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2019 Vol. 41, No. 6

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2019, 41(6): Ⅰ-Ⅹ.
Abstract(199) PDF-CN(65)
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2019, 41(6): .
Abstract(262) PDF-CN(160)
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Deformation zoning model of piedmont thrust, western China, and its petroleum response
XU Xuhui, FANG Chengming, LIU Jinlian, ZHAO Li, LU Jianlin, HUANG Zeguang
2019, 41(6): 779-790. doi: 10.11781/sysydz201906779
Abstract(867) PDF-CN(180)
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The deformation structure and zonation model of piedmont thrust in an intra-continental composite system is an effective method of studying hydrocarbon accumulation regularity. The conjoint analysis of the characteristics of deep geological structures and sedimentary cover in the main piedmont thrust belt, western China indicate that the deformation of the intra-continental piedmont thrust belts is controlled by the different detachments and also by the geometric form and location of the compound land mass. The intra-continental composite piedmont thrust belt is essentially a deformation system formed by an orogenic wedge step sliding along different levels of soft strata from the orogenic wedge to the basin. Four zonation models divide the intra-continental piedmont thrust belt using the depth of main detachment as a key factor combined with deformation style. The models include a thick belt, a transition belt and a thin belt from the orogenic region to the basin, and a transition belt is further divided into transition Ⅰ belt and transition Ⅱ belt. Each belt has its unique characteristics with respect to deformation strata, deformation styles, fault-rupture mechanism, folding styles, fault-related fold principles and geometric theory. The deformation style of the intracontinental thrust belt clearly influences hydrocarbon accumulation regularity. The industrial oil and gas is mainly distributed in the transition zone. During accumulation, oil and gas in transition Ⅰ belt also adjusted, so the present petroleum reservoirs are mainly residual and always in the front part of the belt. Oil and gas in the transition Ⅱ belt mainly accumulated at the late stage and in the center of the belt. Therefore, the key factor for accumulation is the matching style of fault shape and seal. The transition from thick belt to thin belt in the central and western piedmont thrust belt is the key area for seismic technology development and exploration deployment.
Compound intracontinental piedmont thrust structure transformation and its formation mechanisms
FANG Chengming, ZHAO Li
2019, 41(6): 791-799. doi: 10.11781/sysydz201906791
Abstract(638) PDF-CN(132)
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The transformation types from thick-skinned to thin-skinned structures in compound intracontinental piedmont controls the development of complicated thrust structures in central and western China. No single dynamic model can generalize and explain the causes of the multi-type thrust structure. Joint analysis of deep and shallow structures shows that there are four types of transformation from thick-skinned to thin-skinned structures in the piedmont of central and western China. These are named transition zones Ⅰ, Ⅱ, Ⅰ+Ⅱ and the non-transition zone, according to the form of forward transfer and expansion of tectonic displacement and the geological structure it produces. The four transformation types have specific structural characteristics. The first three types are mainly converted by basement detachment and slippage. Due to the development of a deep slippage layer and different boundary conditions, different structural styles such as imbricate thrusting, triangular zone and double structure are formed. As to the non-transition type, overthrust faults accommodate the abrupt transformation between thick-skinned and thin-skinned structures, without obvious basement detachment or slippage. Large-scale nappe structure is the main structural style of this transformation type. The difference of transition type and thrust structure is mainly due to the different intracontinental deformation responses of different deep geological structures and boundary conditions in the compound continents with multi-continental blocks splicing together under the action of plate margin subduction or collision. The formation of transitional zone Ⅱ and transitional zone Ⅰ+Ⅱ piedmont thrust structures follows the structural model of "intracrustal subduction and reverse detachment thrust", while the non-transitional zone and transitional zone I conform to the structural model of "intracrustal bidirectional subduction and balanced uplift thrust" and "multi-level basement detachment and detachment thrust" respectively.
