Volume 25,Issue 2,2018 Table of Contents
2018, 25(2):1-7.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.001
Abstract:
By means of X-ray diffraction analysis and environmental scanning electron microscope observation，the occurrence characteristics of dolomite and its relative abundance in shale drilled by Well Liye1 were studied to discuss the significance of relative abundance of dolomite on vertical sequence interfaces. Two kinds of dolomite in shale drilled by Well Liye1 were determined as euhedral dolomite and irregular microcrystalline based on their occurrence. Euhedral dolomite is characterized by two periods of recrystallization diagenesis，whose boundaries are similar to those of overgrowth rim；while irregular microcrystalline is characterized by origin dolomite. Dolomite in the shale drilled by Well Liye1 is a primary dolomite，part of which experienced the reformation of diagenetic recrystallization. The formation of dolomite can be divided into two stages. The first stage is the chemical precipitation of primary micrite and microcrystalline dolomite，and the second stage is the recrystallization through differential capillary pumping between laminae. It was proposed for the first time that the change of relative abundance of dolomite can be used as a typical marker for dividing the interface between the third and the fourth sequences of shale in the study area，which is corresponding to the high porosity reservoir. In the longitudinal direction，the closer the dolomite is to the sequence boundary，the higher the relative abundance of dolomite is，and the relative abundance of dolomite is lower when it is far away from the sequence boundary. The shale with high content of clay minerals developing at the upper of the fourth member of Shahejie Formation is characterized by high dolomite abundance.The content of illite developing at the lower of the third member of Shahejie Formation is relative low and the mixing content of illite/smectite is relative high，resulting in a high relative abundance of dolomite. It is indicated that the decrease of illite content and the increase of illite/smectite are favorable for the formation of dolomite.
By means of X-ray diffraction analysis and environmental scanning electron microscope observation，the occurrence characteristics of dolomite and its relative abundance in shale drilled by Well Liye1 were studied to discuss the significance of relative abundance of dolomite on vertical sequence interfaces. Two kinds of dolomite in shale drilled by Well Liye1 were determined as euhedral dolomite and irregular microcrystalline based on their occurrence. Euhedral dolomite is characterized by two periods of recrystallization diagenesis，whose boundaries are similar to those of overgrowth rim；while irregular microcrystalline is characterized by origin dolomite. Dolomite in the shale drilled by Well Liye1 is a primary dolomite，part of which experienced the reformation of diagenetic recrystallization. The formation of dolomite can be divided into two stages. The first stage is the chemical precipitation of primary micrite and microcrystalline dolomite，and the second stage is the recrystallization through differential capillary pumping between laminae. It was proposed for the first time that the change of relative abundance of dolomite can be used as a typical marker for dividing the interface between the third and the fourth sequences of shale in the study area，which is corresponding to the high porosity reservoir. In the longitudinal direction，the closer the dolomite is to the sequence boundary，the higher the relative abundance of dolomite is，and the relative abundance of dolomite is lower when it is far away from the sequence boundary. The shale with high content of clay minerals developing at the upper of the fourth member of Shahejie Formation is characterized by high dolomite abundance.The content of illite developing at the lower of the third member of Shahejie Formation is relative low and the mixing content of illite/smectite is relative high，resulting in a high relative abundance of dolomite. It is indicated that the decrease of illite content and the increase of illite/smectite are favorable for the formation of dolomite.
ZHANG Hui
,
HU Wangshui
,
LI Wei
,
CHEN Zhuxin
,
HAO Meng
,
GUO Xiantao
,
FAN Zhong
,
GORDON Benkane
,
CHEN Zhangwen
2018, 25(2):8-14.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.002
Abstract:
The paleo-topography maps of different geologic evolutionary stages are hard to be correlated with each other in horizontal and vertical with flexibly and high resolution. To solve this problem，a method for paleo-topography evolution establishment was first proposed，comprising of two types of methods and three models which included a cut-out section method based on a 3D model of key strata boundary and a balanced cross section method comprising of the same key strata boundary during different evolutionary stages based on forward and inverse modeling. Furthermore，the existence of paleotopography evolutionary behaviors such as inheritance，hiatus and transformation（positive topography transformation or negative topography transformation）was analyzed and certified and the identification signatures during paleo-topography evo? lution were further discussed. The geological applications and implications of key strata paleo-topography evolution were summarized，including the analysis of paleo-topography evolutionary behaviors，tectonic-sedimentary coupling relationships under different tectonic mechanisms，progressive tectonic deformation and trap and hydrocarbon accumulation evolution. A paleo-topography evolutionary section of the Sinian top in the northwest of Sichuan Province was selected as an example to verify the geological applications and implications of paleo-topography evolution，which offered a new approach for the paleo-topography evolution analysis and provided an effective way to realize fine correlation of local paleo-topography evolution，and it was also applied to improve space-time resolution，flexibility and accuracy of paleo-topography evolution studies.
The paleo-topography maps of different geologic evolutionary stages are hard to be correlated with each other in horizontal and vertical with flexibly and high resolution. To solve this problem，a method for paleo-topography evolution establishment was first proposed，comprising of two types of methods and three models which included a cut-out section method based on a 3D model of key strata boundary and a balanced cross section method comprising of the same key strata boundary during different evolutionary stages based on forward and inverse modeling. Furthermore，the existence of paleotopography evolutionary behaviors such as inheritance，hiatus and transformation（positive topography transformation or negative topography transformation）was analyzed and certified and the identification signatures during paleo-topography evo? lution were further discussed. The geological applications and implications of key strata paleo-topography evolution were summarized，including the analysis of paleo-topography evolutionary behaviors，tectonic-sedimentary coupling relationships under different tectonic mechanisms，progressive tectonic deformation and trap and hydrocarbon accumulation evolution. A paleo-topography evolutionary section of the Sinian top in the northwest of Sichuan Province was selected as an example to verify the geological applications and implications of paleo-topography evolution，which offered a new approach for the paleo-topography evolution analysis and provided an effective way to realize fine correlation of local paleo-topography evolution，and it was also applied to improve space-time resolution，flexibility and accuracy of paleo-topography evolution studies.
