,
LI Wenhua
2019, 26(6):115-121.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.015
Abstract:
The Type I and II reservoir resources suitable for chemical flooding in Shengli Oilfield have been basically produced，and the resource replacement is difficult by chemical flooding. An injection-production coupling technology is designed to prolong the economic validity period of polymer flooding projects at later stage. Based on the physical simulation experiment，a visualized simulated displacement apparatus is used to study the swept volume and the residual oil distribution characteristics under conventional injection-production and injection-production coupling technology at the later stage of polymer flooding. The results show that compared with conventional injection-production methods，injection-production coupling approach can change the direction of conventional streamline，enlarge the swept volume and produce the remaining oil in low permeability area to achieve the purpose of enhancing oil recovery. Taking Ng3-4 unit in No.8 Block of Gudong Oilfield during polymer flooding at the later stage as an example，a reservoir numerical model for the Ng32 Submember is established. The optimization of injection-production coupling structure and implementation cycle is performed by numerical simulation. The results show that the coupling technology for chemical flooding can effectively transform the existing streamlines，expand the swept area of the diversion streamline，reduce the usage of chemical agents and further improve oil recovery in the reservoir under extra-high water cut stage. The optimized coupling structure of injection-production is the symmetrical structure with the ratio of production time between one round to two rounds being 1∶1. The production time of each round is three months. Then ten well groups are selected to carry out field test. After field implementation，the water-cut returning trend is effectively controlled，the dry powder of polymer is reduced by 10.8 tons per month and the incremental oil production per ton of polymer is increased by 7.6 t/t. The enhanced oil recovery is predicted to further increase by 1.7%.
The Type I and II reservoir resources suitable for chemical flooding in Shengli Oilfield have been basically produced，and the resource replacement is difficult by chemical flooding. An injection-production coupling technology is designed to prolong the economic validity period of polymer flooding projects at later stage. Based on the physical simulation experiment，a visualized simulated displacement apparatus is used to study the swept volume and the residual oil distribution characteristics under conventional injection-production and injection-production coupling technology at the later stage of polymer flooding. The results show that compared with conventional injection-production methods，injection-production coupling approach can change the direction of conventional streamline，enlarge the swept volume and produce the remaining oil in low permeability area to achieve the purpose of enhancing oil recovery. Taking Ng3-4 unit in No.8 Block of Gudong Oilfield during polymer flooding at the later stage as an example，a reservoir numerical model for the Ng32 Submember is established. The optimization of injection-production coupling structure and implementation cycle is performed by numerical simulation. The results show that the coupling technology for chemical flooding can effectively transform the existing streamlines，expand the swept area of the diversion streamline，reduce the usage of chemical agents and further improve oil recovery in the reservoir under extra-high water cut stage. The optimized coupling structure of injection-production is the symmetrical structure with the ratio of production time between one round to two rounds being 1∶1. The production time of each round is three months. Then ten well groups are selected to carry out field test. After field implementation，the water-cut returning trend is effectively controlled，the dry powder of polymer is reduced by 10.8 tons per month and the incremental oil production per ton of polymer is increased by 7.6 t/t. The enhanced oil recovery is predicted to further increase by 1.7%.
2019, 26(6):122-128.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.016
Abstract:
Horizontal wells with large-scale hydraulic fracturing is required for the effective development of the tight oil reservoirs due to extra-low permeability. After fracturing，there exists two porous media with quite different percolation laws，that is matrix and fracture. A new production analysis model is needed to meet the demand of dynamic analysis of fractured horizontal wells in the tight oil reservoirs. Based on the different percolation laws of the matrix and fracture in the tight oil reservoirs，a coupled production model of a multi-stage fractured horizontal well in the dual-media formation is proposed and solved by using finite volume method on the basis of unstructured hybrid grids. Meanwhile，the typical Blasingame curve of the fractured horizontal well in the tight oil reservoirs is obtained，and the characteristics of the Blasingame curve are analyzed. The development stages of the fractured horizontal well can be divided into three stages：fracture linear flow， boundary-dominated flow and transition flow. The threshold pressure gradient，fracture numbers，fracture spacing and fracture length have major effects on the Blasingame curve. Blasingame curve moves down linearly with the increase of threshold pressure gradient in the later stage of boundary-dominated flow，and disperses upward with the increase of fracture numbers in the early and middle stages，and moves up with the increase of fracture spacing and fracture length in the middle transitional flow stage，but the effect of fracture spacing on the Blasingame curves is more significant.