Influence of diagenetic evolution on tight sandstone reservoir flow capacity: Chang 8 reservoir of Yanchang Formation in southern Maling, Ordos Basin
XIAO Hui, WANG Haonan, YANG Yindi, KE Changyan, SHE Haiqin
2019, 41(6): 800-811. doi: 10.11781/sysydz201906800
Abstract(901) PDF-CN(165)
Abstract:
The difference in diagenetic evolution is the main reason for the difference in microscopic pore-throat structure affecting storage and flow capacity of reservoirs. The diagenesis and porosity evolution of the Chang 8 reservoirs in the southern Maling area of the Ordos Basin were studied quantitatively via many types of experiments, including thin sections, scanning electron microscopy, cathodoluminescence, X-ray diffraction, high pressure mercury intrusion and nuclear magnetic resonance. The Chang 8 sandstones have similar rock types, with lower compositional and higher structural maturities. The stage of diagenetic evolution is from the late stage A to the early stage B. The difference in diagenetic evolution is mainly reflected in the difference between the contents of rigid and plastic particles on compaction. For sandstones with relatively high compaction, dissolution is the main factor controlling reservoir quality. For sandstones that have undergone a certain compaction, in which residual intergranular pores are still developing, the filling degree of chlorite films and calcareous cement is the key factor affecting reservoir quality. Quantitative calculation of pore evolution reveals that the pore reduction rates due to compaction and cementation are 49.51% and 30.6%, respectively. The amount of dissolution is 7.0%. Compaction is the main factor that causes reservoir densification in this area. Different diagenetic transformation types have different effects on the development characteristics of reservoir pore structure. Reservoirs with chlorite film shows the best quality. The feldspar dissolution-based reservoir has better reservoir capacity, but poorer permeability. Reservoirs with strong compaction and calcium cementation are relatively poorer quality. The degree of compaction, chlorite cementation, dissolution and calcium filling are the main factors affecting the pore size, reservoir capacity and permeability.
Diagenesis and hydrocarbon accumulation of the Cambrian Longwangmiao Formation in Anyue, Sichuan Basin
ZHU Lianqiang, YUAN Haifeng, LIN Xuemei, ZENG Wei, XU Yunqiang
2019, 41(6): 812-820. doi: 10.11781/sysydz201906812
Abstract(865) PDF-CN(130)
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The Cambrian Longwangmiao Formation in the Sichuan Basin is old, deeply buried with extensive diagenetic transformations, which was affected by important tectonic movements such as Caledonian, Indosinian and Himalayan, so that the hydrocarbon accumulation process is complex. The mineral diagenesis sequence of the Longwangmiao Formation was determined by core observation, petrological type analysis and thin section observation combined with cathodoluminescence characteristics. The characteristics of hydrocarbon fluid inclusions in different diagenetic minerals were analyzed, and the homogenization temperature of symbiotic brine inclusions was tested to clarify reservoirs in the Longwangmiao Formation based on the sequence of mineralization. Combined with the thermal evolution history of the Longwangmiao reservoir in Anyue, the hydrocarbon accumulation periods and time were determined. The results showed that the identified fluid inclusions captured by five diagenetic minerals, such as dolomite and quartz, recorded the five stages of hydrocarbon accumulation events. The first stage is the Middle Triassic filling, the second stage is the Early Jurassic filling, the third stage is the Middle Jurassic wet gas filling, the fourth stage is the late period of Early Cretaceous, and the fifth stage of dry gas filling is the adjustment of the gas reservoir since the Late Cretaceous. The adjustment of gas reservoirs during the Himalayan tectonic movement is an important period for the formation of Longwangmiao Formation gas reservoirs, which is about 40 Ma.