2018, 25(2):15-19.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.003
Abstract:
The apparent resistivity curves of conventional dual laterolog often present polarization angle at the stratigraphic interface，resulting in distortion of the curve form and occurrence of“pseudo thin layer”phenomenon，which seriously affects the accurate division of the stratigraphic interface and the accurate calculation of the true resistivity of the strata.Based on the finite element numerical simulation technique，the mathematical model of dual laterolog was established. The effects of surrounding rock resistivity，layer thickness，reservoir anisotropy，well diameter and well inclination on polarization angle and amplitude of dual laterolog apparent resistivity were studied. The results show that the difference between the resistivity of the target layer and the resistivity of the surrounding rock is larger，and the polarization angle of the dual laterolog is more obvious. The effect of layer thickness on the polarization angle is complicated. When the thickness of the strata is thinner than the thickness resolved by instrument measurement，the polarization angle disappears. The anisotropy of the reservoir will cause the amplitude of the polarization angle to change，but the influence on geometry of the polarization angle is small. As the well diameter becomes larger，the polarization angle tends to disappear. The larger the well inclination is，the gentler the polarization angle is. The polarization angle of dual laterolog apparent resistivity curve is the result influenced by many factors. In the work of polarization angle correction，all factors should be considered comprehensively.
The apparent resistivity curves of conventional dual laterolog often present polarization angle at the stratigraphic interface，resulting in distortion of the curve form and occurrence of“pseudo thin layer”phenomenon，which seriously affects the accurate division of the stratigraphic interface and the accurate calculation of the true resistivity of the strata.Based on the finite element numerical simulation technique，the mathematical model of dual laterolog was established. The effects of surrounding rock resistivity，layer thickness，reservoir anisotropy，well diameter and well inclination on polarization angle and amplitude of dual laterolog apparent resistivity were studied. The results show that the difference between the resistivity of the target layer and the resistivity of the surrounding rock is larger，and the polarization angle of the dual laterolog is more obvious. The effect of layer thickness on the polarization angle is complicated. When the thickness of the strata is thinner than the thickness resolved by instrument measurement，the polarization angle disappears. The anisotropy of the reservoir will cause the amplitude of the polarization angle to change，but the influence on geometry of the polarization angle is small. As the well diameter becomes larger，the polarization angle tends to disappear. The larger the well inclination is，the gentler the polarization angle is. The polarization angle of dual laterolog apparent resistivity curve is the result influenced by many factors. In the work of polarization angle correction，all factors should be considered comprehensively.
2018, 25(2):20-28.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.004
Abstract:
The interpretation of sedimentary facies remains controversial since the sediment is complex in the SDG area，west Sichuan Depression，Sichuan Basin. Considering the complex sedimentary characteristics in the Penglaizhen Formation of the SDG area，the sediment provenance direction was determined under the control of structure and sedimentary background through analyzing the stable heavy mineral and rock debris combination based on cores and measurements results from 25 cored wells and logging data of 313 wells. On this basis，the lithofacies type and their genetic environments were interpreted. Combined with the previous research results，the typical characteristics and identification marks of shallow water delta were dissected and then the sedimentary evolution characteristics were summarized to establish the sedimentary genetic model of shallow water delta based on the principle of“point-line-plane-volume”. The study results show that the SDG area has favorable geological conditions for the formation of shallow water delta，and the sand is characterized by fine granularity and wide distribution，but the single sand body is thin and small. The cumulative probability curves of granularity shows that the deposition was controlled by traction current which results in typical lithofacies combinations，and the deposited sand bodies have obvious fluvial-dominated characteristic at both sides of（underwater）distributary channels and their front，and the channel was reformed obviously. Based on the further exploration of sedimentary characteristics and sedimentary facies，five kinds of sedimentary models were put forward for shallow water delta，which are the model of fluvial-controlled blocky sand in delta plain，the model of fluvial-controlled blocky sand in delta front，the model of fluvial-controlled debouch bar in delta front，the model of tide-controlled sheet sand in delta front-prodelta transition zone and the model of tide-controlled far sand bar in delta front，and the model of tide-controlled far sand bar in delta front is proposed for the first time in the SDG area.
The interpretation of sedimentary facies remains controversial since the sediment is complex in the SDG area，west Sichuan Depression，Sichuan Basin. Considering the complex sedimentary characteristics in the Penglaizhen Formation of the SDG area，the sediment provenance direction was determined under the control of structure and sedimentary background through analyzing the stable heavy mineral and rock debris combination based on cores and measurements results from 25 cored wells and logging data of 313 wells. On this basis，the lithofacies type and their genetic environments were interpreted. Combined with the previous research results，the typical characteristics and identification marks of shallow water delta were dissected and then the sedimentary evolution characteristics were summarized to establish the sedimentary genetic model of shallow water delta based on the principle of“point-line-plane-volume”. The study results show that the SDG area has favorable geological conditions for the formation of shallow water delta，and the sand is characterized by fine granularity and wide distribution，but the single sand body is thin and small. The cumulative probability curves of granularity shows that the deposition was controlled by traction current which results in typical lithofacies combinations，and the deposited sand bodies have obvious fluvial-dominated characteristic at both sides of（underwater）distributary channels and their front，and the channel was reformed obviously. Based on the further exploration of sedimentary characteristics and sedimentary facies，five kinds of sedimentary models were put forward for shallow water delta，which are the model of fluvial-controlled blocky sand in delta plain，the model of fluvial-controlled blocky sand in delta front，the model of fluvial-controlled debouch bar in delta front，the model of tide-controlled sheet sand in delta front-prodelta transition zone and the model of tide-controlled far sand bar in delta front，and the model of tide-controlled far sand bar in delta front is proposed for the first time in the SDG area.