Horizontal wells with large-scale hydraulic fracturing is required for the effective development of the tight oil reservoirs due to extra-low permeability. After fracturing，there exists two porous media with quite different percolation laws，that is matrix and fracture. A new production analysis model is needed to meet the demand of dynamic analysis of fractured horizontal wells in the tight oil reservoirs. Based on the different percolation laws of the matrix and fracture in the tight oil reservoirs，a coupled production model of a multi-stage fractured horizontal well in the dual-media formation is proposed and solved by using finite volume method on the basis of unstructured hybrid grids. Meanwhile，the typical Blasingame curve of the fractured horizontal well in the tight oil reservoirs is obtained，and the characteristics of the Blasingame curve are analyzed. The development stages of the fractured horizontal well can be divided into three stages：fracture linear flow， boundary-dominated flow and transition flow. The threshold pressure gradient，fracture numbers，fracture spacing and fracture length have major effects on the Blasingame curve. Blasingame curve moves down linearly with the increase of threshold pressure gradient in the later stage of boundary-dominated flow，and disperses upward with the increase of fracture numbers in the early and middle stages，and moves up with the increase of fracture spacing and fracture length in the middle transitional flow stage，but the effect of fracture spacing on the Blasingame curves is more significant.
2019, 26(6):129-135.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.017
Abstract:
Facing global energy shortage，shale gas has become a research hotspot as new unconventional resources. A 3D geological model is established to analyze the effect of injection rate of CO2 or mixture of CO2 and N2 as well as percentage of N2 in mixed gas on shale gas production by numerical simulation of the Yanchang Formation shale in Ordos Basin. Results show that the injection of CO2 or mixture of CO2 and N2 at the rate of 0.05，0.5 and 1 kg/s can increase shale gas production，and the injection of mixed gas obtains better recovery than injection of CO2 only. When CO2 is only injected at the rate of 0.05 kg/s，shale gas production is increased by 13.21% after 30 years with no CO2 breakthrough in methane production wells. When the mixture of CO2 and N2 is injected at the rate of 0.05 kg/s，N2 will occur in the methane production wells. The ratio of N2 is larger，the content of N2 is higher after breakthrough. However，in order to avoid gas content in the methane production well exceeding the 10% when the breakthrough occurs，it is necessary to strictly control the injection rate of CO2 or mixture of CO2 and N2 as well as percentage of N2 in the mixed gas.
Facing global energy shortage，shale gas has become a research hotspot as new unconventional resources. A 3D geological model is established to analyze the effect of injection rate of CO2 or mixture of CO2 and N2 as well as percentage of N2 in mixed gas on shale gas production by numerical simulation of the Yanchang Formation shale in Ordos Basin. Results show that the injection of CO2 or mixture of CO2 and N2 at the rate of 0.05，0.5 and 1 kg/s can increase shale gas production，and the injection of mixed gas obtains better recovery than injection of CO2 only. When CO2 is only injected at the rate of 0.05 kg/s，shale gas production is increased by 13.21% after 30 years with no CO2 breakthrough in methane production wells. When the mixture of CO2 and N2 is injected at the rate of 0.05 kg/s，N2 will occur in the methane production wells. The ratio of N2 is larger，the content of N2 is higher after breakthrough. However，in order to avoid gas content in the methane production well exceeding the 10% when the breakthrough occurs，it is necessary to strictly control the injection rate of CO2 or mixture of CO2 and N2 as well as percentage of N2 in the mixed gas.
2019, 26(6):136-142.
DOI: 10.13673/j.cnki.cn37-1359/te.2019.06.018
Abstract:
The proppants in fractures are usually used to prevent fracture closure. The membrane covering proppant with new functions is developed to enhance the hydrophobic-lipophilic capability. The proppants with function of controlling water cut to increase oil production is developed by using hydrophobic material to cover the surface of proppants according to the lotus leaf principle. The coated proppants are packed into the fractures to make the fracture have low flow conductivity for water phase and high flow conductivity for oil phase. The capacity of oil permeability and water plugging of the coated proppants layer are tested using sand-packed model. Then，the experiments of water flooding are carried out in the fractures filled with conventional proppants and coated proppants respectively by using the large-scale 3D flooding equipment. Results show that the hydrophobic-lipophilic capability of the layer filled with coated proppants is better than that of the layer filled with conventional proppants；when the displacement pressure difference is lower than 0.4 MPa，the hydrophobic-lipophilic capability becomes little higher and the hydrophobic performance is enhanced more than 10%. In addition，the oil recovery of fractures filled with coated proppants is 3.95% higher than that of the fractures filled with conventional proppants.
The proppants in fractures are usually used to prevent fracture closure. The membrane covering proppant with new functions is developed to enhance the hydrophobic-lipophilic capability. The proppants with function of controlling water cut to increase oil production is developed by using hydrophobic material to cover the surface of proppants according to the lotus leaf principle. The coated proppants are packed into the fractures to make the fracture have low flow conductivity for water phase and high flow conductivity for oil phase. The capacity of oil permeability and water plugging of the coated proppants layer are tested using sand-packed model. Then，the experiments of water flooding are carried out in the fractures filled with conventional proppants and coated proppants respectively by using the large-scale 3D flooding equipment. Results show that the hydrophobic-lipophilic capability of the layer filled with coated proppants is better than that of the layer filled with conventional proppants；when the displacement pressure difference is lower than 0.4 MPa，the hydrophobic-lipophilic capability becomes little higher and the hydrophobic performance is enhanced more than 10%. In addition，the oil recovery of fractures filled with coated proppants is 3.95% higher than that of the fractures filled with conventional proppants.
Online Submit
Reviewer
Editor
Reader
Quick Search
External Links