Source rock characteristics and depositional environment of Lower Sinian Doushantuo Formation in northeastern Sichuan and western Hubei
ZHANG Daoliang, YANG Shuaijie, WANG Weifeng, FU Xiaodong, ZHANG Jianyong, LI Wenzheng
2019, 41(6): 821-830. doi: 10.11781/sysydz201906821
Abstract(866) PDF-CN(165)
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The dark shale of the Doushantuo Formation is an important source rock of the Neoproterozoic Sinian in northeastern Sichuan and western Hubei. A series of outcrop profiles in this area at Fujiagou, Chenjiawan and Huajipo were observed and sampled. The characteristics and depositional environment of source rocks of the Doushantuo Formation were identified by means of organic geochemical analysis, organic matter type and major-trace element analysis. The source rocks of the Doushantuo Formation are 50-250 m thick, with maximums of Zhenba-Chengkou and Yichang-Wufeng. The abundance of organic matter is relatively high, averaging 2%. The hydrocarbon-generating organic matter is diverse, but mainly phytoplankton. Source rocks have good organic matter types, mainly type I-II1. Organic matter is in the stage of overmature thermal evolution and generates gas. In this study, the depositional environment of hydrocarbon source rocks was analyzed by using element geochemical indices which show that the source rocks of the Doushantuo Formation were formed in a suboxic to anoxic environment, but differences exist in different areas. Source rocks in the northeastern Sichuan were deposited in a deep water shelf environment with relatively stable energy, low salinity and suboxic to anoxic conditions. Source rocks in the western Hubei were formed in a platform inner sag environment with high energy, low salinity and anoxic conditions.
Occurrence and accumulation characteristics of natural gas hydrate in the eastern Nankai Trough, Japan
ZHAO Kebin
2019, 41(6): 831-837. doi: 10.11781/sysydz201906831
Abstract(535) PDF-CN(80)
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The geological setting and occurrence characteristics of natural gas hydrate in the eastern Nankai Trough offshore Japan have been analyzed and summarized based on the research of gas hydrate drilling expeditions and the Integrated Ocean Drilling Program conducted in this area. As part of the convergent continental margin with strong tectonic activity, the Nankai Trough has well-developed fault and fracture systems, and is rich in gravity flow sediments. Especially in the continental slope of the northern trough with water depth shallower than 2 000 m, a series of fore-arc basins exist, filled with widely distributed unconsolidated Quaternary sediments. The deposition rate of these young sediments is rather high, providing favorable conditions for the formation of gas hydrate. Analyses of the drilling cores taken from this area indicate that the gas hydrate is type I, comprising 99.9% or more methane. The carbon isotopic analysis shows that methane forming the gas hydrate is typically microbial. The gas hydrate occurs commonly in a dispersive state, filling in the pores of the sediment, preferentially accumulating in the sand-rich sediments. The hydrate saturation in the sand-rich intervals is commonly 50%-60% and can reach as high as 80%-90%; whereas the hydrate saturation in the shale layers is extremely low.
Carbon isotope compositions of individual alkanes in highly mature source rocks from Northern Guizhou Depression
BAO Jianping, NI Chunhua, ZHU Cuishan, ZHAN Zhaowen, JIANG Xingchao, SHEN Xu
2019, 41(6): 838-848. doi: 10.11781/sysydz201906838
Abstract(621) PDF-CN(121)
Abstract:
Straight chain alkanes and various biomarkers such as steranes and terpanes and compound-specific carbon isotope compositions of individual n-alkanes in the saturate fractions of extracts from highly mature source rocks and crude oil from the Hu 47 well in the Northern and Southern Guizhou depressions were analyzed using GC-MS and GC-CSIRMS. The distribution and composition of regular steranes and terpanes in those source rocks are very similar and have lost their original geochemical significance. However, crude oil from the well Hu 47 contains abundant low molecular biomarkers such as tricyclic terpanes and pregnanes while C27-35 hopanes and C27-29 steranes are depleted, suggesting that it is a condensate with high maturity. There are bimodal distributions for n-alkanes with a minimum at n-C20 or n-C21 in most source rocks. Normally, this phenomenon should not appear in highly mature source rocks. However, for both bimodal and unimodal distributions of n-alkanes in those source rocks, the carbon isotope compositions of individual n-alkanes are similar. The δ13C values are between -28‰ and -31‰ and decrease with increasing n-alkane carbon number, suggesting that bimodal or unimodal n-alkanes have a similar source in highly mature source rocks. There is an obvious negative tendency in carbon isotope compositions of individual compounds with increasing carbon number of individual n-alkanes in light oil from the well Hu 47, but their δ13C values are lighter by about 3‰ compared with those in highly mature source rocks. This could be related to the fractionation of carbon isotope during the thermal evolution of organic matter. Therefore, when carbon isotope compositions of individual n-alkanes are used in oil-source correlation, it is important to avoid a large maturity difference between the crude oils and source rocks.