2018, 25(2):29-36.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.005
Abstract:
Quantitative reconstruction of paleoclimate is the key to the research on fine-grained sediments. To solve this problem，three factors that can reflect the paleoclimate were proposed，which are moisture index，terrigenous clastic and carbonate. Based on these factors，the paleoclimate indicator was extracted by SPSS，and a method for paleoclimate quantitative reconstruction was established. The larger the value of paleoclimate indicator，the more humid the paleoclimate. To a certain extent，this method overcomes the limitations in paleoclimate reconstruction using single method and keeps the relevant information of the selected factors to reflect the paleoclimate，and thus the reconstruction result is more reasonable and more practical. Using the established method，the paleoclimate was reconstructed based on data of Wells Fanye1 and Niuye1 in Dongying Sag during deposition of the upper Es4 and the lower Es3. Meanwhile，the effect of the paleoclimate on fine-grained sediments was studied from three aspects，including organic matter abundance，sedimentary structure and lithofacies. The results show that there are four paleoclimatic cycles during the deposition of the upper Es4 and the lower Es3 in Dongying Sag，which are arid to semi-arid，semi-humid to humid，semi-arid and semi-arid to semi-humid. The paleoclimate changed gradually from arid to humid. As a result，a fine-grained sedimentary lithofacies evolution sequence developed vertically，which are organic-rich laminated limestone lithofacies，organic-rich laminated argillaceous dolomite lithofacies，organic-rich layered argillaceous dolomite lithofacies，organic-rich laminated argillaceous limestone lithofacies，organic-rich laminated lime mudstone lithofacies，organic-rich layered argillaceous limestone lithofacies and organic-rich layered lime mudstone lithofacies.
Quantitative reconstruction of paleoclimate is the key to the research on fine-grained sediments. To solve this problem，three factors that can reflect the paleoclimate were proposed，which are moisture index，terrigenous clastic and carbonate. Based on these factors，the paleoclimate indicator was extracted by SPSS，and a method for paleoclimate quantitative reconstruction was established. The larger the value of paleoclimate indicator，the more humid the paleoclimate. To a certain extent，this method overcomes the limitations in paleoclimate reconstruction using single method and keeps the relevant information of the selected factors to reflect the paleoclimate，and thus the reconstruction result is more reasonable and more practical. Using the established method，the paleoclimate was reconstructed based on data of Wells Fanye1 and Niuye1 in Dongying Sag during deposition of the upper Es4 and the lower Es3. Meanwhile，the effect of the paleoclimate on fine-grained sediments was studied from three aspects，including organic matter abundance，sedimentary structure and lithofacies. The results show that there are four paleoclimatic cycles during the deposition of the upper Es4 and the lower Es3 in Dongying Sag，which are arid to semi-arid，semi-humid to humid，semi-arid and semi-arid to semi-humid. The paleoclimate changed gradually from arid to humid. As a result，a fine-grained sedimentary lithofacies evolution sequence developed vertically，which are organic-rich laminated limestone lithofacies，organic-rich laminated argillaceous dolomite lithofacies，organic-rich layered argillaceous dolomite lithofacies，organic-rich laminated argillaceous limestone lithofacies，organic-rich laminated lime mudstone lithofacies，organic-rich layered argillaceous limestone lithofacies and organic-rich layered lime mudstone lithofacies.
2018, 25(2):37-41.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.006
Abstract:
The mineral composition analysis and static and dynamic mechanical parameters synchronous test were used to analyze the experimental rock mechanics of the thick Paleogene gypsiferous mudrocks in the Yubei area in the southwest of the Tarim Basin. The results indicated that under uniaxial conditions，the gypsiferous mudrock showed obvious characteristic of elastic deformation，while under triaxial conditions，its elastic-plastic characteristics were obvious. Under formation confining pressure conditions，with the increase of axial load，the gypsiferous mudrock had experienced five stages such as initial compaction，linear elastic deformation，nonlinear stability extensional deformation，nonlinear unsteady extension deformation and macroscopic rupture. Compared to the gypsiferous mudrocks（GMR），argillaceous anhydrite rocks（AR）had higher VP，VS and VP/VS. There was a very good positive correlation between VP/VS and the anhydrite content. While the anhydrite content increased from about 10% to 90%，the VP/VS value increased from 1.63 to 1.88 and the increase amplitude was significant. And then the conversion relationship of time difference between longitudinal wave and transverse wave of gypsiferous mudrock samples were obtained precisely. The dynamic Young’s modulus，Poisson’s ratio and shear modulus of AR were obviously higher than that of GMR. The conversion relationships among dynamic and static mechanical parameters of the gypsiferous mudrocks were obtained finally.
The mineral composition analysis and static and dynamic mechanical parameters synchronous test were used to analyze the experimental rock mechanics of the thick Paleogene gypsiferous mudrocks in the Yubei area in the southwest of the Tarim Basin. The results indicated that under uniaxial conditions，the gypsiferous mudrock showed obvious characteristic of elastic deformation，while under triaxial conditions，its elastic-plastic characteristics were obvious. Under formation confining pressure conditions，with the increase of axial load，the gypsiferous mudrock had experienced five stages such as initial compaction，linear elastic deformation，nonlinear stability extensional deformation，nonlinear unsteady extension deformation and macroscopic rupture. Compared to the gypsiferous mudrocks（GMR），argillaceous anhydrite rocks（AR）had higher VP，VS and VP/VS. There was a very good positive correlation between VP/VS and the anhydrite content. While the anhydrite content increased from about 10% to 90%，the VP/VS value increased from 1.63 to 1.88 and the increase amplitude was significant. And then the conversion relationship of time difference between longitudinal wave and transverse wave of gypsiferous mudrock samples were obtained precisely. The dynamic Young’s modulus，Poisson’s ratio and shear modulus of AR were obviously higher than that of GMR. The conversion relationships among dynamic and static mechanical parameters of the gypsiferous mudrocks were obtained finally.
2018, 25(2):42-49.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.007
Abstract:
In order to study the characteristics and controlling factors of the reservoir rocks in the 4th member of the Xujiahe Formation in the Western Sichuan，the methods of outcrop and core observation，thin section analysis，porosity and permeability test，CL，SEM and XRD were used. The results show that the main rock lithology of the fourth member of Xujiahe Formation in the study area is medium-grained lithic sandstone with good sorting and medium or poor grinding roundness. The cementation types are mainly pore-filling type and compression type. The average porosity is 6.22%. The average permeability is 0.279 mD. The secondary pores consist of intergranular dissolved pores and intragranular dissolved pores，which are the main reservoir space. The relatively high-quality reservoirs are controlled by sedimentary facies belts，clastic components，rock structure and diagenesis. The subaqueous distributary channel，the estuary dam of delta front and the superimposed distributary channel of delta plain are favorable sedimentary microfacies. Medium-grained and well-sorted lithic sandstone with high quartz content and low lithic content has the best reservoir performance. Secondary pores generated by feldspar and debris dissolution can effectively increase the reservoir space，which accounts for about 85% of the total porosity and is the key to the formation of high quality reservoirs. Fractures can increase permeability to a certain extent and play an active role in improving storage capacity of reservoirs.
In order to study the characteristics and controlling factors of the reservoir rocks in the 4th member of the Xujiahe Formation in the Western Sichuan，the methods of outcrop and core observation，thin section analysis，porosity and permeability test，CL，SEM and XRD were used. The results show that the main rock lithology of the fourth member of Xujiahe Formation in the study area is medium-grained lithic sandstone with good sorting and medium or poor grinding roundness. The cementation types are mainly pore-filling type and compression type. The average porosity is 6.22%. The average permeability is 0.279 mD. The secondary pores consist of intergranular dissolved pores and intragranular dissolved pores，which are the main reservoir space. The relatively high-quality reservoirs are controlled by sedimentary facies belts，clastic components，rock structure and diagenesis. The subaqueous distributary channel，the estuary dam of delta front and the superimposed distributary channel of delta plain are favorable sedimentary microfacies. Medium-grained and well-sorted lithic sandstone with high quartz content and low lithic content has the best reservoir performance. Secondary pores generated by feldspar and debris dissolution can effectively increase the reservoir space，which accounts for about 85% of the total porosity and is the key to the formation of high quality reservoirs. Fractures can increase permeability to a certain extent and play an active role in improving storage capacity of reservoirs.
ZHAI Lihua
,
LIN Yanbo
,
QIN Zhi
,
XIONG Tao
,
BAO Zhidong
,
GU Yufeng
,
YANG Shangfeng
,
SHEN Jinjiang
,
XIE Yaran
2018, 25(2):50-57.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.008
Abstract:
In recent years，a large number of low resistivity oil reservoirs have been discovered in Chang4+5 member of Yanchang Formation of Jiyuan area，Ordos Basin. But there are many theoretical and technical problems in the genetic mechanism and identification methods，which often results in misidentification or loss of oil reservoirs in the study area. To study the genetic mechanism and identification methods of low resistivity oil reservoirs in Chang4+5 member of Yanchang Formation in Jiyuan area，a series of measurements and analysis such as core and thin section observation，SEM observation，XRD and mercury injection tests etc.，combining with data of logging，oil testing and production，were used. The result shows that low amplitude structure，complex relationship between oil and water，high immobile water saturation and high formation water salinity are the main causes of low resistivity oil reservoirs in Chang4+5 member. Among which，the high immobile water saturation in the study area is controlled by fine particle size，high clay content and complex pore structure.The case study shows that three methods of identifying low resistivity oil reservoirs were proposed in this paper：a qualitative contrast method of identifying reservoirs adjacent to low resistivity oil reservoirs；a quantitative identification method of analyzing mobile water of low resistivity oil reservoirs based on a three dimensional model of the relationship among clay content，ratio of porosity to permeability and immobile water saturation；and a crossplot method of identifying low resistivity oil reservoirs fast and accurately. These methods can improve the coincidence rate between the nterpretation results and the oil test results.
In recent years，a large number of low resistivity oil reservoirs have been discovered in Chang4+5 member of Yanchang Formation of Jiyuan area，Ordos Basin. But there are many theoretical and technical problems in the genetic mechanism and identification methods，which often results in misidentification or loss of oil reservoirs in the study area. To study the genetic mechanism and identification methods of low resistivity oil reservoirs in Chang4+5 member of Yanchang Formation in Jiyuan area，a series of measurements and analysis such as core and thin section observation，SEM observation，XRD and mercury injection tests etc.，combining with data of logging，oil testing and production，were used. The result shows that low amplitude structure，complex relationship between oil and water，high immobile water saturation and high formation water salinity are the main causes of low resistivity oil reservoirs in Chang4+5 member. Among which，the high immobile water saturation in the study area is controlled by fine particle size，high clay content and complex pore structure.The case study shows that three methods of identifying low resistivity oil reservoirs were proposed in this paper：a qualitative contrast method of identifying reservoirs adjacent to low resistivity oil reservoirs；a quantitative identification method of analyzing mobile water of low resistivity oil reservoirs based on a three dimensional model of the relationship among clay content，ratio of porosity to permeability and immobile water saturation；and a crossplot method of identifying low resistivity oil reservoirs fast and accurately. These methods can improve the coincidence rate between the nterpretation results and the oil test results.
2018, 25(2):58-63.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.009
Abstract:
Calcite cement is widely distributed in the tight sandstone of Fuyu oil reservoir in Sanzhao Sag，and calcite cementation is an important controlling factor for reservoir densification. In this paper，taking calcite cement as the research object，the formation time and origin of calcite were identified by thin section identification，cathodoluminescence，inclusion test，laser Raman spectroscopy and scanning electron microscopy. The results show that the main types of calcite cements in Fuyu oil reservoir are fine-grained calcite and coarse-grained calcite. The fine-grained calcite fills intergranular pores and grows into crystal stock calcite，or replaces the tiny crystals of feldspar and precipitates in the dissolution pore or micropore in the surface of feldspar，which sometimes can cement many particles and grows into mosaic calcite；the coarse grained calcite is characterized by residual pore filling and distributes irregularly. The calcite cement developed in two periods. The first period is in Nenjiang Period（78-77 Ma years ago），and the formation temperature is 89.5-110.2 ℃；the second period is in Mingshui Period（73-65 Ma years ago），and the formation temperature is 122.6-134.3 ℃. The formation of early calcite is related to biogenic gas，and the formation of late calcite is related to the decarboxylation of organic acid.The formation of calcite cement in the two periods greatly destroys the reservoir physical property，which is the important reason for reservoir densification.