Geochemical characteristics and origin of oil from different strata in Shunbei oil and gas field, Tarim Basin
LUO Mingxia, XIA Yongtao, SHAO Xiaoming, WU Xian
2019, 41(6): 849-854. doi: 10.11781/sysydz201906849
Abstract(899) PDF-CN(113)
Abstract:
Volatile-light oil or oil sands have been found in the Ordovician, Silurian and Cretaceous strata in Shunbei oil and gas field, Tarim Basin. The geochemical characteristics of oil or oil sands from these strata are obviously different. Generally, they can be divided into two genetic types. (1) Oil in the Ordovician and Silurian:The Pr/Ph value is <1, the carbon isotope of the whole oil and n-alkanes is light, and the C21TT/C23TT ratio is also <1. The dibenzothiophene content is dominant among dibenzothiophene, dibenzofuran and fluorene. These features all indicate that the oil is marine sapropelic. But their maturities are different. Oil is mature in the Silurian and highly mature in the Ordovician. (2) Oil in the Cretaceous:The Pr/Ph value is>1.6, the carbon isotope of the whole oil is relatively heavier, and the C21TT/C23TT ratio is>1. The oil is rich in C24 tetracyclic terpenoids and C30 rearranged hopanes. Thus, they are of continental origin. Altogether, oil in the Ordovician and Silurian strata is from the Cambrian source rocks, which are isogenous and non-synchronous reservoirs. Oil in the Cretaceous strata mainly comes from continental source rocks of the northern Kuche Depression.
Geochemical characteristics of crude oil and oil-source correlation of Shahejie Formation in Linnan Sub-Sag, Huimin Sag, Bohai Bay Basin
LIU Fei, ZHU Gangtian, HE Sheng, WANG Yongshi, LIU Qing
2019, 41(6): 855-864. doi: 10.11781/sysydz201906855
Abstract(650) PDF-CN(105)
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The Huimin Sag is a significant petroleum unit in the Jiyang Depression. This work reports a systematic study of the geochemical characteristics of 20 crude oil samples and 4 source rock samples collected from the Linnan Sub-Sag of the Huimin Sag and interpretations of maturity, sedimentary environment and organic matter sources. Oil-source rock relationship was established by using the biomarker parameters of the source rock and crude oil samples. To classify the oils and to interpret the oil-source correlation, various effective parameters were selected and processed using cross-plots and cluster analysis. The results showed that the crude oils have entered the mature stage, with continental-lacustrine-basin hybrid parent materials and a weakly oxidizing to weakly reducing depositional environment. Most of the crude oils had a high content of saturated hydrocarbon, low contents of resins and asphaltene, "platform" bimodal chromatograms of n-alkanes, low content of gammacerane and high content of 4-methyl steranes. According to the differences of the geochemical characteristics of certain areas, crude oils were divided into the south zone oils and the north zone oils. Compared with the south zone oils, the north zone oils possessed lower ratios of 4-methyldecane/C29R and Ts/Tm, and higher ratios of C29 norhopane/C29 Ts, 1,2,7-/1,2,6-trimethylnaphthalene and phenanthrene/∑methyl phenanthrenes. The organic matter type of the source rocks of the fourth member of Shahejie Formation in the Linnan Sub-Sag is type Ⅲ, and the abundance of organic matter is low. The organic matter of the source rocks of the third member of Shahejie Formation is dominated by type Ⅱ, and the abundance of organic matter is high. The lower and middle sections of the third member of Shahejie Formation are the main source rocks of the sub-sag. By systematically comparing the geochemical characteristics of the crude oils and the source rocks, it was found that the crude oils from the third and fourth members of Shahejie Formation of the Linnan Sub-Sag came from the source rocks of the lower and middle sections of the third member of Shahejie Formation.