Calcite cement is widely distributed in the tight sandstone of Fuyu oil reservoir in Sanzhao Sag，and calcite cementation is an important controlling factor for reservoir densification. In this paper，taking calcite cement as the research object，the formation time and origin of calcite were identified by thin section identification，cathodoluminescence，inclusion test，laser Raman spectroscopy and scanning electron microscopy. The results show that the main types of calcite cements in Fuyu oil reservoir are fine-grained calcite and coarse-grained calcite. The fine-grained calcite fills intergranular pores and grows into crystal stock calcite，or replaces the tiny crystals of feldspar and precipitates in the dissolution pore or micropore in the surface of feldspar，which sometimes can cement many particles and grows into mosaic calcite；the coarse grained calcite is characterized by residual pore filling and distributes irregularly. The calcite cement developed in two periods. The first period is in Nenjiang Period（78-77 Ma years ago），and the formation temperature is 89.5-110.2 ℃；the second period is in Mingshui Period（73-65 Ma years ago），and the formation temperature is 122.6-134.3 ℃. The formation of early calcite is related to biogenic gas，and the formation of late calcite is related to the decarboxylation of organic acid.The formation of calcite cement in the two periods greatly destroys the reservoir physical property，which is the important reason for reservoir densification.
2018, 25(2):64-71.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.010
Abstract:
The marine sandstone reservoirs are characterized with strong energy of edge and bottom water. Conventional experimental standards barely reveal reservoir percolation characteristics under high oil recovery rate after high intensity water flooding. The experiment process of the high-multiple water drive was improved based on sealed coring data of Xijiang 24-3 Oilfield. The actual situation was simulated after water injection multiple was increased from conventional 30 PV to 2 000 PV. The variation of physical properties and remaining oil in marine sandstone reservoir after high-multiple water drive were analyzed systematically from six aspects，including mineral composition，pore-throat structure，wettability，oilwater relative permeability curve，residual oil saturation and oil displacement efficiency. Therefore，the characterization method and numerical simulation method were established for obtaining the ultimate displacement efficiency of this type of reservoir. The results show that microscopic pore-throat structure and mineral composition both change after the high-multiple water drive，which has an impact on the wettability and relative permeability curves as well as the residual oil saturation and oil displacement efficiency. The change of physical properties of the oil reservoir is favorable to oil displacement，the residual oil saturation dropped obviously and the oil displacement efficiency was enhanced obviously.
The marine sandstone reservoirs are characterized with strong energy of edge and bottom water. Conventional experimental standards barely reveal reservoir percolation characteristics under high oil recovery rate after high intensity water flooding. The experiment process of the high-multiple water drive was improved based on sealed coring data of Xijiang 24-3 Oilfield. The actual situation was simulated after water injection multiple was increased from conventional 30 PV to 2 000 PV. The variation of physical properties and remaining oil in marine sandstone reservoir after high-multiple water drive were analyzed systematically from six aspects，including mineral composition，pore-throat structure，wettability，oilwater relative permeability curve，residual oil saturation and oil displacement efficiency. Therefore，the characterization method and numerical simulation method were established for obtaining the ultimate displacement efficiency of this type of reservoir. The results show that microscopic pore-throat structure and mineral composition both change after the high-multiple water drive，which has an impact on the wettability and relative permeability curves as well as the residual oil saturation and oil displacement efficiency. The change of physical properties of the oil reservoir is favorable to oil displacement，the residual oil saturation dropped obviously and the oil displacement efficiency was enhanced obviously.
2018, 25(2):72-76.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.011
Abstract:
Conventional polymer is easy to degrade and difficult to inject in extra-high temperature（95-120 ℃）and midlow permeability（50-100 mD）reservoirs. Evaluation method of emulsifying property and thickening property of the emulsion-surfactant was established for enhancing oil recovery of the extra-high and mid-low permeability reservoirs. Structure-activity relationship of the emulsion-surfactant was researched. The emulsion-surfactant flooding system was developed. The viscosifying emulsion was formed at 110 ℃ with more than 90% of solubilizing water ratio and more than 100% of viscosity increase rate by emulsification. The physical simulation results showed that the oil recovery was improved by 17.7%-22.1% when emulsion-surfactant flooding system（emulsified-viscosifying emulsion surfactant and low IFT surfactant）was injected into the system alternately for several times. The pilot test of emulsion-surfactant flooding was carried out in Chun17-1 unit of Chunhua Oilfield. Three cycles were injected alternately in February 2017，and the obvious oil increasing effect has been observed in the oil wells. Emulsion-surfactant flooding technology has created a new type of development method，which provides technical support for enhancing oil recovery in the extra-high temperature and mid-low permeability reservoirs.
Conventional polymer is easy to degrade and difficult to inject in extra-high temperature（95-120 ℃）and midlow permeability（50-100 mD）reservoirs. Evaluation method of emulsifying property and thickening property of the emulsion-surfactant was established for enhancing oil recovery of the extra-high and mid-low permeability reservoirs. Structure-activity relationship of the emulsion-surfactant was researched. The emulsion-surfactant flooding system was developed. The viscosifying emulsion was formed at 110 ℃ with more than 90% of solubilizing water ratio and more than 100% of viscosity increase rate by emulsification. The physical simulation results showed that the oil recovery was improved by 17.7%-22.1% when emulsion-surfactant flooding system（emulsified-viscosifying emulsion surfactant and low IFT surfactant）was injected into the system alternately for several times. The pilot test of emulsion-surfactant flooding was carried out in Chun17-1 unit of Chunhua Oilfield. Three cycles were injected alternately in February 2017，and the obvious oil increasing effect has been observed in the oil wells. Emulsion-surfactant flooding technology has created a new type of development method，which provides technical support for enhancing oil recovery in the extra-high temperature and mid-low permeability reservoirs.