Methane isotope fractionation characteristics of shale gas and its significance as a productivity indicator
GAO Yuqiao, GAO Hequn, HE Xipeng, DING Anxu, ZHANG Peixian, HE Guisong
2019, 41(6): 865-870. doi: 10.11781/sysydz201906865
Abstract(836) PDF-CN(157)
Abstract:
Carbon isotopes of methane in shale gas provide an important index for studying isotope fractionation characteristics and the gas production process. The carbon isotope variation of shale gas during in situ gas content measurement was studied for 10 shale gas wells of Wufeng-Longmaxi formations in 6 large blocks in the southeastern Sichuan Basin and the basin margin transition zone (the basin margin-transition zone of southeastern Chongqing). The fractionation characteristics of methane under different pressure systems and different subformations were studied, and the relationships between the isotopes of shale gas and its physical and gas-bearing properties were discussed. The production stages of typical shale gas wells were divided by drainage data.δ13C1 gradually increased during shale gas desorption, while the carbon isotope of methane in overpressure shale gas was smaller. From the outside of the basin margin to the inside, the carbon isotope of methane gradually became lighter, and in the longitudinal direction, with the increase of depth, the methane isotope becomes lighter. Greater porosity of shale, higher content of free gas and better preservation conditions of shale correlate with less fractionation of carbon isotopes. Finally, the desorption stage of shale gas was divided by methane isotope fractionation, and the isotopes of production gas was compared with that of core desorption gas of well L in the Wulong syncline as an example. The δ13C value of gas released corresponded to that of core sample after continuous desorption of 0.9 h, and its recovery rate was about 24.8%, which was still in the initial stage of drainage production.
Physical modeling of thrusting structure zonation in front of an intracontinental orogen
ZHAO Li, LIAO Zongting, XU Xuhui, FANG Chengming, LU Jianlin
2019, 41(6): 871-878. doi: 10.11781/sysydz201906871
Abstract(560) PDF-CN(121)
Abstract:
Existing experimental models do not simulate complete deformation zones, and do not totally match with the background of the composite intracontinental thrust belt in China. This work simulated the zonal characteristics in thrust structures and the reverse fault evolution in the transitional zone by building a "compression-collision" model which has rheological heterogeneity in vertical and horizontal directions. The geometric analysis shows that the improved model can simulate the complete deformation zones. The order is thick-skinned zone, transitional zone and thin-skinned zone from hinterland to foreland, which correspond to the orogen, thrust belt and basin, respectively. Moreover, fault development in the experimental model corresponds well with the geolo-gical model. The Kinematic analysis shows that the development of reverse faults in the transitional zone has gone through three stages:brittle deformation, ductile-brittle deformation and ductile deformation, but the evolution of thrust faults varies with the presence or absence of a detachment layer. Besides, the small initial fracture angle and short evolution time are the controls for the formation of thrust belts in which the dip angle of the front thrust fault is less than that of the back one.
Quantitative characterization of development of permeable interlayers in continental shale strata
WANG Baohua, LI Hao, LU Jianlin, LÜ Jianhong, WANG Miao, ZHAO Linjie
2019, 41(6): 879-884. doi: 10.11781/sysydz201906879
Abstract(917) PDF-CN(103)
Abstract:
Exploration practice shows that the development of sandstone interlayers or carbonate interlayers in organic-rich shale intervals is one of the key factors for shale oil enrichment and high yield. At present, there is no quantitative evaluation model or method for the development degree of these interlayers. The quantitative evaluation model of relative hypertonic interlayers in shale is established. It is of great significance to improve the quantitative evaluation process. A mathematical model for characterizing the development of the interlayers is established by using the position and dispersion of interlayers in a formation. Based on seismic inversion data, three-dimensional structural modeling and drilling data of the lithology properties of the formation, the virtual/actual drilling lithology data is used as the calculation unit, and the sandstone thin interlayer index (STI) is used as the constraint value. The developmental strength (DS), distribution position (DP) and dispersion coefficient (DC) of the well were calculated. Then, the STI is calculated by normalization, and the main source direction is determined by the results of sedimentary facies research. The STI plane distribution of the target layer is calculated by Kriging interpolation. Using the above method, the STI of the upper part of the Shahejie Formation in the Dongying Sag was calculated. Compared with the existing drilling test results, the STI of the high-yield well is mainly between 0.4 and 0.8, indicating that the STI distribution range has a guiding significance for shale oil exploration.