2018, 25(2):77-82.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.012
Abstract:
In order to quantitatively and qualitatively study the effect of formation rhythm，concentration of foaming agent and gas liquid ratio on oil displacement efficiency during nitrogen foam flooding process in bottom water reservoir，the bottom water reservoir model was established by CMG numerical simulation software，and the test scheme was separately designed according to the design principle of Box-Behnken Design（BBD）center combination in response surface methodology and single factor analysis. The mathematical regression model between the factors and the increment of oil recovery was established，and the degree of influence of all factors on recovery increment and their effect were clarified. In addition，the factors were optimized. The results show that the mathematical regression model has a good fitting effect on the experimental data and the effects sequence from large to small is formation rhythm，foaming agent concentration and gas liquid ratio.Under the experimental conditions of positive rhythm formation，6% of concentration of foaming agent and 1∶2-1∶1 of the gas liquid ratio，the recovery increment is higher. Quantitative and qualitative study on the influence of various factors on the recovery increment has great significance to deeply understand the mechanism of nitrogen foam flooding for EOR in similar bottom water reservoirs.
In order to quantitatively and qualitatively study the effect of formation rhythm，concentration of foaming agent and gas liquid ratio on oil displacement efficiency during nitrogen foam flooding process in bottom water reservoir，the bottom water reservoir model was established by CMG numerical simulation software，and the test scheme was separately designed according to the design principle of Box-Behnken Design（BBD）center combination in response surface methodology and single factor analysis. The mathematical regression model between the factors and the increment of oil recovery was established，and the degree of influence of all factors on recovery increment and their effect were clarified. In addition，the factors were optimized. The results show that the mathematical regression model has a good fitting effect on the experimental data and the effects sequence from large to small is formation rhythm，foaming agent concentration and gas liquid ratio.Under the experimental conditions of positive rhythm formation，6% of concentration of foaming agent and 1∶2-1∶1 of the gas liquid ratio，the recovery increment is higher. Quantitative and qualitative study on the influence of various factors on the recovery increment has great significance to deeply understand the mechanism of nitrogen foam flooding for EOR in similar bottom water reservoirs.
2018, 25(2):83-89.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.013
Abstract:
According to the complex production performance and great productivity difference of individual well in the tight oil reservoir，the flow mechanism under coupling of multiple media was researched based on the reservoir characteristic of the presence of different types of pore and natural fracture. The storage-percolation modes of the tight oil reservoir were divided into four types based on various fracture types，scales and development degree combined with static data of seismic interpretation，well logging analysis and core slice，which are multi-scale fracture-pore type，macro-fracture-pore type，micro-fracture-pore type and pore type. Different storage-percolation modes have various pore-fracture coupling modes with various flow characteristics and productivity characteristics. By means of reservoir engineering and numerical simulation，the performance characteristics under different storage-percolation modes were analyzed based on the static and dynamic data. The comparison of the results shows that the well productivity would be the highest when large and micro fractures with different scales form the complex fracture network. Suitable reservoir reformation mode should be adopted according to various storage-percolation modes. Natural fractures and artificial fractures may form fracture network and the matrix may be connected effectively. The producing degree of the matrix and the recovery degree of the tight oil reservoir may be increased when the initial production and production scale were increased.
According to the complex production performance and great productivity difference of individual well in the tight oil reservoir，the flow mechanism under coupling of multiple media was researched based on the reservoir characteristic of the presence of different types of pore and natural fracture. The storage-percolation modes of the tight oil reservoir were divided into four types based on various fracture types，scales and development degree combined with static data of seismic interpretation，well logging analysis and core slice，which are multi-scale fracture-pore type，macro-fracture-pore type，micro-fracture-pore type and pore type. Different storage-percolation modes have various pore-fracture coupling modes with various flow characteristics and productivity characteristics. By means of reservoir engineering and numerical simulation，the performance characteristics under different storage-percolation modes were analyzed based on the static and dynamic data. The comparison of the results shows that the well productivity would be the highest when large and micro fractures with different scales form the complex fracture network. Suitable reservoir reformation mode should be adopted according to various storage-percolation modes. Natural fractures and artificial fractures may form fracture network and the matrix may be connected effectively. The producing degree of the matrix and the recovery degree of the tight oil reservoir may be increased when the initial production and production scale were increased.
2018, 25(2):90-95.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.014
Abstract:
The thermophilic bioemulsifier-producing bacteria，Geobacillus stearothermophilus SL-1，was chosen as target species to study growth characteristics and tendency on interface. Simultaneously，the experiment of the displacement effect and mechanism of residual oil after water flooding with strain SL-1 were carried out by microscopic simulation visual model. The results reveal that Geobacillus stearothermophilus SL-1 has hydrocarbon degradation activity using crude oil as sole carbon source. Under compound extreme environment of high temperature（65 ℃）and high pressure（10 MPa），SL-1 bacteria can multiply and metabolize with crude oil so as to degrade oil；biosurfactants produced from the bacteria can emulsify crude oil，change rock surface wettability and disperse residual oil emulsion to oil drops；the oil-water interfacial tension and viscosity of crude oil can be reduced effectively，and the rheology of residual oil may be improved. All kinds of residual oil such as membrane residual oil，columnar residual oil and blind end residual oil have been displaced effectively.At last the oil recovery rate was increased by 12.84%.