Structural characteristics and formation mechanism in Dongxin Oilfield, Jiyang Depression, Bohai Bay Basin: insights from physical simulation
LI Xiao, HU Qiuyuan, YANG Guang, MA Fanglei, YANG Jianlei, WEI Zhenzhen, SUN Xiao
2019, 41(6): 885-892. doi: 10.11781/sysydz201906885
Abstract(967) PDF-CN(101)
Abstract:
The structural characteristics and formation mechanism of faults in the Dongxin Oilfield of the Jiyang Depression were systematically studied through the analyses of geometric and kinematic characteristics, genetic mechanism and structural physical simulation experiments. The structural form in the study area gradually trends toward complexity from east to west. The Xinzhen structural belt in the east is mainly composed of parallel structures, presenting a simple structural style. The transitional belt in the middle is composed of parallel and oblique structures, presenting a grid structural style. The Dongying structural belt in the west is composed of en echelon and broom-like structures, presenting a complex structural style. Vertically, there are five main fault combination styles in this region, including negative flower-like, inverse "Y" shaped, step-like, graben and horst, showing a typical "cabbage" complex fault system. Physical simulation results fit the actual geological conditions well. The experimental results further confirm that the fault structural assemblage pattern in the Dongxin area is the product of the superposition of Cenozoic extensional-strike-slip stress field and magmatic bottom rifting. Its fundamental driving force is derived from the NW-SE extensional stress field, the right strike-slip of the Tanlu fault zone and the upwelling of plastic materials such as magma.
Sealing performance evaluation of fault fracture zone of different structures based on geomechanical methods: a case study in M area, Chezhen Sag, Jiyang Depression, Bohai Bay Basin
WANG Ze, SHANG Lin, GONG Lirong, WANG Tongda
2019, 41(6): 893-900. doi: 10.11781/sysydz201906893
Abstract(720) PDF-CN(98)
Abstract:
Fault sealing performance is an important control on the distribution of oil and gas reservoirs. A shattered fault zone can be identified easily in outcrops but difficult in the subsurface. Some fault fracture zones were identified and the development patterns were classified. Dynamic rock mechanical parameters were obtained from well logging data, and then corrected according to the rock static parameters obtained by triaxial stress experiments. Finally, using the Ansys software, a numerical simulation of the sealing coefficients of fault fracture zones in three development modes (fault gouge, fault breccia and induced fracture zone) was carried out. The development mode of the fault fracture zone in M area was divided into the fault fracture zone with only fractures developed, the undeveloped fault gouge and the fault fracture zone with a complete structure. The fault fracture zone with a complete structure shows the best sealing performance, followed by the fault fracture zone where the fault gouge is not developed. The fault fracture zone with only fractures developed shows the worst sealing performance. They are mostly open faults, and the fracture zone often becomes an oil and gas migration pathway.
Evolution characteristics and controls of shale nanopores during thermal maturation of organic matter
LI Chuxiong, XIAO Qilin, CHEN Qi, JIANG Xingchao
2019, 41(6): 901-909. doi: 10.11781/sysydz201906901
Abstract(827) PDF-CN(130)
Abstract:
Organic maturity is one of the main factors controlling the formation and evolution of nanopores in shale. The whole process of hydrocarbon generation was modeled for lacustrine shale in the 2nd member of Nenjiang Formation in the Changling Sag of Songliao Basin by using hydrous pyrolysis experiments in a closed system (Ro=0.61%-4.01%). Shale samples at different thermal evolution stages were solvent extracted. Based on geochemical analysis results of organic carbon content, N2 adsorption and mineral composition, the formation and evolution characteristics and influencing factors of nanopores during thermal maturity of organic matter were systematically studied. The BJH pore volume and BET specific surface area of shale increase greatly after pyrolysis experiments, and the variation ranges are 0.006 73-0.101 61 cm3/g and 0.60-15.75 m2/g, respectively. Thermal degradation of kerogen and cracking of residual hydrocarbons promote the rapid development of nanopores in the mature to high maturity stage, and growth rate of nanopores slows down with weakening of hydrocarbon generation ability of organic matter in the over-mature stage. Liquid hydrocarbon is generated and fills nanopores during peak oil generation, which inhibits the formation of nanopores. Generation and expulsion of oil and gas play a leading role in development of nanopores. Organic nanopores may develop while solid pyrobitumen continuously enriched. Illitization of clay minerals and quartz dissolution are conducive to the development of nanopores.