The thermophilic bioemulsifier-producing bacteria，Geobacillus stearothermophilus SL-1，was chosen as target species to study growth characteristics and tendency on interface. Simultaneously，the experiment of the displacement effect and mechanism of residual oil after water flooding with strain SL-1 were carried out by microscopic simulation visual model. The results reveal that Geobacillus stearothermophilus SL-1 has hydrocarbon degradation activity using crude oil as sole carbon source. Under compound extreme environment of high temperature（65 ℃）and high pressure（10 MPa），SL-1 bacteria can multiply and metabolize with crude oil so as to degrade oil；biosurfactants produced from the bacteria can emulsify crude oil，change rock surface wettability and disperse residual oil emulsion to oil drops；the oil-water interfacial tension and viscosity of crude oil can be reduced effectively，and the rheology of residual oil may be improved. All kinds of residual oil such as membrane residual oil，columnar residual oil and blind end residual oil have been displaced effectively.At last the oil recovery rate was increased by 12.84%.
15 Analysis of influencing factors of reservoir stimulation effect in multi-cluster staged fracturing
2018, 25(2):96-102.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.015
Abstract:
Hydraulic fracturing is the main exploitation means of low permeability and ultra low permeability oil and gas reservoirs，and its effect on stimulated reservoir is affected by many factors. The stimulated reservoir area is an important index of evaluating the fracturing effect，but its main influencing factors are not clear. Therefore，a mechanical model of multi-cluster staged fracturing of horizontal well was established. The numerical simulation analysis technique and scalar damage variable model were used to simulate the stimulated reservoir area and the initiation and propagation of hydraulic fractures for multi-cluster staged fracturing. The results show that the interference between fractures is one of the important factors affecting the reservoir stimulation effect；for the multi-cluster staged fracturing，the increase of stage spacing can improve the stimulation effect；in the case of low stress difference，increasing injection rate makes the stimulated reservoir area expand by 32.1%. When the fluid viscosity is high，improving injection rate makes the stimulated reservoir area increase by 70.6%. High viscosity fluid，large injection rate and low stress difference can effectively improve the stimulated reservoir area.
Hydraulic fracturing is the main exploitation means of low permeability and ultra low permeability oil and gas reservoirs，and its effect on stimulated reservoir is affected by many factors. The stimulated reservoir area is an important index of evaluating the fracturing effect，but its main influencing factors are not clear. Therefore，a mechanical model of multi-cluster staged fracturing of horizontal well was established. The numerical simulation analysis technique and scalar damage variable model were used to simulate the stimulated reservoir area and the initiation and propagation of hydraulic fractures for multi-cluster staged fracturing. The results show that the interference between fractures is one of the important factors affecting the reservoir stimulation effect；for the multi-cluster staged fracturing，the increase of stage spacing can improve the stimulation effect；in the case of low stress difference，increasing injection rate makes the stimulated reservoir area expand by 32.1%. When the fluid viscosity is high，improving injection rate makes the stimulated reservoir area increase by 70.6%. High viscosity fluid，large injection rate and low stress difference can effectively improve the stimulated reservoir area.
2018, 25(2):103-108.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.016
Abstract:
In order to avoid conducting complex viscosity test of formation heavy oil，simplify the solving process of PR viscosity prediction model and finally improve the applicability of prediction model，a viscosity prediction model of Gubei heavy oil was established based on correction of acentric factor. Based on dehydration，blending tests and viscosity tests under different water cuts of heavy oil，the viscosity correlation of ground degassed crude oil viscosity with water cut and temperature for PR equation was established to simplify the related viscosity experiment. It can also be used to improve accuracy of PR viscosity prediction equation by correcting the calculation error of Edmister acentric factor. The viscosity prediction model of Gubei1-38 heavy oil was established for numerical simulation taking environment parameters of formation heavy oil with multi-factor and multi-level as initial conditions. The test and calculation results show that high content of heavy fraction results in the increase of formation pressure，and viscosity reduction effect is not obviously related to the light fraction，while temperature，water content and gas-liquid ratio is the main influencing factors of viscosity of the formation heavy oil.
In order to avoid conducting complex viscosity test of formation heavy oil，simplify the solving process of PR viscosity prediction model and finally improve the applicability of prediction model，a viscosity prediction model of Gubei heavy oil was established based on correction of acentric factor. Based on dehydration，blending tests and viscosity tests under different water cuts of heavy oil，the viscosity correlation of ground degassed crude oil viscosity with water cut and temperature for PR equation was established to simplify the related viscosity experiment. It can also be used to improve accuracy of PR viscosity prediction equation by correcting the calculation error of Edmister acentric factor. The viscosity prediction model of Gubei1-38 heavy oil was established for numerical simulation taking environment parameters of formation heavy oil with multi-factor and multi-level as initial conditions. The test and calculation results show that high content of heavy fraction results in the increase of formation pressure，and viscosity reduction effect is not obviously related to the light fraction，while temperature，water content and gas-liquid ratio is the main influencing factors of viscosity of the formation heavy oil.
2018, 25(2):109-114.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.017
Abstract:
Hydraulic fracturing technology is an important method to increase oil and gas production. In reservoirs such as shale and sandstone，different degrees of natural fractures develop. When hydraulic fracturing is used for fractured reservoirs，the existence of natural fracture has a significant impact on the formation and development degree of hydraulic fracture，especially for fracture network. In order to analysis the rock failure process，a two-dimensional plane-strain calculation model based on the FEM（finite element method）was established considering the development of natural fractures.The formation process of hydraulic fractures and complex fracture network in the hydraulic fracturing process were researched，and its influencing factors were analyzed. Grid-coverage method based on box counting method was introduced to measure the fractal dimension of the complex reservoir fractures and the fracturing effect obtained by numerical simulation was evaluated. The simulation results suggest that the development of natural fractures definitely affects the produced fractures.When propagating near natural fractures，hydraulic fractures will bifurcate，slip along the natural fracture for extension，or directly propagate through the natural fractures in its previous direction，and form a complex hydraulic fracture or a fracture network. Dense natural fractures with larger trace length can result in larger fractal dimension of hydraulic fractures and better reformation effect of the fractured reservoirs.