High temperature effects on rock physical properties of organic-rich shale
XIONG Jian, LIN Haiyu, LIU Xiangjun, LIANG Lixi, HUANG Hong, LI Xiansheng
2019, 41(6): 910-915. doi: 10.11781/sysydz201906910
Abstract(856) PDF-CN(129)
Abstract:
The Longmaxi Formation shale in the Sichuan Basin was used to study the changing physical properties of shale after high temperature treatment and the influences of high temperature on the rock mechanical properties of shale. As the temperature increases, the color of shale specimens gradually changes from black to gray. The quality of shale samples decrease slowly first and then rapidly with the increase of temperature, but the porosity and permeability increase slowly at first and then rapidly. The significant changes in quality, porosity and permeability indicate that there is a threshold temperature in this process, and the threshold temperature of the Longmaxi Formation shale range from 300 to 400℃. With the increase of temperature, the acoustic time difference of longitudinal wave and shear wave decreases, while the attenuation coefficient of longitudinal and shear wave increases. With the increase of temperature, the uniaxial compressive strength and the elastic modulus of shale samples decrease, while changes in Poisson's ratio are not obvious.
Effect of pretreatment methods on determination of diamondoids in crude oils
LI Erting, XIANG Baoli, MA Wanyun, XIONG Yongqiang, WANG Ming, MI Julei
2019, 41(6): 916-922. doi: 10.11781/sysydz201906916
Abstract(495) PDF-CN(72)
Abstract:
The content of diamondoids in crude oils of different density from the Junggar Basin was analyzed by gaschromatography-mass spectrometry-mass spectrometry to investigate the effect of group component separation and direct injection on the determination of diamondoids in crude oils. The group component separation method will result in the loss of adamantane from crude oils, especially a large loss of single adamantanes with relatively lower density. However, the group component separation method is conducive to the enrichment of low-mass adamantane compounds in low-maturity crude oils, especially the diadamantane compounds which are less affected by volatilization, and thus more favorable for detection. The group component separation process has little effect on the isomerization index of adamantane, but has a great influence on the concentration index. Therefore, in order to reduce the loss of diamondoids during preparation, complex pretreatment should be avoided as much as possible. The direct injection method is the best pretreatment method for the determination of adamantane compounds in normal oils, light oils and condensates. For some low-maturity crude oil samples, the group component separation method can be considered.
Application of reliable technology in SEC reserve evaluation of South China Sea Gas Field
WANG Qingshuai
2019, 41(6): 923-930. doi: 10.11781/sysydz201906923
Abstract(586) PDF-CN(56)
Abstract:
Reserve assessment of major oil and gas companies around the world is based on the SEC Guidelines issued by the US Securities and Exchange Commission in 2010. This edition expanded the types of "reliable technology" that can be used to determine proved reserves. Since the publication of the guidelines, CNOOC has continuously tried to explore the application of "reliable technology" in the assessment of natural gas reserves, and has formed a number of "reliable technologies" that have gradually been recognized by third-party evaluation agencies and auditing companies. The article discusses the meaning of "reliable technology". It combines domestic and foreign studies to enumerate the disclosure principles and conditions of "reliable technology", and demonstrates some "reliable technology" which has been widely used in the evaluation of SEC reserves in the western South China Sea gas field in recent years, such as the use of geophysical information, the use of pressure data to calculate reserves, the installation of a platform compressor to reduce the pressure and improve the recovery technology in the late stage of gas field development. In recent years, through the application of "reliable technology", CNOOC has made the evaluation results closer to the actual development of the gas field, which guaranteed the objectivity and accuracy of the evaluation results and the stability of the company's reserve replacement rate. It provides a reference case for the domestic natural gas field reserve assessment.
2019, 41(6): 931-931.
Abstract(295) PDF-CN(77)
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