Hydraulic fracturing technology is an important method to increase oil and gas production. In reservoirs such as shale and sandstone，different degrees of natural fractures develop. When hydraulic fracturing is used for fractured reservoirs，the existence of natural fracture has a significant impact on the formation and development degree of hydraulic fracture，especially for fracture network. In order to analysis the rock failure process，a two-dimensional plane-strain calculation model based on the FEM（finite element method）was established considering the development of natural fractures.The formation process of hydraulic fractures and complex fracture network in the hydraulic fracturing process were researched，and its influencing factors were analyzed. Grid-coverage method based on box counting method was introduced to measure the fractal dimension of the complex reservoir fractures and the fracturing effect obtained by numerical simulation was evaluated. The simulation results suggest that the development of natural fractures definitely affects the produced fractures.When propagating near natural fractures，hydraulic fractures will bifurcate，slip along the natural fracture for extension，or directly propagate through the natural fractures in its previous direction，and form a complex hydraulic fracture or a fracture network. Dense natural fractures with larger trace length can result in larger fractal dimension of hydraulic fractures and better reformation effect of the fractured reservoirs.
2018, 25(2):115-1320.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.018
Abstract:
The premise of maintaining high fracture conductivity in channel fracturing is that the proppant pillar fully supports the fracture，but it is not clear whether the fracture can be fully supported by the proppant pillar with different thicknesses and diameters. Based on the elastic mechanics theory，a finite element model of the proppant pillar contacted with formation was established to study the optimal laying spacing between the neighbouring proppant pillars with different thicknesses and diameters under closure pressure，that is，the optimal laying spacing of the proppant pillar. When the distance between the adjacent proppant pillars is less than the optimal laying spacing，the proppant pillar can fully support the fracture，otherwise the fracture closes partially and the fracture conductivity decreases. Based on the optimal laying spacing and the material conservation laws，the optimal pulse time for clean fluid was calculated. The results show that the higher the closure pressure and the construction displacement are，the shorter the pulse time for clean fluid is. When the fracture width is larger，the pulse time becomes longer. In the process of the entire channel fracturing，the construction displacement should be increased and the pulse time for clean fluid should be reduced in high closure pressure reservoir，while the pulse time for clean fluid should be increased in low closure pressure reservoir.
The premise of maintaining high fracture conductivity in channel fracturing is that the proppant pillar fully supports the fracture，but it is not clear whether the fracture can be fully supported by the proppant pillar with different thicknesses and diameters. Based on the elastic mechanics theory，a finite element model of the proppant pillar contacted with formation was established to study the optimal laying spacing between the neighbouring proppant pillars with different thicknesses and diameters under closure pressure，that is，the optimal laying spacing of the proppant pillar. When the distance between the adjacent proppant pillars is less than the optimal laying spacing，the proppant pillar can fully support the fracture，otherwise the fracture closes partially and the fracture conductivity decreases. Based on the optimal laying spacing and the material conservation laws，the optimal pulse time for clean fluid was calculated. The results show that the higher the closure pressure and the construction displacement are，the shorter the pulse time for clean fluid is. When the fracture width is larger，the pulse time becomes longer. In the process of the entire channel fracturing，the construction displacement should be increased and the pulse time for clean fluid should be reduced in high closure pressure reservoir，while the pulse time for clean fluid should be increased in low closure pressure reservoir.
2018, 25(2):121-126.
DOI: 10.13673/j.cnki.cn37-1359/te.2018.02.019
Abstract:
Permeability jail，where both gas and water cannot flow effectively，may exist in the relative permeability curve of cores of tight gas reservoirs whose permeability is below 0.05 mD. The investigation of gas and water flow in the permeability jail of the tight sandstone cores in the Western Sichuan Basin should be based on the reasonable determination of permeability jail boundaries. A method to determine permeability jail boundaries of the tight sandstone cores from the Western Sichuan Basin was proposed. Factors including relative permeability factor at the cross-over point，gas relative permeability curvature factor and water relative permeability curvature factor were defined to describe the properties of rock and fluids.The method was applied to study permeability jail boundaries of tight sandstone cores from the Western Sichuan Basin.And the influence of permeability jail on gas production of the tight sandstone gas reservoir was analyzed. Results show that permeability jail of tight sandstone cores from the Western Sichuan Basin occupies water saturation region ranging from 63% and 91%，which approximates the initial water saturation of the Sichuan Basin（40%-70%）. During the gas development，due to drilling，well completion and hydraulic fracturing fluids retention in the reservoir，water saturation near wellbore areas can rise to permeability jail and then reduce gas production. The permeability jail has the most significant effect on gas production at the beginning of the production in the tight sandstone gas reservoir. It can delay the peak gas production for hundreds of days.
Permeability jail，where both gas and water cannot flow effectively，may exist in the relative permeability curve of cores of tight gas reservoirs whose permeability is below 0.05 mD. The investigation of gas and water flow in the permeability jail of the tight sandstone cores in the Western Sichuan Basin should be based on the reasonable determination of permeability jail boundaries. A method to determine permeability jail boundaries of the tight sandstone cores from the Western Sichuan Basin was proposed. Factors including relative permeability factor at the cross-over point，gas relative permeability curvature factor and water relative permeability curvature factor were defined to describe the properties of rock and fluids.The method was applied to study permeability jail boundaries of tight sandstone cores from the Western Sichuan Basin.And the influence of permeability jail on gas production of the tight sandstone gas reservoir was analyzed. Results show that permeability jail of tight sandstone cores from the Western Sichuan Basin occupies water saturation region ranging from 63% and 91%，which approximates the initial water saturation of the Sichuan Basin（40%-70%）. During the gas development，due to drilling，well completion and hydraulic fracturing fluids retention in the reservoir，water saturation near wellbore areas can rise to permeability jail and then reduce gas production. The permeability jail has the most significant effect on gas production at the beginning of the production in the tight sandstone gas reservoir. It can delay the peak gas production for hundreds of days.
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